class is most common in region 4 (60%) and region 6 (38%). Estuarine emergent 

 wetlands represent a high proportion of total estuarine areas in region 1 

 (14%) and 2 (15%), respectively, and comprise 23% and 34% of the estuarine 

 intertidal habitat. Region 5 also has a relatively large amount of emergent 

 marshes (13%). The distribution of estuarine habitats in each town is 

 included in appendix A of chapter 2. The distribution of estuarine systems, 

 subsystems, and classes is depicted on atlas map 1. 



ABIOTIC FACTORS 



Abiotic factors influence the biotic composition of an ecosystem, 

 geology, hydrography, and climate of estuarine areas are addressed below. 



The 



Geology 



The biological communities that comprise the estuarine system often are 

 related to substratum types. NWI categories often are defined by substratum 

 characteristics (figure 5-7). Since the estuarine system is composed of many 

 varieties of substrata, the geological substrata (e.g., mud, cobble, and sand) 

 are described in the class level discussion. The size distribution of 

 sediment particles (e.g., sand, mud, cobble, and gravel) by habitat is given 

 in figure 5-8. The composition of, formation of, and primary abiotic forces 

 (e.g., currents) affecting the substrata of the estuarine system are 

 summarized in table 5-3. A general discussion of coastal estuarine geology is 

 found under "Geology," page 2-35in chapter 2. 



INTERTIDAL 



BEACH/BAR 



SAND 

 GRAVEL 

 COBBLE 



ROCKY SHORE 



BOULDER 



FLAT 



SUBTIDAL 



SAND 

 MUD 



UNCONSOLIDATED 

 BOTTOM 



AQUATIC BED 



^-•- 



-MUD- 



• KELP BEDS- 



EEL GRASS BEOS- 



Figure 5-8. 



Size distribution of sediment particles in estuarine habitats 

 of coastal Maine. Dots indicate dominant size, arrows indicate 



range. 



5-14 



