Relative influence of physical and anthropogenic variables on instream habitat in Silver Creek, Idaho
Schultz, Briana Corry
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The Silver Creek watershed is a spring creek ecosystem. Spring creeks are a unique, understudied component of stream habitat in the Northern Rocky Mountains. Spring creeks are unique because they have relatively constant temperatures, abundant macrophytes, and high levels of dissolved oxygen. With changing land management and increased suburban and exurban development across the West, spring creeks are becoming more recognized for their outstanding resource potential. However, little is known about these ecosystems. The goal of this study was to determine whether natural or anthropogenic variables are more strongly associated with instream habitat quality in Silver Creek while characterizing its natural, instream, and anthropogenic variables. Ten instream variables commonly used to assess runoff-dominated streams, seven natural variables, and fourteen anthropogenic variables were identified and sampled at eighteen locations within the Silver Creek watershed. Trends indicate that higher elevation (tributary) stream channels have lower slopes, are more narrow, more shallow, contain less sediment, and are bordered by a higher percentage of riparian lands than lower elevation (main stem) stream channels. Spearman rank correlation coefficients (R-values) and p-values were evaluated with 27% (19 of 70) of correlations significant at all sample locations in the natural and instream variables data set. Natural variables with the most correlations observed in relation to instream habitat variables were elevation, watershed area, and stream slope. Spearman rank correlation coefficients (R-values) and p-values were evaluated with 3% (5 of 150) of correlations significant at all sample locations in the anthropogenic and instream data set. Anthropogenic variables with the most correlations observed between instream habitat variables were percent developed acres, percent total riparian acres, and structure density. Overall, natural variables influence instream habitat more than anthropogenic variables. Correlations showed that as elevation increases, watershed area decreases, and width, average depth, maximum depth, and sediment depth all decrease. Future studies of Silver Creek should increase sample size, which would help to more adequately capture the habitat of the Silver Creek watershed and increase the potential for stronger, more discernible correlations.