5-28 A comparison of the primary productivity (tons of dry 

 weight produced per acre per year) for different types 

 of terrestrial and aquatic systems in the world. Shaded 

 bars indicate general ranges (Teal and Teal 1969) 5-50 



5-29 Simplified energy flow model for an 



estuarine system in Maine 5-51 



5-30 The relationship between depth of water and nitrate 

 concentration (a) , and the subsequent nutrient 

 character of the marine waters entering the marine 

 waters entering the Sheepscot and Kennebec 

 estuaries (b) (Garside, unpublished ) 5-55 



5-31 Nitrate concentration ( M) and salinity (ppt) in the 



Sheepscot estuary in September 1976 (Garside et al. 1978) . . 5-56 



5-32 Factors controlling flushing in seven Maine estuaries, 



based on application of the model described on page 5-59 



For example, in the Kennebec estuary 40% of the estuary's 



volume is provided by river flow, about 28% by tidal 



input, and 32% is residual at low tide 5-61 



5-33 Generalized size distribution of organic carbon particles 



in seawater (adapted from Sharp 1973) 5-66 



5-34 Schematic diagram of the organic matter cycle in 



the estuarine system 5-66 



5-35 Physical conditions of the estuarine water column 

 during summer (stratified) and winter (well mixed) 

 which affect phytoplankton growth. Arrows indicate 

 mixing; N= nutrients; dots are phytoplankton (Yentsch 1977) . 5-68 



5-36 Comparison of the boundaries of the physical intertidal 

 zone and the littoral (biological intertidal) zone with 

 increasing exposure to wave action (adapted from Lewis 1964) . 5-77 



5-37 Monthly measurements of chlorophyll-a concentrations 

 (mg/m ) in upper Penobscot Bay for 1974 to 1975 

 (Bertrand 1977) 5-79 



5-38 Relation of phytoplankton species diversity to 

 phytoplankton population size in marine and 

 estuarine waters (Hulburt 1963) 5-82 



5-39 The comparative distribution of marine, brackish, and 

 freshwater species along a salinity gradient in a 

 German estuary (after Remane 1934) 5-86 



xx iv 



