Lake Assessment Report - Select Lakes in Superior National Forest, 2006

In 2006 the Minnesota Pollution Control Agency (MPCA) and Superior National Forest (SNF) cooperated to conduct water quality assessments on five priority SNF lakes: Greenwood, Devil Track, Wilson, Moose, and Trout. Lakes were sampled monthly May through September, with an emphasis on the eutrophication indicators total phosphorus (TP), chlorophyll-a and Secchi transparency. In addition to the standard water quality parameters, water mercury and cations / anions were sampled on Wilson and Devil Track Lakes. Data were compared with representative and minimally-impacted (reference) lakes within the Northern Lakes and Forest (NLF) ecoregion of northeast Minnesota. Summer-mean water quality values for all five were well within or below the typical range for minimally-impacted lakes in the NLF. A further comparison of the SNF lakes' TP, chlorophyll-a and Secchi data with the draft eutrophication criteria values for NLF ecoregion lakes indicated that each of the lakes met these draft water quality standards. As such, the data indicate excellent water quality in all five lakes. This is likely the result of limited (or no) lakeshore development and the majority of the watersheds composed of forest land under public ownership. Two of the lakes (Moose and Trout) are entirely or partially within the Boundary Waters Canoe Area Wilderness. Three of the SNF lakes: Greenwood, Wilson, and Devil Track, have sufficient historical data to begin to assess water quality variability and trends. Based on these data, water quality has not changed significantly over the period of record (1980's to the present). Also a comparison with sediment diatom-reconstructed TP values based on 20 NLF lakes suggests that all five lakes are well within the typical range of pre-European TP values for NLF lakes. It will be valuable to continue to monitor the water quality of these lakes in the future so that temporal trends; as well as the impacts of climate, such as the severe drought of 2006, might be more fully evaluated. Continued monitoring will also be valuable to the long-term management and protection of these lakes by the Superior National Forest and the State of Minnesota.