The Fate of PHOSPHORUS

Nutrient releases from sediments provide a way for point and nonpoint source loadings to influence water quality conditions for several years. This is because particulate organic matter, which settles into the sediment in lakes, impoundments, and the depositional areas of rivers and estuaries, undergoes anaerobic decomposition and produces inorganic nutrients that can be released later. Therefore, accounting for the source of sediment-bound nutrients can be an important component of total maximum daily load (TMDL) analyses. An advanced mathematical model that includes the calculation of nutrient releases from the sediment has been used to evaluate point and nonpoint source phosphorus control for a 137-km (85-mi) section of the Upper Mississippi River near Minneapolis-St. Paul. Minn.. The model, calibrated with data collected during a range of hydrologic conditions from 1985 to 1996, has been used to simulate water quality conditions under several scenarios involving nutrient reductions. In the simulations, the 12-year hydrodynamic transport was repeated through two cycles to evaluate water quality conditions for a future 24-year period.