Inundation influences on bioavailability of phosphorus in managed wetland sediments in agricultural landscapes.

604 Agricultural runoff carries high nutrient loads to receiving waters, contributing to eutrophication. Managed wetlands can be used in integrated management eff orts to intercept nutrients before they enter downstream aquatic systems, but detailed information regarding sorption and desorption of P by wetland sediments during typical inundation cycles is lacking. Th is study seeks to quantify and elucidate how inundation of wetland sediments aff ects bioavailability of P and contributions of P to downstream systems. A managed wetland cell in Tunica County, Mississippi was subjected to a simulated agricultural runoff event and was monitored for bioavailable phosphorus (water-extractable P [Pw], Fe-P, and Al-P) of wetland sediments and water level during the runoff event and for 130 d afterward. Inundation varied longitudinally within the wetland, with data supporting signifi cant temporal relationships between inundation and Pw desorption. Concentrations of Pw were signifi cantly higher at the site that exhibited variable hydroperiods (100 m) as compared with sites under consistent inundation. Th is suggests that sites that are inundated for longer periods of time desorb less Pw immediately to the environment than sites that have periodic or ephemeral inundation. Concentrations of iron oxalate and NaOH-P were signifi cantly higher at the least inundated site as compared with all other sites (F = 5.43; p = 0.001) irrespective of time. Th ese results support the hypothesis that increased hydraulic residence time decreases the bioavailability of P in wetland sediments receiving agricultural runoff . Th is fi nding suggests that the restoration of wetlands in the mid-southern United States may be hydrologically managed to improve P retention. Inundation Infl uences on Bioavailability of Phosphorus in Managed Wetland Sediments in Agricultural Landscapes