New York State and Onondaga County have developed a total maximum daily load (TMDL) for phosphorus entering Onondaga Lake. Agricultural runoff was identified as a main source of phosphorus within the watershed. During a Phase I project, suites of best management practices (BMPs)
were implemented on farms that resulted in reductions in phosphorus and nitrogen loads greater than 50%. During this Phase II project, individual agricultural BMPs were implemented and evaluated for performance. A structural BMP known as a bark filter system was implemented at the
Bloom farm. The bark filter system intercepts and treats milk parlor wastewater through a settling tank and wood chip disposal bed before it reaches the receiving water. The settling tank reduced solids and biochemical oxygen demand (BOD) concentration by more than 50%, but did not
reduce phosphorus or nitrogen concentrations. A significant decrease in BOD, phosphorus and nitrogen was observed in the bark filter effluent, which was likely the result of physical removal of pollutants as the wastewater being passed through the wood chips and dilution with groundwater. A
soil management BMP known as a nutrient management plan was implemented at the Rohe farm. The nutrient management plan included operational practices pertaining to corn field management, such as modifying the time and amount of manure application. Runoff from a field with a nutrient management
plan (i.e., test plot) was compared to runoff from a field that was not managed according to a nutrient plan (i.e., control plot). Runoff from the test plot had significantly lower concentrations of phosphorus and nitrogen than runoff from the control plot during the spring runoff period,
but the runoff from the plots had similar concentrations during the remainder of the year. Concentrations of phosphorus and nitrogen in the control plot runoff were high in the spring because of the heavy manure loads it received throughout the winter. The test plot received some manure during
the winter, but it was a light application compared to the control plot. The control plot received higher fertilizer application rates than the test plot after the spring runoff period, but no significant difference in phosphorus and nitrogen concentrations were observed throughout the summer
and autumn. The Phase I and Phase II data show that agricultural BMPs reduce the load of nutrients reaching the receiving waters in the Onondaga Lake watershed. It was recommended that the final stage of this project include modeling to extrapolate the results of Phase I and II to the entire
watershed to help develop a watershed plan for meeting the TMDL.
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