deposits also influence the chemistry of the runoff. These factors in Maine 

 lakes are discussed by Davis and coworkers (1978a). 



The coastal zone is underlain by a variety of bedrock types. Region 1 is 

 predominantly metasedimentary , with some calcareous content in the rocks 

 slightly inland from Casco Bay. Region 2, also, is underlain by 

 metasediments , largely gneiss, quartzite, schist, and phyllite, with minor 

 calcareous content in a few areas. Areas of granite also occur in region 2, 

 especially in the northern area. Region 3 has metasediments in some areas and 

 granite in others. Region 4 contains a variety of metasedimentary rocks, some 

 with minor calcareous content (e.g., around Hammond Pond). A large area of 

 granite occurs at the eastern part of the region (around Craig Pond) . Region 

 5 is predominantly granite, diorite, and gabbro (e.g., around Narraguagas 

 Lake) but also includes areas of metasediments (especially schist) in the west 

 (around Ellsworth), and slate, metasandstone , and quartzite in the east 

 (around Columbia). Region 6 has a complex pattern of volcanic rocks (rhyolite 

 and basalt flows, and tuff; e.g., around Rocky Lake), granite, diorite, and 

 gabbro, metasedimentary rocks (e.g., phyllite and schist), and areas of 

 interbedded metavolcanic and metasedimentary rocks. Bedrock geology maps of 

 the coastal zone are available (Maine Geological Survey 1978). 



Bedrock in the uplands of the coastal zone is overlain by thin glacial till, 

 except in occasional areas on ridges, where it is exposed. The till is 

 composed largely of rocks derived from within a few kilometers of the site of 

 deposition and therefore reflects the nature of the bedrock nearby that was in 

 the path of the glacial flow. Peat deposits frequently occur in the lowlands. 

 They are often contiguous with lakes, or streams draining into lakes, and the 

 dissolved organic matter they release creates a yellowish or brownish color in 

 the water of the lakes. Much of the lowland is covered by a deposit of 

 glaciomarine silt-clay; for example, in the north and west areas of region 2 

 and near Rockland in region 4 (Smith and Anderson 1974) . Maps of the 

 surficial geology of the coastal zone are available showing the above- 

 mentioned deposits (Maine Geological Survey 1977). 



Calcareous sedimentary and metasedimentary rocks generally yield waters with 

 higher concentrations of critical biogenic nutrients than waters of 

 predominantly siliceous rocks. Because rocks with calcareous content occupy 

 only a small fraction of the coastal zone the runoff (where unpolluted) from 

 most of the watersheds is a relatively dilute, infertile solution, as is 

 suggested by the low alkalinities of coastal zone lakes. The alkalinity of 

 lake surface waters in the coastal zone averages only 8.0 ppm as CaCO 3, with 

 no great difference from region to region, except for a small number of lakes 

 on relatively calcareous rock in region 4 that have alkalinities of 15 to 26 

 ppm (table 7-4; appendix table 2). However, the direct relationship of 

 watershed rock and runoff chemistry to lake productivity is sometimes 

 obscured. Two reasons for this are: (1) lake morphology has a major 

 influence on productivity; (2) the edaphically fertile watersheds are those 

 whose agricultural acreage is greatest, and the effect of agriculture on soil 

 is to increase nutrient runoff and resultant inputs to surface water. Data 

 for coastal zone lakes are inadequate to definitively attribute productivity 

 differences from lake to lake to edaphic causes. However, Cowing and Scott 

 ( in preparation ) found that among the 43 Maine lakes they studied those 

 surrounded by relatively calcareous deposits had slightly greater 



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