Final Report on Sediment Diatom Reconstructions for Four Itasca County Lakes

Abstract

Due to potential threats to water quality and fishery health, four lakes in Itasca County (Minnesota) were selected for retrospective analyses. Primary goals were to determine background conditions and track probable long-term degradation, timing of impacts and remediation. The lakes range from developed (Buck, Shallow and Round lakes) to currently undeveloped (Willeys Lake). Sediment cores were collected from each lake and sediment intervals were dated using isotopic analyses. Diatom assemblages were assessed from sediment intervals and inferred trophic conditions in the profiles were derived using a regional diatom-based model for Minnesota lakes. Fossil remains, in concord with other stratigraphic indicators (organic and inorganic materials, sedimentation rates, other biological entities), were used to reconstruct the ~200-year history of each lake system. Buck Lake experienced eutrophication and other anthropogenic impacts, but in recent decades the lake has at least partly remediated. Shallow Lake has apparently undergone numerous nearshore anthropogenic shifts, but development has not resulted in an overall increase in nutrient concentrations. Water quality response to early watershed modifications of Round Lake was limited but eutrophication became a problem in the latter portion of the 20th century due to historic and recent land use activities. Despite being selected as an “undeveloped” lake, Willeys Lake showed some subtle impacts due to likely deforestation in the lake’s catchment.