THE EFFECT OF LAND USE ON THE NUTRIENTS AND ORGANIC CONTAMINANTS IN THE WATER AND SEDIMENT OF THE RAPPAHANNOCK RIVER

     The documented degradation of the Chesapeake Bay is a huge environmental concern. Excess nutrients, mainly nitrogen and phosphorous, from point and nonpoint sources pollute the water, causing overproduction of algae. Excess algae destroy the ecosystem by preventing sunlight from reaching aquatic plants. Algal decay also lowers dissolved O₂, further stressing the ecosystem. Organic contaminants, such as pesticides and constituents of consumer products, may also pollute the bay. The Chesapeake Bay's drastic decrease in oysters is only one of many visible repercussions of this pollution.       This research aims to determine whether the Rappahannock River is a significant source of pollutants in the Chesapeake Bay. Five sampling locations were chosen to represent different land use surrounding the river including forest, agriculture, and human development. Water samples were taken periodically and analyzed for nitrate and phosphate using spectroscopic analyses. Sediment samples were also taken from some of the sampling locations and analyzed for phosphate and organic contaminants using colorimetric analysis and gas chromatography-mass spectrometry (GC-MS), respectively.

Sampling began in May 2007 and continues on a monthly basis. In the city of Fredericksburg, the concentration of nitrate increased during the summer of 2007. During the same period, samples from sites below the city had lower concentrations of NO₃^-, presumably due to dilution and uptake by aquatic plants and algae. During the winter of 2007 nutrient levels increased in the agricultural areas due to lowered aquatic primary productivity. Overall, NO₃^- concentrations have not been at harmful levels during this short sampling time: the majority of samples have been under 0.8 mg/L NO₃^-. Phosphate in water has also been low during the sampling period: readings have varied between 2.00 and 20.00 µg P / L. Currently, PO₄^3- concentrations do not appear to follow a spatial trend in the river water.  The concentrations in dried sediment were between 20.00 and 40.00 mg P / kg. This was well over 100 times the amount found in water, indicating the important role of sediment in nutrient retention. Preliminary GC-MS analysis of sediment has indicated organic contamination, possibly steroid products, but further analysis is needed to confirm identification.