PATTERNS IN SEDIMENT P FRACTIONATION WITHIN A MIXED LAND-USE WATERSHED

The Northrup Creek watershed is a small mixed land-use watershed within the lake plain region of Lake Ontario, immediately west of Rochester, NY that is a 303(d) impaired waterbody due to high P. General stream water chemistry finds pH values in the range of 7.5 to 8 with high alkalinity. Recent studies show elevated soluble reactive phosphorus and total phosphorus values in excess of 250 μg/L and 700 μg/L, respectively. With a long history of P input from agriculture and a recently decommissioned wastewater treatment plant, these values are not unexpected. Here we investigated sediment P that is a legacy of historic and ongoing P inputs. Sediment samples were collected at 12 locations that correspond to previously studied subwatershed segments. Samples were subjected to a series of laboratory analyses to evaluate P fractionation including a sequential extraction procedure. Results of the P sequential extraction show variations in P fractionation that may be attributed to variations in land-use. Overall, Ca associated P dominates due to general water chemistry. The organic P fraction, up to 30% of total P, is found downstream of agricultural areas. Phosphorus associated with Fe-Mn reducible fractions increases downstream of the former wastewater treatment plant typically ranging from 20% to 25% of total P. Aluminum associated P varies throughout the watershed and is related to sediment texture.