Groundwater contribution keeps trophic status low in Sylvan Lake, Alberta, Canada

Abstract

Water well drilling records combined with geologic observation around Sylvan Lake suggest a permeable, fractured groundwater-bearing channel sandstone extends along the northeast margin of the lake, and is surrounded by a matrix of shale with small sandy interbeds. Chloride and water isotope mass-balance approaches found groundwater fluxes were 37 to 43% of total annual lake water inputs, and were consistent with Darcy flux estimates for the channel sandstone. The groundwater contribution to the lake water budget contributes to an estimated lake-water residence time ranging from 22 to 30 years, which is much lower than other lakes in the region and lakes of similar size. Groundwater through-flow in the hydraulically connected channel sandstone unit of the Paskapoo Formation appears to play a critical role in maintaining the relatively low total dissolved solids (and trophic status) of Sylvan Lake, as compared to other lakes in south-central Alberta. Due to the hydraulic connection of the sandstone channel with Sylvan Lake, land use along the north side of the lake (above the sandstone channel unit) should be carefully considered to mitigate groundwater (and consequently lake water) quality impacts.