Resilience of Estuarine Ecosystems with Environmental Change

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Estuaries are presently subject to stresses from climate warming, increased rates of sea level rise with climate warming, nutrient loading from urban development and agriculture, introduction of invasive species, and changes in sediment supplies due to land use change in their watersheds. This proposal focusses on the resilience of a major ecosystem of cold climate estuaries – salt marshes. These are grassy meadows flooded daily by tides. To survive with rising sea level marsh soil must accumulate volume and increase in elevation. It is thought that production of organic matter by marsh plants is a major driver of this process, critical to the ecosystem's resilience. Indeed, salt marshes store so much organic matter in their soil that they are one of the world's most efficient carbon sinks, providing a benefit (ecosystem service) to society and its carbon is referred to as “blue carbon”.***Two major stresses on the Eastern Canada coastline are nutrient loading and invasion by an exotic strain of common reed (Phragmites australis) on the St. Lawrence Estuary coast. Both are assumed to affect the C storage in salt marsh soils. Phragmites is exceptionally productive, but there have been no measurements comparing rates of C stored in its soil to that of the native plants communities it is invading. Increased availability of nutrients has been shown to both enhance root production by marsh vegetation and decrease root production, so it is not clear whether soil C storage would increase or decrease, thus what the affect is on marsh resilience to accelerated sea level rise. The research proposed here is intended to answer these questions in the context of salt marshes of Eastern Canada and advance the science of marsh dynamics. A greater understanding of these processes has not just scientific value, but informs coastal management.***Extensive area of salt marsh has been lost in globally, as well as in Canada, and efforts are underway to restore them. Blue carbon is so valued that the carbon stored through restoration of salt marshes can be sold on voluntary C markets – if the C is stored by the salt marsh ecosystem. Exceptional amounts of C has been measured in a restored marsh on the Bay of Fundy, but the source (internal or external?) of the C is not clear. The research proposed here will determine the source of C and controls on its storage. This will answer important questions needed for applying C credits to fund restoration, but also increase our knowledge of wetland biogeochemistry.