Stable Isotopes and Bayesian Modeling Methods of Tracking Sources and Differentiating Bioavailable and Recalcitrant Phosphorus Pools in Suspended Particulate Matter

Understanding the sources of different phosphorus (P) pools and their bioavailability under imposed biogeochemical environments in a watershed is limited largely due to the lack of appropriate methods. In this research, phosphate oxygen isotope ratios and Bayesian modeling on fingerprinting elements were applied as two novel methods to identify sources and relative recalcitrancy of particulate P pools suspended in water in the continuum of sources from land to the mouth of a coastal estuary to the Chesapeake Bay. Comparative analyses of sizes, relative ratios, and oxygen isotope values of particulate P pools in the creek water suggested that the NaHCO₃-P pool was bioavailable, whereas NaOH-P and HCl-P pools were recalcitrant during P transport along the creek. Agricultural field soil, streambank, and river bottom sediments were major sources of particulate P and their contributions varied significantly at the headwater and downstream regions of the creek. Bayesian modeling based on fingerprinting elements suggested that tides played a major role in forming particulate matter from estuarine sources at the creek mouth region and importing it upstream. These findings provide new insights into the origin and fate of particulate P and the fidelity of isotope and fingerprinting methods in source tracking of P in tidally influenced watersheds.