Factsheet – Seasonal and Hydrological Controls of Bioavailability of Organic Phosphorus in Agricultural Drainage Waters

Intensive agriculture in the US Midwest has been linked to various water quality problems including eutrophication of surface waters, the proliferation of nuisance algae, and degradation of water quality. Past studies of Phosphorus (P) export from agricultural fields have largely focused on inorganic P (Pi), but have paid scant attention to the organic P constituents (Po) in agricultural drainage waters. This is probably due to the assumption that the Po fractions are not bioavailable. However, several lake studies have shown that a significant portion of Po can be converted into available P forms through enzyme-mediated hydrolysis. Similar investigations have not been conducted with agricultural drainage waters. This project assessed the amount of hydrolysable Po in drainage waters from an agricultural field in the School Branch watershed (Indiana), elucidated the factors controlling the composition and bioavailability of Po, and determined the extent to which this pool of organic P can become available to algae and contribute to eutrophication of receiving water bodies.