Distributed Connectivity Between a Large Lake System and Terrestrial Hydroclimate

The flux of water to the atmosphere through evapotranspiration is notoriously difficult to quantify at large spatial scales, and the importance of this ‘recycled' water to most continental ecosystems is poorly known. As humans modify the continental climate, vegetation, and the amounts and distribution of standing water on the land surface, these changes may have implications for the hydroclimate of far-afield regions. Here we report results of a stable isotope survey of shallow groundwaters across Michigan's Lower Peninsula. Our data allow us to estimate the magnitude and spatial distribution of evaporation-derived recycled water inputs, originating from evaporation off of Lake Michigan, to this region. The fraction of lake-derived water exhibits a strong W-E gradient, with lake-adjacent regions receiving up to ~15% of the total groundwater recharge from this source. The total water subsidy to the study region is only 15 - 20% of the net annual evaporation from Lake Michigan, and measureable amounts of lake-derived precipitation were found across the entire study region. This implies that changes in climate and the water balance of this large lake system will have effects on the water inputs to ecosystems and groundwater reservoirs across a large region of the Midwestern USA, the potential severity of which can be quantified through stable isotope mapping.