Cootes Paradise Marsh is a hypereutrophic coastal wetland of Lake Ontario that has received sewage from the town of Dundas, Ontario for over eight decades. As such, sediments are nutrient rich and phosphorus release from the sediments is substantial. Release rates of soluble reactive phosphorus from frozen sediments collected at eleven representative sites in the marsh were highly variable, ranging from 0.96 to 28.28 mg m2 d−1. We wanted to evaluate spatial variance of the benthic microbial community and determine if this variation could be correlated to phosphorus release rates from corresponding sediments. Fresh sediment samples were collected from the same sites and characterized on the basis of sole-carbon-source utilization patterns through a Principal Components Analysis. Microbial communities located closest to the sewage outfall, had a high affinity for phosphorylated substrates, and used mainly carbohydrates, and were separated from communities located distal to the sewage source, which readily used polymers and simple sugars. Subsequently, sediment samples were collected from two sources and kept frozen for later phosphorus-release experiments while comparable samples were also collected to characterize the benthic microbial community from these sites. Phosphorus-release rates and utilization of specific substrates for the frozen sediment samples were significantly correlated (Spearman's Rank Correlation Analysis; P = 0.041), indicating a direct link between release and patterns of carbon utilization. Microbial communities of freshly collected sediments differed significantly from those of frozen sediments, and these differences were also observed for corresponding phosphorus-release rates. We conclude that the microbial community structure likely plays a major and direct role in the release and uptake of phosphorus from the sediment in Cootes Paradise Marsh.

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