Chemical and Biological Assessment of Land-Use Impacts on Water Quality in the Sweetwater Valley of Tennessee

Abstract

An integrated approach of biological and chemical analyses was used to determine the impact of land use on stream health in four sub-watersheds along Sweetwater Creek in southeast Tennessee. By monitoring the mass loading of water quality constituents from flow proportional samples and determining an Index of Biotic Integrity (IBI) and an Ephemoroptera, Plecoptera, and Trichoptera (EPT) taxa count, a comparison was made of the impact of land-use on water quality. The Sweetwater Creek watershed, which covers 6,216 ha, was subdivided into four sub-watersheds based on the following land uses: Agricultural (1,943 ha), Rural (1,166 ha), Mixed (1,295 ha), and Urban (1,632 ha). A stage-discharge curve was developed for each sub-watershed sampling site. The stream stage was monitored using a water level sensor connected to a datalogger. Based on the stream level, the flow volume was calculated and accumulated in the datalogger until a preset value was reached which triggered a pump sampler. Laboratory analyses from these flow proportional samples along with corresponding stream discharge values allowed the calculation of mass loading of the stream. With these data, direct comparisons were made between the subwatersheds for the following: chloride, nitrate, sulfate, and total suspended solids (TSS). While many chemical measures of water constituents are frequently used to quantify water quality, a biological health assessment, using indicator species, may also be used to determine water quality. The results of the mass loading analyses showed the Rural, Mixed, and Agricultural sub-watersheds were similar. In the Mixed sub-watershed, TSS values decreased, which was probably due to stream shape, which caused the water velocity to decrease resulting in sediment deposition. Mass loading from the Urban sub-watershed was as much as ten times greater for each of the constituents during the storm event evaluated. The Index of Biotic Integrity (IBI) value, which is based on the presence or absence of fish species, was very poor (22) for the Urban stream reach; the Mixed and Rural stream reaches were rated poor (32), and the Agricultural stream reach was rated poor/fair (38). The Ephemeroptera, Plecoptera, and Trichoptera (EPT) ratings, which are based on the count of taxa of these three orders of macroinvertebrates that are known to be sensitive to pollution, were similar to the IBI ratings; the Urban stream reach yielded the lowest counts, The Mixed and Agricultural stream reaches had slightly higher counts than the Urban reach, and the Rural stream reach had the highest EPT taxa count for each of the three sampling events. A habitat assessment analysis of the stream reaches supported the conclusions from the IBI index and EPT taxa count.