The dynamic nature of sediment and organic constituents in TSS
The Chattooga River Watershed, located in NE Georgia, NW South Carolina, and SW North Carolina, contains some of the most scenic and valuable water resources in the region. The Chattooga River is designated as a wild and scenic river and serves as the headwaters for water supplied to numerous cities. The mix of public and private lands presents considerable challenges to addressing sources of stream degradation. The EPA has listed several streams in the Chattooga Watershed as being impaired by suspended sediment and has established Total Maximum Daily Loads (TMDLs). These TMDLs are based upon determining acceptable levels of suspended sediment; however, TSS was used as a surrogate for suspended sediment. We are using continuous monitoring of flow and sampling TSS, suspended sediment, and particulate organic matter on four tributaries of the Chattooga River to determine the nature of TSS loading in these streams. We have found that TSS concentrations do not necessarily reflect suspended sediment concentrations. The organic and mineral components of TSS vary between streams. While the benchmark, forested stream in our study did have lower levels of TSS, it did have relatively high TSS levels during storm events, similar to those of impacted streams. However, organic matter was a proportionately larger component of TSS in the forested streams whereas mineral sediment comprised the greatest fraction of TSS in streams more heavily impacted by land use change and roads. The streams listed as threatened or impaired had significantly higher levels of TSS than the benchmark stream. However, TSS and mineral sediment in one of the impaired streams were significantly lower than a stream listed as only being threatened. The relevance of a sediment TMDL based on suspended load is questionable because the sediment impacts to the stream biota and aquatic habitat are caused by bedload.