Hydrologic, metabolic and chemical regulation of water-column metabolism and atmospheric CO2 exchange in a large continental reservoir during spring and summer

Abstract

Abstract Large continental reservoirs are important sinks of terrestrially-derived carbon (C), yet exhibit high inter-annual variability in net CO 2 exchange with the atmosphere due to incompletely understood interactions between supply of solutes (C, nutrients, pH) and lake metabolism. Here we quantified the interaction between hydrology, aquatic metabolism and atmospheric CO 2 exchange in the lacustrine Qu'Appelle arm of Lake Diefenbaker, Canada, by comparing total phytoplankton abundance (as Chlorophyll a ), net primary productivity (NPP), ratios of microbial productivity (P) to respiration (R), and chemically-enhanced CO 2 flux over four springs and summers (2010–2013) with contrasting hydrologic characteristics. Overall, dissolved oxygen (DO) concentrations were correlated inversely ( R 2 adj = 0.63, p 18 O values of DO indicating a strong metabolic coupling in this polymictic basin, whereas correlations between concentration and C isotope ratios of dissolved inorganic carbon (DIC) were not significant ( R 2 adj 1, the basin was slightly autotrophic and CO 2 was captured from the atmosphere. In contrast, the Qu'Appelle arm was a substantial source of CO 2 during 2012 when river discharge was low, pH was 2 exchange ( R 2 adj CO2-pH = 0.84, p 2 dynamics on seasonal and inter-annual scales.