Completion Report Mille Lacs Lake Paleolimnology Project

Abstract

Mille Lacs Lake is a high-priority lake in terms of its size and premier walleye fishery, and it has a relatively small watershed compared to the size of the lake surface. Expected future increases in development of the lakeshore have prompted a desire to know about water quality baselines for this important lake. This paleolimnological study examines a sediment core collected in late winter of 2002 using radioisotope dating, loss-on-ignition analysis of organic and inorganic sediment components, and diatom analysis as a proxy for nutrient loading. Land use changes in the watershed have caused accelerating soil erosion from 1960 until the present day. Diatom counts show a decline of benthos-dominated assemblages starting by the 1950s, with greater dominance of planktonic species for the last 60 years. This indicates nutrient loading increases and water transparency decreases. The core-top, representing conditions in 2001, shows the highest relative abundance of planktonic diatom species, indicating that nutrient loading is still increasing. Preliminary diatom- based reconstructions of past lakewater total phosphorus concentrations show that nutrient loading in Mille Lacs has increased approximately 30% during the past half century and remains at an historical high level.