Changes in sediment-water column phosphorus interactions following sediment disturbance

Stream and ditch sediments are an important part of the ecosystem that can play a pivotal role in buffering nutrient and contaminant concentrations in surface water. Removal of existing sediments and deposition of new sediments will change the physiochemical parameters controlling P transport in drainage ditches; however, these phenomena are not well documented. This study was conducted to determine the impact of severe storms on sediment P interactions with water column P in tile-fed drainage ditches within agricultural watersheds in northeast Indiana. Easily exchangeable P (MgCl2 extractable) in ditch sediments ranged from 0.5 to 1.32 mg kg−1. The equilibrium P concentration (EPCo) between the aqueous phase and sediments ranged from 0.02 to 0.11 mg L−1. When comparing sediment EPCo with dissolved P concentrations in ditch water, sediments acted as a P sink in five of the seven data collection sites. The ability of the sediment to buffer water column P, as measured by the slope of the linear relation used to calculate sediment EPCo, ranged from 2.7 to 13.8 mg P sorbed kg−1 sediment per unit in mg P L−1 in the aqueous solution. In contrast to previous studies, chemical amendments did not alter easily exchangeable P in sediments nor sediment EPCo and the slopes observed in the linear P sorption isotherms. While chemical amendment can be used to increase P sorption by sediments and reduce exchangeable P in sediments, this showed that this practice should be targeted to times of the year when they would be the most effective.