Wetland delineation -- one of the federal government's most controversial activities -- should be handled by a single agency using a single manual for guidance, concluded a panel of scientists convened by the National Research Council.

Their report, "Wetlands: Characteristics and Boundaries," was requested by Congress after a storm of controversy arose in the late 1980s and early 1990s over how wetlands should be identified. While recommending a number of changes, the panel concluded that current regulatory practices are largely on track.

"Many of the conclusions and recommendations underscore the committee's confidence in the fundamental soundness of current regulatory practice for characterizing and delineating wetlands," the panel stated in its report. "Changes that have been suggested by the committee typically involve refinements of practice rather than drastic change."

Wetlands have become one of the most contentious environmental issues in recent years, largely because of changes in how wetlands are identified or "delineated" on property. Delineations are important because they tell landowners which portions of their land could fall within the jurisdiction of wetland regulatory programs and therefore require a permit before they can be filled.

Four agencies -- the U.S. Department of Agriculture, the U.S. Fish and Wildlife Service, the Army Corps of Engineers and the EPA -- have used different delineation techniques over the years.

But attempts to consolidate those manuals have proven difficult. A common manual developed by the four agencies in 1989 was criticized as being overly broad in its wetland definition by many landholders, while another manual developed by the Bush administration in 1991 was criticized as being overly narrow by environmentalists.

After those controversies, Congress ordered the Corps to revert to its old 1987 manual. The EPA dropped its manual and began using the Corps manual as well. The Department of Agriculture's Natural Resource Conservation Service uses another manual. And the USF&WS uses yet another wetland identification technique for its National Wetlands Inventory, though that is not used for regulatory purposes.

To make wetland determinations more uniform, the scientists recommend that a common manual be used by all the agencies and that wetland delineators undergo similar training.

The panel said the core of a new national manual could be drawn from the existing manuals. But they also suggested that the manual be supplemented with specialized regional information for different areas of the country to take into account varying climatic and geologic conditions.

Even more ambitiously, they recommend that wetland regulatory actions be consolidated into a single federal agency. The involvement of so many federal agencies reduces the overall consistency of wetland delineations, the report said.

One example, the panel said, was a 1994 agreement by the EPA, Corps and NRCS that allowed NRCS delineations on farm land to be used for all federal regulatory purposes on those lands. While that may draw clearer lines of authority for agricultural lands, the scientists said, it will only add to overall confusion unless NRCS delineations achieve the same results as those done by other agencies. It will be difficult for the public to accept that a particular set of landscape features is a legal wetland if delineated by [the Corps] on nonfarm property, but not so if delineated by NRCS on a farm, the report stated.

While the identification of wetlands should have a scientific basis, scientific principles do not necessarily dictate regulatory actions, the panel said. Therefore, the scientists established a reference definition for wetlands apart from a regulatory definition [see box].

The reference definition notes that wetlands are characterized by three factors: hydrology, soils and vegetation. Of these, hydrology is the most important because without recurrent, sustained periods of saturation, the conditions will not be present for the hydric soils and unique vegetation types that characterize wetlands.

While the reference definition sets a broad guide for a regulatory definition, the latter definition ultimately depends largely on policy, not scientific, decisions, the panel said.

For example, one of the toughest issues for wetland delineation is that the boundary of a wetland may occur over a broad transition zone. In this zone, wetland hydrology may change from year-to-year, and even from decade-to-decade. Likewise, vegetation may change because of hydrology and competition with different species.

If the regulatory objective is to completely protect the wetland, regulators would need to place a regulatory boundary on the outermost extent of that transition zone. By contrast, if the regulatory intent is to focus on agricultural or economic interests while protecting a core wetland area, regulators may set the boundary at the innermost part of the transition zone.

But the scientists cautioned against schemes to broadly designate wetlands as having high, medium or low values based on some general assessment of the purposes served by the wetlands, as has been proposed in the House-passed Clean Water Act and in similar legislation pending in the Senate. Examples of categories that have been suggested as having low value include wetlands smaller than 10 acres and those within heavily industrial or intensely developed areas.

The report said that the scientific basis is weak for regulating some wetlands differently than others. It said wetlands that some contend have little value including those which are flooded intermittently, isolated wetlands, agricultural wetlands and those in headwater areas perform the same functions as other wetlands and should be treated accordingly.

Agricultural wetlands can be particularly important, the report said, because they serve as a sink to capture nutrients and other agricultural pollutants contained in runoff. Wetlands on agricultural lands should not be regulated differently from other wetlands, the report said. These wetlands may have many of the same attributes as do other wetlands, including maintenance of water quality, and there is no scientific basis for delineating them under definitions or federal manuals different from those applicable to other wetlands.

The study was funded by the EPA and the USDA Natural Resources Conservation Service. The National Research Council is the principal operating agency of the National Academy of Sciences and the National Academy of Engineering. It is a private, non-profit institution that provides science and technology advice under a congressional charter.

Copies of the report, Wetlands: Characteristics and Boundaries, are available from the National Academy Press,1-800-624-6242. Copies are $37.95, plus $4 for shipping and handling.