July 6 (UPI) -- More than half of the wetlands in the contiguous United States have been lost in the past 200 years, causing serious damage to a vital link in America's ecosystems, and scientists say that while the destruction continues, the rate has slowed considerably.

Wetlands have unique soil and vegetation composition that allows them to buffer the conditions that lead to floods as well as providing natural water purification and habitat to thousands of species of plants and animals.

Some of the more common forms of wetlands are marshes, swamps, river banks, bayous, peat bogs and shallow portions of lakes and ponds.

There are about 104 million acres of wetlands in the 48 contiguous states and each year there is a net loss of 27,000 acres, according to the 1997 national resources inventory by the Natural Resources Conservation Service of the U.S. Department of Agriculture.

The rate is down sharply from the 250,000 acres per year loss from the mid-1970s to the mid-1980s and also is a reduction from the 1986 to 1992 average of 59,000 acres per year lost, as reported by the U.S. Fish and Wildlife Service.

Historically, most wetlands loss in the United States has been from the conversion of wetlands to agricultural land. However, this trend recently has changed and development now is the leading cause of wetland loss.

The NRCS inventory shows currently 49 percent of wetlands loss is due to development and about 26 percent from agricultural conversion. The drop in agricultural conversion is attributed to federal programs that no longer compensate framers who convert wetlands while encouraging wetlands restoration.

As the cause of wetlands loss has shifted away from agricultural conversion, a section of the Clean Water Act, designed to prevent the wetlands loss, is receiving more attention.

Section 404 of the Clean Water Act requires developers to apply, through the U.S. Army Corps of Engineers, whenever a construction project may impact a wetland. If it is determined that wetlands will be lost, the developer is required to either preserve it or create another wetland area.

Although the law may have helped, monitoring and enforcement has not gone far enough, according to a report released last week by the National Academy of Sciences.

The NAS report, titled, "Compensating for Wetland Losses Under the Clean Water Act," said the Army Corps of Engineers has failed to follow up to see if wetlands creation projects were actually completed.

Additionally, the academy concluded projects artificially constructed do not adequately replace the functions of naturally occurring wetlands. Developers are destroying about 24,000 acres a year and applying for permits to create 42,000 acres a year, according to the NAS report. The problem is not all of the permits issued actually result in new wetlands.

The committee chairwoman of the NAS report, Joy Zedler, professor of botany and Aldo Leopold chair of restoration ecology at the University of Wisconsin in Madison, told United Press International: "It's a cumulative impact issue. Because we've already lost 53 percent of the wetlands in the contiguous United States, every additional acre of wetlands that's lost is adding onto this history of destruction. Some states have lost close to 90 percent, for example in the heavily agricultural areas of Ohio, Illinois, Iowa, Missouri and also California."

Robin Mann, head of the National Wetlands Committee for the Sierra Club, told UPI the NAS report conclusion was welcomed.

"There is an over reliance on mitigation for the section 404 regulatory program administered by the Corps and the over reliance is resulting in net losses area-wise," Mann said. "But more importantly, and what the Academy's report was really addressing, is the functional replacement is just not happening. It confirms our desire to see a re-commitment to avoidance and minimization of wetlands impacts."

But Mann expressed concerned over continuing the reduction of the loss of wetlands acres.

"Certainly there are positive indicators in the substantial reduction in losses that we've seen. Our big concern is making sure that those reductions continue," Mann said. "For a decade we've committed to no net loss and we're not there yet."

U.S. wetlands protection was dealt a severe blow in January of this year when the U.S. Supreme Court ruled 5 to 4 that 8 million acres of wetlands not connected to larger water systems are not eligible for federal protection. The decision will impact heavily on migratory water fowl, which often stop off at what are called prairie potholes, unless states pass their own legislation to protect these wetlands.

"We were very disappointed with that decision and in our consultation with environmental lawyers we're persuaded that legally it wasn't a very well derived decision," Mann said.

One of the worst wetlands problems in the United States is in the Mississippi River basin, where hundreds of thousands of acres were converted to farmland. This has contributed not only to floods, as the sponge-like qualities of the wetlands were lost, but also to massive fertilizer run-off which causes huge algae growth in the Gulf of Mexico, resulting in oxygen depleted waters and the loss of fishing grounds.

The unique combination of water-saturated soil and microbes that function in this oxygen-free environment allow for changing the form of nitrogen from harmful nitrates to nitrogen gas, which makes up 80 percent of the air we breathe.

A multi-state task force has agreed restoring wetlands will be one method used to reduce the nitrogen-caused dead zone in the Gulf of Mexico.

"It's not just along the river that we need to do this but on all the tributaries," Zedler said. "Every farm could have a narrow buffer. In urban areas, every house could have a depression that collects run-off from the lawn. And we could use less fertilizer. The cost of not doing it is very high. The loss of net economic gain in the Gulf of Mexico is an issue because of lost or displaced fisheries."

The Mississippi River is only one example. In North Carolina the state has formed water management agencies for each of its 17 water basins. Along the Illinois River a number of projects are in the process of buying-up farmland that can be converted back to wetlands.

Some folks in the homebuilding business are not happy with the whole section 404 process and think it should be scrapped.

Susan Asmus, vice president for environmental policy at the National Association of Homebuilders, told UPI: "If the nation wanted a wetlands protection law they should pass one specific to wetlands protection. Part of the problem is that the Clean Water Act defines wetlands very broadly and under the Clean Water Act."

Asmus said the way wetlands are delineated out in the field, they can be wet for only seven days during the year and still considered a wetland area.

"Well, I know of puddles in parking lots that are there for seven days a year," Asmus said. "That's not what Congress intended

Copyright 2001 by United Press International.