GROUNDWATER INFLUX AS A PREDICTOR FOR DETERMINING FRESHWATER MUSSEL DENSITY AND ABUNDANCE

Abstract

Nearly three-quarters of North America's native freshwater mussel species are considered endangered, threatened, or species of special concern. In response, state and federal agencies are developing management plans that incorporate relocation of adults into current or historic range to facilitate recovery. Identification of relocation sites will be critical to decision making and planning for the translocation of this resource and recovery potential. Hydrologic controls, such as surface-hyporheic water exchange, substrate size, and shear stress are suspected to influence mussel distribution within this cobble-bed river. Half-barrel seepage meters were placed in 5 sites, varying from high to low mussel density, to record the amount of exchange across the sediment-water interface for one day periods. Areas of high mussel density contained mean hyporheic exchange rates from 25 to 105 cm/d for both upward and downward flows. Conversely, areas of low mussel density showed mean exchange rates of 54 to 209 cm/d for upward and downward flow. Findings suggest that there is an inverse relationship between hyporheic exchange and mussel population density, while thermal exchange and substrate size appears not to correlate. Principle Component Analysis showed strong correlations between mussel count and density and shear stress and velocity. For this study hyporheic exchange rates do not appear useful as a predictor in determining mussel density and abundance.