Hydrological and landscape controls on the chemical response of lakes in northern Wisconsin to environmental pressures

Abstract:

The response of lake chemistry to environmental stressors such as climate change or acid deposition is mediated by the landscape setting of the lake and the surrounding catchment. Hydrological delivery of solutes through surface runoff or groundwater can buffer against the impacts of anthropogenic change. Since there is often variability in these processes across a region, lakes will not react uniformly to these regional scale pressures. Understanding the landscape-level controls on lake chemistry will help determine lake sensitivity to future environmental change. Our objective is to classify seepage lakes in terms of their hydrology and landscape characteristics to explain variability in lake chemistry in northern Wisconsin. We present data from synoptic surveys of more than 90 seepage lakes across the Chequamegon-Nicolet National Forest of northern Wisconsin that ranged in size from 1.6 to 75 ha, conducted in the summers of 2013 and 2014. Seasonal groundwater sampling and precipitation chemistry are used to construct mixing models to quantify hydrological inputs to the lakes. The catchments of these lakes are difficult to delineate, as they are relatively small and at times have significant groundwater input, so we calculate landscape characteristics for fixed buffer zones around the lake. The chemical composition of the lakes varies widely across the landscape; for instance, dissolved organic carbon concentrations range from 2.9 to 39 mg/L, and calcium concentrations range from 0.4 to 5.3 mg/L. To explain this variability, we explore interactions between landscape features and hydrology and suggest a framework by which to classify the chemical composition of these lakes.