Comparison of Summer and Winter Oxygen Consumption Rates in a Temperate Dimictic Lake

Abstract

In a temperate dimictic lake in southern Ontario, the winter rate of oxygen loss determined from oxygen profiles differed considerably from the summer hypolimnetic rate, although the sediment oxygen demand (SOD) and water column oxygen demand (WOD) did not change significantly (SOD: winter = 0.018 mg O2∙L−1∙d−1, summer = 0.020 mg O2∙L−1∙d−1; WOD: winter = 0.032 mg O2∙L−1∙d−1, summer = 0.027 mg O2∙L−1∙d−1). In summer, the sum of SOD and WOD (0.047 mg O2∙L−1∙d−1) closely approximated the hypolimnetic deficit (0.040 mg O2∙L−1∙d−1), but in winter, SOD plus WOD (0.050 mg O2∙L−1∙d−1) greatly overestimated the observed consumption rate (0.003 mg O2∙L−1∙d−1). Measurement of primary production and an estimate of rainwater influx revealed that both could be significant sources of oxygen input during winter. Although both WOD and SOD were found to vary significantly between 10 sampling sites, a central station yielded seasonal mean values that closely approximated those obtained from combining the data from all stations.