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Benthic metabolism was measured in a large regulated river with the goal of describing spatial differences in benthic metabolism associated with substrate (cobble vs sand), habitat type (main channel vs backwater) and flow regulation (regulated vs unregulated) during the summer months. Metabolism was estimated using benthic chambers deployed over one-week periods in two reaches of the Saint John River in New Brunswick, Canada. A two-way ANOVA comparing substrate type and month found both GPP and ER differed among months, with the greatest rates occurring in August. However, only ER differed significantly between substrate types, with cobble substrate exhibiting greater rates. ER also differed between habitat types with greater rates in the backwater channel. GPP only differed between habitat types among months, peaking in July. Assessment of flow regulation showed differences between sites and among months, with GPP greater in the regulated reach and rates highest in June (unregulated) and July (regulated). ER only differed between regulated and unregulated sites in July, with higher rates at the regulated site. This study demonstrates that there are strong spatial and temporal trends for benthic metabolism in a large river.

Craig Irwin (Primary Presenter/Author), Western University, Department of Geography, London, Ontario, Canada, N6A 5C2,;

Joseph Culp ( Co-Presenter/Co-Author), Environment and Climate Change Canada and Canadian Rivers Institute, Department of Biology, University of New Brunswick, Fredericton, New Brunswick, Canada, E3B 5A3,;

Adam G. Yates ( Co-Presenter/Co-Author), Western University & Canadian Rivers Institute,;