A meta-analysis of environmental flow standards and thresholds in Texas rivers

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Diane Le Bouille, Ryan McManamay, Kayla Garrett and Lydia Roush, Department of Environmental Science, Baylor University, Waco, TX, David Young, Coastal Fisheries, Water Resources Branch, Texas Parks and Wildlife Department, San Antonio, TX, Kevin Mayes, Inland Fisheries, Texas Parks and Wildlife Department, Joe Trungale, Texas Conservation Science, Austin, TX, Ryan Smith, The Nature Conservancy, San Antonio, TX

Background/Question/Methods
The protection of natural flow regimes promotes the sustenance of riverine ecosystems and their services to society. The Texas Parks and Wildlife Department, in collaboration with other agencies and stakeholders, have developed strategies for restoring and protecting natural hydrologic regimes. These strategies have included research programs aimed at identifying environmental flow targets, hydrologic alteration, and flow deficits. Among these concerted efforts is the development of a statewide Environmental Flow Information Toolkit (EFIT), which can be used to evaluate environmental flow targets and flow deficits to design strategies for environmental flow implementation. To inform the EFIT, literature examining ecological responses to hydrologic alteration was compiled for the entire state of Texas and surrounding regions, such as the Great Plains Landscape Conservation Cooperative. Through a meta-analysis, information on hydrologic variation and ecological responses were extracted from literature with particular emphasis on documenting scientifically based hydrologic thresholds, i.e., tipping points beyond which river ecosystems experience ecological degradation, such as loss of fish species, habitat, or important services. These thresholds were compared to previous hydrologic thresholds established by Texas Instream Flow Program studies and thresholds recommended by expert science teams during the Texas environmental flow standards process. Additionally, the literature review yielded a gap-analysis of fish SGCN and river systems that would benefit from more instream flow studies.
Results/Conclusions
Over 1,500 sources were identified and, of these, roughly 260 contained information relevant to fish species of greatest conservation need in Texas. Data on flow-ecology relationships were extracted for over 80 of these studies. Despite the numeric rarity of large rivers, thresholds were more commonly identified in these systems. Small and intermittent systems were rarely studied. Overall, tipping points identified by scientific sources and scientific committee tipping points were lower (more conservative) than thresholds established within environmental flow standards, which take into account human demands. Ultimately, our results provide evidence of hydrologic thresholds, and underscore their importance in environmental flow management.