Water Resources Research Act Program

Details for Project ID 2020IN068B

Seasonal and hydrological controls of bioavailability of organic phosphorus in agricultural drainage waters

Institute: Indiana
Year Established: 2020 Start Date: 2020-03-01 End Date: 2021-02-28
Total Federal Funds: $15,000 Total Non-Federal Funds: $30,681

Principal Investigators: Pierre-Andre Jacinthe

Abstract: The water quality impact of phosphorus (P) exported from croplands in the US Midwest is well documented. Monitoring efforts have generally focused on the inorganic P (Pi) fractions, a preference largely dictated by the assumption that Pi is immediately available to algae. However, in some settings, the amount of organic P (Po) loss can be significant, and may represent another P source that can sustain algal growth in receiving water bodies. At the present, the bioavailability of Po is largely unknown.Our monitoring activities (2015-2019) at two Central Indiana agricultural watersheds have shown that Po was the dominant form of P exported, ranging between 63 and 92% of total P load. In light of these observations, we investigated the bioavailability of Po in drainage waters, and examined the effect of hydrologic flow path (surface runoff vs subsurface tile discharge) and season on the biochemical attributes of Po. The pool of bioavailable P was determined using the filter strip method (retention of Pi + Po fractions available to algae on FeO-impregnated filters). Enzyme assays were conducted to quantify the enzymatically-hydrolysable fractions of Po or EHP (monester, diester, phytate) in drainage waters. Initial results have shown that EHP concentration was generally higher in the summer, and consistently higher (2-fold) in tile waters than in surface runoff. We plan to: (i) continue these measurements through summer 2020 to assess annual variability, and (ii) conduct additional analysis using NMR spectroscopy to gain further insight into the speciation and dynamics of Po in agricultural waters. Overall, these initial results indicate that a sizable portion of the dissolved Po pool, once presumed to be not bioavailable, can in fact be hydrolyzed and converted to Pi, fueling algal growth. Results of this study have clear implications for P management and water quality protection in agricultural landscapes.