CHARACTERISTICS OF PALUSTRINE WETLANDS 



Wetland Development 



Palustrine wetlands develop (1) where water tables are higher than the sur- 

 rounding topography, resulting in hydric (moist) soils, (2) where lake basins 

 have become shallow through accumulation of biotic (plant and animal remains) 

 and abiotic (mineral) sediments, and (3) where beaver have blocked drainage. 

 Palustrine wetlands are not necessarily permanent features of the landscape. 

 Over a period of hundreds of thousands of years palustrine wetlands may occupy 

 a site that develops from open water to an emergent wetland to scrub/shrub 

 wetland to forested wetland to upland forest. This process is termed 

 succession. The type of palustrine community (whether a marsh or bog) and the 

 duration of each of the vegetation stages depend on prevailing abiotic condi- 

 tions (below). Furthermore, all palustrine wetlands do not necessarily pass 

 through the complete successional sequence. Certain factors (e.g., fire and 

 beaver dams) may cause wetlands to regress to an earlier condition. Thus, a 

 scrub-shrub wetland may be flooded by beaver resulting in conditions favoring 

 an open water emergent wetland. 



The patterns of palustrine succession outlined in figure 8-3 illustrate that 

 marshes and bogs are the two basic sequences of serai (successional) stages 

 occurring in coastal Maine freshwater wetlands. These types are classified by 

 their dominant vegetative cover. Differences between these types are 

 described in table 8-4 and in "Biota", below. 



The development of a typical coastal Maine boglike palustrine wetland may 

 begin with deposition of organic sediment from floating plant types (such as 

 algae and pondweeds) over the inorganic clay bottom of a lake. This organic 

 sediment eventually builds up the lake bottom to a depth where rooted plants 

 (such as pond lilies and bulrushes) are capable of growing. The pond eventu- 

 ally is filled completely with sediment and the pond lilies and bulrushes are 

 replaced by grasses, sedges, and sphagnum moss, which forms dense mats. At 

 this stage the organic deposit builds up and out beyond the original limits of 

 the unfilled water body. The water table also rises with the elevation of or- 

 ganic deposit, thus allowing further growth of the moss into domes and/or 

 plateaus and allowing for a perched water table above the land surface margins 

 of the bog. Figure 8-3 depicts these stages of bog development. 



Marsh wetlands in coastal Maine develop similarly but usually do not form 

 dense floating mats of vegetation; rather, vegetation is rooted into the min- 

 eral substrate. As organic matter accumulates it mixes with the mineral 

 sediments. This gradually fills the basin from the bottom upwards resulting 

 eventually in an upland forest system. Under natural conditions, the succes- 

 sional sequence may occur over a period of hundreds or thousands of years. 



Physical Characteristics 



No comparative data base, other than the size information discussed in the 

 preceding section, is available on the physical characteristics of individual 

 wetlands in coastal Maine. Data on temperature and transparency of individual 

 wetlands are lacking. Certain physical characteristics of bog wetlands in 

 Maine have been described by Cameron (1975). She recognized five basic types 



8-9 



10-80 



