Technical Abstract: Agricultural runoff carries high nutrient loads to receiving waters contributing to eutrophication. Managed wetlands can be used in integrated management efforts 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. This study seeks to quantify and elucidate how inundation of field managed wetland sediments affects 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 and Fe-, 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 significant temporal relationships between inundation and Pw desorption. Pw concentrations were significantly higher at the site which exhibited variable hydroperiod (100 m) as compared to sites under consistent inundation. This 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. Feox and NaOH-P concentrations were significantly higher at the least inundated site as compared to all other sites (F = 5.43; p = 0.001) irrespective of time. Evidently, it is hypothesized that increased hydraulic residence time can decrease the bioavailability of phosphorus in wetland sediments receiving agricultural runoff. This finding suggests that the restoration of wetlands in the Mid-South may be hydrologically managed to improve P retention.