94 • Wetlands: Their Use and Regulation 



Table 13.— Probable Causes of Saltwater Vegetated Wetland Changes 



Acres Cause of loss 



Saltwater wetland loss to: 



Deep water 268,000 Dredging for canals, port and nnarina development, erosion 



Urban use 107,000 Fill for development 



Unconsolidated shore 50,000 Dredged material disposal, removal of vegetation for recreational 



development, death of vegetation 

 Freshw/ater vegetated wetlands .... 25,000 Increased freshwater outflow, dike construction 



Agriculture 9,000 Diking for conversion 



Other uses 11,000 Filling for port development 



Other nonvegetated 12,000 — 



Total 482,000 



Acres Cause of gain 



Saltwater wetland gain from: 



Deep water 54,000 Natural establishment of vegetation, marsh creation efforts 



Nonvegetated types 44,000 Same as deep water 



Other uses 8,000 Same as deep water 



Agriculture 2,000 Destruction of dikes 



Freshwater vegetated wetlands .... 1,000 Reductions in freshwater outflow, dike construction, increased 



saltwater inflow 



Total 109,000 



SOURCE: Data from FWS National Wetland Trends Study, 1983. 



from nonvegetated types. Reasons for these changes 

 probably include natural establishment of vegeta- 

 tion and marsh-creation efforts associated with 

 dredged-material disposal and erosion-control prac- 

 tices. Other uses were responsible for 7 percent of 

 these gains, and abandonment of agricultural lands 

 accounted for 2 percent of the gains. The remain- 

 ing 1 percent were gains from freshwater vegetated 

 wetlands that may be associated with reductions in 

 freshwater outflow, destruction of dikes, or in- 

 creased saltwater flow. 



Regional Trends 



Using national figures of wetland losses and gains 

 can be misleading. Farm ponds — such as in Mis- 

 souri — even with aquatic plant improvements 

 through plant succession, cannot compensate for 

 potholes lost in the prairie-pothole area. A wide 

 variety of migratory birds uses the latter for repro- 

 duction and rarely or infrequently uses the former. 

 Regional information on wetland use was obtained 

 by OTA from four primary sources: NWTS, other 

 inventory and trend studies, permit information, 

 and interviews. 



NWTS (8) 



For OTA's study, NWTS grouped its data into 

 13 regions so that wetland losses and gains on 

 regional levels could be analyzed. The regions are 



listed in table 14 and shown in figure 9. Although 

 this study was based on a stratified random sam- 

 pling, very large standard errors are associated with 

 its data on a regional level.' The regional data re- 

 flect actuEil losses and gains in wetlands and other 

 land uses at the sample sites. Such data indicate 

 probable trends in wetland use in a region, especial- 

 ly if they can be supported by other sources of 

 evidence. 



Regional data provide an average picture over 

 a large area and do not necessarily reflect the ac- 

 tual status of wetlands within a single State in the 

 region. For example, in the Upper Midwest, Illinois 

 lost 186,905 acres, or 23 percent, of the wetlands 

 that were present in the mid- 1 950 's; Wisconsin lost 

 133,872 acres, or 3 percent, of wetlands present in 



'The following explanation of statistical reliability is from W. E. 

 Frayer & Associates, "Status and Trends of Wetlands and Deepwater 

 Habitats in the Coterminous United States, 1950's to 1970's — Final 

 Draft 1982." National Wedands Inventory, Office of Biological Serv- 

 ices, U.S. Fish and Wildlife Ser\'ice; 



Standard errors for overall wetland loss figure for physiographic 

 regions range from a low of 1 1 percent of the measured loss in the gulf 

 coastal zone to a high of over 134 percent of the measured loss in the 

 intermontane region. The majority of the standard errors for physio- 

 graphic regions are from 15 to 35 percent of the measured loss. Reliahili- 

 ty can be stated generally as "we are 68 percent confident that the true 

 value is within the interval constructed by adding to and subtracting 

 from the entry the SE%/100 times the entry." For example, if an entry 

 is 1 million acres and the SE percent is 20, then we are 68-pcrcent con- 

 fident that the true value is between 800,000 and 1.2 million acres. 

 An equivalent statement for 95-percent confidence can be made by add- 

 ing and subtracting twice the SE%/100 to and from the entry, 

 respectively. 



