Sediment phosphorus flux in an Oklahoma reservoir suggests reconsideration of watershed management planning

Abstract

A reservoir model of Lake Wister, Oklahoma, indicated that internal sources dominated phosphorus (P) loading to the waterbody, and that a watershed management plan need not address external P sources. To test this claim, we evaluated internal P loading by measuring sediment oxygen demand (SOD) and quantifying soluble reactive P (SRP) release from sediments to the overlying water column. Sediment cores from 3 sites were incubated at 21 C under quiescent conditions. Average SOD rates were between 9.9 and 22.6 mg/m 2/h (240-540 mg/m 2/d) across the three sites, where the shallow headwaters site had the least SOD. Average SRP release rate measurements varied from <0 to 3.30 mg/m 2/d across the sites, and measurements were greatest under anaerobic conditions in the cores collected from deep water near the dam and the water intake structure. Measured values were an order of magnitude less than those used to calibrate the previous reservoir model. The new data contradict the findings of the earlier reservoir model and suggest that internal P cycling would not be the dominant P source. Thus, external P sources to Lake Wister must be considered in watershed management planning. A watershed-based strategy that focuses on both internal and external P sources is needed to improve overall water quality in this drinking water supply reservoir. © 2012 Copyright Taylor and Francis Group, LLC.