4. Diatom‐based Paleolimnological Assessment of Long Term Water Quality Trends, Near Forrest Island, Lake of the Woods, Ontario

Abstract

Lake of the Woods (LOW) is a large, international freshwater body that shares borders with Ontario, Manitoba, and Minnesota. Previous studies from the LOW have found that water quality is spatially variable in this complex lake. The current perception is that cyanobacterial blooms have increased in frequency and intensity, generating much interest in determining whether increased nutrients have resulted in water quality deterioration. To address this concern, paleolimnological techniques will be used to examine changes in diatom assemblage over the last ca. 200 years on a dated sediment core retrieved near Forrest Island, close to the city of Kenora, Ontario. Comparisons will be made to other LOW sites that are elevated in total phosphorous (TP) and experience algal blooms (impact sites) as well as a site with low TP that does not experience algal blooms (reference site). Based on the Forrest Island diatom shifts, the following questions will be examined: (1) What is the baseline condition of this site? (2) Have diatom assemblages and/or water quality changed over time? (3) If so, are these changes comparable to other LOW sites?; and (4)What are the potential mechanisms for these changes? To aid our interpretation, a diatom‐based inference model for TP will be applied downcore to examine whether TP concentrations have changed over the last few centuries. Additionally, other mechanisms such as recent warming will also be examined. Results from this study could have important implications related to the impacts of multiple stressors on the LOW