Climate 



Climatic factors play major roles in determining biological productivity and 

 types of biota in lakes, especially on a world-wide scale (Brylinsky and Mann 

 1973). However, within relatively restricted regions with "one climate," 

 nonclimatic factors, such as lake morphometry (Richardson 1975) and rock 

 chemistry, are more influential in determining variations between lakes. 

 While it is true that within the coastal zone of Maine there are climatic 

 gradients (see chapter 2, "The Coastal Maine Ecosystem"; Davis 1966 and 

 Lautzenheiser 1972), the ranges of these gradients are not great enough to 

 affect within-zone variation in lacustrine productivity to the degree that 

 nonclimatic factors do. Nevertheless, some differences attributable to 

 climatic gradients are perceivable between the lakes of the various regions. 

 For example, summer surface-water temperatures, when averaged by region (table 

 7-2) , roughly parallel the southwest to northeast gradient of July air 

 temperatures (Lautzenheiser 1972). Also, the ice-clearing dates for the 

 coastal zone lakes in the southwest (early April) have averaged a week or more 

 earlier than in the northeast (mid-to late April) during the past several 

 decades (Fobes 1974). The southwest to northeast climate gradient is clearly 

 reflected in the terrestrial vegetation of the coastal zone (Davis 1966) but 

 present data on lake biota do not indicate an unequivocal correlation between 

 biota and climate differences. Within the coastal zone, differences in the 

 biota and productivity of lakes seem to be caused mainly by nonclimatic 

 factors . 



Other Atmospheric Factors 



The atmosphere affects lakes significantly by its input of pollutants, 

 including nutrients, acids, and heavy metals. The latter two pollutants 

 originate mostly in the burning of fossil fuels and the smelting of sulfide 

 ores. Acidic precipitation (and the resultant decreasing pH of lakes) and 

 associated heavy metal inputs are of growing concern in Maine (Davis et al. 

 1978b and Norton et al. 1978). In other, similar regions (e.g., Adirondack 

 Mountains, New York; southern Norway) important negative impacts on lake 

 systems have already been documented (Schofield 1976 and Braekke 1976). 



Atmospheric inputs of phosphorus may constitute major portions of the 

 phosphorus budget of lakes with relatively undisturbed watersheds where 

 edaphic inputs are low (Peters 1977). 



The "average" hydrogen ion concentration (pH) in Maine lakes possessing pH 

 data showed a decline from a pH of 6.8 in 1937 to pH 6.0 in 1974 (Davis et al. 

 1978b). Due to the logarithmic nature of the pH scale, this decrease in the 

 "average pH" may be caused by only a small percentage of lakes where major 

 increases in hydrogen ion concentrations have taken place. In the summer of 

 1978 a sampling of pH at 37 Maine lakes that were selected for susceptibility 

 to acidification (due to low alkalinity water) resulted in a pH range from 5.7 

 to 6.7. Thirty-two had decreased in pH (median decrease 0.4, maximum 1.1) 

 since about 1940 (Davis et al. 1979). Lakes in the coastal zone, although 

 often of very low alkalinity and therefore of low acid-buffering capacity, are 

 probably somewhat more resistant to the effects of acidic precipitation than 

 lakes farther inland. This resistance is created by small amounts of 

 buffering substance in the cyclical salts that coastal zone lakes receive via 

 the atmosphere from the nearby ocean. Nevertheless, lakes in the vicinity of 



7-16 



