The importance of upland flow paths in determining urban effects on stream ecosystems

Abstract

AbstractMitigation of urban effects on streams requires an understanding of the paths by which urban effects are transmitted from catchments to streams and how those effects are attenuated with distance. We assessed whether modeling attenuation from impervious surfaces and septic tanks along drainage lines improved prediction of 3 instream ecological indicators. Eleven regression models were calculated for each indicator (Escherichia coli, NO3/NO2, and Stream Invertebrate Grade Number Average Level [SIGNAL; a macroinvertebrate assemblage composition index]). Predictor variables included imperviousness or septic-tank density with no attenuation (i.e., total imperviousness and tank density), with overland attenuation (exponential decay with distance along topographic flow paths to stormwater drain or to stream), and with overland and instream attenuation (exponential decay with distance travelled within the stream). Escherichia coli was best predicted by the weighted density of septic tanks, with their infl...