Modelling Sediment Oxygen Demand in Lakes

Abstract

<p>Field and laboratory investigations were carried out to explore sediment oxygen demand (SOD) and its component parts. An in situ measurement device was built, tested and applied in Hamilton Harbour. Techniques were developed to measure SOD and oxygen uptake by chemical oxidation (CSOD). Sediment samples were taken from Hamilton Harbour and seven other lakes in Northern Ontario and Cape Breton Island. All samples were analyzed for organic content and selected samples were placed in laboratory columns. Experiments were conducted in which oxygen uptake was measured within the columns under controlled conditions. Sediment oxygen demand was fractioned into portions attributable to chemical oxidation, biological respiration and direct macroinvertebrate respiration.</p> <p>Models were selected to describe the dependence of each portion of SOD on oxygen concentration and temperature. Where possible, mechanistic explanations are presented for the models selected. Results indicate that the chemical portion of SOD is dependent on oxygen concentration in the manner of a first-order reaction and that it responds to temperature change in a manner typical of a mixed bacterial community. At high oxygen concentrations, anaerobic metabolic activity is found to be the limiting factor in CSOD. Bacterial and macroinvertebrate oxygen uptake are dependent on oxygen concentration at low concentrations, following a Monod kinetic form. These fractions respond to temperature in the same fashion as the chemical portion. Macroinvertebrates contribute a large part of the direct respiration as well as having a profound effect on the total community respiration.</p>