HISTORIC ALGAL BLOOMS IN THE BELGRADE LAKES: MODELING A MAINE WATERSHED

The cultural eutrophication of small lakes has become a growing concern for the communities which surround them, particularly those in which the economic base is closely tied to surface water quality and where population has increased dramatically in recent years. The Belgrade Lakes watershed in south central Maine is a both a recreational facility for residents and a summer destination for tourists from out of state. Between 1970 and 1980 towns within the watershed experienced population increases of up to 55%. Since then populations have continued to rise but at a slower rate. Residents of the watershed have expressed concern over the apparent increase in frequency of summer algal blooms in the lakes during the past thirty years.

We have evaluated secchi depth data and other water quality parameters (e.g. water temperature, pH, alkalinity, DO) for the period of 1975 to 1999 in an attempt to document the historic occurrence of algal blooms in the Belgrade Lakes. Three of the seven lakes have suffered algal blooms during this time period. East Pond, first in the chain of seven lakes, bloomed in 1976, 1987, 1991, 1993, 1994, 1995, 1998, and 1999. North Pond, the second lake in the chain, bloomed in 1994, 1995, and 1998 while Salmon Pond bloomed in 1976, 1984, and 1985. The four other lakes: McGrath, Long, Messalonskee, and Great Pond have not bloomed. While the frequency of algal blooms in the lakes that have suffered blooms appears to have increased, the cause(s) of the blooms has been unclear.

We have examined correlations between water quality data and bloom occurrence in the Belgrade Lakes watershed in light of climatological data in an attempt to establish the cause(s) of the algal blooms. These correlations identify physical and chemical parameters that are potential indicators of algal blooms and will inform the development of functional relationships that will eventually be incorporated in a numerical model of the entire watershed.