Dissolved organic matter dynamics in stream ecosystems

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One of the most obvious environmental changes caused by humans is the alteration of the landscape. Usuallythis involves the reduction of forested cover at the expense of agricultural and urban areas. Almost inevitably,these changes in land use affect the quality and quantity of surface and subsurface waters because of alteredconnections between the land and water. For rivers in these landscapes, new landscape connections can modifyorganic matter (generally measured in carbon units as dissolved organic carbon, DOC) which now originatesprimarily from agricultural crops, manure and urban waste instead of natural vegetation, soils and wetlands.Novel linkages with modified landscape and rivers also change the chemistry of river carbon, which canchange the healthy functioning of our rivers. In this project, I will examine how the DOC changes in qualityand quantity in river watersheds of contrasting land use from the Great Lakes Basin in South-central Ontario.These data will be used to further examine how land use alterations of physical (e.g., streamflow), chemical(e.g., nutrients), and biological (e.g., stream foodwebs) alter the processing and export of DOC. In doing so, Iwill test how agriculturally and urban-derived DOC and nutrients affects microbial growth, food webcomposition, and ecosystem function such as the decay of materials (leaf-litter), nutrient uptake by algae andnitrogen recycling. Finally, I will test for river DOC responses to climate change because these might beaffected by periods of warm weather and drought. This research will help us understand how human-derivedmaterials (agricultural fertilizers and residential waste) will affect the health and integrity of aquatic systems.