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Hydric soils data have also been used in some instances to approximate wetland acreage. Hydric soils are those soils described by the Soil Conservation Service that are saturated, flooded, or ponded long enough during the growing season to develop anaerobic conditions in the upper part. Under normal circumstances, these soils support wetland vegetation and can be used as an indicator of wetlands.⁷⁷ The National Technical Committee for Hydric Soils has developed criteria to identify hydric soil series and has produced a list of soils within the United States that are hydric. The publication Soil Taxonomy⁷⁸ lists soil acreage estimates for the United States. Because soil characteristics change slowly, even following drainage, summation of the soil acreages indicative of wetland conditions should approximate the wetland acreage that existed at the time of settlement. Summing the acreage estimates of soils with aquic suborders* results in a total for the lower 48 states of 211 million acres. There are an additional 165 million acres of soils with aquic suborders in Alaska. (refer to Table 2)

The U.S. Department of Agriculture's Economic Research Service⁷⁹ has also estimated original wetland acreages for the lower 48 states. Their estimate was based upon land in drainage in 1950, plus the maximum of inventoried wetlands based upon the U.S. Fish and Wildlife Service's wetland trends study⁷² or the U.S. Department of Agriculture's national resources inventory,⁸⁰ whichever was greater. The estimated total of original wetlands in the lower 48 states using this method was 217 million acres.

The final data set that is comparable on a national basis was also produced by the U.S. Department of Agriculture's Economic Research Service. It details farm drainage trends in the United States.⁸¹ Because a very high percentage of wetland losses has been due to agricultural conversion,⁷² these data may be used to approximate the percentage of wetland area lost to agricultural drainage over time. By adding drainage figures to estimated existing wetland acreage, this method indicates that a total of 213 million acres once existed in the conterminous 48 states. It is interesting to note that three of the national data sets hinge on estimates of agricultural drainage. This is not unreasonable given that the vast majority of wetland losses have been due to agricultural conversion. Figure 5 illustrates the extent and location of artificially drained agricultural land in the United States.

*Aquic suborder soils, as defined by Soil Taxonomy, are those soils that have a reducing regime that is virtually free of dissolved oxygen because the soil is saturated by ground water or by water of the capillary fringe.