Storm Water Export of Nitrogen, Phosphorous, and Carbon from Developing Catchments in the Upper Piedmont Physiographic Province

Impacts on water quality caused by land use change from forests and pastures to housing subdivisions were evaluated in catchments undergoing active development in the upper Piedmont physiographic province of South Carolina. Specific attention was focused on the export of nitrogen, phosphorus and carbon from these catchments during storm events. Three catchments with varying stages of development were compared to categorize the effects of land disturbance. Storm events occurring within a four year period of 2004 through 2007 were studied for changes in water quality within catchment streams. Due to the potential large input of surface runoff to streams following rainfall, storm events allowed for the largest impact of development to local water quality. The water quality parameters studied included dissolved organic carbon, total dissolved nitrogen, nitrate, dissolved organic nitrogen (DON), total phosphorous, and total suspended solids. The nutrients were chosen because of their importance to biological systems and impact on water quality. Nutrient export is important as the downstream location, Lake Greenwood, has had problems with algae blooms in the past which are affected by the amount of available nutrients. Suspended solids were studied primarily for the correlation they have with runoff from catchments, as well as similarities in behavior to certain nutrients such as phosphorous. Calculations of event mean concentrations (EMC), area-normalized cumulative loads (CL), specific ultraviolet absorbance (SUVA), and molar ratios of organic carbon to organic nitrogen (C/N ratio) were used to quantify the changes. The EMC and CL values showed the change in the mass of nutrients loadings to the streams over time. Seasonal conditions, such as rainfall and antecedent dry weather, largely impacted the calculated values. The latter calculations revealed how the composition of organic matter may have been altered. Additionally, all constituents were graphed alongside flow, as were SUVA and C/N ratios. These graphs allowed for further study of changes evoked by development. Results from this study revealed that the nutrient export from disturbed catchments was often affected more by seasonal variation than by degree of development. However, development tended to increase the rate at which nutrients (nitrogen and phosphorous) were exported from the catchments and resulted in flushes for both TDN and nitrate relative to the flow. However, TSS experienced the largest increase in the rate of export. The amount of TSS transported was also increased by development despite the use of best management practices. The hydrographs changed with more developed catchments displaying steep rising and falling limbs in addition to quicker responses to rainfall. Development also impacted the fraction of aromatic carbon exported during storm events by lowering the aromatic fraction of organic carbon in the stream during the largest flow peaks. Evidence of this was based on observed relationships between the SUVA and the storm flow during periods of development for each catchment