Effects of climate and land use changes on water quantity and quality of coastal watersheds of Narragansett Bay.

Land use is rapidly changing in coastal watersheds, with implications on eutrophication of coastal watersheds. The long-term consequences of climate change on these impacts are critical to watershed management. With coastal watersheds facing frequent hypoxic events and cultural eutrophication, the coupled influence of land use and climate change can lead to policies under nonstationarity assumptions. This study aims to model a regional coastal watershed system using a dynamic simulation with future land use and climate stressors for watershed sustainability. The efficacy of current nutrient management efforts may be limited or undone if future changes in climate or land use increase nutrient and sediment loads to the Narragansett Bay. The baseline model was calibrated and validated to accurately reflect watershed processes to simulate water quantity and quality under the independent and combined influence of future climate and land scenarios. Results show significant effects of climate change and land-use change on the watershed, with demonstrated impacts on sediment loading, organic N, organic P, and nitrates. Climate impacts were much more significant than land-use effects, but land-use impacts displayed greater regional variation. The results from combined simulations indicate that future climate and land-use change will likely negatively impact the coastal system and need restoration efforts that consider nonstationarity. However, the results also highlight the potential to utilize land use to mitigate and adapt to climate change impacts.