Historical loading and current sorption capacity of phosphorus in the sediments of Delta Marsh

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Hope, Christopher Kevin
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Delta Marsh is a freshwater inland coastal wetland located along the southern basin of Lake Manitoba, Canada. Spanning over 19,000 hectares, Delta Marsh is a eutrophic wetland complex that was formerly a world-renowned destination for waterfowl hunting. Over the past half century, the marsh has been in a state of decline due to invasive plant and animal species, stabilized water levels, and eutrophication due to increased nutrient loading from surrounding development. This prompted a coalition of organizations, including Ducks Unlimited Canada, to begin the “Delta Marsh: Restoring the Tradition” project in 2008 aimed at revitalizing the ecological processes and human traditions of the marsh. The objectives of this study were to investigate the marsh sediments to determine their historic rates of phosphorus accumulation and the current ability to bind phosphorus. I determined how nutrient levels have changed in the marsh over time as well as the ability for surface sediments to act as a sink or a source of phosphorus to the marsh. This was accomplished by collecting two sets of core samples; ten 50-cm cores dated using 210Pb and 137Cs and twenty-two 5-cm cores utilized for phosphorus sorption experiments. All core samples were analyzed for sediment physiochemical parameters including phosphorus concentrations, metal cations, and organic matter. For the most part, surficial sediments acted as a phosphorus sink with some inter-season variability. Furthermore, I found that phosphorus in the sediments, and by proxy the marsh waters, have been both increasing and becoming more labile over the past century (particularly since 1960), potentially indicating increasing eutrophic conditions in the marsh. These results varied across the marsh, with the largest nutrient increases occurring in the west side of the marsh, and higher phosphorus concentrations in the emergent and wet meadow vegetation zones relative to the open-water. Overall, these results indicate that although the marsh sediments are acting as a sink for phosphorus, the marsh is an increasingly eutrophic system, with a particular risk for algal blooms on the west side.
Delta marsh, Phosphorus, Sorption, Maintoba, Lake Manitoba, 210Pb, 137Cs, University of Manitoba