large-size lakes in Maine are meso-oligotrophic (moderately nutrient-poor) and 

 oligotrophic (nutrient-poor); only a small percentage are eutrophic. 

 Available data on chlorophyll-a, epilimnetic total phosphorus, and Secchi disc 

 transparency in coastal Maine lakes indicate slightly more productive 

 conditions (still mesotrophic for most lakes) in the coastal zone than in 

 Maine lakes in general. 



"Brown water" is a term that is often used to define water conditions in 

 Maine. It usually indicates low pH. Of the 133 lakes in the coastal zone 

 with color information, 22% are brown-water lakes. More than 40% of the lakes 

 in regions 1 to 3 and <17% in regions 3 to 6 are brown-water lakes. Most 

 brown water lakes have contiguous areas of acidic wetland or peat bog. The 

 brown dissolved organic matter that accounts for the water color contributes 

 to the depletion of oxygen in the stratified deep water. 



Oxygen profiles are available from the 68 coastal zone lakes that have 

 hypolimnia. Nineteen percent of these had no oxygen near the bottom by August 

 or September and 68% had <4 ppm (unsuitable for cold water fishes). Of the 94 

 coastal zone lakes for which some oxygen data are available, regardless of 

 whether sustained thermal stratification is present in summer, 48% had <4 ppm 

 free oxygen in the hypolimnia. 



Cyclical salt (salts carried to the sea by rivers and returned to the land in 

 precipitation and dry fallout) levels are most significant in lakes close to 

 the sea. Adams Pond (Boothbay) , Southport reservoir (unnamed) and Long Pond 

 (Isle au Haut) , three lakes that are near the sea, had sodium concentrations 

 of 4.4 to 6.7 ppm, 14 ppm, and 17.7 ppm, respectively. Sodium concentrations 

 in Maine lakes that are farther inland and which have similar conductances are 

 only 2 to 3 ppm, approximately (Davis et al. 1978a). Lakes near the sea may 

 have relatively high conductances in relation to their alkalinities (appendix 

 table 2). For example, Jordan Pond in region 5 had an alkalinity of only 3.0 

 ppm as CaC03 but had a conductance of 41 micromhos/cm, probably due mostly to 

 sodium chloride (appendix table 2) . 



Data on chemical parameters other than those discussed above (e.g., nitrogen, 

 silicon) are available for too few coastal zone lakes to warrant discussion 

 but are included in appendix table 2. 



The above data indicate that the general chemical characteristics of lakes are 

 almost uniform among regions and that the slight differences found cannot be 

 interpreted. The coastal zone lakes are not highly productive, as indicated 

 by low conductance, low pH, and low alkalinity, total phosphorus, and 

 chlorophyll-a, and are typical of lakes in forested areas of Maine. Atypical 

 lakes generally are those that are affected significantly by human input of 

 nutrients . 



THERMAL STRATIFICATION AND LAKE ZONATION 



Certain limnological characteristics are typical of the freshwater lakes of 

 coastal Maine. For the sake of clarity, the coastal lakes are described in 

 this section on the basis of water temperture, principally as it relates to 

 thermal stratification, and aspects of biological function that are determined 

 by light penetration and zones of production. 



7-10 



