CHEMICAL CHARACTERISTICS 



Measurements of some of the major chemical characteristics of lakes in the 

 coastal zone were made from 1938 to 1978, between late July and early 

 September (table 7-4). Although all the data are not comparable, because of 

 sampling deficiencies, major characteristics and some trends are clear. 



Differences among average alkalinity levels in the regions show no trends. In 

 Maine lakes the common range of alkalinity (as ppm CaCOo ) is 5 to 30, with 

 most of the larger lakes nearer the low point of this range (Davis et al. 

 1978a). These alkalinity levels are very low by worldwide standards. Low 

 alkalinity is characteristic of soft water and is consistent with low pH. The 

 pH of lake waters among the regions varies little but differences between 

 surface water (pH 6.6) and bottom waters (pH 6.0) are apparent (table 7-4). 

 Specific conductances (as pmhos/cmS at 25^C) are low in Maine lakes, commonly 

 between 20 and 80, with most of the larger lakes <50. In the coastal zone 

 lakes the conductance of water showed little difference between near-bottom or 

 near-surface waters but a general decrease from 43 to 30 in surface waters (41 

 to 28 in bottom waters) from western regions (regions 1 to 3) to eastern 

 regions (regions 4 to 6) was apparent. The alkalinity range for lake surface 

 waters was to 19 (n=74) , and the conductance range was 7 to 52 (n=19) in the 

 coastal zone. 



In Maine lakes that do not receive a significant input of nutrients from 

 industrial wastes alkalinity and conductance ranges clearly parallel 

 concentrations of natural nutrients (phosphorus in particular; Davis et al. 

 1978a). However, this relationship is not observed among the 30 coastal zone 

 lakes for which both alkalinity and total phosphorus readings are available. 

 Alkalinity levels are controlled by the chemistry of watershed bedrock and 

 surficial deposits, and by the acidity of precipitation. Phosphorus levels, 

 in addition to being controlled by the latter factors, also are affected by 

 lake morphometry. Since these factors vary among the 30 coastal zone lakes 

 the relationship between alkalinity and total phosphorus is obscured. 



The total phosphorus averages for all lakes range from 7 to 16 ppb for surface 

 waters and from 12 to 36 ppb for bottom waters. Concentrations of total 

 phosphorus in Maine lakes that are not severely polluted range from 2 to 15 

 ppb (Davis et al. 1978a; Cowing and Scott 1975, 1976, 1977, and in 

 preparation ) . In the absence of significant agricultural acreage, excessive 

 shoreline residential development, or other sources of pollution, total 

 phosphorus concentrations are usually less than 10 ppb (Davis et al. 1978a). 

 Surface waters of 63 coastal lakes (table 7-4; appendix table 1) average 11 

 ppb total phosphorus and range from a trace to 30 ppb. The higher values 

 suggest that anthropogenic enrichment is taking place at certain lakes 

 (appendix table 1). Five of the lakes with high phosphorus levels are in the 

 Cobbossee Watershed District in region 2. Studies of these lakes indicate 

 that excessive phosphorus is a result of agricultural and residential 

 development in the watersheds (Gordon 1977; Cobbossee Watershed District 1977a 

 and b) . 



Measurements of chlorophyll-a concentrations (table 7-4) are generally low 

 among the regions (2 ppb to 9 ppb) and in the coastal zone as a whole (6 ppb) 

 but range as high as 24 ppb in some lakes. Such high chlorophyll is 

 indicative of eutrophic (nutrient-rich) conditions. A majority of mid-to 



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