The Effects of Local Riparian Zone and Streambed Sediment on the Abundance, Diversity and Distribution of Freshwater Fishes in Piedmont Streams of South Carolina

Previous research has revealed that dominant watershed land cover types (e.g., pasture, forest, agriculture) do not adequately explain the observed trends in diversity, abundance and distribution of freshwater fish populations in rural habitats. However, most studies investigate the effects of land cover at very large spatial scales, but fish are mobile enough that they may be selecting habitats at a much smaller spatial scale. As such, we conducted a study to see if extremely localized changes in riparian zones and habitat quality better explain distribution patterns of stream fishes in the South Carolina Piedmont. At each location, data were collected in two different 60 m reaches of the same streams, approximately 100 m apart, with each reach containing a differing extent of local riparian cover. We collected fish, measured aspects of the riparian zone immediately adjacent to the stream, did a grain size analysis of streambed sediment and collected geomorphology, water chemistry and land cover data. We hypothesized that fishes would be more abundant, and populations more diverse, in reaches with riparian zones containing more ground and canopy cover, and where sediment composition was more homogenous. Results demonstrated no significant effects of local riparian cover, likely because of the limited scope of our measurements. We did see an unexpected positive correlation between Simpson’s Diversity and percent agricultural and pasture landcover, and a negative correlation between percent forest cover and Simpson’s diversity, however. This may be explained, in part, by the negative correlations between percent forest cover and average sediment size and skewing, as well as the positive correlations between sediment skewing with percent crop cover. Thus, initial results indicate that local riparian vegetation may not be as influential as streambed sediment composition in structuring freshwater fish assemblages