Comparing abiotic and biotic parameters when assessing streams within a geologically diverse area (Bartow County, GA)

During the summer of 2000, we sampled twenty-two stream sites in Bartow County (Georgia) for fish, macro-invertebrates, water quality, habitat condition, and bacterial indicators as part of a county-wide watershed assessment. Three major geological regions occur within the county (to the west rocks are mainly limestone, to the north shales and sandstones, and to the east and southeast harder metamorphic rocks). Because the county is so geologically diverse yet all sites are within the same drainage basin, this data set provides a rare opportunity to examine the influence of watershed geology within a relatively small geographic area on parameters and metrics traditionally used to assess anthropogenic impacts.Principal component analysis (PCA) and other comparisons indicate that most biotic and abiotic parameters over all sites are related to one another in ways expected among sites that vary due to anthropogenic impacts. Multimetrics developed for fish and for invertebrates reflected trends along the primary PCA ‘water quality’ factor (turbidity, suspended solids, and BOD), whereas site geology did not reflect trends across this factor. As expected dissolved ions (as well as alkalinity and pH) were strongly related to watershed geology, but other less obvious water quality parameters such as nitrate were also associated with geologic location.Most individual metrics that are traditionally used to assess invertebrate and fish communities did not appear to be influenced by geology, but rather by anthropogenic habitat and water changes. In addition, differences in taxonomic composition of invertebrate communities were associated with watershed geology. Any given invertebrate community within the western limestone region was most similar (based on similarity indices of species composition) to other communities within this same region. Communities within the other two regions were not similar to western communities, but not distinctly different from each other. Because water chemistry between streams of western limestone and streams of northern shale-sandstone are more similar, geological influences on invertebrate species distribution may reflect physical stream characteristics (such as streambed morphology and substrate characteristics) rather than water chemistry.While underlying geology strongly affected many water quality parameters, biotic measures were relatively independent of these water quality effects, indicating biotic parameters are reliable in assessing degradation in a geologically diverse basin.