Stream Conductivity and Road Salt Relationships to Land Use and Fish Assemblages in Maryland Streams

Stream conductivity reflects both landscape and anthropogenic interactions, although increasing chloride input from road salt application is very important.  Employing a spatially extensive database derived from the Maryland Biological Stream Survey (MBSS), relationships of stream conductivity (as the chloride surrogate) to stream MBSS fish metrics, abundance, biomass, and assemblages were determined to estimate potential salt effects.    For MBSS sites there were strong relationships of stream conductivity and chloride with both impervious surface and road density.  For the Maryland Piedmont, observed conductivity values between 230 - 540 μS/cm caused important alterations in the biotic community as measured by the fish metrics, thus affecting fish species assemblages associated with chloride concentrations ranging from 33 to 108 mg/L.  Maryland Coastal, Coldwater, and Highland species assemblages displayed variable responses of conductivity.  If regional conductivity and chloride levels continue to increase or remain high from road deicing due to increasing urbanization in a watershed and/or climatic changes, differences in stream fish assemblages and therefore fish diversity may become even more apparent.  Because of the linkage between salt usage and impervious road surfaces resulting from urbanization, it is critical to manage effectively road salt use to protect biotic resources.