Upper Midwest Long-Term Monitoring (UMWLTM) Program

The Upper Midwest Long-term Monitoring Program lakes were initially part of a larger EPA-funded project (http://www.epa.gov/airmarkets/assessments/TIMELTM.html) to investigate trends in the acid-base chemistry of lakes in sensitive regions of the US. At the start of the project in 1983, the UMW lakes included lakes in Voyageurs National Park in Minnesota, north-central Wisconsin, and the upper peninsula of Michigan. The lakes represent low alkalinity systems considered most sensitive to acid deposition, which increased from east to west across the 3-state region. Lakes in Wisconsin and Michigan were primarily seepage lakes. Over time the sampling frequency declined (from spring, summer and autumn to only autumn) and lakes were dropped from the initial set of lakes due to funding constraints. The longest period of record is from 1983 to 2000.