River Continuum Concept Ecological Limit Functions for Fish and Benthic Data in Virginia

The ecological limit functions (ELF) developed in cooperation with the Virginia Department of Environmental Quality (DEQ) are a graphical representation of the current and historical state of aquatic biota in Virginia streams.  The goal of this study was to quantify the potential species richness and habitat response to flow alteration using available long-term ecological data. Fish and benthic richness patterns were discerned from Ecological Limit Functions (ELFs) that describe the relations between streamflow and species richness. This River Continuum Concept (RCC) ELF framework, employing Virginia’s extensive fish and benthic richness database, may provide an alternative method for assessing flow depletion impacts without the need for extensive habitat characterization or in-depth flow modeling.  The ELFs were used to calculate rate of change in richness represented by the ELF slope as a function of drainage area, annual streamflow, or monthly streamflow and annual or monthly flows.  Species richness responses varied as a function of hydrologic unit classification (from larger regions HUC6 to smaller basins HUC10), ecoregion, or major drainage.