As the human population continues to increase, the effects of land use change on streams and their watersheds will be one of the central problems facing humanity, as we strive to find ways to preserve important ecosystem services, such as drinking water, irrigation, and wastewater processing. This dissertation explores the effects of land use change on watershed nitrate concentrations, and on several biogeochemical ecosystem functions in streams, including nitrate uptake, ecosystem metabolism, and heterotrophic carbon processing.

In a literature synthesis, I was able to conclude that nitrate concentrations in streams in forested watersheds tend to be correlated with soil solution and shallow groundwater nitrate concentrations in those watersheds. Watershed disturbances, such as ice storms or clear-cutting, did not alter this relationship. However both urban and agricultural land use change increased the nitrate concentrations in streams, soil solution, and groundwater, and altered the correlation between them, increasing the slope and intercept of the regression line. I conclude that although the correlation between these concentrations allows for predictions to be made, further research is needed to better understand the importance of dilution...

Urbanization causes myriad changes in watershed processes, ultimately disrupting the structure and function of stream ecosystems. Urban development introduces contaminants (human waste, pesticides, industrial chemicals). Impervious surfaces and artificial drainage systems speed the delivery of contaminants to streams, while bypassing soil filtration and local riparian processes that can mitigate the impacts of these contaminants, and disrupting the timing and volume of hydrologic patterns. Aquatic habitats where biota live are degraded by sedimentation, channel incision, floodplain disconnection, substrate alteration and elimination of reach diversity. These compounding changes ultimately lead to alteration of invertebrate community structure and function. Because the effects of urbanization on stream ecosystems are complex, multilayered, and interacting, modeling these effects presents many unique challenges, including: addressing and quantifying processes at multiple scales, representing major interrelated simultaneously acting dynamics at the system level, incorporating uncertainty resulting from imperfect knowledge, imperfect data, and environmental variability, and integrating multiple sources of available information about the system into the modeling construct. These challenges can be addressed by using a Bayesian modeling approach. Specifically...