INFLUENCE OF GLACIAL LANDFORM AND LANDSCAPE POSITION ON GROUNDWATER AND PHOSPHORUS DYNAMICS OF SHALLOW LAKES ON THE BOREAL PLAINS

Shallow lake-wetland complexes are ubiquitous throughout the Boreal Plain (BP) eco-region, and represent important water resources and wildlife habitat across a large portion of western Canada. Rapid and extensive land use disturbances within the BP due to oil and gas exploration/ extraction and forestry operations, threaten the biological and functional diversity of these aquatic ecosystems. Best management strategies to sustain surface water quantity, quality and ecosystem structure require knowledge of the natural variability in hydrology and water chemistry of shallow lakes, as well as the dominant pathways for water and nutrient exchange of lakes with the surrounding landscape prior to disturbance.

A field-based comparative study of three shallow lake-wetland complexes in contrasting glacial landscape types (coarse-textured outwash, fine-textured till moraines and lacustrine plains) within the BP of the Western Boreal Forest of Alberta, Canada demonstrated a distinct landform control on the proportion of source waters, flow paths and surface-groundwater interactions influencing concentrations of lake total dissolved phosphorus ([TDP]). Lakes located on fine-textured landforms had high [TDP] linked to the occurrence of shallow groundwater loadings from adjacent wetlands and organic lake sediments with TDP-rich porewaters. In contrast, the lowest lake [TDP] occurred on the coarse-textured landform, reflecting a greater proportion of mineral groundwater inputs originating from low TDP sources. Dynamic seasonal groundwater flow reversals and exchange of TDP between the lakes and riparian wetlands were common, particularly in fine-textured landforms. Results of this study provide a conceptual framework for the timing and scale of water flow paths (larger-scale flow systems versus short, shallow flow paths) influencing phosphorus loadings to lakes in differing hydrogeological landscapes, directing management strategies that may reduce impacts of land use disturbances on productivity of shallow lakes across the BP.