Sentinel Lake Assessment Report Ten Mile Lake (11-0413) Cass County, Minnesota

The Minnesota Pollution Control Agency (MPCA) is working in partnership with the Minnesota Department of Natural Resources (MDNR) on the Sustaining Lakes in a Changing Environment (SLICE) Sentinel Lakes Program. The focus of this interdisciplinary effort is to improve understanding of how major drivers of change such as development, agriculture, climate change, and invasive species can affect lake habitats and fish populations, and to develop a long-term strategy to collect the necessary information to detect undesirable changes in Minnesota Lakes (Valley 2008). To increase our ability to predict the consequences of land cover and climate change on lake habitats, SLICE utilizes intensive lake monitoring strategies on a wide range of representative Minnesota lakes. This includes analyzing relevant land cover and land use, identifying climate stressors, and monitoring the effects on the lake's habitat and biological communities. The Sentinel Lakes Program has selected 24 lakes for long-term intensive lake monitoring (Figure 1). The "Deep" lakes typically stratify during the summer months only. "Shallow" lakes are defined as mixing continuously throughout the summer. "Cold Water" lakes are defined as lakes that either harbor cisco (Coregonus artedi) or lake whitefish (Coregonus clupeaformis) and are the focus of research funded by the Environmental Trust Fund (ETF). Ten Mile Lake was selected to represent a deep mesotrophic lake in the Northern Lakes and Forests (NLF) ecoregion. Ten Mile Lake is a 2,042 hectare (5,072 acre) lake with a maximum depth of 63 meters (208 feet) and a mean depth of 16 meters (51 feet). Ten Mile Lake is located just north of Hackensack, Minnesota in Cass County, within the Leech Lake River major watershed. The lake is 26% littoral with one public access on the southwestern shore. The total contributing watershed for Ten Mile Lake is 10,031 hectares (24,828 acres). Ten Mile Lake is a clear, deep lake that is well-mixed in the spring, but is stratified during the rest of the summer forming a distinct thermocline. Based on recent water quality assessment data (June-September of 2008 & 2009), Ten Mile Lake is considered to be mesotrophic with total phosphorus (TP), chlorophyll-a (chl-a), and Secchi values of: 11 micrograms per liter (μg/L), 2 μg/L, and 4.9 meters (16 feet) respectively. TP and chl-a are below the typical ranges (based on reference lakes) for the NLF ecoregion. No nuisance algal blooms were observed and transparency was typically high during the summer. As a result, Secchi transparency for Ten Mile Lake was deeper than the typical range for the NLF ecoregion.