Hydrology to guide conservation: a gain-loss study in the Devils River, Texas

Authors: David Young, Sarah Robertson

Year: 2022

Abstract

In groundwater dependent streams that support stable habitats and highly endemic species, environmental heterogeneity along the stream gradient creates a mosaic of habitats that change through time and space. In karst settings, stream-aquifer interactions in the form of streamflow gains (springs) and losses (aquifer recharge) have been shown to influence habitat complexity and aquatic assemblages. The spatial and temporal patterns of gains and losses are important to understanding the relationship between groundwater and streamflow and for identifying factors that promote or limit species distribution. The Devils River, considered by many to be the most pristine and ecologically intact river in Texas, is home to federal and state listed fish and mussel species. Coarse streamflow studies have been previously conducted however, high spatial resolution gain-loss data is lacking, as are measurements recorded over various hydrologic conditions. This study provides a systematic, fine-resolution gain-loss study along 42 miles of the spring-fed Devils River of the Edwards-Plateau Aquifer in south-west Texas. Discharge measurements were repeated at 20 sites across five events in 2021 and 2022. Results indicate a spatially consistent pattern of gains and losses despite varying flow conditions with two significant gaining reaches and two losing reaches which decreased streamflow by approximately 10 and 70% respectively. This study supports refinements to the conceptual model of the aquifer and allows for a better understanding of surface-groundwater interactions for the Devils River, something critical to understanding the relationship between environmental conditions and available habitat for imperiled species. The implications suggest that groundwater conservation management should focus on springs and spring habitats and include losing reaches which are the most suspectable habitat to drying. This along with other hydrology and biology data collection efforts are critical in informing future water management strategies protective of native species habitats in this groundwater dependent system.