Export of Organic Matter from a Coastal Freshwater Wetland to Lake Erie: an Extension of the Outwelling Hypothesis

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Abstract

I tested the hypothesis that seiches in large lakes play a role similar to tides in marine system by exporting detrital carbon from coastal wetlands to adjacent open waters. The study was conducted at a wetland site located along the shore of the Lake Erie. Water samples were collected at the outlet of the marsh, during inflow and outflow events, over a 19-month period. Water isotopes were also measured in the lake and in the marsh to establish the magnitude of the mixing between the two water masses. On average, the concentrations of the outflow water samples was enriched by 7.3 mg DOC l-1 and 3.4 mg POC l-1compared to the inflow water samples, while no difference observed in inorganic carbon fluxes. Organic carbon was exported during fall, winter and early spring which coincide with period of organic matter decomposition. Such a concept of outwelling is not new for marine ecosystem, but is demonstrated in this study for the first time in a large lake setting influenced by seiche events. Ultimately to understand the role that these fluxes may play in maintaining the integrity of the wetland-lake system, it will be necessary to investigate whether the detrital material exported from coastal freshwater wetlands is incorporated into the open lake foodweb.

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