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Great Lakes coastal wetlands are essential land-water linkages, which regulate the fate of materials and nutrients from watersheds prior to discharge into the nearshore zone of the Great Lakes. With climate change increasing storm activity and wind events within the Great Lakes Basin, a fulsome understanding of nutrient processing and fate within coastal wetlands is essential. We evaluated across- and -- within wetland water quality and nutrient loadings as a function of climate and seiche activity over a decade (2009-2018) in three drowned river mouthed wetlands of Lake Ontario. Notably, celled sites had significantly higher concentrations of total phosphorus, phosphate, and organic nitrogen compared to non-celled sites (permutational analysis of variance p-value < 0.001). These differences were associated with increased solar radiation and lake level variability (i.e., seiche inundation), thus we infer celled sites are important locations for the mobilization of legacy phosphorus. To further characterize the relative effect seiche activity has on phosphorus loadings to the nearshore zone of Lake Ontario, we developed a structural equation model. We confirmed that seiche events resuspend sediments, which cause a significant increase of phosphorus loadings to the coastal zone of Lake Ontario (p-value < 0.001). Our results indicate that climate and seiche events influence coastal wetland water quality and should be considered when assessing nearshore zone water quality. [ABSTRACT FROM AUTHOR]

Although Great Lakes coastal wetlands are considered "keystone" ecosystems, surprisingly little is known about their dynamic role in regulating nutrient loadings to receiving waters. Based on over a decade of spatially explicit monitoring, the Toronto and Region Conservation Authority determined that four coastal wetlands (Rouge Marsh, Duffin's Marsh, Carruthers Marsh, and Frenchman's Bay) vary in their capacity to be net-sinks or net-sources of phosphorus to Lake Ontario. To improve our understanding of phosphorus fate and dynamics in these coastal wetlands, we deployed continuous (every 30 min) multiparameter (dissolved oxygen, conductivity, turbidity, pH) sondes just above the sediment surface in each study wetland for eight weeks (Aug. - October) in 2022. A suite of phosphorus and nitrogen samples were collected weekly with other water quality variables. We will present these findings with an emphasis on the role of dissolved oxygen and nitrate concentrations in mediating internal phosphorus loading. [ABSTRACT FROM AUTHOR]