Lake and Reservoir Management

One of the primary goals of lake monitoring programs is to develop data bases which can be used to evaluate trends in water quality over time. Detecting trends inthetrophic status of lakes over tame requires comprehensive data sets spanning several years. Of the parameters commonly used to characterize lake trophic state-phosphorus, chlorophyll a, and Secchi transparency, the latter would seem to be the best measure to focus on for the following reasons: ease of measurement, low cost, amenable for volunteer monitoring, ability to collect a large number of measurements during the sampling season, and the ability to obtain measurements on a large number of lakes over a long period of time. Minnesota's Citizen Lake-Monitoring Program (CLMP), initiated in 1973, provides a unique opportunity for characterizing trophic status and trends for Minnesota's lakes. For example, in 1991 550 participants collected data on over 600 lakes. In this study we evaluate the usefulness of citizen volunteer data for assessing trends; identify data sets necessary to detect subtle trends in lake trophic state; characterize the expected year to year variation in mean summer transparency; and conduct individual case studies using supporting data to evaluate whether statistically identified trends can be corroborated with other information.