productivities than the others. Studies by Davis and coworkers (1978a) at 

 Maine lakes are in agreement. 



17 



Morphometry 



Data on the morphometry of coastal zone lakes are discussed under 

 "Distribution of the Lacustrine System," above. The effect of morphometry on 

 productivity is discussed under "Temperature Characteristics" above. The 

 shallowness of most coastal zone lakes has an important influence on their 

 productivity, or trophic state (Richardson 1975). The relationship may be 

 illustrated by an analysis of coastal zone lakes for which relevant data are 

 available. Phosphorus (total), chlorophyll-a , and plankton (especially algae) 

 concentrations are used as indices of biological productivity (Davis et al., 

 1978a) in Maine lakes. For Maine lakes with low water color, Davis and 

 coworkers (1978a) observed that total phosphorus concentrations in near- 

 surface waters, chlorophyll-a concentrations in near-surface waters, and the 

 inverse of Secchi disc transparency (an approximate index of plankton or 

 seston concentrations) were all correlated. Data for these parameters in 

 shallow lakes (<18 m; 60 ft) and deep lakes (>18 m; 60 ft) in the coastal zone 

 indicate that the shallower lakes are more productive on a per unit volume 

 basis (table 7-5) . 



Table 7-5. Comparison of Trophic Indicators for Shallow (<18 m) 

 versus Deep (>18in) Coastal Maine Lakes with Low Water 

 Color ^''^. 



Trophic indicator 



Shallow 



Deep 



Secchi disc transparency (m) 



Total phosphorus (ppb) 



Chlorophyll-a (ppb) 



^n=number of lakes: T=trace 



"Lakes for which data are unavailable are not included, 



7-21 



10-80 



