30 



Forces Changing Wetlands 



Wetlands represent a dynamic natural environment 

 which are subjected to both human and natural forces. 

 These forces directly result in wetland gains and losses as 

 well as affect their quality. Table 2 outlines major causes 

 of wetland loss and degradation. 



Table 2. Major causes of wclland loss and degradation 

 (Zinn and Copeland I9H2: Gosselink and Ban- 

 nmnn 1980). 



Human Threats 

 Direct: 



1 . Drainage for crop production, timber production 

 and mosquito control. 



2. Dredging and stream channelization for naviga- 

 tion channels, flood protection, coastal housing 

 developments, and reservoir maintenance. 



3. Filling for dredged spoil and other solid waste 

 disposal, roads and highways, and commercial, 

 residential and industrial development. 



4. Construction of dikes, dams, levees and seawalls 

 for flood control, water supply, irrigation and 

 storm protection. 



5. Discharges of materials (e.g., pesticides, herbi- 

 cides, other pollutants, nutrien' loading from do- 

 mestic sewage and agricultural runoff, and 

 sediments from dredging and filling, agricultural 

 and other land development) into waters and 

 wetlands. 



6. Mining of wetland soils for peat, coal, sand, 

 gravel, phosphate and other materials. 



Indirect: 



1 . Sediment diversion by dams, deep channels and 

 other structures. 



2. Hydrologic alterations by canals, spoil banks, 

 roads and other structures. 



3. Subsidence due to extraction of groundwater, 

 oil. gas. sulphur, and other minerals. 



Natural Threats: 



1. Subsidence (including natural rise of sea level) 



2. Droughts 



3. Hurricanes and other storms 



4. Erosion 



5. Biotic effects, e.g., muskrat. nutria and goose 

 "eat-outs." 



Natural events influencing wetlands include rising sea 

 level, natural succession, the hydrologic cycle, sedimen- 

 tation, erosion, beaver dam construction and fire. The 

 rise in sea level, for example, both increases and de- 

 creases wetland acreage depending on local factors. 

 Along the eastern shore of Chesapeake Bay. it is allowing 



coastal wetlands to establish in former upland pine areas, 

 while permanently flooding wetlands at lowest eleva- 

 tions. Rising sea level is one factor converting salt 

 marshes to bay bottoms in Louisiana. Natural succession 

 and fire typically change the vegetation of a wetland 

 usually with no net loss or gain. However, fire in Alas- 

 ka's permafrost wetlands may convert the area to non- 

 wetland. Disturbance of the vegetative cover can cause 

 the frostline to recede, and dry site plants may become 

 established. The hydrologic cycle refers to the natural 

 cycle of wet and dry periods over time . Great Lakes water 

 levels, for example, fluctuate drastically on a roughly 20- 

 year cycle. This adds an important dimension to wet- 

 lands, making them vulnerable to drainage during dry 

 periods. Similar conditions have resulted in wetland 

 drainage in the Prairie Pothole Region. The activities of 

 beavers create or alter wetlands by damming stream chan- 

 nels. Thus, natural forces act in a variety of ways to 

 create, destroy and modify wetlands. 



Human actions are particularly significant in determin- 

 ing the fate of wetlands. Unfortunately, many human 

 activities are destructive to wetlands, either converting 

 them to agricultural or other lands or degrading their 

 quality. Key human impacts include drainage for agricul- 

 ture; channelization for flood control; filling for housing, 

 highway, industry and sanitary landfills; dredging for 

 navigation channels, harbors and marinas; reservoir con- 

 struction; timber harvest; peat mining; oil and gas extrac- 

 tion; strip mining; groundwater extraction; and various 

 forms of water pollution and waste disposal. A few ac- 

 tions do, however, create wetlands. Construction of farm 

 ponds and, in some cases, reservoirs and irrigation pro- 

 jects may increase wetland acreage, although valuable 

 natural wetlands may be destroyed in the process. Marsh 

 creation and restoration of previously altered wetlands 

 can also be beneficial. Federal and state fish and wildlife 

 agencies traditionally manage wetlands to improve their 

 value to waterfowl. Wetland protection efforts serve to 

 help maintain and enhance our Nation's wetland re- 

 sources, despite mounting pressures to convert them to 

 other uses. 



Recent National Wetland 

 Trends 



Information on historical wetland gains and losses is 

 limited and often subjective. The Service recently com- 

 pleted a scientifically sound study of the current status 

 and recent trends of U. S. wetlands between the mid- 

 1950's and mid-1970's (Frayer, et al. 1983). Ahhough 

 the results of this study are valid at the national level, few 

 comparable statistics exist for individual states. The fol- 

 lowing discussions will summarize the results of the Ser- 

 vice's national study and other regional studies. Specific 

 problem areas where wetlands are in greatest jeopardy 

 will be highlighted. 



