Many studies report stream degradation from direct anthropogenic impacts by correlating increased catchment impervious cover percentage (IC) with worsening stream health. However, this correlation can be less useful when predicting stream health in catchments with little to no IC. Our study characterizes catchments by combining hydrologic soil groups (HSG) with land cover and maintenance, known as Curve Numbers (CN), to predict stream health thresholds across a wide gradient of land cover conditions, particularly when IC is nominal or nonexistent. We did not compare the CN method with IC, but regressed two commonly used variables. The independent variable is the CN and the response variable is an index based on a rapid biological assessment protocol for wadable streams, known as the Family Benthic Index (FBI). The FBI is an index of organic pollution that rates stream reaches with published values that range from “Very Poor” to “Excellent” to categorize stream health. Generally, increasing CNs indicate increasing IC with slower infiltration velocity. CNs are commonly applied across the United States and other regions to estimate runoff quantity. However, we only investigated if CNs could reliably predict stream health (FBI). We sampled catchments (n = 178) in western North Carolina, US and found that CN can predict stream health (FBI) reasonably well (r2=0.78, p<0.0001). The FBI determination is based on rapid biological assessment protocol that relies on the identification of benthic macroinvertebrates collected from riffles to the family level using Hilsenhoff's Family Benthic Index (FBI). Our results suggest that a CN less than 70 indicated “Good” or better stream health categories (lower CNs have less IC and higher infiltration velocity). CNs greater than 70 suggest stream health below the “Good” classification. Future research includes replicating this method in other catchments and comparing this method to other indices such as IC or embodied energy in a landscape, which were not tested in this paper. Water quality professionals and scientists can calibrate this method for other catchments to inform decision making to address stream health.
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