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Wetlands - Loss In Wetland Acreage

acres losses million mid

When the first Europeans arrived in America, there were an estimated 215 million acres of wetlands in the mainland forty-eight states; today there are approximately 105.5 million acres. In the intervening years, more than 50% of the wetlands in the lower forty-eight states have been lost. Wetlands have been drained, dredged, filled, leveled, and flooded to meet human needs. Although natural forces such as erosion, sedimentation, and rise or drop in sea level may erase wetlands over time, 95% of the wetland losses since 1780 are believed to have been caused by humans. Many of the nation's older cities, such as New York City, Baltimore, Philadelphia, New Orleans, and Charleston, are built on filled wetlands.

The USFWS has been tracking wetland losses. In Wetland Losses in the United States 1780s to 1980s (1990), the USFWS reported that twenty-two states had lost more than 50% of their wetlands, an area equal to the size of California. (See Figure 7.5.) Seven states (California, Indiana, Illinois, Iowa, Missouri, Kentucky, and Ohio) had lost more than 80% of their wetlands. According to the report, for the first time in United States history, there are fewer than fifty million acres of forested wetlands in the conterminous United States.

In its first wetlands status and trends report in 1983, the USFWS estimated the wetland loss between the mid-1950s and the mid-1970s (the years prior to wetland protection) at 458,000 acres per year. In 1991 the USFWS reported that estimated wetland loss in the mid-1970s to mid-1980s had declined to 290,000 acres per year. In its Wetlands Overview (December 2004), the loss rate reported by the EPA was 60,000 acres annually, an almost 87% reduction from the mid-1970s level. The decline in wetland loss was attributed to "increased public awareness of the functions and value of wetlands and the need to protect them, the implementation and enforcement of wetland protective measures, elimination of incentives to drain wetlands, private land initiatives, coastal monitoring and protection programs, and wetland restoration and creation actions."

In their 2000 305 (b) filings with the EPA, nine states reported wetland losses. Figure 7.6 shows the sources contributing to these losses. Filling and draining were cited by five states as sources of wetland loss. Agriculture, residential development, and urban growth were cited among other causes.

The states also identified the leading causes of the loss of wetland integrity, that is, the impairment of wetland functions. Six of the nine reporting states identified sedimentation or siltation as the leading cause. Flow alterations, nutrients, filling and draining, habitat alterations, and metals also were cited as causes of loss of wetland integrity. (See Figure 7.7.) The primary sources identified as causing integrity loss were agriculture, construction, and hydrologic modification. (See Figure 7.8.)

Not all wetland losses result in the total obliteration of a wetland. The conversion of a wetland from one type to another may be considered a "loss" because the wetland has changed in one or more functions, particularly if the change results in a wetland perceived as less valuable.

For example, the USFWS reported that between 1986 and 1997 (the latest data available) four million acres of forested wetland were removed. The removal was the result of timbering and other practices that removed the tree canopy but left the wetland character, that is, did not drain or fill the wetland. Loss of forest canopy can radically change the hydrology and wildlife habitat value of a wetland. Most of the forested wetlands were converted to freshwater shrub (2.8 million acres) or emergent wetlands (0.5 million acres). Other conversions include upland land use, ponds, and lakes and rivers.

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