BUILDING A FRAMEWORK FOR ASSESSING CLIMATE-CHANGE IMPACTS ON COMMON LOON HABITAT SUITABILITY IN NORTHERN WISCONSIN

A major focus of the U.S. Geological Survey’s Trout Lake Water, Energy and Biogeochemical Budgets (WEBB) project is the development of a watershed model to allow predictions of hydrologic response to future conditions including land-use and climate. The coupled groundwater/surface-water model GSFLOW was chosen for this purpose because it could easily incorporate an existing groundwater flow model and it provides for simulation of surface-water processes.

The Trout Lake watershed in Northern Wisconsin is underlain by a highly conductive glacial outwash sand aquifer. In this area, stream flow is dominated by groundwater contributions; however, surface runoff does occur during intense rainfall periods and spring snowmelt, and locally in near-stream/lake areas where the unsaturated zone is thin. Model calibration was performed using the PEST automated parameter estimation suite of software and the time-series processing utility. The calibrated model was used to simulate the hydrologic response of the study lakes to a variety of climate-change scenarios culled from the IPCC Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Results from the simulations indicate climate change could result in substantial changes to the hydrologic budgets of the selected study lakes.

A framework of models is being constructed to assess the impact of climate change on the suitability of lakes for common loon use. Previous research indicates several physical attributes of lakes, including water chemistry and clarity, are associated with breeding territory selection by Wisconsin common loons. A refined loon lake habitat suitability model is being developed using additional data collected on lakes in the Trout Lake watershed and central Wisconsin. Results from the hydrologic simulations, along with particle tracking within the groundwater portion of the flow model, will be used to develop predictions of solutes into the selected lakes. Estimates of solute concentrations within the groundwater system will be based on relating flow-path residence time to concentrations based on geochemical modeling of the system. A lake model will then be used to predict changes in the key water-chemistry measures relevant to the loon lake habitat suitability model.