Tracing the Sources and Biogeochemical Cycling of Phosphorus in Aquatic Systems Using Isotopes of Oxygen in Phosphate

Phosphorous (P) is an essential nutrient for all living organisms and when available in surplus could cause eutrophication in aquatic systems. While P has only one stable isotope, P in most organic and inorganic P forms is strongly bonded to oxygen (O), which has three stable isotopes, providing a system to track phosphorus cycling and transformations using the stable isotopes of O in phosphate (PO₄), δ¹⁸O_p. This isotope system has only recently been utilized in aquatic environments. Available data obtained from different settings indicate that δ¹⁸O_p of dissolved phosphate in aquatic systems can be applied successfully for identifying sources and cycling of phosphate in a broad range of environments. Specifically, work to date indicates that δ¹⁸O_p is useful for deciphering sources of phosphate to aquatic systems if these sources have unique isotopic signatures and if phosphate cycling within the system is limited compared to input fluxes. In addition, because various processes are associated with distinct fractionation effects, the δ¹⁸O_p tracer can be utilized to determine the degree of phosphorous cycling within the biomass and shed light on the processes imprinting the isotopic signatures. As a better understanding of the systematics of and various controls on δ¹⁸O_p is gained, it is expected that δ¹⁸O_p would be extensively applied in research geared to understand phosphorous dynamics in many environments.