Validation of an Environmental Flow Recommendation in Texas

Validation of recommended environmental flow regimes by quantifying biotic and abiotic responses are necessary for refining recommendations. Currently, most Texas rivers are managed under the theory of the Natural Flow Paradigm, the basis for the established environmental flow recommendations. The purpose of our study is to validate instream flow recommendations implemented on the Lower Brazos, Guadalupe, and San Antonio Rivers. Study objectives are to investigate macroinvertebrate and fish assemblages and to assess ecological responses to instream flow recommendations (e.g., subsistence, base, 1 per season, 1 per year). Fourteen sites associated with USGS gaging stations were visited over a period of twelve months with visits classified into flow tiers based on the preceding fifteen days. Riffle and run habitats were sampled for swift water specialists and diet (gut fullness) and condition factor (HSI) was investigated. Over 50 hypotheses were tested among basin, season and flow tier.  Relative abundance of slackwater fish and occurrence of fluvial fish differed among flow tiers, whereas relative abundance of fluvial fishes differed in run habitats among flow tiers. This insight will be used to understand ecological responses to the current implemented flow recommendations to maintain a sound ecological environment.