Spatial and temporal patterns of redox-sensitive and bio-relevant micronutrients in a large complex binational lake system: Lake of the Woods

Abstract

We analyzed lower water column redox-sensitive and bio-relevant (Al, Fe, Mn) micronutrient data between 2018 and 2019 to assess spatial and seasonal variability within Lake of the Woods (LoW) as they relate to continued eutrophication and water quality issues. The sediment–water interface represents a dynamic linkage between the sediment and overlying water column, dominated by diffusive flux and particulate resuspension. The complexity of LoW basins, shoreline extent, and underlying geology (situated on both the Canadian Shield and Glacial Lake Agassiz Lakebed sediments) creates variable water quality conditions, with cyanobacterial and harmful algal blooms (cHABs) particularly prevalent in the southern basins. We used a multivariate approach to differentiate basins within LoW, to better understand potential mechanisms underlying eutrophication and cHAB development. A unique signature of redox-sensitive metals was observed above the lakebed suggesting differential impacts of diffusive flux and resuspension dynamics, with significantly different micronutrient signatures between locations on vs off the Canadian Shield. The basins on the Glacial Lake Agassiz lakebed including Big Traverse, Little Traverse, Morson and Bishop were statistically comparable (p > 0.05), and significantly different from those on the Canadian Shield (p < 0.05). Correlations between bio-relevant element vanadium (element potentially used in nitrogen fixation) and chlorophyll-a), suggest potential elemental drivers of cyanobacterial ecology in LoW. An integration of multi-disciplinary research may serve to better address water quality issues as they relate to underlying geology and improve monitoring programs into the future to further delineate the physical-biogeochemical processes differentially impacting basins within LoW.