Effects of Saltwater Intrusion on Anuran Occupancy in Big Thicket National Preserve, Texas

Science Center Objects

WARC researchers sampled anuran populations at sites within Big Thicket National Preserve to explore saltwater intrusion on these populations.

The Science Issue and Relevance: Disease and climate change, and their interaction, are thought to be leading causes of observed widespread amphibian declines in the last 30 years. Climate change results in sea-level rise and increased frequency and intensity of droughts and tropical systems. The resultant saltwater intrusion from these events impacts anuran (i.e., frog and toad) populations inhabiting coastal wetlands, such as the tidal-influenced lower Neches River in southeast Texas. The effects of saltwater intrusion here are exacerbated by anthropogenic influences, primarily the deepening of the channel from Sabine Pass to the Port of Beaumont to facilitate petrochemical maritime traffic. The channel is 40 feet deep at present, but work began in 2019 to deepen the channel to 48 feet, which will potentially result in more often and more severe periods of saltwater intrusion. The Lower Neches Valley Authority (LNVA) has had a permanent saltwater barrier since 2003 on the Neches River in Beaumont, which ensures freshwater availability for municipal, agricultural, and industrial uses.

Saltwater barrier along the Neches River

Saltwater barrier along the Neches River in Beaumont, Texas

(Credit: Brad Glorioso. Public domain.)

 

Methodology for Addressing the Issue: We sample anuran populations using time-constrained nighttime visual encounter surveys with concurrent vocalization surveys at 32 sites below, and 20 sites above, the saltwater barrier. We randomly selected sites in accessible tributaries of the Neches River within Big Thicket National Preserve boundaries. During surveys, we try to capture all anurans observed, identify them to species, and measure their snout-vent length. Environmental data, including air temperature, relative humidity, and salinity are collected at each survey. In addition, we have nine salinity loggers placed strategically throughout the study area and make use of long-term salinity data provided by gauges maintained by the LNVA. Anuran data are analyzed in the site occupancy framework. This method produces an estimate of the proportion of area occupied for each species given imperfect detection of the species using sampling covariates.

Map of study area

Map of study area showing the southern and northern sites separated by the saltwater barrier.

(Public domain.)

 

 

 

 

Future Steps: We suspended field work for this line of study in 2018, but we are working on publications resulting from this study.