Coupled terrestrial and aquatic regional responses to land use change and climate variability in a temperate New England watershed

Abstract:

Climate change and land use interact to alter hydrology, biogeochemistry, and ecosystem function. Regional scale analyses that link terrestrial and aquatic ecosystems across spatial scales are needed to understand the mechanisms of response and tradeoffs among different ecosystem services. We coupled the terrestrial ecosystem model, PnET, with a river network model, FrAMES, to explore how terrestrial and aquatic conditions simultaneously respond to variation and changes in climate and land use. We applied the coupled model to the Merrimack R. watershed, NH/MA, USA, to understand how impacts vary at different nested basin scales. The coupled PnET-FrAMES predicts variables relevant to key ecosystem services including snow pack, runoff, woody biomass accumulation, net carbon sequestration, nitrogen runoff, discharge, conductivity, water temperature, aquatic denitrification, and nitrogen flux. We used statistically downscaled high and low emission scenarios of GCMs (GFDL CM2.1) to explore projected future responses to 2100. Some variables were more sensitive (snowpack, runoff, net carbon sequestration, water temperature) than others (woody biomass, conductivity, nitrogen concentration) to interannual climate variability. Water quality and terrestrial ecosystem responses were more sensitive to land use changes. Water quality responses are buffered in large rivers due to the dilution capacity of forested areas of the watersheds, but this dilution capacity is altered by future climate changes. Coupled terrestrial-aquatic models at regional scales using downscale climate projections will be essential for planning adaption and mitigation strategies in response to future climate and land use change.