88 • Wetlands: Their Use and Regulation 



Table 11.— Relationship Between Wetland Types Used for This Report^ 



NWTS wetland classification National Wetland 



types discussed in this chapter Trends Study code Wetland types discussed in chapter 2 



Estuarine (saltwater): 



• Intertidal vegetated: 



Emergents 3 Salt and brackish marsh (coastal) 



Forested/scrub/shrub 4 Mangrove (coastal) 



• Intertidal nonvegetated: 



Unconsolidated shore 5 Mudflats (coastal) 



Other 7 Submerged beds (coastal) 



• Deep water: 



Subtidal 2 Submerged beds (coastal) 



Palustrine (freshwater): 



• Vegetated: 



Forested 8 Wooded swamp, bottom land hardwood, bog, pocosin (inland) 



Scrub/shrub 9 Bog, pocosin (inland) 



Emergent 10 Freshwater marsh, saline marsh, freshwater tidal marsh (inland) 



Tundra'' — Tundra 



• Nonvegetated: 



Unconsolidated shore 11 — 



Open water 12 — 



Other 13 — 



Lacustrine (lakes): 



• Deep water 14 — 



^Terminology for wetlands used In this chapter includes the classification used by NWTS (the recently adopted USFWS Classification System, with minor modifications 

 to distinguish vegetated and nonvegetated types, and large or deepwater areas from small or shallow-water areas); the old USFWS Circular 39 Classification System; 

 and lay language- Since strict correlations cannot be made between these three categories and information obtained by OTA, all three categories are used in this 

 chapter. The use of this variety of terminology Is intended to clarify, rather than confuse, the discussion. 



"Tundra not Included in NWTS data. Under the recent USf=WS classification system it is a palustrine/moss-llchen wetland. 



SOURCE: W. E. Frayer. T. J. Monahan. D. 0. Bowden. and F. A. Grayhlll, "Status and Trends of Wetlands and Deepwater Habitats In the Coterminous United States. 

 1950'sto 1970's," Department of Forest and Wood Services. Colorado State University, Fort Collins. Colo.. 1983, p. 31. 



Figure 6.— Changes in Wetlands Since the 1950's 

 (thousands of acres) 



Wetland lost 

 15,132 



Unchanged wetland 

 89,554 



New wetland 

 3.708 



SOURCE; Original data from FWSs National Wetland Trends Study. 1982. 



Factors Affecting Wetland Loss 



Major sources of loss identified in NWTS include 

 conversions to agricultural use, urban use, deep 

 water (lakes, subtidal areas), nonvegetated wet- 

 lands, and other uses (such as forestry, rangeland, 

 and mining). Major development activities associ- 

 ated with these losses of wetlands included dredg- 

 ing and excavation, filling, draining and clearing, 

 and flooding. These same activities were respon- 

 sible for wetland losses in Alaska, although fill ac- 

 tivities are probably the major source of Alaskan 

 losses. 



Wetland characteristics may change and acreages 

 increase or decrease in response to natural factors 

 apart from, or in addition to, the development ac- 

 tivities listed above. For example, variations in 

 climate have a major influence on the size and vege- 

 tation of wedands in the prairie-pothole region and 

 in Nebraska, as well as on the ease with which they 

 can be altered for agricultural use (6,9). Natural 

 succession and activity of increased beaver popula- 



