Influence Of Urban Canopies On Throughfall Nutrient Composition And Dom Optical Properties, And The Decomposition Of Urban Leaf Litter

Abstract

Due to the rapid growth of large and densely populated cities, urban municipalities increasingly search for green solutions to manage urban air and water pollution. Expansion of urban tree cover has been popular among cities in an effort to mitigate air pollution and reduce stormwater volumes. While this growth of urban forests has had positive environmental impacts, little is known regarding the interactions between precipitation and canopy cover and the resulting nutrient fluxes particularly to stormwater. Previous studies have shown variability in atmospheric deposition onto tree canopies between urban and forested areas where canopies closer to anthropogenic sources have increased nutrient fluxes in throughfall. In addition, throughfall composition has been shown to differ by tree species and canopy structure. To address research gaps centered around the nutrient fluxes present in throughfall, I collected throughfall under multiple Fraxinus sp.(ash) trees in four St. Paul public parks for one growing season and analyzed for nutrients to determine rates of wet deposition under tree canopies. Optical properties of dissolved organic matter (DOM) were analyzed using excitation emission matrices (EEMs) to determine forms of organic matter present within urban throughfall. Leaf litter was also collected during autumn from various locations within an urban environment such as directly below canopies, parking lots, streets, and storm drains to determine the changes in nutrient composition along the pathway to storm drains. Leaf litter was analyzed for percent total carbon and nitrogen. I designed collections around trees as part of the Minneapolis-St. Paul Long Term Ecological Research Program (MSP LTER) with the goal of better understanding the role of urban forests in the hydrologic cycle and the nutrient pathways to stormwater and surface water.