Climate and Water Monitoring at Big Bend National Park: Water Year 2024

Susan Singley, Kara Raymond, Tani Hubbard

Please cite this publication as:

Singley, S., K. Raymond, and T. Hubbard. 2026. Climate and Water Monitoring at Big Bend National Park: Water Year 2024. Science Report NPS/SR—2026/486. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/2318787

Abstract

The Chihuahuan Desert Inventory and Monitoring Network monitors climate, groundwater, and 18 springs each year at Big Bend National Park, Texas. We report on climate and water resources together because surface water conditions are closely related to climate conditions. Climate data, including temperature, precipitation, and reconnaissance drought index, from five weather stations are retrieved at The Climate Analyzer (climateanalyzer.org). Big Bend National Park staff use automated methods to monitor eight park groundwater wells. We retrieve data for a ninth well from the Texas Water Development Board database. We assess the condition of 18 springs, measure spring discharge and wetted extent (area that contained water), collect core water quality and water chemistry data, note any wetland plants and invasive plants and animals, and sample for environmental DNA (eDNA) to detect rare species, invasive species, and pathogens. Each spring is somewhat unique, and Texas has not adopted water quality standards that apply across the diversity of springs in the state. We collect water quality data at the springs to form a baseline reference of natural variance. Overall, there was less total annual rainfall than average, though higher than average precipitation in October and November occurred at three of the weather stations. The drought index indicated the park was drier than average for the fifth year in a row. The park was generally warmer than average, and the number of extremely hot days increased. Average groundwater levels decreased in seven wells, and three of those had their lowest water level since monitoring began. The other two wells had small increases in water levels. We were able to measure wetted area at 15 springs, nine of which were drier than in other years, while the other six were similar to prior measurements. Bois D’Arc Spring was completely dry. There was significant vegetation trampling and grazing by horses at Painted Hills Spring, heavy cattle and horse trampling at Solis Spring, trash and human trampling at De La Ho Spring, and human trampling at Mule Ears Spring. We observed new wetland plants at Cattail Falls (flatsedge) and Chilicotal Spring Complex (centaury) and new invasive plants at Solis Spring (Lehmann lovegrass) and Shelf Spring (buffelgrass). We detected Rio Grande leopard frogs in eDNA samples from eight of the springs. In five of these springs, we also detected chytrid. Red spotted toad was detected in one eDNA sample at Tiptoe Spring.

Intense thunderstorm cells in front of an orange sunset pouring rain on blue mountains and desert hills with spiky desert plants in the foreground.
Storms over Big Bend National Park.

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Overview

Together, climate and hydrology shape ecosystems and the services they provide, particularly in arid and semi-arid ecosystems. Understanding changes in climate, groundwater, and surface water is key to assessing the condition of park natural resources—and often, cultural resources.

At Big Bend National Park (Figure 1), Chihuahuan Desert Inventory and Monitoring Network scientists study how ecosystems may be changing by taking measurements of key resources, or “vital signs,” year after year—much as a doctor keeps track of a patient’s vital signs. This long-term ecological monitoring provides early warning of potential resource problems, allowing managers to mitigate them before they become worse. At Big Bend National Park, we monitor climate, groundwater and springs, among other vital signs. Surface water and groundwater conditions are closely related to climate conditions. Because they are better understood together, we report on climate in conjunction with water resources. Reporting is by water year (WY), which begins in October of the previous calendar year and goes through September of the water year (e.g., WY2024 runs from October 2023 through September 2024). This article reports the results of climate and water monitoring at Big Bend National Park in WY2024.

Figure 1. Map of Big Bend National Park showing five weather stations. Two stations (Panther Junction and Chisos Basin) are in the center of the park, Persimmon Gap station is inside the northern boundary, Rio Grande Village station is on the eastern edge of the park, and Castalon station is along the southwestern edge of the park.
Figure 1. Monitored weather stations at Big Bend National Park.

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Climate and Weather

There is often confusion over the terms “weather” and “climate.” In short, weather describes short-term meteorological conditions (e.g., it’s currently raining or snowing, it’s a hot or frigid day), and climate reflects patterns of weather at a given place over longer periods of time (seasons to years). Climate is the primary driver of ecological processes on Earth. Climate and weather information provide context for understanding the status or condition of other park resources.

Methods

We report on five National Oceanic and Atmospheric Administration Cooperative Observer Program (NOAA COOP) weather stations at Big Bend National Park (Table 1, Figure 1). These stations provide reliable, long-term climate datasets for analyses in this climate and water report. The long-term averages used for comparison in this report are from NOAA and are based on 1991–2020 data, except averages from the Rio Grande Village Texas station, which are based on 2006–2020 data because the station was established in 2006. Data from these stations are accessible through The Climate Analyzer. 

Table 1. Weather stations at Big Bend National Park.
Station Name Station ID# Elevation (ft) Year Established
Chisos Basin 411715 5300 1943
Panther Junction 416792 3740 1955
Persimmon Gap 416959 2870 1952
Castolon 411524 2170 1947
Rio Grande Village Texas 417624 1857 2006

Results

Precipitation and Air Temperature–Chisos Basin (COOP)

Highlights: Annual precipitation was well below average despite October and November being very wet. Temperatures were hotter than average, with nearly three times more extremely hot days.

Annual precipitation at the Chisos Basin station in WY2024 was 11.33″ (28.78 cm), 7.00″ (17.78 cm) less than the 1991–2020 average. WY2024 started wetter than average; the October precipitation total (Figure 2) was nearly three times the average, and November received over 50% more precipitation than average. However, monthly precipitation totals for the rest of the water year were substantially below average, except for July, which was slightly wetter. The largest rainfall deficits occurred in June and August, which received 2.45″ (6.22 cm) and 2.41″ (6.12 cm) less than average, respectively. Extreme daily rainfall events (≥1.00″; 2.54 cm) occurred on 2 days, half the average annual frequency of 4 days. The two extreme rainfall events occurred on 02 October 2023 (1.60″; 4.06 cm) and 06 July 2024 (1.59″; 4.04 cm). The mean annual maximum temperature at the Chisos Basin station in WY2024 was 75.0°F (23.9°C), 1.5°F (0.8°C) above the 1991–2020 average. The mean annual minimum temperature in WY2024 was 53.6°F (12.0°C), 1.3°F (0.7°C) above average. Mean monthly maximum and minimum temperatures in WY2024 varied up to 5.5°F (3.1°C, see May as an example) relative to the 1991–2020 monthly averages (Figure 2). Mean monthly maximum temperatures were warmer than average in every month except November and March. Mean monthly minimum temperatures were warmer than average in every month except January, March, and July. Extremely hot temperatures (≥90.0°F; 32.2°C) occurred on 60 days in WY2024, nearly triple the average frequency of 22.1 days. Extremely cold temperatures (≤30.0°F; −1.1°C) occurred on 14 days, 5 less than the average frequency of 18.9 days.

Figure 2. Climogram showing maximum temperatures were warmer than those for 1991–2020 in every month except November and March. Minimum temperatures were warmer than average in every month except January, March, and July. Precipitation for WY2024 was lower than average in every month except October, November, and July.
Figure 2. Climogram showing monthly precipitation and mean maximum and minimum air temperatures in water year (WY) 2024 and the 1991–2020 averages at Chisos Basin station, Big Bend National Park. Data source: The Climate Analyzer; climateanalyzer.org.

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Precipitation and Air Temperature–Panther Junction (COOP)

Highlights: Precipitation was substantially below average most of the year, but 50% greater than average in October, November, and July. Overall, temperatures were warmer, and there were more than twice as many extremely hot days than average.

Annual precipitation at the Panther Junction station in WY2024 was 8.25″ (20.96 cm), 4.75″ (12.07 cm) less than the 1991–2020 annual average. Monthly precipitation totals (Figure 3) for October, November, and July were approximately 50% greater than the long-term averages. Precipitation during all other months was substantially less than average. December and April were completely dry, and minimal precipitation occurred in March and May. The largest monthly precipitation deficits occurred in May and August, which received 1.29″ (3.28 cm) and 1.80″ (4.57 cm) less than average, respectively. Extreme daily rainfall (≥1.00″; 2.54 cm) occurred on 1 day, less than the average annual frequency of 2.5 days. This event occurred on 07 July 2024 (1.33″; 3.38 cm). The mean annual maximum temperature at the Panther Junction station in WY2024 was 81.7°F (27.6°C), 2.9°F (1.6°C) above the 1991–2020 average. The mean annual minimum temperature in WY2024 was 57.1°F (13.9°C), 3.0°F (1.7°C) above average. Mean monthly maximum and minimum temperatures in WY2024 (Figure 3) differed by as much as 7.4°F (4.1°C; see May as an example) relative to the 1991–2020 monthly averages (Figure 3). Mean monthly maximum and minimum temperatures were above average in every month except two: the mean maximum was below average in November, and the mean minimum was below average in January. Extremely hot temperatures (≥98.0°F; 36.7°C) occurred on 56 days in WY2024, over twice the average frequency of 25 days. Extremely cold temperatures (≤31.0°F; −0.6°C) occurred on 12 days, 10 less than the average frequency of 22.1 days.

Figure 3. Climogram showing maximum temperatures were warmer than those for 1991–2020 in every month except November. Minimum temperatures were warmer than those for 1991–2020 in every month except January. Precipitation for WY2024 was lower than average in every month except October, November, and July.
Figure 3. Climogram showing monthly precipitation and mean maximum and minimum air temperatures in water year (WY) 2024 and the 1991–2020 averages at Panther Junction station, Big Bend National Park. Data source: The Climate Analyzer; climateanalyzer.org.

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Precipitation and Air Temperature–Persimmon Gap (COOP)

Highlights: October and November were very wet, but most of the water year was drier than average. Overall, temperatures were warmer than average, and there were nearly twice as many extremely hot days.

Annual precipitation at the Persimmon Gap station in WY2024 was 5.76″ (14.63 cm), 5.09″ (12.93 cm) less than the 1991–2020 annual average. WY2024 started wetter than average; the October precipitation total was 85% more than the 1991–2020 average and November received over three times the average amount of rain. Monthly precipitation totals (Figure 4) for the rest of the water year were substantially below average, except for February, which was slightly wetter. May was completely dry. The largest deficits occurred in July and September, which received 1.50″ (3.81 cm) and 1.49″ (3.78 cm) less than average, respectively. There were no extreme daily rainfall events (>1.00″; 2.54 cm) in WY2024 compared to the average annual frequency of 2.4 days. The mean annual maximum temperature at the Persimmon Gap station in WY2024 was 84.6°F (29.2°C), 1.6°F (0.9°C) above the 1991–2020 average. The mean annual minimum temperature in WY2024 was 55.8°F (13.2°C), 2.1°F (1.2°C) above average. Mean monthly maximum and minimum temperatures in WY2024 varied by up to 4.8°F (2.7°C, see October as an example) relative to the 1991–2020 monthly averages (Figure 4). Mean monthly maximum temperatures were warmer than average in every month except November and January. Mean monthly minimum temperatures were warmer than average in every month except January and March. Extremely hot temperatures (≥103.0°F; 39.4°C) occurred on 42 days in WY2024, nearly twice the average frequency of 22.2 days. Extremely cold temperatures (≤28.0°F; −2.2°C) occurred on 15 days, about two less than the average frequency of 16.6 days.

Figure 4. Climogram showing maximum temperatures were warmer than than the 1991–2020 averages in every month except November and January. Minimum temperatures were warmer than average in every month except January and March. Precipitation for WY2024 was lower than average in every month except October, November, and February.
Figure 4. Climogram showing monthly precipitation and mean maximum and minimum air temperatures in water year (WY) 2024 and the 1991–2020 averages at Persimmon Gap station, Big Bend National Park. Data source: The Climate Analyzer; climateanalyzer.org.

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Precipitation and Air Temperature–Castolon (COOP)

Highlights: Castolon received about two thirds the average annual precipitation, mostly coming in October and November. High temperatures were cooler than average in the winter and warmer than average in the summer. Low temperatures were warmer than average most of the year.

Annual precipitation at the Castolon station in WY2024 was 6.61″ (16.79 cm), 3.25″ (8.26 cm) less than the 1991–2020 annual average. WY2024 started wetter than average; the October precipitation total was over twice the 1991–2020 average and November received 69% more precipitation than average (Figure 5). May and July totals were slightly above average. Precipitation totals in all other months were substantially less than average, with December, March, and April being completely dry. The largest monthly rainfall deficits occurred in June, August, and September, which received 1.06–1.16″ (2.69–2.95 cm) less than average. Extreme daily rainfall events (≥1.00″; 2.54 cm) occurred on 2 days, the same as the average annual frequency of 2.1 days. Extreme rainfall events occurred on 24 October 2023 (1.22″; 3.10 cm) and 06 July 2024 (1.59″; 4.04 cm). The mean annual maximum temperature at the Castolon station in WY2024 was 88.9°F (31.6°C), 0.5°F (0.3°C) above average. The mean annual minimum temperature in WY2024 was 59.2°F (15.1°C), 2.1°F (1.1°C) above average. Mean monthly maximum and minimum temperatures in WY2024 varied up to 5.4°F (3.0°C; see November as an example) relative to the 1991–2020 monthly averages (Figure 5). Mean monthly maximum temperatures were generally cooler than average in the cool season (October–March) and warmer than average during the warm season (April–September). Mean monthly minimum temperatures were warmer than average in all months except January and March. Extremely hot temperatures (≥108.0°F; 42.2°C) occurred on 29 days in WY2024, 4 more than the average frequency of 24.7 days. Extremely cold temperatures (≤30.0°F; −1.1°C) occurred on 18 days, similar to the average frequency of 18.7 days.

Figure 5. Climogram showing maximum temperature averages were cooler than the 1991–2020 averages in the first six months and warmer in the last six months. Minimum temperature averages for WY2024 were warmer than the 1991–2020 averages in every month except January and March. Precipitation for WY2024 was lower than average in every month except October, November, May, and July.
Figure 5. Climogram showing monthly precipitation and mean maximum and minimum air temperatures in water year (WY) 2024 and the 1991–2020 averages at Castolon station, Big Bend National Park. Data source: The Climate Analyzer; climateanalyzer.org.

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Precipitation and Air Temperature–Rio Grande Village Texas (COOP)

Highlights: Rio Grande Village had a very dry year compared to average. Overall, temperature highs and lows were above average, and there were twice as many extremely hot days.

Annual precipitation at the Rio Grande Village Texas station in WY2024 was 4.48″ (11.38 cm), 7.58″ (19.25 cm) less than the long-term average. Only December and July precipitation totals were similar to the 2006–2020 averages (Figure 6). All other months received substantially less precipitation than average. March through May was completely dry. The largest monthly precipitation deficits occurred in May, June, August, and September, receiving 1.20–1.53″ (3.05–3.89 cm) less than average. There were no extreme daily rainfall events (>1.00″; 2.54 cm) in WY2024, less than the average annual frequency of 1.5 days. The mean annual maximum temperature at the Rio Grande Village Texas station in WY2024 was 91.5°F (33.0°C), 1.9°F (1.1°C) above the 2006–2020 average. The mean annual minimum temperature in WY2024 was 56.0°F (13.3°C), 1.5°F (0.8°C) above average. Mean monthly maximum and minimum temperatures in WY2024 varied up to 6.0°F (3.4°C; see May as an example) relative to the long-term monthly averages (Figure 6). Mean maximum monthly temperatures were warmer than average in every month except November, January, and March. Mean monthly minimum temperatures were warmer than average in every month except January and March. Extremely hot temperatures (≥109.0°F; 42.8°C) occurred on 55 days in WY2024, nearly twice the average frequency of 30 days. Extremely cold temperatures (≤26.0°F; −3.3°C) occurred on 20 days, 4 less than the average frequency of 24.3 days.

Figure 6. Climogram showing maximum temperatures were warmer than the 2006–2020 averages in every month except November, January and March. Minimum temperatures were warmer than average in every month except January and March. Precipitation totals for WY2024 were similar to the 2006–2020 averages in two months, and substantially below average in 10 months.
Figure 6. Climogram showing monthly precipitation and mean maximum and minimum air temperatures in water year (WY) 2024 and the 2006–2020 averages at Rio Grande Village Texas station, Big Bend National Park. Data source: The Climate Analyzer; climateanalyzer.org.

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Drought

Highlight: The park was drier than average in WY2024 for the fifth consecutive year except at Chisos Basin, which has been drier than average for three years in a row.

Reconnaissance drought index (Tsakiris and Vangelis 2005) provides a measure of drought severity and extent relative to the long-term climate. It is based on the ratio of average precipitation to average potential evapotranspiration (the amount of water loss that would occur from evaporation and plant transpiration if the water supply was unlimited) over short periods of time (seasons to years). The reconnaissance drought indices for Big Bend National Park indicate that WY2024 was drier than the 1991–2024 average for the fifth consecutive year from the perspective of both precipitation and potential evapotranspiration at all monitoring locations except Chisos Basin, which has been drier than average for three consecutive years (Figures 7–11).

Figure 7. Bar graph showing conditions were drier than the average since water year 2022.
Figure 7. Reconnaissance drought index for Chisos Basin station at Big Bend National Park, water years (WY) 1991–2024. Drought index calculations are relative to the time period selected (1990–2024). Choosing a different set of start/end points may produce different results. N/A = insufficient data to generate reliable estimates. Data source: The Climate Analyzer; climateanalyzer.org.

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Figure 8. Bar graph showing conditions were drier than average since water year 2020.
Figure 8. Reconnaissance drought index for Panther Junction station at Big Bend National Park, water years (WY) 1991–2024. Drought index calculations are relative to the time period selected (1990–2024). Choosing a different set of start/end points may produce different results. N/A = insufficient data to generate reliable estimates. Data source: The Climate Analyzer; climateanalyzer.org.

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Figure 9. Bar graph showing conditions were drier than average since water year 2020.
Figure 9. Reconnaissance drought index for Persimmon Gap station at Big Bend National Park, water years (WY) 1991–2024. Drought index calculations are relative to the time period selected (1990–2024). Choosing a different set of start/end points may produce different results. N/A = insufficient data to generate reliable estimates. Data source: The Climate Analyzer; climateanalyzer.org.

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Figure 10. Bar graph showing conditions were drier than average since water year 2020.
Figure 10. Reconnaissance drought index for Castolon station at Big Bend National Park, water years (WY) 1991–2024. Drought index calculations are relative to the time period selected (1990–2024). Choosing a different set of start/end points may produce different results. N/A = insufficient data to generate reliable estimates. Data source: The Climate Analyzer; climateanalyzer.org.

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Figure 11. Bar graph showing conditions were drier than average since water year 2020.
Figure 11. Reconnaissance drought index for Rio Grande Village Texas station at Big Bend National Park, water years (WY) 2007–2024. Drought index calculations are relative to the time period selected (2006–2024). Choosing a different set of start/end points may produce different results. N/A = insufficient data to generate reliable estimates. Data source: The Climate Analyzer; climateanalyzer.org.

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Groundwater

Groundwater is one of the most critical natural resources of the American Southwest, providing drinking water, irrigating crops, and sustaining rivers, streams, and springs throughout the region. 

Methods

Groundwater at Big Bend National Park is monitored in nine wells. Eight wells have been monitored by park staff since 2012 using automated methods: Contractor’s, Gallery, Gambusia, K-Bar #6, K-Bar #7, Oak Springs #1, T-3, and Th-10. One well, Panther Junction #10, has been monitored by the Texas Water Development Board (TWDB) since 2007 using automated methods. TWDB data are available at the TWDB Database.

Results

Highlights: Recent declines in groundwater levels continued across seven wells, three of which hit their lowest water level on record. Water levels in T-3 and TH-10 wells rose slightly.

Average groundwater levels in seven wells decreased between WY2023 and WY2024 (based on a subset of available WY2023 data): Contractor’s, Gallery, Gambusia, K-Bar #6, K-Bar #7, Oak Springs #1, and Panther Junction #10 wells (Table 2, Figure 12). Decreases were ≤1.32 ft (0.40 m) except at Panther Junction #10 well, which decreased 12.39 ft (3.78 m). Average water level in wells T-3 and TH-10 rose ≤0.25 ft (0.08 m) since WY2023. Three wells recorded their lowest water level in the monitoring record in WY2024: Gallery, Gambusia, and Oak Springs #1 wells.

Table 2. Groundwater monitoring results in water year (WY) 2024, Big Bend National Park (amsl = above mean sea level; bgs = below ground surface). Due to missing data, most of these WY2023 average elevations are based on a subset of WY2023 data, except for Panther Junction #10, which has a complete set of WY2023 data, and Contractor’s and Oak Springs #1, where averages are based on data from other water years.
State Well Area of Park Wellhead
Elevation
(ft)		 Mean Depth
to Water
(ft bgs)		 Mean Water
Level Elevation
(ft amsl)		 Elevation Change
from WY2023
(± ft)		 Elevation Change (± ft)
from Earliest Recorded
Water Level (year)
Gambusia Rio Grande 1855.00 6.52 1848.48 −0.78 −2.52 (1984)
Gallery Rio Grande 2126.00 19.66 2106.34 −1.32 −9.14 (1969)
K-Bar #7 Panther Junction 3460.00 68.04 3391.96 −1.15 5.55 (1984)
TH-10 Panther Junction 3466.00 42.87 3423.13 0.19 −7.28 (1967)
K-Bar #6 Panther Junction 3498.00 106.82 3391.18 −1.21 0.09 (1984)
T-3 Panther Junction 3617.20 97.27 3519.93 0.25 10.89 (1964)
Panther Junction #10 Panther Junction 3887.00 163.79 3723.21 −12.39 −2.29 (2006)
Contractor’s A Chisos Basin 3753.00 42.50 3710.50 −1.26 B −1.00 (1971)
Oak Spring #1 A Chisos Basin 4165.00 61.93 4103.07 −0.84 C −28.10 (1989)

A Water levels are based on one manual measurement.

B Change in elevation compared to a single manual measurement in WY2021 because of missing data.

C Change in elevation compared to WY2022 because of missing data.

Figure 12. Line graph showing water levels at nine wells. Three wells had their lowest water level in WY2024. Panther Junction # 10, K-Bar #7, K-Bar #6, and T-3 wells had the most variation over time.
Figure 12. Depth to water in feet below ground surface (ft bgs) at nine groundwater monitoring wells at Big Bend National Park, 2011–2024. A break in a continuous line indicates missing data.

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Rio Grande Wells

Water levels in Gallery and Gambusia are consistently shallow and have demonstrated low variability; water level changes have ranged within 7.99 ft (2.44 m) and 3.08 ft (0.94 m), respectively. Both wells are close to the Rio Grande and respond to changes in river flow, often increasing in late summer or fall following high flow events. However, this signal is weaker at Gambusia, which is likely regulated by nearby springs.

Panther Junction Wells

Water level elevations in wells K-Bar #6 and K-Bar #7 have been very similar for the entire monitoring record as they are 0.45 mi (0.72 km) apart and completed in the same aquifer. Water levels in both wells peaked in 2019 following a large rain event in 2018, and their water levels have been slowly declining since then. T-3 well exhibits similar periods of increasing and decreasing water levels even though it is >130 ft (39.6 m) higher than the K-Bar wells. Water level in Panther Junction #10 well is the most variable of the Big Bend National Park monitoring wells, with a range of 143 ft (43.6 m) in water level elevation change over the monitoring record. This is likely due to rapid infiltration of rain though fractured volcanic rock, which then seeps to deeper aquifers. TH-10 well water level has been very stable, showing only 13.60 ft (4.14 m) of variation in water level over the monitoring record, with muted responses to large rain events compared to the other Panther Junction wells.

Chisos Basin Wells

Water levels in Contractor’s well appear to respond quickly to rain events, indicating rapid infiltration similar to Panther Junction #10 well; however, the response in Contractor’s well is much more muted. Water levels in Oak Springs #1 well showed the greatest decline since the first measurement in 1989 but water levels have been stable with little variation since 2011 when more frequent monitoring began.

Springs

Background

Springs, seeps, and tinajas (discrete pools in a rock basin or impoundments in bedrock) are small, relatively rare biodiversity hotspots in arid lands. They are the primary connection between groundwater and surface water and are important water sources for plants and animals. For springs, the most important questions we ask are about persistence (How long was there water in the spring?) and water quantity (How much water was in the spring?). WY2024 springs sampling at Big Bend National Park occurred between 01 February and 20 February 2024. Water persistence is monitored continuously throughout the water year, but in this report, we only present WY2024 persistence data up to the sampling visit date for each spring.

Methods

Chihuahuan Desert Network springs monitoring is organized into the four modules described below (see McIntyre et al. 2018 for additional details) and eDNA inventories. All data have undergone certification processes to ensure they have been verified and validated for accuracy, are complete, and are fully documented. Data used in this report are available to park staff on the NPS DataStore and can be provided upon request.

Site Characterization

This module provides context for interpreting change in the other modules. We record GPS locations, draw a site diagram, and describe the spring type (e.g., helocrene, limnocrene, rheocrene, or tinaja) and its associated vegetation in this module. Helocrene springs emerge as low-gradient wetlands, limnocrene springs emerge as pools, and rheocrene springs emerge as flowing streams. This module is completed once every five years or after significant events.

Site Condition

We estimate the level of natural and anthropogenic disturbances and the level of stress on vegetation and soils at the spring on a scale of 1–4, where 1 = undisturbed, 2 = slightly disturbed, 3 = moderately disturbed, and 4 = highly disturbed. Types of natural disturbances can include flooding, drying, fire, wildlife impacts, windthrow of trees and shrubs, beaver activity, and insect infestations. Anthropogenic disturbances can include roads, off-highway vehicle trails, hiking trails, livestock and feral-animal impacts, removal of invasive non-native plants, flow modification, and other evidence of human use of the spring site. We take repeat photographs from the same location and perspective to show the spring and its landscape context. We note the presence of certain obligate wetland plant species (plant species that almost always occur only in wetlands), facultative wetland plant species (plant species that usually occur in wetlands, but also occur in other habitats), and invasive non-native crayfish and American bullfrog (Rana catesbeiana). We also record the density of invasive non-native plants using a qualitative scale (1–5 plants, scattered patches, evenly distributed patches, or a matrix). We complete the site condition module during each springs monitoring visit.

Water Quantity

We measure the persistence of surface water, amount of spring discharge, and wetted extent (area that contained water). To estimate persistence, we analyze the variance of temperature measurements taken by two logging thermometers placed at or near the orifice (spring opening). Because water mediates variation in diurnal temperatures, data from a submerged sensor will show less daily variation than data from an exposed, open-air sensor; this tells us when the spring was wet or dry. Surface discharge is measured with a timed sample of water volume. Wetted extent is a systematic measurement of the physical length (up to 100 m), width, and depth of surface water. It is assessed using a technique for either standing water (e.g., limnocrene and helocrene springs) or flowing water (e.g., rheocrene springs). We complete discharge and wetted extent measurements during each visit when possible. Water persistence measurements are continuous throughout the year.

Water Quality

We measure core water quality and water chemistry parameters. Core water quality parameters include water temperature, pH, specific conductivity (a measure of dissolved compounds and contaminants), dissolved oxygen (how much oxygen is present in the water), and total dissolved solids (an indicator of potentially undesirable compounds). Discrete measurements of these parameters are collected with a multiparameter meter. If the meter fails calibration checks, we do not present data. Water chemistry is assessed by collecting surface water samples and estimating the concentration of major ions with a photometer in the field. These parameters are collected at one or more sampling locations within a spring. Data are presented only for the primary sampling location within each spring. Each perennial spring is somewhat unique, and Texas has not adopted water quality standards that would apply across the diversity of springs described here. Ongoing, long-term data collection at each spring will improve our understanding of the natural range in water quality and water chemistry parameters for a given site. We complete the water quality module during each visit when possible.

eDNA Inventory of Rare and Invasive Species and Pathogens

We inventory rare species, invasive species, and pathogens in perennial springs using environmental DNA (eDNA) techniques. In 2023 and 2024, four or more water samples (250 mL/sample) were collected and filtered (0.45 µm) from each spring and then preserved in ethanol prior to DNA extraction and analysis by the Goldberg Lab at Washington State University. Our target organisms for the inventory include American bullfrog (Rana catesbeiana), chytrid fungus (Batrachochytrium dendrobatidis), ranavirus (Iridoviridae), red spotted toad (Bufo punctatus), Rio Grande leopard frog (Rana berlandieri), and Woodhouse’s toad (Anaxyrus woodhousii).

Results

Bois D’Arc Spring

Highlights: The spring and all previously wet orifices were dry when we visited in February 2024. The temperature sensor was buried in sediment, so persistence data may be unreliable.

Bois D’Arc Spring (Figures 13 and 14) is a rheocrene spring (a spring that emerges into one or more stream channels). The spring is located within a bedrock canyon on the north side of the Chisos Mountains. It forms an intermittent channel that has ranged in length from 0 m to over 100 m in recent years. The WY2024 visit occurred on 01 February 2024, and the spring was dry.

Figure 13. A person standing on exposed bedrock pointing to a low spot in a rocky streambed in a desert canyon, with brown grasses and shrubs along one side. Two other scientists are behind them, one holding a pole with an instrument mounted on top and the other sitting on the ground holding a clipboard.
Figure 13. The primary emergence of Bois D’Arc Spring in Big Bend National Park was dry in February 2024.

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Figure 14. View of desert hillside and canyon dotted with cacti, shrubs, and grasses. There is a small pool of water on the floor of the canyon and a person is sitting on exposed bedrock next to backpacks and monitoring equipment.
Figure 14. Overview of the canyon and surrounding landscape at Bois D’Arc Spring at Big Bend National Park, February 2024. The primary emergence is in the center bottom of the image.

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Site Condition

In WY2024, we rated Bois D’Arc Spring slightly disturbed by feral animals because there was an aoudad (Ammotragus lervia) carcass observed near the spring (rated undisturbed to slightly disturbed in the past); slightly disturbed by recent flooding based on fresh recent gravel deposits and uprooted vegetation within the channel (rated undisturbed to moderately disturbed in the past); highly disturbed by drying because there was no water in any of the previously wetted orifices, and there were upland species in the riparian area (rated undisturbed to highly disturbed in the past); and slightly disturbed by wildlife, with scat and evidence of animal bedding (rated undisturbed to moderately disturbed in the past; Figure 15). No other natural or human-caused disturbances were observed at Bois D’Arc Spring in WY2024.

Figure 15. Two images: One is a patch of tall, dried bunch grasses next to scrubby desert plants on a slope with large areas of exposed rock. The other image shows tufts of dried grass that are partially flattened on the ground in a shrubby area.
Figure 15. Examples of disturbance at Bois D’Arc Spring in WY2024. Left: invasive non-native Lehmann lovegrass (Eragrostis lehmanniana) in scattered patches. Right: a wildlife bedding area.

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As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Bois D’Arc Spring in WY2024. We found one invasive non-native plant species at the spring: scattered patches of Lehmann lovegrass (Eragrostis lehmanniana, scattered to evenly distributed patches observed in 2018–2023). We observed two obligate/facultative wetland plant species: monkeyflower (Mimulus sp., a forb observed in 2018–2021) and mule-fat (Baccharis salicifolia, a shrub observed in 2019).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, four water samples were collected from isolated pools of water near Bois D’Arc Spring. Similar to WY2023, none of our target organisms were detected.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 16). The temperature sensor indicated that Bois D’Arc Spring was wetted (contained water) for all 124 days (100%) measured in WY2024 up to the visit but the sensor was buried in sediment, so the readings may be false, especially since the spring was completely dry when we visited. In prior water years, the spring was wetted 5.8–88.5% of the days measured across entire years.

Figure 16. Area chart showing a pattern of drying in the summer months, which extended into the winter in 2023. The spring contained water in winter 2019, 2020, and 2024. Data are missing from August 2020 to March 2021, and July 2021 to March 2022.
Figure 16. Water persistence through 01 February 2024 in Bois D’Arc Spring, Big Bend National Park. The sensor was completely buried in sediment at the time of our visit, which may have produced false wetted readings. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

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Discharge was not measured in WY2024 at the primary sampling location since the spring was dry. Discharge estimates ranged from 0.8–7.8 L/min (0.2–2.1 gal/min) in 2019–2020 (Table 3). The flowing water method for wetted extent was not used in WY2024 because the spring was dry. Past data are summarized in Table 4.

Table 3. Discharge data (L/min; mean ± SD) for Bois D’Arc Spring in water year (WY) 2024 could not be measured as the spring was dry: the range of means from prior years is given. c.n.s. = could not sample.
Sampling Location WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
005 c.n.s. (0.8–7.8) 2019–2020 (2)

Table 4. Wetted extent of Bois D’Arc Spring could not be measured in 2024 as the spring was dry: length and average (± SD) width and depth of Bois D’Arc Spring (measured within the first 100 m of springbrook length) from prior years is given. c.n.s. = could not sample.
Measurement WY2024 Value
(Range of Prior Values/Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (cm) c.n.s. (23.7–93.1) 2018–2023 (5)
Depth (cm) c.n.s. (0.9–8.9) 2018–2023 (5)
Length (m) c.n.s. (2.2–100.0) 2018–2023 (5)
Water Quality

Core water quality data and water chemistry data were not collected at the primary sampling location in WY2024 because the spring was dry. Past data are summarized in Tables 5 and 6.

Table 5. Core water quality data for Bois D’Arc Spring could not be collected in water year (WY) 2024 as the spring was dry: the range of values from prior years is given. c.n.s. = could not sample.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
002 Dissolved oxygen (mg/L) c.n.s. (7.66–11.81) 2021–2023 (2)
002 pH c.n.s. (7.86–9.64) 2021–2023 (2)
002 Specific conductivity (µS/cm) c.n.s. (240.3–319.5) 2021–2023 (2)
002 Temperature (°C) c.n.s. (9.5–11.7) 2021–2023 (2)
002 Total dissolved solids (mg/L) c.n.s. (156–208) 2021–2023 (2)

Table 6. Water chemistry data (mg/L) for Bois D’Arc Spring could not be collected in water year (WY) 2024 as the spring was dry: the range of values from prior years is given. c.n.s. = could not sample. b.d.l. = below detection limit.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
002 Alkalinity (CaCO3) c.n.s. (75–90) 2021–2023 (2)
002 Calcium (Ca) c.n.s. (22–52) 2021–2023 (2)
002 Chloride (Cl) c.n.s. (0–4) 2021–2023 (2)
002 Magnesium (Mg) c.n.s. (b.d.l.–10) 2021–2023 (2)
002 Potassium (K) c.n.s. (0.0–1.8) 2021–2023 (2)
002 Sulphate (SO4) c.n.s. (0) 2021–2023 (2)

Cattail Falls

Highlights: The spring contained water when we visited and normally has water year round, though persistence data are unavailable for WY2024. We observed flatsedge, a wetland plant that had not previously been detected. Rio Grande leopard frogs were detected in all eDNA samples and chytrid fungus in one. The site is heavily trampled by hikers.

Cattail Falls (Figures 17 and 18) is a rheocrene spring (a spring that emerges into one or more stream channels). The spring is in Cattail Canyon on the northwest side of the Chisos Mountains. It begins high in the mountains and flows over a steep pouroff into a wide pool. A channel flows out of the pool, forming deep, clear plunge pools surrounded by boulders and dense vegetation. The springbrook has consistently reached 95–98 m in length (measured from the base of the falls) in recent years. The WY2024 visit occurred on 06 February 2024, and the spring contained water.

Figure 17. A person beside a dark, reflective pool pointing to the base of a sheer, dark cliff face dripping with water that borders the pool.
Figure 17. Cattail Falls at Big Bend National Park, February 2024. Since the actual orifice is inaccessible above the waterfall, our monitoring begins at the base of the falls.

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Figure 18. Reflective pools of water surrounded by large boulders, bright green plants, and leaf litter. Trees line the channel and some overhang the streambrook.
Figure 18. Downstream view of the springbrook, midway down the channel, and surrounding landscape at Cattail Falls in Big Bend National Park, February 2024.

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Site Condition

In WY2024, we rated Cattail Falls as highly disturbed by hiking trails because there was trampling of riparian vegetation by hikers (Figure 19). A popular hiking trail leads to the spring and crosses the springbrook. Vegetation cover is reduced on approximately 50% of the area surrounding the pool at the base of the falls, especially where the trail crosses the springbrook. In the past, we rated the spring moderately to highly disturbed by human use and hiking trails. We also rated the spring as slightly disturbed by windthrow as there were downed trees in and across the springbrook (rated undisturbed to moderately disturbed in the past). No other natural or human-caused disturbances were observed at Cattail Falls in WY2024. Native frogs, tadpoles, and frog eggs were observed in the pools in WY2024.

Figure 19. A dirt path alongside water in a canyon with steep rock walls, small trees, and large boulders.
Figure 19. A hiking trail and trampling along the streambank at Cattail Falls in WY2024.

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As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Cattail Falls in WY2024, nor did we find any invasive non-native plants at the spring. We observed six obligate/facultative wetland plant species: bluestem (Andropogon sp., a grass observed in 2018–2023); cattail (Typhaceae, observed in 2018–2023); flatsedge (Cyperus sp., not previously observed); lobelia (Lobelia sp., a forb observed on three site visits between 2017 and 2023); maidenhair fern (Adiantum sp., observed in 2018–2023); and a member of the rush family (Juncaceae, observed in 2018–2023).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, 10 water samples were collected from Cattail Falls. Rio Grande leopard frog was detected in all 10 samples and chytrid fungus, the pathogen responsible for chytridiomycosis in amphibians, was detected in one sample. In WY2023, chytrid was detected in five of the 10 water samples collected. We were unable to test for Rio Grande leopard frog in WY2023 samples.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 20). Temperature sensor data are missing because of sensor failure, so there is no estimate of persistence for WY2024. In prior water years, the spring was wetted (contained water) 96.3–100% of the days measured across entire years.

Figure 20. Area chart showing Cattail Falls Spring was persistently wet since monitoring began in 2018 except for a short dry period in the fall of 2018. Data are missing for the annual monitoring cycle beginning in March 2020 and March 2023.
Figure 20. Water persistence through 06 February 2024 in Cattail Falls, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

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Discharge was estimated at 33.3 ± 2.3 L/min (8.8 ± 0.6 gal/min), which was lower than previous measurements of 40.1–72.1 L/min (10.6–19.0 gal/min) in 2018–2023 (Table 7). Wetted extent was evaluated using a method for flowing water. Overall, the wetted extent of Cattail Falls was comparable to prior years. The total springbrook length was 96.8 m (317.6 ft), which is consistent with the historical range of 94.7–98.9 m (310.7–324.5 ft). Width and depth along the springbrook averaged 3.6 m (11.8 ft), and 12.4 cm (4.9 in), respectively, both similar to prior means. (Table 8).

Table 7. Discharge data (L/min; mean ± SD) for Cattail Falls in water year (WY) 2024 and a range of means from prior years.
Sampling Location WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
003 33.3 ± 2.3 (40.1–72.1) 2018–2023 (6)

Table 8. Length and average (± SD) width and depth of Cattail Falls (measured within the first 100 m of springbrook length) in water year (WY) 2024 and ranges of length values and width and depth means from prior years.
Measurement WY2024 Value
(Range of Prior Values/Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (m) 3.6 ± 4.0 (3.0–4.2) 2018–2023 (6)
Depth (cm) 12.4 ± 4.6 (6.1–16.3) 2018–2023 (6)
Length (m) 96.8 (94.7–98.9) 2018–2023 (6)
Water Quality

Core water quality (Table 9) and water chemistry (Table 10) data were collected at the primary sampling location on the river left edge of the main pool at the base of the falls in WY2024. Dissolved oxygen, pH, and temperature were all within the ranges of prior measurements. Specific conductivity and total dissolved solids values were higher than in prior years. Values for chloride, magnesium, and potassium were within ranges of prior values, while values for alkalinity, calcium, and sulphate were higher.

Table 9. Core water quality data for Cattail Falls in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 6.42 (3.44–8.49) 2018–2023 (6)
001 pH 7.56 (7.04–8.10) 2018–2023 (6)
001 Specific conductivity (µS/cm) 489.9 (200.7–459.4) 2018–2023 (6)
001 Temperature (°C) 10.5 (9.5–14.6) 2018–2023 (8)
001 Total dissolved solids (mg/L) 318.4 (130.0–299.0) 2018–2023 (6)

Table 10. Water chemistry data (mg/L) for Cattail Falls in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 180 (25–130) 2018–2023 (6)
001 Calcium (Ca) 58 (2–54) 2018–2023 (6)
001 Chloride (Cl) 10 (1–27) 2018–2023 (6)
001 Magnesium (Mg) 13 (7–14) 2018–2023 (6)
001 Potassium (K) 1.6 (1.3–1.9) 2018–2023 (6)
001 Sulphate (SO4) 126 (33–93) 2018–2023 (6)

Chilicotal Spring Complex

Highlights: The spring contained water year round and discharge was similar to the previous measurement. The site was highly disturbed by a recent flood. We observed the wetland plant centaury for the first time, and we detected Rio Grande leopard frogs and chytrid in eDNA samples.

Chilicotal Spring Complex (Figures 21 and 22) is a rheocrene spring (a spring that emerges into one or more stream channels). The spring complex is inside a drainage in the desert shrublands northeast of Chilicotal Mountain. It emerges from the side of a steep and densely vegetated bank, forming a springbrook that can reach up to 200–500 m in length, but is typically only accessible in the upper reaches. The WY2024 visit occurred on 15 February 2024, and the spring contained water.

Figure 21. Close-up of a tangled thicket of branches and foliage surrounding a wetted area. A person’s arm can be seen pointing at the wet ground.
Figure 21. The primary emergence of Chilicotal Spring Complex under thick brush on a hillside at Big Bend National Park, February 2024.

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Figure 22. A desert drainage containing green shrubs and trees that flows out into a series of brown, dry desert washes through sandy desert hills. Distant mountains are visible on the horizon.
Figure 22. Overview of Chilicotal Spring Complex and the surrounding landscape at Big Bend National Park, February 2024. The primary emergence is out of view on the left, and the springbrook continues from left to right down the densely vegetated drainage.

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Site Condition

In WY2024, we rated Chilicotal Spring Complex highly disturbed by recent flooding because of fresh gravel deposition, channel incision, wrack, scouring, and flood debris in the channel (rated undisturbed to highly disturbed in the past; Figure 23). No other natural or human-caused disturbances were observed at Chilicotal Spring Complex in WY2024. One live frog, one dead frog, and multiple tadpoles (species unknown) were incidentally observed during the site visit.

Figure 23. Left image shows large patches of dried grasses along a wet channel surrounded by desert slopes of exposed rock and sparse desert plants. Right image shows gravel and debris patches above the stream channel and branches and other plant material clumped in a tree along the channel.
Figure 23. Examples of disturbance at Chilicotal Spring Complex in WY2024. Left: a matrix of invasive non-native Lehmann lovegrass (Eragrostis lehmanniana). Right: evidence of recent flooding (gravel deposition, wrack, flood debris).

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We did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Chilicotal Spring Complex in WY2024. We did find two species of invasive non-native plants at the spring: a matrix of Bermudagrass (Cynodon dactylon, scattered patches to a matrix observed in 2017–2023) and 1–5 saltcedar plants (Tamarix sp., 1–5 plants observed in 2017–2023). We observed eight obligate/facultative wetland plant species: bluestem (Andropogon sp., a grass observed in 2017–2021); cattail (Typhaceae, observed in 2017–2023); centaury (Centarium sp., a forb not previously observed); cottonwood (Populus sp., a tree observed in 2019–2023); mule-fat (Baccharis salicifolia, a shrub observed in 2017–2023); a member of the rush family (Juncaceae, observed in 2018–2023); tamarisk (Tamarix sp., a tree observed in 2017–2023); and willow (Salix sp., a tree observed in 2017–2023).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, nine water samples were collected from Chilicotal Spring Complex. Rio Grande leopard frog was detected in five of the samples and chytrid fungus, the pathogen responsible for chytridiomycosis in amphibians, was detected in four samples. In WY2023, chytrid fungus was detected in two of the eight samples collected. We were unable to test for Rio Grande leopard frog in WY2023 samples.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 24). The temperature sensor indicated that Chilicotal Spring Complex was wetted (contained water) for all 138 days (100%) measured in WY2024 up to the visit. In prior water years, the spring was wetted 51.4–100% of the days measured across entire years.

Figure 24. Area chart showing drying at Chilicotal Spring Complex in the summer and fall of 2018, 2019, and 2020. Data are missing for the period between sensor deployments in 2021 and 2022. Since sensor deployment in 2022, the spring has had water.
Figure 24. Water persistence through 15 February 2024 in Chilicotal Spring Complex, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

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Discharge was estimated at 18.4 ± 0.3 L/min (4.9 ± 0.1 gal/min), which was consistent with the one prior measurement for this sampling location of 18.1 L/min (4.8 gal/min) in 2023 (Table 11). Wetted extent was not measured at Chilicotal Spring Complex in WY2024. In past years, springbrook lengths have ranged from a measured 22.1 m (72.5 ft) to estimates of more than 100 m (more than 328 ft; Table 12).

Table 11. Discharge data (L/min; mean ± SD) for Chilicotal Spring Complex in water year (WY) 2024 and a range of means from prior years.
Sampling Location WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
001 18.4 ± 0.3 (18.1) 2023 (1)

Table 12. Length and average (± SD) width and depth of Chilicotal Spring Complex (measured within the first 100 m of springbrook length) in water year (WY) 2024 and ranges of length values and width and depth means from prior years. c.n.s. = could not sample.
Measurement WY2024 Value
(Range of Prior Values/Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (cm) c.n.s. (40.1–575.9) 2018–2023 (6)
Depth (cm) c.n.s. (1.3–21.8) 2018–2023 (6)
Length (m) c.n.s. (22.1–100.0) 2018–2023 (6)
Water Quality

Core water quality (Table 13) and water chemistry (Table 14) data were collected at the primary sampling location. In WY2024 all water quality and chemistry values were within the ranges of prior measurements.

Table 13. Core water quality data for Chilicotal Spring Complex in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 6.24 (5.22–8.69) 2018–2023 (6)
001 pH 7.65 (7.44–7.80) 2018–2023 (6)
001 Specific conductivity (µS/cm) 353.3 (343.5–381.1) 2018–2023 (6)
001 Temperature (°C) 13.6 (10.3–17.6) 2018–2023 (8)
001 Total dissolved solids (mg/L) 229.7 (222.9–248.0) 2018–2023 (6)

Table 14. Water chemistry data (mg/L) for Chilicotal Spring Complex in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 145 (135–185) 2018–2023 (6)
001 Calcium (Ca) 34 (26–46) 2018–2023 (6)
001 Chloride (Cl) 8 (8–23) 2018–2023 (6)
001 Magnesium (Mg) 13 (5–80) 2018–2023 (6)
001 Potassium (K) 0.6 (0.0–1.4) 2018–2023 (6)
001 Sulphate (SO4) 6 (0–8) 2018–2023 (6)

De La Ho Spring

Highlights: The spring has contained water year round since monitoring began in 2018. The wetted area was smaller than in any prior year. We detected Rio Grande leopard frogs and chytrid in the eDNA samples.

De La Ho Spring (Figures 25 and 26) is a helocrene spring (a spring that emerges into marshy, wet meadow settings—low-gradient wetlands) located about 3 km southeast of Cerro Castolon. The spring is a shallow pool surrounded by a dense thicket of trees and shrubs and is confined by a rock wall on one bank. The pool has measured up to 7.5 m long and 4.4 m wide in recent years. The WY2024 visit occurred on 05 February 2024, and the spring contained water.

Figure 25. A person points to a small wetted area in a dense thicket of dry, thorny bushes with leaf litter in the foreground.
Figure 25. The primary emergence at De La Ho Spring in Big Bend National Park, February 2024. The orifice is on the upstream edge of a shallow pool, where water is accessible under thick brush.

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Figure 26. Thick green and yellow vegetation obscuring the ground and most of the sky.
Figure 26. Overview of the dense vegetation surrounding De La Ho Spring at Big Bend National Park, February 2024.

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Site Condition

In WY2024, we rated De La Ho Spring slightly disturbed by trespass livestock based on the presence of cattle feces and tracks in the drainage leading to the spring (rated undisturbed to slightly disturbed in the past). No other natural or human-caused disturbances were observed at De La Ho Spring in WY2024.

As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at De La Ho Spring in WY2024. We recorded one invasive non-native plant species at the spring: scattered patches of tree tobacco (Nicotiana glauca, 1–5 plants to scattered patches observed in 2017–2023; Figure 27). We observed three obligate/facultative wetland plant species: mule-fat (Baccharis salicifolia, a shrub observed in 2017–2023); a member of the rush family (Juncaceae, observed in 2018–2023); and willow (Salix sp., a tree observed in 2017–2023).

Figure 27. A person holds a long stem of a green, leafy plant among a dense thicket of vegetation.
Figure 27. An invasive non-native tree tobacco (Nicotiana glauca) plant at De La Ho Spring in February 2024.

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eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, four water samples were collected from De La Ho Spring. Rio Grande leopard frog and chytrid fungus, the pathogen responsible for chytridiomycosis in amphibians, were found in all four samples. In WY2023, chytrid fungus was detected in three of the four water samples collected. We were unable to test for Rio Grande leopard frog in WY2023 samples.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 28). The temperature sensor indicated that De La Ho Spring was wetted (contained water) for all 128 days (100%) measured in WY2024 up to the visit. In prior water years, the spring was wetted 100% of the days measured across entire years.

Figure 28. Area chart showing De La Ho Spring has been continuously wetted since the first sensor deployment in 2018.
Figure 28. Water persistence through 05 February 2024 in De La Ho Spring, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

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As in past years, there was no measurable discharge. Wetted extent was evaluated using a method for standing water. In WY2024, width averaged 2.5 m (8.1 ft), length averaged 3.9 m (12.6 ft), and depth averaged 5.3 cm (2.1 in). In WY2024, average width and length were lower than any prior measurements in the last six years, while depth remained within its historical range (Table 15).

Table 15. Average (± SD) width, depth, and length of De La Ho Spring in water year (WY) 2024 and a range of means from prior years.
Measurement WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (m) 2.5 ± 0.2 (2.7–4.4) 2018–2023 (6)
Depth (cm) 5.3 ± 5.0 (2.0–17.5) 2018–2023 (6)
Length (m) 3.9 ± 1.8 (4.9–7.5) 2018–2023 (6)
Water Quality

Core water quality (Table 16) and water chemistry (Table 17) data were collected at the primary sampling location along the edge of the pool next to the rock wall in WY2024. Values for dissolved oxygen, pH, specific conductivity, and total dissolved solids were within ranges recorded in previous years, while water temperature was lower than previous values. Alkalinity, chloride, magnesium, potassium, and sulphate values were within ranges of prior measurements, while the calcium level was slightly higher than previously observed.

Table 16. Core water quality data for De La Ho Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 1.75 (0.18–16.69) 2018–2023 (6)
001 pH 7.43 (7.39–8.89) 2018–2023 (6)
001 Specific conductivity (µS/cm) 590.0 (495.7–612.0) 2018–2023 (6)
001 Temperature (°C) 11.9 (17.6–26.0) 2018–2023 (8)
001 Total dissolved solids (mg/L) 383.3 (317.0–398.0) 2018–2023 (6)

Table 17. Water chemistry data (mg/L) for De La Ho Spring in water year (WY) 2024 and a range of values from prior years. b.d.l. = below detection limit.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 180 (b.d.l.–185) 2018–2023 (6)
001 Calcium (Ca) 28 (14–26) 2018–2023 (6)
001 Chloride (Cl) 17 (6–17) 2018–2023 (6)
001 Magnesium (Mg) 10 (b.d.l.–13) 2018–2023 (6)
001 Potassium (K) 4.4 (2.6–4.8) 2018–2023 (6)
001 Sulphate (SO4) 80 (40–118) 2018–2023 (6)

Government Spring

Highlights: The spring contained water when we visited in February 2024, but persistence data are missing for the year. There was trash and vegetation trampling related to the hiking trail nearby. We detected Rio Grande leopard frog in one of the four eDNA samples.

Government Spring (Figures 29 and 30) is a limnocrene spring (a spring emerging as a pool). The spring is near an established campsite and the intersection of Grapevine Hills Road and the main park road. The spring is diverted into a locked springbox, and it also forms a pool located 15–20 m away, with no surface channel connecting the two. The pool has been measured up to 4 m wide and 6.5 m long in recent years. Water in the springbox and pool is cool and clear with significant leaf litter from surrounding trees. The WY2024 visit occurred on 03 February 2024, and the spring contained water.

Figure 29. Person standing on top of a rectangular concrete structure surrounded by dense shrubs and leaf litter, under a blue sky.
Figure 29. Springbox at Government Spring at Big Bend National Park, February 2024.

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Figure 30. Person standing on the bank next to a pool of water surrounded by leaf litter, dried grasses, and leafless shrubs.
Figure 30. Pool at Government Spring in Big Bend National Park, February 2024.

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Site Condition

In WY2024, we rated Government Spring moderately disturbed by roads with a road that is about 50 m from the spring (rated undisturbed to moderately disturbed in the past); moderately disturbed by contemporary human use because of the presence of trails, trash, and vegetation trampling (rated slightly to highly disturbed in the past); highly disturbed by hiking trails, with a social trail leading directly to the riparian area from a nearby campsite (rated slightly to highly disturbed in the past); and highly disturbed by flow modification since flow is diverted into a springbox (rated highly disturbed in the past; Figure 31). No other natural or human-caused disturbances were observed at Government Spring in WY2024.

Figure 31. Four images: two images show scattered patches of dried grasses, another is a social trail through green and leafless shrubs in a desert landscape, and the last is a closeup of coyote scat in a rocky area.
Figure 31. Examples of disturbance at Government Spring in February 2024. Clockwise from top left: scattered patches of invasive non-native Bermudagrass (Cynodon dactylon); scattered patches of invasive non-native Lehmann lovegrass (Eragrostis lehmanniana); wildlife scat; and a social trail leading to the spring.

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As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Government Spring in WY2024. We found three species of invasive non-native plants at the spring: scattered patches of Bermudagrass (Cynodon dactylon, scattered patches to evenly distributed patches observed in 2019–2023); scattered patches of Lehmann lovegrass (Eragrostis lehmanniana, scattered patches to evenly distributed patches observed in 2020–2023); and scattered patches of horehound (Marrubium vulgare, scattered patches observed in 2019–2023). We observed three obligate/facultative wetland plant species: common buttonbush (Cephalanthus occidentalis, a shrub observed in 2021–2023); cottonwood (Populus sp., a tree observed in 2019–2023); and mule-fat (Baccharis salicifolia, a shrub observed in 2019–2023).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, four water samples were collected from Government Spring. Rio Grande leopard frog was detected in one of the four samples. In WY2023, none of our target organisms were detected, but we were unable to test for Rio Grande leopard frog that year.

Water Quantity

Temperature sensor data are missing because the sensor failed, so there is no estimate of persistence for WY2024 (Figure 32). In prior water years, the spring was wetted (contained water) 53.4–84.9% of the days measured across entire years.

Figure 32. Area chart showing the spring has alternated between wet and dry periods most of the time, except when it was mostly wetted from spring through fall of 2019 and winter of 2022. Data are missing starting a few weeks after sensor deployment in 2022 through the 2023 visit. The spring was wetted for about a month after the 2023 deployment, followed by a month of dry, and then there are missing data through the 2024 visit.
Figure 32. Water persistence through 03 February 2024 in Government Spring, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

NPS

As in past years, there was no measurable discharge. Wetted extent was evaluated using a method for standing water. The total pool length was 3.5 m (11.5 ft), shorter than previous values of 3.6–6.5 m (11.8 to 21.3 ft). Average width was 2.5 m (8.2 ft), which was consistent with previous values, while depth was 7.5 cm (3.0 in), shallower than in prior years (Table 18).

Table 18. Average (± SD) width, depth, and length of Government Spring in water year (WY) 2024 and a range of means from prior years.
Measurement WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (m) 2.5 ± 0.5 (2.4–4.0) 2019–2023 (5)
Depth (cm) 7.5 ± 4.3 (10.0–13.5) 2019–2023 (5)
Length (m) 3.5 ± 2.2 (3.6–6.5) 2019–2023 (5)
Water Quality

Core water quality (Table 19) and water chemistry (Table 20) were collected at the primary sampling location inside the springbox in WY2024. Water temperature and pH were within the ranges of prior measurements, while dissolved oxygen was slightly higher and specific conductivity and total dissolved solids were slightly lower than previously observed. The values for chloride, magnesium, potassium, and sulphate were within the ranges recorded in prior years. The level of alkalinity was much lower, and the level of calcium was much higher. These out-of-range values may reflect a data processing error. Continued monitoring will inform us of the range of normal values for this site.

Table 19. Core water quality data for Government Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 3.50 (2.14–3.12) 2019–2023 (11)
001 pH 7.22 (7.07–8.47) 2019–2023 (11)
001 Specific conductivity (µS/cm) 222.0 (224.8–232.2) 2019–2023 (11)
001 Temperature (°C) 17.9 (17.2–19.2) 2019–2023 (14)
001 Total dissolved solids (mg/L) 144.3 (146.0–151.0) 2019–2023 (11)

Table 20. Water chemistry data (mg/L) for Government Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 26 (80–105) 2019–2023 (5)
001 Calcium (Ca) 80 (20–26) 2019–2023 (5)
001 Chloride (Cl) 7 (4–13) 2019–2023 (5)
001 Magnesium (Mg) 13 (9–13) 2019–2023 (5)
001 Potassium (K) 1.1 (0.0–1.2) 2019–2023 (5)
001 Sulphate (SO4) 5 (1–8) 2019–2023 (5)

Grapevine Spring

Highlights: The spring had water year round, and the wetted area was similar to prior years. We detected Rio Grande leopard frog and chytrid in the eDNA samples.

Grapevine Spring (Figures 33 and 34) is a rheocrene spring (a spring that emerges into one or more stream channels). The spring is northeast of the Grapevine Hills. It emerges from an undercut bank inside a wash, forming a narrow channel with slow flow and a series of small, shallow pools. In recent years, springbrook length has ranged from 15–47 m. Aquatic plants and animals are abundant at the spring. The WY2024 visit occurred on 03 February 2024, and the spring contained water.

Figure 33. A pool of dark, still water surrounded by overhanging branches of dried and green vegetation and exposed rock faces.
Figure 33. The primary emergence of Grapevine Spring flows from an undercut bank inside a wash at Big Bend National Park, February 2024.

NPS

Figure 34. A shaded drainage lined with a mix of dried and green vegetation. A bank with exposed soil lines and exposed rock cliff faces is on one side of the stream, and leafless tree branches are visible in the background.
Figure 34. Downstream view at Grapevine Spring in Big Bend National Park, February 2024. The spring emergence is out of view on the right, and the spring flows from right to left in this view.

NPS

Site Condition

In WY2024, we rated Grapevine Spring as moderately disturbed by flooding because of enhanced soil erosion on the banks around the spring orifice and channel (rated undisturbed to slightly disturbed in the past; Figure 35). Adult Rio Grande leopard frogs and tadpoles were observed during the site visit. No other natural or human-caused disturbances were observed at Grapevine Spring in WY2024.

Figure 35. Two images: animal tracks in dried tan mud between pebbles and leaf litter and a dried animal skull with two antlers that is missing the lower jaw on the ground with scattered dried leaves and thick, dried brush around it.
Figure 35. Examples of disturbance at Grapevine Spring in WY2024. Left: wildlife tracks. Right: a skull at the spring.

NPS

As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana), nor did we find any invasive non-native plants at Grapevine Spring in WY2024. We observed three obligate/facultative wetland plant species: maidenhair fern (Adiantum sp., a fern observed in 2018–2023); mule-fat (Baccharis salicifolia, a shrub observed in 2017–2023); and spikerush (Eleocharis sp., a sedge observed in 2018–2023).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, five water samples were collected from Grapevine Spring. Rio Grande leopard frog was detected in all five samples and chytrid fungus, the pathogen responsible for chytridiomycosis in amphibians, was detected in four of the five samples. In WY2023, chytrid fungus was detected in all five of the samples collected. We were unable to test for Rio Grande leopard frog in WY2023 samples.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 36). The temperature sensor indicated that Grapevine Spring was wetted (contained water) for all 126 days (100%) measured in WY2024 up to the visit. In prior water years, the spring was wetted 72.6–100% of the days measured across entire years.

Figure 36. Area chart showing that Grapevine Spring has been mostly wetted since the initial sensor deployment in 2018. The only drying was observed in the summer and fall of 2021.
Figure 36. Water persistence through 03 February 2024 in Grapevine Spring, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

NPS

Discharge was not measured in WY2024 at the primary sampling location because there was no measurable flow. Discharge was estimated at 3.9 L/min (1.0 gal/min) in 2022, the only prior measurement (Table 21). Wetted extent was evaluated using a method for flowing water. Overall, the wetted extent at Grapevine Spring was comparable with prior years. The total springbrook length was 19.8 m (65.6 ft), which was within the previously recorded range of 15.1–47.0 m (49–154 ft). In WY2024, width and depth along the springbrook averaged 74.5 cm (29.3 in) and 11.7 cm (4.6 in), respectively. Both values were consistent with past measurements (Table 22).

Table 21. Discharge data (L/min; mean ± SD) for Grapevine Spring in water year (WY) 2024 and a mean from a prior year. c.n.s. = could not sample.
Sampling Location WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
007 c.n.s. (3.9) 2022 (1)

Table 22. Length and average (± SD) width and depth of Grapevine Spring (measured within the first 100 m of springbrook length) in water year (WY) 2024 and ranges of length values and width and depth means from prior years.
Measurement WY2024 Value
(Range of Prior Values/Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (cm) 74.5 ± 79.6 (54.4–102.0) 2018–2023 (6)
Depth (cm) 11.7 ± 22.2 (1.8–31.0) 2018–2023 (6)
Length (m) 19.8 (15.1–47.0) 2018–2023 (6)
Water Quality

Core water quality (Table 23) and water chemistry (Table 24) data were collected at the primary sampling location about 2–3 m away from the actual orifice, where the pool becomes safely accessible. Dissolved oxygen, pH, specific conductivity, water temperature, and total dissolved solids were all within the ranges of prior measurements. The water chemistry sample was taken after water quality and wetted extent had been measured, which may have affected our results. The values for alkalinity, calcium, magnesium, and potassium were within the ranges recorded in prior years, while levels of chloride and sulphate were lower.

Table 23. Core water quality data for Grapevine Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 2.67 (2.01–6.92) 2018–2023 (6)
001 pH 7.28 (7.10–7.56) 2018–2023 (6)
001 Specific conductivity (µS/cm) 534 (528–602) 2018–2023 (6)
001 Temperature (°C) 16.0 (14.0–17.4) 2018–2023 (8)
001 Total dissolved solids (mg/L) 347.5 (344.0–390.0) 2018–2023 (6)

Table 24. Water chemistry data (mg/L) for Grapevine Spring in water year (WY) 2024 and a range of values from prior years. b.d.l. = below detection limit.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 240 (80–265) 2018–2023 (6)
001 Calcium (Ca) 64 (26–82) 2018–2023 (6)
001 Chloride (Cl) 2 (4–48) 2018–2023 (6)
001 Magnesium (Mg) 9 (b.d.l.–26) 2018–2023 (6)
001 Potassium (K) 0.4 (0.0–0.8) 2018–2023 (6)
001 Sulphate (SO4) 23 (36–62) 2018–2023 (6)

Lorn Spring

Highlights: The spring contained water when we visited in February 2024, but persistence data are missing for the year. The wetted area was shallower and narrower than in prior years. The site is largely undisturbed.

Lorn Spring (Figures 37 and 38) is a hanging garden spring (a complex, multi-habitat spring that emerges along geologic contacts and seeps, drips, or pours onto underlying walls). The spring is located inside a wash, northwest of the Grapevine Hills. Lorn Spring slowly drips from a rock face covered in maidenhair fern (Adiantum sp.) at the base of a north-facing cliff. Water from the hanging garden collects in small pools of cool, clear water at the base of the cliff, the largest of which is typically no more than 2 m long by 2 m wide. The WY2024 visit occurred on 04 February 2024, and the spring contained water.

Figure 37. A person standing in the sand next to a rock face with a patch of green ferns growing across its base. The person is pointing at a small wet patch at the base of the rock face.
Figure 37. The primary emergence at Lorn Spring in Big Bend National Park, February 2024. Water seeps out from along cracks in the rock face and collects into small pools at the base of the cliff.

NPS

Figure 38. Three people stand off to the side of a sandy drainage next to a rocky cliff with vegetation clinging to its base. The area immediately at the base of the cliff appears damp. The people are holding equipment and a clipboard.
Figure 38. Overview of the landscape surrounding Lorn Spring at Big Bend National Park, February 2024.

NPS

Site Condition

In WY2024, we did not observe any natural or human-caused disturbances at Lorn Spring.

As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Lorn Spring in WY2024. We recorded three species of invasive non-native plants at the spring (Figure 39): scattered patches of yellow bluestem (Bothriochloa ischaemum, scattered patches observed during two site visits between 2020 and 2023); scattered patches of Bermudagrass (Cynodon dactylon, scattered patches observed during three site visits between 2017 and 2023); and scattered patches of Lehmann lovegrass (Eragrostis lehmanniana, 1–5 plants to scattered patches observed in 2017–2023). We observed three obligate/facultative wetland plant species: common buttonbush (Cephalanthus occidentalis, a shrub observed in 2020–2023); maidenhair fern (Adiantum sp., observed in 2019–2023); and mule-fat (Baccharis salicifolia, a shrub observed in 2017–2023).

Figure 39. A person points to a rock face with wildlife tracks in the wet sand below it and a patch of low grasses growing at the base.
Figure 39. Scattered patches of invasive non-native Bermudagrass (Cynodon dactylon) are growing across the base of the hanging garden at Lorn Spring in February 2024.

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eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, one water sample was collected from Lorn Spring. As in WY2023, none of our target organisms were detected.

Water Quantity

Temperature sensor data are missing because the sensor failed, so there is no estimate of persistence for WY2024 (Figure 40). In prior water years, the spring was wetted (contained water) 42.1–100% of the days measured across entire years.

Figure 40. Area chart showing drying at Lorn Spring through the summers of 2020 through 2022. A comparatively longer period of drying was observed in 2020. Data are missing for the time period between visits in 2019 and 2020, as well as the time period between visits in 2023 and 2024.
Figure 40. Water persistence through 04 February 2024 in Lorn Spring, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

NPS

Discharge was estimated at 0.4 ± 0.0 L/min (0.1 ± 0.0 gal/min) in WY2024, consistent with past measurements (0.3–0.6 L/min) over the last five years (Table 25). Wetted extent was evaluated using a method for standing water. In WY2024, width averaged 19.7 cm (7.8 in), length averaged 94.7 cm (37.3 in), and depth averaged 0.7 cm (0.3 in). In WY2024, the pool was shallower and narrower than any prior measurements recorded over the last five years, while length was similar to prior years (Table 26).

Table 25. Discharge data (L/min; mean ± SD) for Lorn Spring in water year (WY) 2024 and a range of means from prior years.
Sampling Location WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
002 0.4 ± 0.0 (0.3–0.6) 2019–2023 (5)

Table 26. Average (± SD) width, depth, and length of Lorn Spring in water year (WY) 2024 and a range of means from prior years.
Measurement WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (cm) 19.7 ± 2.5 (24.5–188.7) 2019–2023 (5)
Depth (cm) 0.7 ± 0.5 (1.3–9.2) 2019–2023 (5)
Length (cm) 94.7 ± 24.2 (58.3–210.7) 2019–2023 (5)
Water Quality

Core water quality (Table 27) and water chemistry (Table 28) data in WY2024 were collected at the primary sampling location where water drips down from the crack in the hanging garden. The values for dissolved oxygen, pH, and water temperature were within the ranges recorded in prior years, while the values for specific conductivity and total dissolved solids were slightly lower. Alkalinity, calcium, magnesium, and potassium values were within the ranges from prior years. The chloride level was slightly lower and sulphate was higher than previously observed.

Table 27. Core water quality data for Lorn Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
002 Dissolved oxygen (mg/L) 8.01 (7.15–11.08) 2019–2023 (5)
002 pH 7.84 (7.50–8.36) 2019–2023 (5)
002 Specific conductivity (µS/cm) 1,771 (1,785–1,808) 2019–2023 (5)
002 Temperature (°C) 14.1 (6.5–16.2) 2019–2023 (6)
002 Total dissolved solids (mg/L) 1,151.3 (1,160.0–1,176.0) 2019–2023 (5)

Table 28. Water chemistry data (mg/L) for Lorn Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
002 Alkalinity (CaCO3) 285 (220–295) 2019–2023 (4)
002 Calcium (Ca) 110 (28–140) 2019–2023 (4)
002 Chloride (Cl) 41 (42–92) 2019–2023 (4)
002 Magnesium (Mg) 27 (5–28) 2019–2023 (4)
002 Potassium (K) 1.8 (1.5–2.8) 2019–2023 (4)
002 Sulphate (SO4) 585 (65–560) 2019–2023 (4)

Lower Croton Spring

Highlights: The spring had water when we visited and has been wet year round since 2019, though data are intermittently missing because of sensor failure, including for WY2024. The wetted area was similar to prior years.

Lower Croton Spring (Figures 41 and 42) is a helocrene spring (a spring that emerges into marshy, wet meadow settings—low-gradient wetlands). The spring is located north of the Chisos Mountains and south of Croton Peak. It forms a pool that is typically about 20 m wide and 20 m long and populated by a dense stand of cattails (Typhaceae). Mineral deposits line the gravelly banks, and shrubs partially surround the pool. The WY2024 visit occurred on 04 February 2024, and the spring contained water.

Figure 41. A person stands at the edge of a patch of dried vegetation that is taller than the person and points at the ground, with mountains in the background.
Figure 41. Lower Croton Spring at Big Bend National Park, February 2024. The spring emerges in a diffuse fashion and forms a shallow pool populated by a dense stand of cattails.

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Figure 42. A desert landscape with a shallow depression filled with tall, dry vegetation, green vegetation in the foreground and distant mountains in the background.
Figure 42. Overview of Lower Croton Spring and the surrounding landscape. Big Bend National Park, February 2024.

NPS

Site Condition

In WY2024, we rated Lower Croton Spring slightly disturbed by contemporary human use based on the presence of trash and footprints at the site (rated undisturbed to moderately disturbed in the past; Figure 43); and slightly disturbed by trespass livestock because of the presence of a horse skull and bones near the spring (rated undisturbed in the past). No other natural or human-caused disturbances were observed at Lower Croton Spring in WY2024.

Figure 43. Two images: Clumps of dried grass with short green grass patches growing around them adjacent to some thick shrubs and open bare ground and human footprints on open ground adjacent to a stream lined with tall, dried grasses.
Figure 43. Examples of disturbance at Lower Croton Spring in WY2024. Left: evenly distributed patches of invasive non-native Bermudagrass (Cynodon dactylon). Right: evidence of contemporary human use of the spring site (footprints in the soil along the banks).

NPS

As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Lower Croton Spring in WY2024. We recorded three species of invasive non-native plants at the spring: evenly distributed patches of Bermudagrass (Cynodon dactylon, evenly distributed patches to a matrix observed in 2018–2023); scattered patches of Lehmann lovegrass (Eragrostis lehmanniana, scattered patches observed in 2018); and 1–5 prickly Russian thistle plants (Salsola tragus, 1–5 plants observed in 2018). We observed three obligate/facultative wetland plant species: cattail (Typhaceae, observed in 2018–2023); flatsedge (Cyperus sp., a sedge observed in 2023); and mule-fat (Baccharis salicifolia, a shrub observed in 2018–2023).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, five water samples were collected from Lower Croton Spring. As in WY2023, none of our target organisms were detected.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 44). Temperature sensor data are missing because of sensor failure, so there is no estimate of persistence for WY2024. In prior water years, the spring was wetted (contained water) 29.1–100% of the days measured across entire years.

Figure 44. Area chart showing Lower Croton Spring has been consistently wetted since the sensor deployment in 2019. Between deployments in 2018 and 2019, the spring was dry for many periods. Data are missing for the period between visit dates in 2022 and 2023 and from September 2023 to the visit date in 2024.
Figure 44. Water persistence through 04 February 2024 in Lower Croton Spring, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

NPS

As in past years, there was no measurable discharge. Wetted extent was evaluated using a method for standing water. In WY2024, width averaged 17.2 m (56.4 ft), length averaged 17.3 m (56.8 ft), and depth averaged 7.0 cm (2.8 in). All measurements were consistent with the ranges of values recorded in the last six years (Table 29).

Table 29. Average (± SD) width, depth, and length of Lower Croton Spring in water year (WY) 2024 and a range of means from prior years.
Measurement WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (m) 17.2 ± 4.9 (13.5–20.1) 2018–2023 (6)
Depth (cm) 7.0 ± 4.5 (4.5–12.7) 2018–2023 (6)
Length (m) 17.3 ± 4.6 (16.1–18.4) 2018–2023 (6)
Water Quality

Core water quality (Table 30) and water chemistry (Table 31) data were collected at the primary sampling location near the edge of the pool in WY2024. During the reading, the water quality sensor was resting in detritus and the values for dissolved oxygen, specific conductivity, and total dissolved solids were not stabilizing. After waiting five minutes, the water quality values were recorded, but these issues may have affected our results. For water chemistry, the sample was collected with a syringe, which may have affected the results for these parameters. All core water quality and water chemistry values were consistent with prior years.

Table 30. Core water quality data for Lower Croton Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 0.07 (0.06–0.82) 2018–2023 (6)
001 pH 7.31 (7.12–7.43) 2018–2023 (6)
001 Specific conductivity (µS/cm) 1,752 (1,716–2,326) 2018–2023 (6)
001 Temperature (°C) 15.3 (12.1–17.5) 2018–2023 (8)
001 Total dissolved solids (mg/L) 1,139.1 (1,118.0–1,511.0) 2018–2023 (6)

Table 31. Water chemistry data (mg/L) for Lower Croton Spring in water year (WY) 2024 and a range of values from prior years. The water chemistry sample was collected with a syringe, which may have affected our results. b.d.l. = below detection limit.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 430 (180–500) 2018–2023 (6)
001 Calcium (Ca) 36 (33–40) 2018–2023 (6)
001 Chloride (Cl) 27 (b.d.l.–120) 2018–2023 (6)
001 Magnesium (Mg) 42 (0–47) 2018–2023 (6)
001 Potassium (K) 1.3 (0.0–4.3) 2018–2023 (6)
001 Sulphate (SO4) 370 (b.d.l.–660) 2018–2023 (6)

Mule Ears Spring

Highlights: The spring had water in February 2024, but persistence data are missing for WY2024. Discharge was lower than in prior years. There was significant human trampling of wetland plants at the spring. We detected Rio Grande leopard frogs in the eDNA samples.

Mule Ears Spring (Figures 45 and 46) is a hanging garden spring (a complex, multi-habitat spring that emerges along geologic contacts and seeps, drips, or pours onto underlying walls). The spring is located north of Mule Ears Peaks. The primary orifice seeps from under ferns on a rock face and creates a small pool bounded by boulders. Spring flow continues out of the pool forming a narrow channel that has ranged from 12 to 36 m long in recent years. A second hanging garden about 8 m downstream of the first adds to the flow as the channel becomes more densely vegetated with shrubs. The WY2024 visit occurred on 05 February 2024, and the spring contained water.

Figure 45. A patch of green ferns, surrounded by boulders, above a small, dark pool of water. Frogs sit in the sun on a rock above the water.
Figure 45. The primary emergence at Mule Ears Spring in Big Bend National Park, February 2024. Frogs cling to a boulder above a small pool where water seeps from the hanging garden on the right.

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Figure 46. A person crouches under a dense thicket of dry branches and points to a small seep of water under an overhanging bank. Bright green ferns are abundant surrounding the seep.
Figure 46. A small hanging garden seeps from under an overhang, contributing flow to the main springbrook at Mule Ears Spring in Big Bend National Park, February 2024.

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Site Condition

In WY2024, we rated Mule Ears Spring slightly disturbed by wildlife, with trails, trampling, and scat along the stream banks (rated undisturbed to slightly disturbed in the past); slightly disturbed by flooding based on signs of soil erosion along the banks, undercutting, infill, and soil deposition in the channel and on the banks above the second orifice (rated undisturbed in the past); moderately disturbed by hiking trails because of fairly heavy use of a popular hiking trail leading directly to the spring (rated moderately to highly disturbed in the past); and moderately disturbed by contemporary human use based on significant trampling of wetland plants on the springbrook banks and small amounts of trash observed at the site (rated undisturbed to moderately disturbed in the past). No other natural or human-caused disturbances were observed at Mule Ears Spring in WY2024.

As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Mule Ears Spring in WY2024. We found three species of invasive non-native plants at the spring: a matrix of Bermudagrass (Cynodon dactylon, scattered patches to evenly distributed patches observed in 2017–2023); scattered patches of annual rabbitsfoot grass (Polypogon monspeliensis, 1–5 plants observed in 2017); and scattered patches of sowthistle (Sonchus sp., 1–5 plants to scattered patches observed in 2018–2023). We observed six obligate/facultative wetland plant species: bluestem (Andropogon sp., a grass observed in 2017–2023); cattail (Typhaceae, observed in 2017–2023); lobelia (Lobelia sp., a forb observed in 2021–2023); maidenhair fern (Adiantum sp., observed in 2018–2023); mule-fat (Baccharis salicifolia, a shrub observed in 2017–2023); and willow (Salix sp.; a tree observed in 2020–2023).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, five water samples were collected from Mule Ears Spring. Rio Grande leopard frog was detected in all five samples. In WY2023, none of our target organisms were detected, but we were unable to test for Rio Grande leopard frog that year.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 47). Temperature sensor data are missing because of sensor failure, so there is no estimate of persistence for WY2024. In prior water years, the spring was wetted (contained water) 100% of the days measured across entire years.

Figure 47. Area chart showing that Mule Ears Spring has been wetted since the initial sensor deployment in 2018. There are no observed periods of drying. Data are missing from May 2023 to the visit date in 2024.
Figure 47. Water persistence through 05 February 2024 in Mule Ears Spring, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

NPS

In WY2024, the estimated volumetric discharge was 1.5 ± 0.04 L/min (0.4 ± 0.01 gal/min), which was below the previous values of 2.5–13.7 L/min (0.7–3.6 gal/min) in 2018–2023 (Table 32). Wetted extent was evaluated using a method for flowing water. Overall, the springbrook was narrower, while length and depth were consistent with previous years. The total springbrook length was 25.8 m (84.6 ft). Previous length measurements were 12.2–36.1 m (40.0–118.4 ft). Width and depth along the springbrook averaged 48.3 cm (19.0 in) and 5.3 cm (2.1 in), respectively (Table 33).

Table 32. Discharge data (L/min; mean ± SD) for Mule Ears Spring in water year (WY) 2024 and a range of means from prior years.
Sampling Location WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
003 1.5 ± 0.04 (2.5–13.7) 2018–2023 (5)

Table 33. Length and average (± SD) width and depth of Mule Ears Spring (measured within the first 100 m of springbrook length) in water year (WY) 2024 and ranges of length values and width and depth means from prior years.
Measurement WY2024 Value
(Range of Prior Values/Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (cm) 48.3 ± 37.8 (52.9–138.7) 2018–2023 (6)
Depth (cm) 5.3 ± 10.2 (4.0–13.3) 2018–2023 (6)
Length (m) 25.8 (12.2–36.1) 2018–2023 (6)
Water Quality

Core water quality (Table 34) and water chemistry (Table 35) data were collected at the primary sampling location in a small pool fed by the main orifice in WY2024. The water chemistry sample was taken after the eDNA sample had been collected and after the EXO sonde had been placed in the water at the sampling location, which may have affected our results. All water quality and water chemistry parameters were within the ranges recorded in prior years, except for the chloride level, which was lower than in prior years.

Table 34. Core water quality data for Mule Ears Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 8.06 (2.72–9.73) 2018–2023 (6)
001 pH 7.55 (7.36–8.09) 2018–2023 (6)
001 Specific conductivity (µS/cm) 590 (561–626) 2018–2023 (6)
001 Temperature (°C) 19.6 (17.9–21.5) 2018–2023 (8)
001 Total dissolved solids (mg/L) 383.1 (365.0–409.5) 2018–2023 (6)

Table 35. Water chemistry data (mg/L) for Mule Ears Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 255 (225–275) 2018–2023 (6)
001 Calcium (Ca) 68 (52–74) 2018–2023 (6)
001 Chloride (Cl) 4 (12–180) 2018–2023 (6)
001 Magnesium (Mg) 17 (5–70) 2018–2023 (6)
001 Potassium (K) 1.4 (0.1–2.7) 2018–2023 (6)
001 Sulphate (SO4) 22 (14–28) 2018–2023 (6)

Painted Hills Spring

Highlights: The spring had water and was wet nearly every day in WY2024 up to the visit in February. There was significant drying at the site and moderate disturbance from horse trampling and grazing.

Painted Hills Spring (Figures 48 and 49) is a rheocrene spring (a spring that emerges into one or more stream channels). The spring is located in a shallow wash on the northern edge of the Painted Hills. It emerges from two distinct bedrock seams in the channel, forming a springbrook that has ranged from 3.5 to 13.7 m in length in recent years. The springbrook consists of disconnected pools with no discernable flow. The WY2024 visit occurred on 16 February 2024, and the spring contained water.

Figure 48. A person points to a large boulder in a rocky streambed in between two shallow, stagnant pools of water surrounded by a shrubby desert landscape.
Figure 48. The primary emergence at Painted Hills Spring at Big Bend National Park, February 2024. The spring consisted of shallow, disconnected pools with no discernable surface flow at the time of the visit.

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Figure 49. A shallow wash in a desert landscape with rocky ground and small pools of shallow, stagnant water flanked by dry grasses. Green shrubs dot the surrounding hillsides, and one leafless tree stands in the upper right corner. Desert mountains are visible in the distance.
Figure 49. Overview of Painted Hills Spring and the surrounding landscape at Big Bend National Park, February 2024. Invasive non-native Bermudagrass (Cynodon dactylon) flanks the pools.

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Site Condition

In WY2024, we rated Painted Hills Spring slightly disturbed by drying because one previously flowing orifice and some previously wetted pools were dry and mineral crust was also observed along the banks (rated slightly to moderately disturbed in the past) and moderately disturbed by feral animals because of grazing, trampling, trails, tracks, and scat from horses (rated undisturbed to slightly disturbed in the past). No other natural or human-caused disturbances were observed at Painted Hills Spring in WY2024.

As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Painted Hills Spring in WY2024. We recorded three species of invasive non-native plants at the spring: a matrix of Bermudagrass (Cynodon dactylon, scattered to evenly distributed patches observed in 2017–2023); scattered patches of Lehmann lovegrass (Eragrostis lehmanniana, scattered to evenly distributed patches observed in 2017–2023); and scattered patches of sowthistle (Sonchus sp., 1–5 plants to scattered patches observed in 2020–2021). We observed three obligate/facultative wetland plant species: cottonwood (Populus sp., a tree observed in 2017–2023); mule-fat (Baccharis salicifolia, a shrub observed in 2017–2023); and willow (Salix sp., a tree observed in 2017–2023).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, four water samples were collected from Painted Hills Spring. Similar to WY2023, none of our target organisms were detected.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 50). The temperature sensor indicated that Painted Hills Spring was wetted (contained water) for 137 of 139 days (98.6%) measured in WY2024 up to the visit. In prior water years, the spring was wetted 0.8–94.1% of the days measured across entire years.

Figure 50. Area chart showing the spring was primarily dry from summer 2019 to fall 2023, except for short intermittently wetted periods during the winter months. Between 2018 and 2019 site visits and from fall 2023 through March 2024, the spring was primarily wet with a few short drying periods. Data are missing for all of WY2017 and the first half of 2018, except for a dry period in winter 2017.
Figure 50. Water persistence through 16 February 2024 in Painted Hills Spring, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

NPS

As in past years, there was no measureable discharge. Wetted extent was evaluated using a method for flowing water. The total springbrook length was 2.8 m (9.2 ft), which is shorter than any length in the past seven years (3.5–13.7 m [11.5–44.9 ft]). The width and depth along the springbrook averaged 114.0 cm (44.9 in) and 0.4 cm (0.2 in), respectively. Average width was greater than in prior years, while average depth remained within the historical range of measurements (Table 36).

Table 36. Length and average (± SD) width and depth of Painted Hills Spring (measured within the first 100 m of springbrook length) in water year (WY) 2024 and ranges of length values and width and depth means from prior years.
Measurement WY2024 Value
(Range of Prior Values/Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (cm) 114.0 ± 62.3 (14.3–79.4) 2017–2023 (7)
Depth (cm) 0.4 ± 0.3 (0.2–1.1) 2017–2023 (7)
Length (m) 2.8 (3.5–13.7) 2017–2023 (7)
Water Quality

Core water quality (Table 37) and water chemistry (Table 38) data were collected at the primary sampling location at the primary orifice in WY2024. A syringe and calibration cup were used to collect and measure the sample for core water quality, and a syringe was used to collect the sample for water chemistry, which may have affected our results. Water temperature was within the range recorded in prior years, but the dissolved oxygen level and pH were higher, and specific conductivity and total dissolved solids levels were lower than previous measurements. Calcium, chloride, magnesium, and sulphate values were within the ranges of measurements in prior years, while alkalinity and potassium levels were lower.

Table 37. Core water quality data for Painted Hills Spring in water year (WY) 2024 and a range of values from prior years. A syringe and calibration cup were used to collect and measure the sample for core water quality in WY2024, which may have affected our results.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 8.61 (3.95–8.22) 2017–2023 (6)
001 pH 8.27 (7.39–8.03) 2017–2023 (6)
001 Specific conductivity (µS/cm) 1,171 (1,177–1,483) 2017–2023 (6)
001 Temperature (°C) 14.3 (9.3–18.2) 2017–2023 (8)
001 Total dissolved solids (mg/L) 761.5 (767.0–964.0) 2017–2023 (6)

Table 38. Water chemistry data (mg/L) for Painted Hills Spring in water year (WY) 2024 and a range of values from prior years. A syringe was used to collect the sample for water chemistry, which may affect our results. b.d.l. = below detection limit.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 300 (358–510) 2017–2023 (6)
001 Calcium (Ca) 40 (32–72) 2017–2023 (6)
001 Chloride (Cl) 21 (b.d.l.–81) 2017–2023 (6)
001 Magnesium (Mg) 22 (b.d.l.–46) 2017–2023 (6)
001 Potassium (K) 0.7 (1.0–2.4) 2017–2023 (6)
001 Sulphate (SO4) 175 (175–280) 2017–2023 (6)

Peña Spring 1

Highlights: The spring has had water year round since monitoring began, but persistence data are periodically missing, including for WY2024. The wetted area was similar to previous years. We detected Rio Grande leopard frogs and chytrid in the eDNA samples.

Peña Spring 1 (Figures 51 and 52) is a rheocrene spring (a spring that emerges into one or more stream channels). The spring emerges inside a drainage near the Chimneys Trail, east of Old Maverick Road. Multiple orifices and a hanging garden inside the wash contribute to a springbrook that has consistently been more than 100 m in length, although typically only the upper reaches are accessible for monitoring. Steep banks and trees overhang the channel. Aquatic life is abundant, including anurans, macroinvertebrates, and a host of wetland plants. The WY2024 visit occurred on 18 February 2024, and the spring contained water.

Figure 51. A Person sitting on the ground pointing straight down at a vegetated area on the ground inside a drainage filled with leaf litter and surrounded by thick vegetation and steep soil banks.
Figure 51. The primary emergence at Peña Spring 1, which flows out from under vegetation on the bottom of a drainage at Big Bend National Park, February 2024.

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Figure 52. View of a small stream with dark brown water under a canopy of trees and downed branches. Leaf litter lines the banks.
Figure 52. Downstream view of Peña Spring 1 and surrounding vegetation at Big Bend National Park, February 2024.

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Site Condition

In WY2024, we rated Peña Spring 1 slightly disturbed by recent flooding, based on gravel deposition, wrack in trees and shrubs along the channel, and signs of bank erosion (rated undisturbed to slightly disturbed in the past) and moderately disturbed by wildlife, with tracks, scat, and bones present at the site (rated slightly to highly disturbed in the past). No other natural or human-caused disturbances were observed at Peña Spring 1 in WY2024. Adult Rio Grande leopard frogs were present in the spring during the site visit.

As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Peña Spring 1 in WY2024. We found two species of invasive non-native plants at the spring: scattered patches of sowthistle (Sonchus sp., 1–5 plants observed in 2023) and 1–5 tamarisk trees (Tamarix sp., which had not been recorded previously, though past surveys may have excluded these trees since they are located just outside the measured springbrook area). We observed eight obligate/facultative wetland plant species: bluestem (Andropogon sp., a grass observed in 2018–2023); cattail (Typhaceae, observed in 2023); cottonwood (Populus sp., a tree observed in 2023); maidenhair fern (Adiantum sp., observed in 2018–2023); mule-fat (Baccharis salicifolia, a shrub observed in 2018–2023); a member of the sedge family (Cyperaceae, observed in 2020); spikerush (Eleocharis sp., a sedge observed in 2018–2023); and willow (Salix sp., a tree observed in 2018–2023).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, seven water samples were collected from Peña Spring 1. Rio Grande leopard frog and chytrid fungus, the pathogen responsible for chytridiomycosis in amphibians, were detected in all seven samples. In WY2023, chytrid fungus was detected in four of the six samples collected. We were unable to test for Rio Grande leopard frog in WY2023 samples.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 53). Temperature sensor data are missing because of sensor failure, so there is no estimate of persistence for WY2024. In prior water years, the spring was wetted (contained water) 100% of the days measured across entire years.

Figure 53. Area chart showing Peña Spring 1 has remained wetted since the initial sensor deployment in 2018, except for two periods when data are missing: from a few weeks after the 2021 deployment until the 2022 deployment and from the 2023 deployment until the 2024 visit.
Figure 53. Water persistence through 18 February 2024 in Peña Spring 1, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

NPS

Discharge was not measured in WY2024 at the primary sampling location because there was no surface flow. Discharge has not been measured since 2017, when flow was estimated at 38.7 L/min (10.2 gal/min; Table 39). Wetted extent was evaluated using a method for flowing water. The total springbrook length was estimated at 200–500 m (656–1,640 ft), however wetted extent was only measured for the first 30 m because of safety and resource damage concerns. In the past, springbrook lengths ranged from a measured 14.4 m (47.2 ft) to estimated lengths of 100–200 m (328–656 ft). In WY2024, width and depth along the first 30 m of the springbrook averaged 1.4 m (4.6 ft) and 5.8 cm (2.3 in), respectively, consistent with the historical ranges (Table 40).

Table 39. Discharge data (L/min; mean ± SD) for Peña Spring 1 in water year (WY) 2024 and a range of means from prior years. c.n.s. = could not sample.
Sampling Location WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
009 c.n.s. (38.7) 2021 (1)

Table 40. Length and average (± SD) width and depth of Peña Spring 1 (measured within the first 100 m of springbrook length) in water year (WY) 2024 and ranges of length values and width and depth means from prior years.
Measurement WY2024 Value
(Range of Prior Values/Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (m) 1.4 ± 0.8 (1.0–1.8) 2018–2023 (6)
Depth (cm) 5.8 ± 6.5 (4.4–10.0) 2018–2023 (6)
Length (m) 30.0 A (14.4–100.0) 2018–2023 (6)

A The total springbrook length was estimated at 200–500 m but wetted extent was only measured for the first 30 m because of safety and resource damage concerns.

Water Quality

Core water quality (Table 41) and water chemistry (Table 42) data were collected at the primary sampling location in WY2024. A syringe was used to collect the sample for water chemistry, which may have affected our results. All water quality and chemistry parameters were within the ranges recorded in prior years.

Table 41. Core water quality data for Peña Spring 1 in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 3.42 (0.48–3.46) 2018–2023 (6)
001 pH 7.24 (7.12–7.46) 2018–2023 (6)
001 Specific conductivity (µS/cm) 819 (816–1,014) 2018–2023 (6)
001 Temperature (°C) 19.7 (18.6–22.3) 2018–2023 (8)
001 Total dissolved solids (mg/L) 532.1 (530.0–659.0) 2018–2023 (6)

Table 42. Water chemistry data (mg/L) for Peña Spring 1 in water year (WY) 2024 and a range of values from prior years. A syringe was used to collect the sample, which may have affected our results. b.d.l. = below detection limit.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 315 (260–340) 2018–2023 (6)
001 Calcium (Ca) 60 (58–100) 2018–2023 (6)
001 Chloride (Cl) 5 (b.d.l.–32) 2018–2023 (6)
001 Magnesium (Mg) 8 (b.d.l.–15) A 2018–2023 (5)
001 Potassium (K) 1.4 (0.2–1.5) 2018–2023 (6)
001 Sulphate (SO4) 116 (104–195) 2018–2023 (6)

A The WY2022 value for magnesium was excluded for not meeting protocol data quality standards.

Red Ass Spring

Highlights: The spring contained water every day measured up to the visit in February 2024. The wetted area was smaller than in any prior year. We detected Rio Grande leopard frogs in one of the eight eDNA samples.

Red Ass Spring (Figures 54 and 55) is a rheocrene spring (a spring that emerges into one or more stream channels). The spring is located in a drainage near the Chimneys formation. Several distinct orifices emerge within a 200 m radius, creating a vibrant complex of hanging gardens, pour-offs, and channels in the vicinity that support large cottonwood (Populus sp.) trees. We focus our monitoring on one orifice and channel within the complex, a shallow, silty-bottomed stream that has ranged from 7.5 to 12.8 m in length during recent visits. The WY2024 visit occurred on 19 February 2024, and the spring contained water.

Figure 54. A person crouches next to a shallow stream in a dry, desert landscape surrounded by mostly dry grasses and whitish rocks and soil.
Figure 54. The primary emergence, which forms a small, silt-bottomed stream, at Red Ass Spring in Big Bend National Park, February 2024. Numerous orifices emerge within a 200-meter radius.

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Figure 55. Panoramic view of a desert landscape with reddish and white soil, dotted with cacti, shrubs, grasses, and rocks. A dark green band of trees and shrubs make up the mid-ground, with a larger, leafy green tree on the far left and desert peaks in the background.
Figure 55. Overview of Red Ass Spring and the surrounding landscape at Big Bend National Park, February 2024. The primary emergence and its associated springbrook are out of view on the right side. Numerous orifices emerge from left to right along the base of the dense vegetation, including a pour-off under the large cottonwood on the far left, a seep flowing in the open in the center, and a hanging garden at the base of the vegetation shown on the upper right.

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Site Condition

In WY2024, we rated Red Ass Spring slightly disturbed by drying, with salt crust on the banks in more than half of the spring system (Figure 56) and a smaller wetted extent than in prior years (rated undisturbed to moderately disturbed in the past). No other natural or human-caused disturbances were observed at Red Ass Spring in WY2024.

Figure 56. White crusting along the banks of a springbrook drainage sloping down a sparsely vegetated desert hill and scientific gear on the ground near the springbrook.
Figure 56. Mineral crusts (evidence of drying) along the banks of the springbrook at Red Ass Spring in February 2024.

NPS

As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Red Ass Spring in WY2024. We recorded one invasive non-native plant species at the spring: a matrix of sowthistle (Sonchus sp., scattered patches observed in 2020–2023). We observed four obligate/facultative wetland plant species: bluestem (Andropogon sp., a grass observed in 2017–2023); cottonwood (Populus sp., a tree observed in 2017–2023); a member of the rush family (Juncaceae, observed in 2019–2023); and maidenhair fern (Adiantum sp., not previously observed, though previous surveys may have excluded this plant for being outside the measured springbrook area).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, eight water samples were collected from Red Ass Spring. Rio Grande leopard frog was detected in one of the samples. In WY2023, none of our target organisms were detected, but we were unable to test for Rio Grande leopard frog that year.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 57). The temperature sensor indicated that Red Ass Spring was wetted (contained water) for all 142 days (100%) measured in WY2024 up to the visit. In prior water years, the spring was wetted 28.7–75.1% of the days measured across entire years.

Figure 57. Area chart showing Red Ass Spring had a pattern of drying in the summer and remaining persistently wetted during the winter months, except for an extended period of drying in the winter of 2020, and a shorter period of drying in winter of 2021.
Figure 57. Water persistence through 19 February 2024 in Red Ass Spring, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

NPS

Discharge was not measured in WY2024 at the primary sampling location because there was no measurable surface flow. In 2018–2023, discharge estimates ranged from 0.3 to 1.1 L/min (0.1–0.3 gal/min; Table 43). Wetted extent was evaluated using a method for flowing water. Overall, wetted extent at Red Ass Spring was the smallest recorded since monitoring began in 2018. The total springbrook length was 6.3 m (19.7 ft), which is notably shorter than the previously recorded range of a measured 7.5 m (24.6 ft) to an estimated 200–500 m (656–1,640 ft). In WY2024, width and depth along the springbrook averaged 39.5 cm (15.6 in) and 0.7 cm (0.3 in), respectively, which were below the ranges of previously recorded values (Table 44).

Table 43. Discharge data (L/min; mean ± SD) for Red Ass Spring in water year (WY) 2024 and a range of means from prior years. c.n.s. = could not sample.
Sampling Location WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
002 c.n.s. (0.3–1.1) 2018–2023 (6)

Table 44. Length and average (± SD) width and depth of Red Ass Spring (measured within the first 100 m of springbrook length) in water year (WY) 2024 and ranges of length values and width and depth means from prior years.
Measurement WY2024 Value
(Range of Prior Values/Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (cm) 39.5 ± 25.0 (42.9–58.4) 2018–2023 (6)
Depth (cm) 0.7 ± 1.1 (0.8–2.2) 2018–2023 (6)
Length (m) 6.3 (7.5–12.8) 2018–2023 (6)
Water Quality

Core water quality (Table 45) and water chemistry (Table 46) data were collected at the primary sampling location in a small pool at the orifice in WY2024. Water temperature and pH were within the ranges of values in prior years, while specific conductivity and total dissolved solids levels were lower, and the dissolved oxygen level was higher. Alkalinity, magnesium, and sulphate values were within the ranges of prior measurements, while calcium and chloride levels were lower, and the potassium level was higher.

Table 45. Core water quality data for Red Ass Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 5.18 (1.76–4.48) 2018–2023 (6)
001 pH 7.34 (7.15–7.55) 2018–2023 (6)
001 Specific conductivity (µS/cm) 732 (806–880) 2018–2023 (6)
001 Temperature (°C) 16.8 (13.1–17.6) 2018–2023 (8)
001 Total dissolved solids (mg/L) 519.1 (526.5–572.0) 2018–2023 (6)

Table 46. Water chemistry data (mg/L) for Red Ass Spring in water year (WY) 2024 and a range of values from prior years. b.d.l. = below detection limit.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 320 (270–330) 2018–2023 (6)
001 Calcium (Ca) 46 (54–66) 2018–2023 (6)
001 Chloride (Cl) 0 (11–59) 2018–2023 (6)
001 Magnesium (Mg) b.d.l. (b.d.l.–13) 2018–2023 (6)
001 Potassium (K) 2.6 (0.0–1.3) 2018–2023 (6)
001 Sulphate (SO4) 72 (67–94) 2018–2023 (6)

Rough Spring B

Highlights: The spring contained water when we visited in February 2024, but persistence data are missing for WY2024. We were unable to measure wetted extent, and plant species were similar to prior years.

Rough Spring B (Figures 58 and 59) is a rheocrene spring (a spring that emerges into one or more stream channels). The spring is located inside a drainage on the north slopes of the Chisos Mountains. It emerges from under thick shrubs inside a bedrock-lined drainage. The spring forms a narrow, intermittent channel that has ranged from 12 m to over 100 m in length at annual visits. The WY2024 visit occurred on 16 February 2024, and the spring contained water.

Figure 58. A person crouches over a small stream surrounded by dry shrubs that overhang the stream, leaf litter, rocks, and bare soil. Science equipment is laid out on the ground.
Figure 58. The primary emergence at Rough Spring B is inside a drainage on the north slopes of the Chisos Mountains at Big Bend National Park, February 2024.

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Figure 59. A desert canyon landscape with a rugged mountain peak in the background, dense, shrubby vegetation in the midground, and rocky soils in the foreground. A person leans into the shrubs.
Figure 59. Overview of Rough Spring B and the surrounding landscape at Big Bend National Park, February 2024. The primary emergence is within the dense vegetation to the left of the person.

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Site Condition

In WY2024, we did not observe any natural or human-caused disturbances at Rough Spring B.

As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Rough Spring B in WY2024. We found three species of invasive non-native plants at the spring: scattered patches of Bermudagrass (Cynodon dactylon, scattered patches to evenly distributed patches observed in 2017–2021); scattered patches of Lehmann lovegrass (Eragrostis lehmanniana, 1–5 plants to scattered patches observed in 2017–2023); and scattered patches of annual rabbitsfoot grass (Polypogon monspeliensis, 1–5 plants to scattered patches observed in 2017–2020). We observed five obligate/facultative wetland plant species: cottonwood (Populus sp., a tree observed in 2017–2023); monkeyflower (Mimulus sp., a forb observed in 2017–2021); mule-fat (Baccharis salicifolia, a shrub observed in 2017–2023); a member of the rush family (Juncaceae, observed in 2018–2023); and willow (Salix sp., a tree observed in 2020–2021).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, four water samples were collected from Rough Spring B. Similar to WY2023, none of our target organisms were detected.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 60). Temperature sensor data are missing because of sensor failure, so there is no estimate of persistence for WY2024. In prior water years, the spring was wetted (contained water) 92.3–100% of the days measured across entire years.

Figure 60. Area chart showing Rough Spring B has been mostly wet since the initial sensor deployment in 2018. There was a short period of intermittent drying in the summer of 2022. Data are missing for the period between deployments in 2020 and 2021 and from June 2023 to the 2024 visit date.
Figure 60. Water persistence through 16 February 2024 in Rough Spring B, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

NPS

Discharge was not measured in WY2024 at the primary sampling location because there was no measurable surface flow. Discharge has not been measured since 2019, when flow was estimated at 6.4 L/min (1.7 gal/min; Table 47). The flowing water method for wetted extent was not used in WY2024 because of access and safety concerns related to poison ivy (Toxicodendron radicans) that is increasingly encroaching on the springbrook. In past years, brook lengths ranged from a measured 12.1 m (39.7 ft) to estimates of over 100 m (over 328 ft; Table 48).

Table 47. Discharge data (L/min; mean ± SD) for Rough Spring B in water year (WY) 2024 and a range of means from prior years. c.n.s. = could not sample.
Sampling Location WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
005 c.n.s. (6.4) 2019 (1)

Table 48. Length and average (± SD) width and depth of Rough Spring B (measured within the first 100 m of springbrook length) in water year (WY) 2024 and ranges of length values and width and depth means from prior years. c.n.s. = could not sample.
Measurement WY2024 Value
(Range of Prior Values/Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (cm) c.n.s. (63.7–96.1) 2018–2022 (5)
Depth (cm) c.n.s. (1.1–3.4) 2018–2022 (5)
Length (m) c.n.s. (12.1–100.0) 2018–2022 (5)
Water Quality

Core water quality (Table 49) and water chemistry (Table 50) data were collected at the primary sampling location near the orifice in WY2024. Dissolved oxygen, pH, and water temperature were within the ranges of prior values, while specific conductivity and total dissolved solids were higher. The values for alkalinity, calcium, chloride, magnesium, and potassium were within the ranges of prior measurements, while the sulphate level was higher.

Table 49. Core water quality data for Rough Spring B in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 4.56 (1.81–4.84) 2018–2023 (6)
001 pH 7.08 (7.05–7.54) 2018–2023 (6)
001 Specific conductivity (µS/cm) 771 (658–761) 2018–2023 (6)
001 Temperature (°C) 15.5 (12.6–20.0) 2018–2023 (8)
001 Total dissolved solids (mg/L) 501.1 (429.0–494.0) 2018–2023 (6)

Table 50. Water chemistry data (mg/L) for Rough Spring B in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 270 (250–310) 2018–2023 (6)
001 Calcium (Ca) 74 (56–85) 2018–2023 (6)
001 Chloride (Cl) 8 (0–93) 2018–2023 (6)
001 Magnesium (Mg) 15 (9–25) 2018–2023 (6)
001 Potassium (K) 0.5 (0.2–1.3) 2018–2023 (6)
001 Sulphate (SO4) 92 (67–87) 2018–2023 (6)

Screwbean Spring

Highlights: The spring had water in February 2024, but persistence data are missing for WY2024. Several orifices were dry, and the wetted area was smaller than in prior years. We detected Rio Grande leopard frogs and chytrid in some of the eDNA samples.

Screwbean Spring (Figures 61 and 62) is a rheocrene spring (a spring that emerges into one or more stream channels). The spring emerges from multiple orifices under a stand of screwbean mesquite (Prosopis pubescens) trees in a wide drainage. Narrow, braided channels meander and dissipate into an open alkali sacaton (Sporobolus airoides) grassland. Multiple intermittently wet seeps are also present in the surrounding area. The surrounding uplands are a sparse creosote shrubland, with large bentonite hills in most directions. The WY2024 visit occurred on 02 February 2024, and the spring contained water.

Figure 61. A person crouched down in clumps of tall grass pointing down at a channel of shallow water lined by bright green vegetation in a dry desert landscape. Leafless shrubs and short trees grow on either side of the channel.
Figure 61. The primary emergence at Screwbean Spring in Big Bend National Park, February 2024. The spring forms narrow, braided channels that dissipate into a flat, open area.

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Figure 62. An open desert landscape with dry grasses and light tan soil in the foreground and midground. A reddish-brown stand of trees stand in the background, with desert mountains in the distance behind them.
Figure 62. Overview of Screwbean Spring and the surrounding landscape at Big Bend National Park, February 2024. The primary emergence is within the stand of screwbean mesquite trees on the upper left, and additional small seeps also flow from the sides of the drainage on the left.

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Site Condition

In WY2024, we rated Screwbean Spring slightly disturbed by drying because three of the four previously flowing orifices were dry and the extent of the wetted area was smaller than in previous years (rated slightly to moderately disturbed in the past). No other natural or human-caused disturbances were observed at Screwbean Spring in WY2024.

We did not look for invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Screwbean Spring in WY2024. We found one invasive non-native plant species at the spring: 1–5 tamarisk trees (Tamarix sp., 1–5 plants to scattered patches observed in 2017–2023). We observed six obligate/facultative wetland plant species: bluestem (Andropogon sp., a grass observed in 2017–2023); cattail (Typhaceae, observed in 2019); centaury (Centarium sp., a forb observed during two site visits between 2020 and 2023); a member of the sedge family (Cyperaceae, observed in 2017–2018); spikerush (Eleocharis sp., a sedge observed in 2018–2023); and tamarisk (Tamarix sp., a tree observed in 2017–2023; Figure 63).

Figure 63. Shrubby, leafless trees growing in a row next to tall grasses around a stream channel in a desert grassland area.
Figure 63. Invasive non-native tamarisk (Tamarix sp.) at Screwbean Spring in February 2024.

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eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, five water samples were collected from Screwbean Spring. Rio Grande leopard frog was detected in two of the samples. In WY2023, chytrid fungus, the pathogen responsible for chytridiomycosis in amphibians, was detected in three of the six samples collected. We were unable to test for Rio Grande leopard frog in WY2023 samples.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 64). Temperature sensor data are missing because of sensor failure, so there is no estimate of persistence for WY2024. In prior water years, the spring was wetted (contained water) 89.2–100% of the days measured across entire years.

Figure 64. Area graph showing Screwbean Spring has been wet since the initial sensor deployment in 2018, except for a short period of drying in the late summer of 2018. Data are missing from July 2023 to the deployment date in 2024.
Figure 64. Water persistence through 02 February 2024 in Screwbean Spring, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

NPS

Discharge was not measured in WY2024 at the primary sampling location because there was no measurable surface flow. In prior years, the discharge estimate range was 2.0–4.3 L/min (0.5–1.1 gal/min; Table 51). Wetted extent has been evaluated using a method for flowing water since 2020. Prior to that (WY2018–WY2019), standing water measurements were used, and these data are shown in Table 52. Overall, the wetted extent of Screwbean Spring in WY2024 was smaller in length and width than in prior years, while depth remained within the historical range. In WY2024, the total springbrook length was 4.9 m (16.1 ft), which is notably shorter than the previously recorded range of a measured 12.0 m (39.4 ft) to an estimated 100–200 m (328–656 ft). Width and depth along the springbrook averaged 36.2 cm (14.3 in) and 1.4 cm (0.6 in), respectively (Table 53).

Table 51. Discharge data (L/min; mean ± SD) for Screwbean Spring in water year (WY) 2024 and a range of means from prior years. c.n.s. = could not sample.
Sampling Location WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
004 c.n.s. (2.0–4.3) 2018–2021 (4)

Table 52. Ranges of average (± SD) width, depth, and length of Screwbean Spring in water years (WY) 2018 and 2019. These measurements were made using a method for standing water. c.n.s. = could not sample.
Measurement Range of Means
(WY2018 and WY2019)		 Prior Years Measured
(# of Visits with Measurements)
Width (m) 9.9–12.6 2018–2019 (2)
Depth (cm) c.n.s. (c.n.s.) 2018–2019 (2)
Length (m) 20.8–34.3 2018–2019 (2)

Table 53. Length and average (± SD) width and depth of Screwbean Spring (measured within the first 100 m of springbrook length) in water year (WY) 2023 and ranges of length values and width and depth means from prior years (WY2020–WY2022). Starting in WY2020, wetted extent was measured using a method for flowing water.
Measurement WY2024 Value
(Range of Prior Values/Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (cm) 36.2 ± 13.6 (51.2–90.2) 2020–2023 (4)
Depth (cm) 1.4 ± 0.5 (2.0–2.8) 2020–2023 (4)
Length (m) 4.9 (12.0–47.3) 2020–2023 (4)
Water Quality

Core water quality (Table 54) and water chemistry (Table 55) data were collected at the primary sampling location near the orifice in WY2024. A syringe was used to collect the water chemistry sample, which may have affected our results. Also, soil contact was made and some silt and detritus were collected in the sample, which also may have affected the results. All water quality and water chemistry values were within the ranges of prior years.

Table 54. Core water quality data for Screwbean Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 3.84 (2.75–6.92) 2018–2023 (6)
001 pH 7.95 (7.75–8.27) 2018–2023 (6)
001 Specific conductivity (µS/cm) 1,651 (1,031–2,006) 2018–2023 (6)
001 Temperature (°C) 18.5 (17.9–19.7) 2018–2023 (8)
001 Total dissolved solids (mg/L) 1,069.7 (669.0–1,306.5) 2018–2023 (6)

Table 55. Water chemistry data (mg/L) for Screwbean Spring in water year (WY) 2024 and a range of values from prior years. A syringe was used to collect the water chemistry sample, and some silt and detritus were collected in the sample, which may have affected our results. b.d.l. = below detection limit.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 265 (195–290) 2018–2023 (6)
001 Calcium (Ca) 28 (22–34) 2018–2023 (6)
001 Chloride (Cl) 27 (19–87) 2018–2023 (6)
001 Magnesium (Mg) 7 (b.d.l.–13) 2018–2023 (6)
001 Potassium (K) 1.5 (0.2–2.6) 2018–2023 (6)
001 Sulphate (SO4) 195 (180–680) 2018–2023 (6)

Shelf Spring

Highlights: The spring contained water all year. The wetted area was similar to other years, though the springbrook was slightly shorter. The site is largely undisturbed, but we observed invasive buffelgrass for the first time.

Shelf Spring (Figures 65 and 66) is a hanging garden spring (a complex, multi-habitat spring that emerges along geologic contacts and seeps, drips, or pours onto underlying walls). The spring flows from a bedrock cliff into a drainage north of Black Gap Road. At the base of the hanging garden, flow becomes subsurface and re-emerges about 5 m down the channel. Surface flow continues intermittently as a small stream with shallow pools under a sometimes dense canopy of smooth sumac and willows. The springbrook has ranged from 24 to 33 m in length at recent visits. The WY2024 visit occurred on 02 February 2024, and the spring contained water.

Figure 65. A person points to a steep rock face with both green and dried vegetation clinging to it; there is green vegetation and moist soil at the base.
Figure 65. The primary emergence at Shelf Spring, a hanging garden that also forms a channel, in Big Bend National Park, February 2024.

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Figure 66. Landscape image of a canyon wall with layers of tan and white rock creating an overhang. Both green and dried vegetation cling to the wall. Thick shrubs and trees grow on the canyon slopes below the overhang.
Figure 66. Overview of Shelf Spring and the surrounding landscape at Big Bend National Park, February 2024. The hanging garden, left of the springbrook, flows under the vegetation in the lower right side of the image and out of view.

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Site Condition

No natural or human-caused disturbances were observed at Shelf Spring in WY2024. Tracks at the site indicated wildlife was using the site (Figure 67).

Figure 67. Scattered depressions in a gray, sandy patch of ground.
Figure 67. Wildlife tracks along the banks of Shelf Spring in February 2024.

NPS

As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Shelf Spring in WY2024. We recorded one invasive non-native plant species at the spring: scattered patches of buffelgrass (Cenchrus ciliaris, not previously observed). We observed four obligate/facultative wetland plant species: bluestem (Andropogon sp., a grass observed in 2018–2023); maidenhair fern (Adiantum sp., observed in 2018–2023); mule-fat (Baccharis salicifolia, a shrub observed in 2018–2023); and spikerush (Eleocharis sp., a sedge observed in 2018–2023).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, five water samples were collected from Shelf Spring. Similar to WY2023, none of our target organisms were detected.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 68). The temperature sensor indicated that Shelf Spring was wetted (contained water) for all 125 days (100%) measured in WY2024 up to the visit. In prior water years, the spring was wetted 100% of the days measured across entire years.

Figure 68. Area chart showing that the spring was persistently wetted for the entirety of the period of record beginning in March 2019. However, there are considerable periods of missing data: the period between deployments in 2018–2019, 2020–2021 and 2022–2023.
Figure 68. Water persistence through 02 February 2024 in Shelf Spring, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

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Discharge was not measured in WY2024 at the primary sampling location because there was no measurable surface flow. Discharge was estimated at 0.7 L/min (0.2 gal/min) in 2023, the only year with discharge data (Table 56). Wetted extent was evaluated using a method for flowing water. Overall, the springbrook at Shelf Spring was shorter and deeper than in the past, while average width remained within the historical range. The total springbrook length was 23.2 m (76.1 ft), shorter than the previously recorded range of 23.9–33.1 m (78.4–108.6 ft). In WY2024, width and depth along the springbrook averaged 14.9 cm (5.9 in) and 4.4 cm (1.7 in), respectively (Table 57).

Table 56. Discharge data (L/min; mean ± SD) for Shelf Spring in water year (WY) 2024 and a range of means from prior years. c.n.s. = could not sample.
Sampling Location WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
004 c.n.s. (0.7) 2023 (1)

Table 57. Length and average (± SD) width and depth of Shelf Spring (measured within the first 100 m of springbrook length) in water year (WY) 2024 and ranges of length values and width and depth means from prior years.
Measurement WY2024 Value
(Range of Prior Values/Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (cm) 14.9 ± 21.5 (10.6–26.0) 2018–2023 (6)
Depth (cm) 4.4 ± 8.4 (0.4–0.9) 2018–2023 (6)
Length (m) 23.2 (23.9–33.1) 2018–2023 (6)
Water Quality

Core water quality (Table 58) and water chemistry (Table 59) data in WY2024 were collected at the primary sampling location in the pool closest to the hanging garden. Values for dissolved oxygen, pH, and specific conductivity were within the ranges of results from prior years, while water temperature and total dissolved solids levels were very slightly higher. Alkalinity, chloride, magnesium, potassium, and sulphate levels were within prior ranges of measurements, while the calcium level was slightly lower than in prior years.

Table 58. Core water quality data for Shelf Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 4.76 (3.74–6.35) 2018–2023 (6)
001 pH 7.32 (7.25–7.93) 2018–2023 (6)
001 Specific conductivity (µS/cm) 576.0 (280.2–576.0) 2018–2023 (6)
001 Temperature (°C) 20.5 (14.2–20.4) 2018–2023 (8)
001 Total dissolved solids (mg/L) 374.7 (182.0–374.0) 2018–2023 (6)

Table 59. Water chemistry data (mg/L) for Shelf Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 205 (195–275) 2018–2023 (6)
001 Calcium (Ca) 36 (38–50) 2018–2023 (6)
001 Chloride (Cl) 22 (9–32) 2018–2023 (6)
001 Magnesium (Mg) 14 (7–34) 2018–2023 (6)
001 Potassium (K) 0.5 (0.0–7.2) 2018–2023 (6)
001 Sulphate (SO4) 57 (40–58) 2018–2023 (6)

Solis Spring

Highlights: The spring contained water in February 2024, but persistence data are missing for WY2024. The wetted area was smaller than in the past. The entire site is heavily disturbed by cattle and horse trampling and browsing. We observed the invasive Lehmann lovegrass for the first time.

Solis Spring (Figures 69 and 70) is a rheocrene spring (a spring that emerges into one or more stream channels) inside a drainage southeast of Talley Mountain. The spring is a complex of seeps on the edge of a shallow drainage, forming small, silt-bottomed pools along the bank. At higher flows, the seeps have formed individual channels that join and flow into the main drainage. Channel length has ranged from 7.7 to 32.5 m in recent years. Thick mineral deposits coat the banks surrounding Solis Spring. The WY2024 visit occurred on 17 February 2024, and the spring contained water.

Figure 69. Two people standing next to a leafless tree on a grassy slope in a desert landscape with whitish crust on the soil and a yellowish rock formation in the background.
Figure 69. The primary emergence at Solis Spring in Big Bend National Park, February 2024. The primary emergence of the spring is next to the tamarisk tree.

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Figure 70. A dry, desert landscape under a clear, blue sky. A collection of backpacks and gear sits on the ground in the bottom right. A sloping canyon and sparse shrubs dot the foreground, and in the distance are desert mountains.
Figure 70. Overview of Solis Spring and the surrounding landscape at Big Bend National Park, February 2024. The primary emergence is just below the center of the image. Additional orifices up the wash on the left and out of view were also flowing at the time of the visit.

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Site Condition

In WY2024, we rated Solis Spring slightly disturbed by exotic plant removal, because of cut tree stumps at the site (rated undisturbed to slightly disturbed in the past); slightly disturbed by drying, with visible salt crust and a diminished wetted area—most of the wetted area was limited to dampened animal tracks (rated undisturbed to moderately disturbed in the past); and highly disturbed by livestock and feral animals because of abundant cattle and horse tracks, browsing, trampling, and trails across the entire site (rated undisturbed to moderately disturbed in the past; Figure 71). No other natural or human-caused disturbances were observed at Solis Spring in WY2024. Tracks, trails, and scat indicated wildlife was using the site.

Figure 71. Three images: White crusts scattered across bare soil with tall tufts of dried grasses; heavily trampled bare areas of dried mud with scattered, dried shrubs around it; and a leafless, short tree next to a person pointing at a white crusted spring orifice.
Figure 71. Examples of disturbance at Solis Spring in February 2024. Clockwise from top left: a drying orifice surrounded by salt crusts; trampling throughout the spring system; and an invasive non-native saltcedar (Tamarix ramosissima) at the primary orifice.

NPS

As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Solis Spring in WY2024. We found four species of invasive non-native plants at the spring: scattered patches of Lehmann lovegrass (Eragrostis lehmanniana, not previously observed); scattered patches of tree tobacco (Nicotiana glauca, 1–5 plants to scattered patches observed in 2022–2023); scattered patches of annual rabbitsfoot grass (Polypogon monspeliensis, 1–5 plants to scattered patches observed during two site visits between 2017 and 2020); and scattered patches of saltcedar (Tamarix ramosissima, 1–5 plants observed in 2017). We observed four obligate/facultative wetland plant species: cattail (Typhaceae, observed in 2017–2023); centaury (Centarium sp., a forb observed in 2020–2023); a member of the rush family (Juncaceae, observed in 2018–2022); and spikerush (Eleocharis sp., a sedge observed in 2018–2023).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, four water samples were collected from Solis Spring. None of our target organisms were detected. In WY2023, chytrid fungus, the pathogen responsible for chytridiomycosis in amphibians, was detected in two of the five samples collected.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 72). Temperature sensor data are missing because of sensor failure, so there is no estimate of persistence for WY2024. In prior water years, the spring was wetted (contained water) 75.6–100% of the days measured across entire years.

Figure 72. Area chart showing Solis Spring has been mostly wet since the initial sensor deployment in 2018. There were short periods of drying in the late spring/early summer of 2018 and summer of 2022. There are missing data from January 2023 to the deployment date in 2024.
Figure 72. Water persistence through 17 February 2024 in Solis Spring, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

NPS

Discharge was not measured in WY2024 at the primary sampling location because there was no measurable surface flow. Discharge data are available for one prior year (2020) when flow was estimated at 0.1 L/min (0.03 gal/min; Table 60). Wetted extent was evaluated using a method for flowing water. Overall, the length and width of the springbrook were smaller than in prior years, while depth remained within the historical range. The total springbrook length was 5.0 m (16.4 ft), which was shorter than any prior measurement: 7.7–32.5 m (25.3 to 106.6 ft). In WY2024, width and depth along the springbrook averaged 2.7 cm (1.1 in) and 0.9 cm (0.4 in), respectively (Table 61).

Table 60. Discharge data (L/min; mean ± SD) for Solis Spring in water year (WY) 2024 and a range of means from prior years. c.n.s. = could not sample.
Sampling Location WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
006 c.n.s. (0.1) 2020 (1)

Table 61. Length and average (± SD) width and depth of Solis Spring (measured within the first 100 m of springbrook length) in water year (WY) 2024 and ranges of length values and width and depth means from prior years.
Measurement WY2024 Value
(Range of Prior Values/Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (cm) 2.7 ± 4.6 (14.0–99.7) 2018–2023 (6)
Depth (cm) 0.9 ± 2.0 (0.1–1.5) 2018–2023 (6)
Length (m) 5.0 (7.7–32.5) 2018–2023 (6)
Water Quality

Core water quality (Table 62) and water chemistry (Table 63) data were collected at the primary sampling location in WY2024. A syringe was used to collect the sample for water chemistry, which may have affected our results. All water quality values (dissolved oxygen, pH, specific conductivity, water temperature, and total dissolved solids) were within the ranges of values recorded in prior years. Alkalinity, chloride, magnesium, potassium, and sulphate levels were similar to prior measurements, while the calcium level was higher.

Table 62. Core water quality data for Solis Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
002 Dissolved oxygen (mg/L) 10.12 (3.47–10.29) 2018–2023 (6)
002 pH 8.26 (7.92–9.62) 2018–2023 (6)
002 Specific conductivity (µS/cm) 3,693 (2,983–16,538) 2018–2023 (6)
002 Temperature (°C) 15 (8.7–16.5) 2018–2023 (8)
002 Total dissolved solids (mg/L) 2,485 (1,937–2,509) 2018–2023 (5)

Table 63. Water chemistry data (mg/L) for Solis Spring in water year (WY) 2024 and a range of values from prior years. A syringe was used to collect the sample, which may have affected our results. b.d.l.= below detection limit.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
002 Alkalinity (CaCO3) 410 (370–440) 2018–2023 (4)
002 Calcium (Ca) 32 (18–24) A 2018–2022 (3)
002 Chloride (Cl) 44 (b.d.l.–115) 2018–2023 (4)
002 Magnesium (Mg) b.d.l. (b.d.l.–13) 2018–2023 (4)
002 Potassium (K) 0.4 (0.1–2.3) 2018–2023 (4)
002 Sulphate (SO4) 142 (55–195) 2018–2023 (4)

A The calcium value from WY2023 is excluded because the value failed to meet the data quality standards.

Tiptoe Spring

Highlights: The spring contained water in February 2024, but persistence data are missing for WY2024. The wetted area of the springbrook was shorter than in any prior year. We observed red spotted toad in one of the eDNA samples.

Tiptoe Spring (Figures 73 and 74) is a rheocrene spring (a spring that emerges into one or more stream channels). The spring is in a drainage on the southeast side of the Grapevine Hills. It emerges inside a fairly open, rocky wash lined with grasses and shrubs. The springbrook has been characterized by shallow, disconnected pools in recent years, and the channel length has ranged from 22.2 to 75.2 m. The WY2024 visit occurred on 20 February 2024, and the spring contained water.

Figure 73. A person stands in a wash in a desert landscape, pointing to a small, wet, muddy area surrounded by grassy banks and exposed soil. A rocky desert mountain makes up the background.
Figure 73. The primary emergence at Tiptoe Spring in Big Bend National Park, February 2024. The spring emerges in a drainage and forms shallow, stagnant pools that appear heavily used by javelina.

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Figure 74. Dry desert landscape with shallow pools in a canyon flanked by slopes of rock and sparse vegetation.
Figure 74. Overview of Tiptoe Spring and surrounding landscape at Big Bend National Park, February 2024. The primary emergence is just left of center, and the spring brook is comprised of disconnected, shallow pools, visible on the bottom right.

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Site Condition

In WY2024, we rated Tiptoe Spring slightly disturbed by drying based on a decrease in wetted extent from previous visits and a lack of discernable surface flow (rated undisturbed to slightly disturbed in the past). No other natural or human-caused disturbances were observed at Tiptoe Spring in WY2024. Tracks and animal trails indicated wildlife was using the site (Figure 75).

Figure 75. Two images: a dry, narrow drainage between steep desert slopes and extensive animal tracks in wet and dry mud in and along a wet streambrook.
Figure 75. Evidence of drying (left) at Tiptoe Spring in February 2024 and extensive animal tracks along the springbrook (right).

NPS

As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Tiptoe Spring in WY2024. We recorded one invasive non-native plant species at the spring: evenly distributed patches of Bermudagrass (Cynodon dactylon, not previously observed). However, given a well-documented history of saltgrass (Distichlis spicata) at the site, we suspect that the observation of Bermudagrass could be a misidentification and we will confirm identification at a future visit. We observed two obligate/facultative wetland plant species: bluestem (Andropogon sp., a grass observed in 2017–2023) and a member of the rush family (Juncaceae, observed in 2018–2023).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, four water samples were collected from Tiptoe Spring. Red spotted toad was detected in one of the samples. In WY2023, none of our target organisms were detected.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 76). Temperature sensor data are missing because of sensor failure so there is no estimate of persistence for WY2024. In prior water years, the spring was wetted (contained water) 50.0–100% of the days measured across entire years.

Figure 76. Area chart showing the spring was wet during times when data are available during 2017, 2018, and 2021–2023. Dry periods occurred during summer 2019 and winter/spring of 2020. Data are missing for the periods between deployments in 2017 and 2018, deployments in 2020 and 2021, deployments in 2022 and 2023, and from May 2023 to the 2024 deployment.
Figure 76. Water persistence through 20 February 2024 in Tiptoe Spring, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

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Discharge was not measured in WY2024 at the primary sampling location because there was no measurable surface flow. In WY2019–WY2021, flow was estimated at 0.4–0.7 L/min (0.1–0.2 gal/min; Table 64). Wetted extent was evaluated using a method for flowing water. The total springbrook length was 17.7 m (58.1 ft), which was shorter than any value in the previously recorded range of 22.2–75.2 m (72.8 to 246.7 ft). In WY2024, width and depth along the springbrook averaged 38.5 cm (15.2 in) and 1.1 cm (0.4 in), respectively, both within the ranges of prior values (Table 65).

Table 64. Discharge data (L/min; mean ± SD) for Tiptoe Spring in water year (WY) 2024 and a range of means from prior years. c.n.s. = could not sample.
Sampling Location WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
005 c.n.s. (0.4–0.7) 2019–2021 (3)

Table 65. Length and average (± SD) width and depth of Tiptoe Spring (measured within the first 100 m of springbrook length) in water year (WY) 2024 and ranges of length values and width and depth means from prior years.
Measurement WY2024 Value
(Range of Prior Values/Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (cm) 38.5 ± 32.4 (13.3–52.2) 2017–2023 (7)
Depth (cm) 1.1 ± 0.6 (0.4–3.2) 2017–2023 (7)
Length (m) 17.7 (22.2–75.2) 2017–2023 (7)
Water Quality

Core water quality (Table 66) and water chemistry (Table 67) data were collected at the primary sampling location (#006) in WY2024. The primary sampling location for water chemistry data was location #001 until WY2023, when it changed to location #006 because there was no water at location #001. Soil contact was made while collecting the water chemistry sample, and some silt and detritus were collected in the sample, which may have affected our results. The values for pH, specific conductivity, water temperature, and total dissolved solids were within ranges of values from prior years, while dissolved oxygen was higher. Since water chemistry data are only available for one prior year at this new location, additional years of monitoring will be needed to establish expected value ranges.

Table 66. Core water quality data for Tiptoe Spring in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
006 Dissolved oxygen (mg/L) 8.93 (3.91–8.91) A 2022–2023 (2)
006 pH 7.99 (7.51–8.48) 2021–2023 (3)
006 Specific conductivity (µS/cm) 894 (775–977) 2021–2023 (3)
006 Temperature (°C) 14.6 (7.7–16.4) 2021–2023 (3)
006 Total dissolved solids (mg/L) 580.2 (504.0–635.0) 2021–2023 (3)

A The dissolved oxygen value from 2021 is excluded because it failed to meet data quality standards.

Table 67. Water chemistry data (mg/L) for Tiptoe Spring in water year (WY) 2024 and values from prior years. b.d.l. = below detection limit.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
006 Alkalinity (CaCO3) 250 (350) 2023 (1)
006 Calcium (Ca) 4 (32) 2023 (1)
006 Chloride (Cl) b.d.l. (1) 2023 (1)
006 Magnesium (Mg) b.d.l. (1) 2023 (1)
006 Potassium (K) 4.6 (1.6) 2023 (1)
006 Sulphate (SO4) 110 (112) 2023 (1)

Water Boy Tinaja

Highlights: The tinaja contained water when we visited in February 2024. The temperature sensor indicated that there was water for the first 35 days of WY2024, after which the sensor failed. There was a feral aoudad carcass at the site.

Water Boy Tinaja (Figures 77 and 78) is a tinaja (small pool in rock basin or impoundment in bedrock). The tinaja is located on the northeast side of the Chisos Mountains. It is typically about 5 m wide by 6 m long and ranges between 0.5 m and 0.9 m deep. Water Boy Tinaja collects runoff from the surrounding bedrock canyon walls, and sometimes a channel flows out of the pool and continues down the canyon, pooling intermittently in low-gradient areas. Large bunch grasses line Water Boy Tinaja’s northwest edge, and a catclaw overhangs the opposite side. Macroinvertebrate life abounds in this deep, clear pool. The WY2024 visit occurred on 01 February 2024, and the tinaja contained water.

Figure 77. Overhead view of a large pool of dark brown water inside a reddish-brown bedrock-lined canyon with a vertical rock wall on one side. Some water braids down through the narrow stream channel below the pool.
Figure 77. A downstream view of Water Boy Tinaja (the large pool) at Big Bend National Park, February 2024.

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Figure 78. Overhead shot of a bedrock-lined canyon below sparsely vegetated desert hills. The canyon channel holds water in distinct pools.
Figure 78. Overview of the landscape around Water Boy Tinaja at Big Bend National Park, February 2024. Water Boy Tinaja is out of view to the right.

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Site Condition

We rated Water Boy Tinaja slightly disturbed by feral animals because of an aoudad (Ammotragus lervia) carcass observed near the tinaja (rated undisturbed to slightly disturbed in the past). No other natural or human-caused disturbances were observed at Water Boy Tinaja in WY2024.

As in past years, we did not observe invasive non-native crayfish or American bullfrog (Rana catesbeiana) at Water Boy Tinaja in WY2024. We found one invasive non-native plant species at the spring: scattered patches of Lehmann lovegrass (Eragrostis lehmanniana, 1–5 plants to scattered patches observed during three site visits between 2017 and 2023). We observed one obligate/facultative wetland plant species: monkeyflower (Mimulus sp., a forb observed in 2017–2020).

eDNA Inventory of Rare and Invasive Species and Pathogens

In WY2024, four water samples were collected from Water Boy Tinaja. Similar to WY2023, none of our target organisms were detected.

Water Quantity

Sensors are deployed and data are downloaded during our annual visit; the dates of these visits are indicated by black diamonds in the persistence graph (Figure 79). The temperature sensor indicated that Water Boy Tinaja was wetted (contained water) for all 35 days (100%) measured in WY2024 up to the visit, though there is an extended period of missing data. In prior water years, the spring was wetted 67.9–100% of the days measured across entire years.

Figure 79. Area chart showing Water Boy Tinaja has been mostly wet since 2017. In the winters of 2018 and 2019, there were periods of drying. Short periods of drying occurred each summer, except in 2020. There are periods of missing data in winter 2023 and 2024.
Figure 79. Water persistence through 01 February 2024 in Water Boy Tinaja, Big Bend National Park. White areas indicate dates before sensors were first deployed or after the WY2024 visit. Black diamonds indicate sensor deployment dates.

NPS

As in prior years, discharge was not measured in WY2024 because the tinaja had no outflow. Wetted extent was evaluated using a method for standing water. Overall, the wetted extent of Water Boy Tinaja was smaller than in any prior year on record (2017–2024), while depth remained within its historical range. In WY2024, width averaged 4.4 m (14.4 ft), length averaged 5.3 m (17.4 ft), and depth averaged 76.5 cm (30.1 in; Table 68).

Table 68. Average (± SD) width, depth, and length of Water Boy Tinaja in water year (WY) 2024 and a range of means from prior years.
Measurement WY2024 Mean
(Range of Prior Means)		 Prior Years Measured
(# of Visits with Measurements)
Width (m) 4.4 ± 0.7 (4.5–4.9) 2017–2023 (7)
Depth (cm) 76.5 ± 19.8 (48.2–90.8) 2017–2023 (7)
Length (m) 5.3 ± 0.7 (5.6–6.3) 2017–2023 (7)
Water Quality

Core water quality (Table 69) and water chemistry (Table 70) data were collected at the primary sampling location in WY2024. All water quality and water chemistry values were within the ranges of values in prior years.

Table 69. Core water quality data for Water Boy Tinaja in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Dissolved oxygen (mg/L) 9.59 (8.18–11.11) 2018–2023 (6)
001 pH 8.49 (8.08–8.90) 2017–2023 (7)
001 Specific conductivity (µS/cm) 234.4 (33.7–435.0) 2017–2023 (6)
001 Temperature (°C) 11.8 (5.0–14.2) 2017–2023 (9)
001 Total dissolved solids (mg/L) 152.4 (96.0–282.8) 2017–2023 (7)

Table 70. Water chemistry data (mg/L) for Water Boy Tinaja in water year (WY) 2024 and a range of values from prior years.
Sampling Location Parameter WY2024 Value
(Range of Prior Values)		 Prior Years Measured
(# of Measurements)
001 Alkalinity (CaCO3) 70 (55–170) 2017–2023 (7)
001 Calcium (Ca) 32 (24–46) 2017–2023 (7)
001 Chloride (Cl) 5 (4–61) 2017–2023 (7)
001 Magnesium (Mg) 8 (3–60) 2017–2023 (7)
001 Potassium (K) 0.7 (0.1–2.1) 2017–2023 (7)
001 Sulphate (SO4) 0 (0–44) 2017–2023 (7)

Past Reports

Previous annual reports can be found at the following links:

Literature Cited

Author Information

Susan Singley 1

Kara Raymond 2  ORCID.org logo https://orcid.org/0009-0004-7265-5919

Tani Hubbard 3  ORCID.org logo  https://orcid.org/0009-0009-8777-4773

1 National Park Service
Chihuahuan Desert Network
New Mexico State University
MSC 3ARP, 3655 Research Dr.
Genesis Building D
Las Cruces, NM 88003

2 National Park Service
Southern Arizona Office
12661 E. Broadway Blvd.
Tucson, AZ 85748

3 Northern Rockies Conservation Cooperative and National Park Service
12661 E. Broadway Blvd.
Tucson, AZ 85748

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