Hydrogeological controls on heterogeneous groundwater discharge to a large glacial lake

Lacustrine groundwater discharge (LGD) can be an important pathway for delivering pollutants to large lakes but this pathway is often neglected. This is in part because characterizing the magnitude and spatial variability of LGD to large lakes is highly resource intensive. To better target efforts, particularly in glacial environments where the hydrogeology is often highly complex, there is a need to understand linkages between spatial LGD patterns and hydrogeological features. The objective of this study was to evaluate the magnitude and spatial variability of nearshore LGD to Lake Simcoe (area = 722 km(2)) and use this information to explore hydrogeological controls on the observed spatial LGD patterns. LGD was quantified by applying a steady state mass balance model to radon-222 ( Rn-222) data obtained from boat surveys conducted along similar to 80% of the lake's shoreline. Overall, LGD was highly spatially variable with total LGD to Lake Simcoe estimated to range from 7 +/- 1% to 16 +/- 2%, respectively, of the total volume of tributary inputs during summer. No large regional scale differences in LGD were found despite the diverse hydrogeological conditions around the lake. Rather, discrete shoreline areas with high LGD were observed around the lake. Areas with high LGD were related to permeable nearshore surficial sediments and tunnel channel aquifers which provide connectivity between large recharge features (moraines), regional aquifer units, and the lake. The study findings are needed to inform ctions aimed at managing non-point pollution sources to large glacial lakes including LGD. (C) 2020 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.