Understanding the mechanisms of non-point source carbon and nutrients in urban watersheds will help to develop policies to maintain surface water quality and prevention of eutrophication. The purpose of this dissertation is to investigate the impact of sodium on carbon and nutrient leaching from the two main contributors; soil and leaf litter, and calculate the sodium exports in a humid subtropical urban river basin. The first chapter reviews the current literature on urbanization in watersheds. Chapter II quantifies the carbon and nutrient in intact soil core leachates and in water extractable solution from urban soils collected from 33 towns and cities across the state of Texas. Chapter III investigates the impact of sodicity and salinity on water extractable organic carbon and nitrogen from vegetation. Chapter IV investigates the export of sodium and chloride from the upper Trinity River basin. The results derived from this study indicate that sodium exports are elevated in urban watersheds and further that sodium in irrigation water elevates the loss of carbon and nutrients from both watershed soil and senesced vegetation and that this may contribute to high concentrations in urban freshwaters.
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