After more than a decade of trying, the state Department of Natural Resources is close to acquiring one of the rarest ecological sites in the world.

The agency this week got the blessings of the Carver County Board to acquire more than 100 acres of the Seminary Fen, a large wetland area near Chanhassen containing a rare calcareous fen.

Environmentalists say that globally only about 500 such formations exist; they thrive in cold groundwater at the bottom of a slope or bluff that is enriched with calcium and magnesium.

"This is very good news, long time coming," said Matt Norton, staff attorney for the Minnesota Center for Environmental Advocacy. "This is an incredibly rare system."

What makes calcareous fens so unusual is that the low oxygen levels of the waters make plants decompose more slowly, resulting in a spongy layer of moss on the soil. They are the rarest and most protected wetlands in Minnesota.

The Seminary Fen, which covers about 160 acres in the Minnesota River Valley between Chanhassen and Chaska, is said to be in good condition with at least a dozen rare or threatened plant species.

"We're very excited about this acquisition," Peggy Booth of the DNR told the Carver County Board, which had to sign off on the purchase. "It's really a one-of-a-kind site."

The deal, which covers 106 of the 160 acres originally sought for purchase, is expected to close in May. The exact purchase price was not disclosed, but Booth said it will be for less than $1.5 million.

In 2004, an unsuccessful effort was put together by the DNR, Chanhassen and others to purchase the 160 acres for $2.1 million. At the time the owners thought the property was worth $3 million.

In 2002, a purchase agreement for the Seminary Fen was signed with a public-private group for $2 million, but then-Gov. Jesse Ventura vetoed money for the purchase.

Norton said his group is a little troubled that the entire Seminary Fen is not being purchased because building on the remaining portion could still disrupt the delicate balance of the groundwater.

That's why the group is also strongly opposed to the Minnesota Department of Transportation's plan to possibly build a Minnesota River bridge near the fen. The fen location is one of a half-dozen options MnDOT is considering for the bridge crossing.

MnDOT was supposed to announce a preferred route for the bridge this month, but that has been put on hold until a new transportation commissioner is named, after the recent ouster of Commissioner Carol Molnau.

"The commissioner has to concur," said Lynn Clarkowski, a MnDOT supervisor. "Now we will have to wait for a new commissioner and no one knows how long that will be."

Still, MnDOT officials said recently that the purchase of the fen acreage will not have much, if any, effect on the agency's decision on where to place the new river crossing.

They point out that regardless of who owns the property, there are still numerous state and federal regulations that govern and limit development near such fens.

"We want to make sure we make the right decision," Clarkowski said. "There are challenges whether the DNR owns the property or not."

A second fen

In addition to the Seminary Fen, the health of another wetland, the Savage Fen, is under dispute across the Minnesota River in Savage.

A developer is proposing a residential subdivision, called the Dan Patch Trail, near the main body of the Savage Fen and the City Council is wrestling with the issue. Neighbors represented by a University of Minnesota environmental law professor are fighting the Dan Patch Trail proposal in court.

The city is considering whether concerns raised by neighbors and by environmental agencies are serious enough to warrant a full-fledged environmental impact review.

Staff writer David Peterson contributed to this report. Heron Marquez Estrada • 612-673-4280