Abstract
The spatial and temporal controls on variability of the relative contributions of groundwater within and between flow systems to shallow lakes in the low-relief glaciated Boreal Plains of Canada were evaluated. Eleven lakes located in a coarse glacial outwash, of varying topographic positions and potential groundwater contributing areas, were sampled annually for stable O and H isotope ratios over the course of 8 years. It was demonstrated that landscape position is the dominant control over relative groundwater contributions to these lakes and the spatial pattern of the long-term isotopic compositions attributed to groundwater overrides interannual variability due to evaporative effects. Lakes at low landscape positions with large potential groundwater capture areas have relatively higher and more consistent groundwater contributions and low interannual variability of isotopic composition. Isolated lakes high in the landscape experience high interannual variability as they have little to no groundwater input to buffer the volumetric or isotopic changes caused by evaporation and precipitation. An alternative explanation that lake morphometry (area and volume) control long-term isotopic compositions is tested and subsequently refuted. Landscape position within coarse outwash is a strong predictor for relative groundwater input; however, surface-water connections can short circuit groundwater pathways and confound the signal. A hydrogeological case study for three of the study lakes is used to contextualize and further demonstrate these results.
Highlights
Shallow lakes in the sub-humid climate of Canada’s Boreal Plains (BP) exist in a fine balance between precipitation and evaporation
This study focuses on 11 lakes on a coarse-textured glaciofluvial outwash that are shallow, cold polymictic lakes, but vary in landscape position, potential groundwater contributing area and lake area
Stable O and H isotope ratios indicate that lakes with lower landscape positions, and associated larger potential groundwater-contributing area, had relatively larger groundwater inputs
Summary
Shallow lakes in the sub-humid climate of Canada’s Boreal Plains (BP) exist in a fine balance between precipitation and evaporation. The hydrology, biogeochemistry, and ecology of boreal shallow lakes are at an ever-increasing risk to impacts due to anthropogenic activity, such as forestry, oil and gas, agriculture, increased wildfire frequency and magnitude, and climate change (ESTR 2014; Ireson et al 2015; Schindler 1998). Shallow lakes, especially those with large catchments areas, have been shown to be sensitive to eutrophication, salinization, and alkalinization as anthropogenic and climatological impacts effects these lakes (Tammelin and Kauppila 2018)
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