A Paleolimnological Study of Net Lake and Lac La Belle, Carlton and Pine Counties, Minnesota

Lac La Belle and Net Lake are located in Carlton and Pine counties. Both lakes are shallow systems with Net Lake reaching approximately 15 feet deep and Lac La Belle at least 16 ft. Net Lake is surrounded by extensive state land holdings and has somedevelopment along its north shore. The lake has been dammed at the outlet for at least50-60 years and is part of the Net River drainage system. Lac La Belle is a shallow, morewetland-like system, with a small area of development on one shoreline. The lake has along history as a stop with a guesthouse along the route from St. Paul to Duluth that wasserved by both rail and stagecoach. Concern for the lakes centers on their currentcondition especially for total phosphorus (TP) levels, because neither lake meets currentstate standards (30 ppb TP) for shallow lakes in the Northern Lakes and Forest (NLF)ecoregion. Net Lake routinely exceeds 40 ppb TP (long-term average TP 40 ppb, chlorophyll a 9 ppb, MPCA 2016a), although there have been no reported algal blooms. Lac La Belle has TP values in excess of 60 ppb and higher long-term average chlorophyll a (43 ppb, MPCA 2016b), and similar to Net Lake, has not had any reports of algalblooms. These impairments have led to questions whether the productivity of the lakeshave changed over time, what the natural or historical condition of the lakes were, whatthe current trajectory of each lake is, and how to best set management goals. Knowledgeof the natural state of a lake and an understanding of the timing and magnitude ofhistorical ecological changes become critical components for any management and remediation plan.