1975 Potential Cropland Survey (11). This Soil Con- 

 servation Service (SCS) survey recorded 21.4 

 million acres of high and medium potential 

 cropland that suffered from wetness. Of these, 16.5 

 million acres had seasonal high water table, 4.6 

 million had problems with drainage outlets, and 

 181,300 were identified as wetland types 3-20. 



1977 National Resources Inventory (NRI) f53j. This 

 SCS inventory identified 41.5 million acres in 

 wetland types 3-20, but none was rated as having 

 high or medium potential for conversion to 

 cropland. 



1979-83 National Wetlands Status and Trends 

 Analysis (NWSTA) fl3j. Conducted by FWS be- 

 tween 1979 and 1983, this study developed 

 statistical estimates of acreage in wetland and deep- 

 water habitat for the lower 48 States during the 

 1950's and the 1970's, and the change in that 

 period. A stratified random sample of 3,635 

 4-square mile units was constructed. Black and 

 white aerial photography from the 1950's and 

 1970's, selected for each sample unit, was inter- 

 preted for wetlands, changes in wetlands, and the 

 cause of change. The sample universe included all 

 private and public wetlands in the lower 48 States, 

 including coastal intertidal areas and inland water 

 bodies. The sample was designed to achieve a 



90-percent probability that estimates are within a 

 10-percent range in each category. 



1982 National Resources Inventory (NRI) (54j. Con- 

 ducted by SCS, this study inventoried soil and 

 related water resources in the lower 48 States, 

 Hawaii, and U.S. Caribbean territories. A two-stage 

 stratified random sample was used to collect data 

 from field observations at 841,860 sample points in 

 nearly 350,000 primary sampling units of approx- 

 imately 160 acres each. The sample universe in- 

 cluded non-Federal rural land classified by both the 

 20 wetland types of FWS Circular 39 and the five 

 major wetland systems used in the NWSTA. The 

 NRI wetland acreage reported for 1982 is smaller 

 than that reported in the NWSTA for three reasons: 

 exclusion of Federal wetlands, possible undercount- 

 ing of intermittently wetlands, and losses of 

 wetlands since the mid-1970's. Advantages of the 

 NRI data over the NWSTA are: assessment of 

 cropland conversion potential; inclusion of soil, 

 vegetation, and wildlife habitat measures; and 

 cross-identification to the SCS Soil Interpretation 

 Data (SOILS Form 5), which includes estimated 

 potential crop yields for wetland soils. The NRI 

 sample was designed to achieve a 95-percent con- 

 fidence interval around estimates of acreages com- 

 prising at least 10 percent of the land area within 

 particular major land resource areas (MLRA's). 



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