Federal and State legislation require the trophic classification of lakes and ponds in the State of Maine as part of a lake management program. In 1974, the State of Maine Department of Environmental Protection (DEP) adopted a preliminary set of procedures for establishing an index of lake trophic status. Also in 1974, this three-year study of selected Maine lakes was initiated to evaluate and improve this trophic classification system.
Analyses of project results led to the following rec-commendations for modifications in Maine's lake-management program. Lake trophic state should be established using a mean annual value of twice monthly observations of chlorophyll a in epilimnetic waters during the open-water season. Actual Trophic State Index (TSI) values for lakes are calculated using the formula: TSI = 77.7 - 27.3 (log annual mean chlorophyll a, in mg/L). In lakes with colors less than or equal to TO platinum-cobalt units, mean annual Secchi disk transparencies may be used for calculation of lake TSI using the formula: TSI = 40.0 + 33.0 (log annual10mean Secchi disk, in meters).
Supplemental information recommended for inclusion in the lake management program should include: morphological, hydrologic, and geologic data; baseline profile water-quality surveys; and benthic invertebrate, vegetation, and cultural surveys. Another recommendation is to change DEP's method of calculating the mean annual runoff for a lake drainage basin to an empirical formula based on drainage area characteristics. This resulted in more accurate estimations of mean annual hydraulic retention times for lakes. Many of these parameters recommended for inclusion in the lake management program will allow comparisons with future surveys to determine the impacts of cultural development on Maine lakes.
