Tracking sources of particulate phosphorus in river waters: a case study in East Creek, a Chesapeake Bay Watershed

Jaisi, DebIncomplete understanding of phosphorus (P) forms and their recalcitrance under imposed environments coupled with methodological limitations to track P sources are obstacles preventing accurate assessment of nutrient loads released to open waters. In this thesis research, the East Creek Watershed in Crisfield, MD, an agricultural runoff dominated watershed, was selected to understand the fate and stability of P from various sources during transport from East Creek to the Chesapeake Bay. To achieve this, P concentrations and phosphate oxygen isotope ratios were compared between sequentially extracted Hedley P pools from potential sources and suspended particulate matter. A transect study from an agricultural field to a drainage ditch was also conducted to identify potential P release pathways. Transect study results suggested soil erosion is a plausible P source to ditch sediments after crop harvest, although dissolved P was the prominent P form in the ditch water column during summer algal blooms which drive sedimentary P release. Comparative analyses of P pools in suspended particulate matter in creek water suggest that particulate P is primarily carried in loosely sorbed and Fe/Al oxide-bound forms. Isotope results suggest loosely sorbed P is bioavailable whereas Fe/Al oxide-bound P and Ca-P precipitates were not accessed by microbes during particulate P transport through the creek. Agricultural field soil, streambank material, and sediments were important sources of legacy P, although mechanism of P release and contribution differed among them. These findings improve understanding on sources and fate of particulate P and are expected to be useful for nutrient management in soils and waterways.University of Delaware, Department of Plant and Soil SciencesM.S