Flow-ecology relationships for rivers in the eastern United States and their environmental flow protection implications

The development of environmental flow standards, or quantitative limits on flow alteration from water management activities, that are applicable across broad spatial scales is one of the central challenges of implementing a state or national water quantity protection program.  Environmental flow standards have been slow to be defined in the Eastern United States, as is the case throughout most of the world.  Recently, an international group of river scientists has developed a scientifically-credible approach to developing regional environmental flow standards entitled, “The Ecological Limits of Hydrologic Alteration (ELOHA)”.  One of the key elements of this framework is development of flow-ecology response relationships through associating degrees of hydrologic alteration with changes in ecological condition.  Work on flow-ecology response relationships designed to be useful for policy-makers has begun in the Eastern United States in states such as Pennsylvania, Tennessee, and Connecticut.  In an example from Pennsylvania, hydrological alteration, defined as permitted water withdrawals as a proportion of the 7Q10, was associated with changes in macroinvertebrate assemblages (e.g., number of EPT taxa, composition of species traits). We will review the progress to date in the Eastern U.S. in developing these quantitative relationships and the challenges associated with translating these results into policy.