PHOSPHORUS TRANSFORMATIONS FROM FIELD SOILS TO LAKE SEDIMENTS

Phosphorus has been identified as one of the major factors influencing the anthropogenic eutrophication of surface waters. In this study, we investigated the transformation of phosphorus species as soil is eroded, transported through a stream, and ultimately deposited in a near-shore sedimentary environment. Conesus Lake, located in Livingston County, New York, has several small sub-watersheds entering around the perimeter of the lake. Graywood Creek is a small watershed, comprising approximately 38 hectares, and dominated by a single dairy farm. Soil samples were collected from six different agricultural fields based on current and past management practices and one forest soil within the watershed. Stream sediment was collected in three shallow pools within the stream, and seven sediment samples were collected within the near-shore area of the lake. These samples were subjected to a sequential extraction procedure (Psenner, 1988) that operationally separates P into five physicochemical phases, pore solution and easily exchangeable, associated with Fe and Mn oxyhydroxides, associated with Al oxyhydroxides, associated with organic matter, and Ca associated P. Results show a trend in the P speciation as field soils are eroded and transported through the stream and deposited in the lake. Field soils were found to have an average of 553.8 mg P/kg with the 45.6 % and 41.5% associated with Al oxyhydroxide and organic matter phases, respectively. Stream sediments were found to have 202.3 mg P/kg. Al-bound P decreased slightly to 37.2%, but organic matter P dropped to 16.8% of the total extractable P. Fe-bound P increased from 9.9% to 34.1%, and Ca-bound P increased from 2.5% to 11.1%. Within the lake sediment, total extractable P drops to an average of 67.5 mg P/kg. Phosphorus associated with Fe oxyhydroxides, Al oxyhydroxides and organic matter range from 13.5% to 20.8%, but Ca-bound P increased to 44.9% of the total extractable P. Exchangeable P is less than 1.25% on average. These results suggest that P is being released to the water column during transport and deposition, and that much of the P remaining in the sediment is being transformed into the more stable Ca-bound phase. The solubilization of P from the sediments has implications for near shore algae blooms and the value of best management practices for agricultural soils.