Table 8-4. The Contrasting Characteristics of Bog and Marsh 



Bog 



Marsh 



Physiography 



Blocked drainage causes an indef- 

 inite accumulation of organic materials; 

 a small quantity of mineral soil is 

 introduced by seepage, inwash, and 

 atmospheric agents. 



Drainage is further congested by 

 the growth of a bog; several 

 small bogs can unite and modify 

 the drainage pattern over a fairly 

 large expanse. This process is 

 reversed only in the very late 

 stage, when trees cover the area. 



Open water is invaded by a floating 

 mat and pools are filled in from top 

 as well as from bottom. 



Drainage pattern does not allow a 

 considerable accumulation of organic 

 materials; the shallow substratum 

 and seepage permit a thorough mixture 

 of organic and mineral sediments. 



Drainage is gradually, if slowly, 

 improved by the growth of swamp 

 vegetation and the corresponding 

 sedimentation. 



Open water is invaded mostly by non- 

 floating vegetation and filling-in 

 is from bottom upwards. 



Physical Conditions 



Water table reaches the surface in 

 the spring and is below the surface 

 during the rest of the year. 

 Often water level is just below the 

 surface in the spring and consider- 

 ably lower in midsummer. 



Adjacent open water generally 

 brownish (dystrophic) . 



Substratum cohesive, resilient, can 

 uphold considerable weight (e.g., man) 



Substratum almost 100% organic and 

 always in the form of peat; mineral 

 content low. 



A false bottom forms in open water, 

 owing to accumulation of colloids. 



Water table well above the surface 

 in the spring and just at surface 

 or slightly below it during the 

 rest of the year. 



Adjacent open water generally turbid, 

 olive-green or dark green (eutrophic) 



Substratum soft, will absorb heavy 

 objects, will not resist pressure. 



Substratum has variable percentage 

 of organic materials, usually not 

 peat; mineral content high. 



No false bottom. 



Dansereau and Segadas-Vianna 1952. 



(Continued) 



8-12 



