Interactions of climate change and land use change in water quality

Climate and land use have significant effects on freshwater quantity and quality. This study examines the complex interactions of climate change and land use change in selected watersheds of the Susquehanna River Basin. A research protocol for investigating such interactions is first developed from a review of relevant literature. The Generalized Watershed Loading Function (GWLF) model is selected to operationalize the protocol. GWLF is able to capture contemporary variations of streamflow and nutrient loads under different land cover, suggesting that the model can be used for exploring potential consequences of climate and land use change. The effects of climate change on streamflow and nitrogen and phosphorus loading are analyzed for six watersheds with different land use characteristics. Mean annual streamflow and nitrogen loads in four watersheds are projected to increase more than 50% under an empirically downscaled, doubled carbon dioxide (CO₂) climate change scenario mainly due to increases in precipitation. Despite slight increases in annual precipitation, increases in temperature reduce annual streamflow and nitrogen loads due to increases in evapotranspiration for two watersheds. The direction of change in phosphorus loads parallel those of nitrogen and streamflow.; At a detailed spatial level, the Conestoga River Basin's response to future environmental conditions around year 2030 (2025–2034) is assessed using two climate models from the Hadley Centre for Climate Prediction and Research and the Canadian Centre for Climate Modeling and Analysis, and an empirical urban growth scenario. Climate change alone increases spring streamflow by 4.8 to 18.1%, leading to increases in nutrient loads in streams. The Canadian Centre model projects 5 to 10% decreases, whereas the Hadley Centre model produces 10 to 15% increases in annual streamflow and nutrient loads. Urban expansion exacerbates the adverse effects of climate change by increasing annual nitrogen loads up to 50%. The magnitude and direction of changes in nutrient loads are sensitive to watershed size, climate and land use scenarios used. Smaller sub-basins exhibit greater effects than the entire watershed. Point source nutrient pollution control could mitigate negative effects of climate and land use change, reducing nitrogen loads to the contemporary baseline level. This research pinpoints the importance of local study to identify subtle changes in local water quality as consequences of climate change and land use change. Changes in the timing and the magnitude of streamflow and nutrient loads have important implications for future water quality management as well as aquatic systems at different watersheds.