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Spatio-temporal variation of benthic metabolism in a large, regulated river

Abstract Large rivers provide important ecosystem services to society, yet little is known about patterns and controls of key ecological functions, such as benthic metabolism, in these ecosystems. This study describes patterns of temporal and spatial variation of benthic metabolism (gross primary production (GPP) and community respiration (CR)) in the Saint John River, New Brunswick, Canada; a large, regulated river. Temporal variation and drivers of metabolism were assessed throughout the summer using measurements of dissolved oxygen from benthic chambers in the river’s wadeable margins. Differences in metabolism between channel locations (main and side channel) and patches of cobble and sand substrates were also determined. Rates of GPP and CR varied in accordance with a quadratic function throughout the summer months with peak rates attained in mid-July. Variability in metabolism was associated with light and water temperature. Spatial heterogeneity in metabolism was not observed between channel locations. Differences in metabolism between substrates were dependent upon time of year, as differences were only observed in early summer. Findings of this study suggest benthic metabolism in the margins of the Saint John River is controlled by variations temperature and light availability that vary with climatic patterns in the summer months. Consequently, these findings have implications for management of river health given projected scenarios of climate change.