Land dedicated to scientific research in south Washington County grew substantially this week when Trust for Public Land completed the purchase of 120 acres in Denmark Township.

The land, bought from private landowner Mike Rygh for $1.14 million, will be added to the 200-acre Lost Valley Prairie Scientific and Natural Area and will remain open to the public for walking, exploring, nature observation, educational use and scientific research.

"The new addition supports a remarkable range of important resources: groundwater recharge, the northernmost occurrence of bedrock bluff prairie, and an intermittent stream that feeds the St. Croix River," said Becca Nash, a trust project manager. "And it is a great place to explore."

Closing of the land purchase -- announced in July -- happened Tuesday. The purchase from Rygh and the subsequent sale of the land at the same price to the Minnesota Department of Resources for long-term management took place the same day, Nash said. The trust specializes in conservation real estate to protect land for public use as parks, greenways, community gardens, urban playgrounds and wilderness.

A celebration Saturday at the original Lost Valley site will include the awarding of a 2009 Champion of Open Space award to site steward Jim Smetana. The celebration, open to the public, also will include a short program to talk about the importance of preserving habitat in the metro area.

The Lost Valley land is the trust's second major purchase along the St. Croix in recent months. In June, it bought 38 acres near Franconia, in southern Chisago County. Both buys are intended to head off development along the St. Croix's ecosystem and save native land before an improved economy renews interest in building houses and roads.

Nash said the new Lost Valley land, which sits about half a mile west of St. Croix Bluffs Regional Park, will remain free of development. The purchase is part of a growing effort in the St. Croix watershed to preserve open spaces and improve water quality.

Smetana has described the land as a botanists' delight that will attract hikers and nature photographers. Birdwatchers, scientific researchers and classes of schoolchildren also are expected to use the land.

The trust said the prairie addition provides habitat for the state-endangered Henslow's Sparrow and also will protect ground and surface water as part of a broader campaign to clean up tributaries that feed the St. Croix.

Lost Valley is one of four scientific and natural areas in Washington County. Minnesota has more than 140 areas statewide. The Minnesota Legislature established the program in 1969 to preserve the state's rarest natural resources.

Kevin Giles • 612-673-4432