Seasonally Variable Sediment Oxygen Demand Kinetics in Lake Erie's Central Basin

Abstract Sediment oxygen demand (SOD) rate measurements in Lake Erie and other lakes are complicated by the fact that SOD can show different degrees of dependence upon water temperature and dissolved oxygen (DO) concentration and different models have been used to describe this process. We incubated sediment cores from three locations within the basin, in factorial with temperature (8°C and 14°C) and time of year. We analyzed SOD kinetics using a phenomenological mixed‐order model where model order is an estimated parameter, a model based on Michaelis‐Menten (MM) kinetics, and a mechanistic model. The mixed‐order model showed that SOD was, on average, a 0.44‐order function of DO concentration, but model order declined from June (mean 0.74) to September (0.21). In the MM kinetics model, the half‐saturation constant decreased from 6.6 mg L −1 in June to 1.0 mg L −1 in September. The mechanistic SOD model indicated a shift from mostly DO diffusion into the sediment in June to mostly reduced substances release in September. Water column oxygen demand (WCOD) was similar across seasons, suggesting that sediment processes were responsible for the seasonal shift in SOD kinetics. All three models predicted plausible changes in DO compared to in situ observations. In addition to estimating rates and kinetics for future modeling studies in the lake, this study shows how the mixed‐order model approach can overcome limitations of using prescribed kinetics (i.e., zero‐ or first‐order) for empirical studies of biogeochemical fluxes that are controlled by a mix of different processes.