Oxygen Concentration and Demand in Lake Erie Sediments

Regular ship-board monitoring of oxygen in the hypolimnion of Lake Erie has been established to monitor the status of the lake and determine if the water quality is meeting the terms of the Great Lakes Water Quality Agreement (GLWQA). However, lake-wide monitoring is expensive and there is a difference of opinion on whether dissolved oxygen depletion rate is a good indicator of the condition of Lake Erie. One the most poorly known components of the Lake Erie oxygen budget is the sediment-oxygen demand (SOD). In this work, vertical oxygen concentration profiles in Lake Erie sediments are measured by incrementally inserting a micro-oxygen electrode. The SOD is the flux of oxygen across the sediment-water interface and is calculated from the oxygen profiles assuming Fickian diffusion at the sediment-water interface. Oxygen consumption was measured in sediments collected on four dates from 3, 13, and 5 stations in the western, central, and eastern basins, respectively. Oxygen concentration profiles in the sediment and the SOD are well described by a diffusion/reaction transport model where oxygen diffuses into the sediment and is consumed by reactions that follow Michaelis-Menten kinetics. The flux of oxygen into the sediment in the central basin in August 2002 was 1.03 ± 0.271 × 10−11 mol O2/cm2/sec, within about 30% of the hypolimnetic oxygen depletion rate derived from monitoring. These results suggest that modeling of oxygen profiles hold promise as an alternative technique to regular monitoring for determining hypolimnetic oxygen depletion rates.