The role of groundwater in loading of nutrients to a restricted bay in a Precambrian Shield lake. Part 1. – Conceptual model and field observations

Abstract Previous studies of the nutrient budgets of lakes in Precambrian Shield regions have generally ignored the role of groundwater as a source or sink (influx or efflux) of nutrients. This paper and its companion (Part 2) address this science gap by probing the role of groundwater in the nutrient balance for a restricted bay of a Precambrian Shield lake that has undergone extensive shoreline development. In Part 1, we introduce a conceptual model of the relevant processes, including the role of groundwater. A cottage study site is described, concentrations of nutrients and septic tracers (artificial sweeteners), water levels and other data are reported. This includes data from samples of the septic wastewater plume in groundwater at the cottage, and samples from the bay. The artificial sweetener data indicate seepage of septic plumes to the bay, but significant attenuation of septic-derived nutrients in the subsurface. These data are used for numerical modeling in Part 2.