Modeling the effects of land use change on surface water quality within the Chicago Metropolitan Statistical Area

Using a partial area hydrology framework and the build-up/wash-off theory, this dissertation explores the role of land use change on surface water quality within a complex metropolitan area. The research specifically examined the relationship between land use structural complexity and surface water quality, the role of seasonal differentials on surface water quality, and the implications of future land use and climate changes on surface water quality. The study was conducted within Lake Calumet watershed and that portion of the Des Plaines River watershed that lies within the Chicago Metropolitan Statistical Area (MSA). Using multi-temporal remotely sensed images, watershed data, historical, and future climate data, the study employed a spatially distributed loosely coupled hydrologic and water quality modeling approach within a Geographic Information System (GIS) to investigate the impacts of land use changes on surface water quality between 1990 and 2010, and also make projections up to 2030. Water quality projections made beyond 2010 were conditioned by the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenario (SRES) B1 and A1B groups. Furthermore, the projections were also based on three future land use/planning scenarios influenced by low density residential growth, normal urban growth, and commercial growth scenarios, respectively.;Results of the study revealed that although land use structural complexity within the Lake Calumet watershed increased between 1990 and 2010, surface water quality within the watershed is not influenced by the structural complexity of land use. Bivariate regression analysis demonstrated that the spatial distribution of pollutants in the watershed have extremely weak association (R 2 < 0.06) with the structural complexity of the landscape. The study further demonstrated that the level of concentration of pollutants heavily depends on the spatio-temporal variations in areas that contribute towards runoff compared to the spatial extent of change in major land classes.;Water quality simulation suggested that with the exception of phosphorus, most of the pollutants modeled within the Des Plaines River watershed between 1990 and 2010 exhibited higher concentration levels during the winter months as opposed to the summer period analyzed. Bivariate correlation analysis further indicated that pollutant loads are identical irrespective of seasons (r 2 > 0.8) but concentration levels vary according to winter and summer seasons (r2 < 0.3).;The responses of pollutant concentration to future land use and climate changes are mostly non- linear and of a complex nature. The general watershed response of suspended solids displayed an increase in concentration levels during the late winter and early spring period of 2020 and 2030 compared to the same season in 2010, while concentration wanes during the summer season. On average, summer periods in 2020 and 2030 exhibited lower phosphorus concentration levels compared to the baseline period of 2010, while the winter season demonstrated a reverse with the exception of the A1B climate scenario for 2030. Nitrate-nitrite evinced higher capacity for dilution under high precipitation and runoff scenarios during the late winter and early spring period compared to other pollutants. Future climate change has the potential to exert larger impact on the concentration of pollutants vis-a-vis the potential impact of land use change. Land use mitigation strategies to preclude potential water quality impairment have to be dynamic in order to respond to the seasonal variations engendered by future climate.