A remarkable mosaic of habitats exists within a relatively small area around the confluence of the Zumbro and Mississippi rivers in southeastern Minnesota. In part, this is because a sand terrace 10 miles long and three miles wide, formed by deposits from glacial melting, supports sand prairie, savanna and woodland communities. Meanwhile, the nearby courses of the Mississippi east of the terrace and the Zumbro to its west are dominated by wetlands that include open water marshes, wet meadows and floodplain forests.
For milllennia, the Zumbro flowed directly into the Mississippi, but when its path became blocked, it formed a braided system of channels that flowed around the north and south sides of the sand terrace. In the 1970s, a man-made channel cut through the terrace provided the Zumbro with a direct course to the Mississippi. Weaver Bottoms, the southern portion of the historic Zumbro channel, once consisted of wetlands, wet meadows, forests, old river channels, lakes and ponds. The construction of a navigation lock and dam on the Mississippi, however, largely changed the bottoms to a shallow, open-water lake, a part of Pool 5 on the Mississippi.
Upstream in the Zumbro's 900,000-acre watershed are the city of Rochester and a landscape vastly altered since the mid-1800s. As floodplain forests were harvested and prairie lands converted to crop production, poor land management led to catastrophic erosion. Improved soil conservation practices have alleviated some erosion, but sediments carried by runoff remain a threat to aquatic life in the Zumbro and its tributaries. In addition, Zumbro sediments are contributing to the filling in of key backwater habitat along the Mississippi.
The Nature Conservancy's efforts within the Zumbro watershed include encouraging the use of soil conservation practices that reduce sedimentation and improve water quality and aquatic habitat. These practices include conservation buffers, grassed waterways, contour strips, conservation tillage, cover crops and increased use of perennial vegetation.
In addition, the Conservancy works closely with the U.S. Army Corps of Engineers, the U.S. Fish and Wildlife Service and the Minnesota Department of Natural Resources to modify the activities of the lock and dam system on the Mississippi in order to create more natural water flows on the Mississippi and lower Zumbro.
The summer lowering (drawdown) of the water level in Pool 5 in 2005 and briefly in 2006 is an example of this work. The 2005 drawdown improved habitat for fish and wildlife, including areas within Weaver Bottoms, by exposing more than 1,000 acres of mudflats and allowing a variety of aquatic plants to grow there.
The Conservancy is also actively working with the Minnesota Department of Natural Resources to protect and restore floodplains along the lower Zumbro.
The habitats along the lower Zumbro shelter numerous plant and animal species of special concern, but the area's most celebrated species is the Blanding's turtle. Listed as a threatened species in Minnesota, an estimated 5,000-plus Blanding's turtles currently inhabit the area. The Minnesota Department of Natural Resources and The Nature Conservancy each have acquired and managed lands and sponsored research for the turtles' protection.
The Conservancy acquired its Weaver Dunes Preserve in 1980 and two years later, the state's Kellogg-Weaver Dunes Scientific and Natural Area was established a half-mile to the north. Both sites protect sandy uplands where the turtles, which spend most of their lives in the surrounding wetlands, return each June to lay their eggs.
Weaver Dunes is part of Minnesota's largest barrens prairie. The native and restored prairies of the area face constant threat from invasive species. The Conservancy serves as a leader in invasive species management in the area.
The work at Weaver Dunes and along the Zumbro River is important locally and on a much wider scale. Lessons learned within the watershed will be shared through the Conservancy's Great Rivers Partnership to advance the Conservancy's national and global efforts to protect the Earth's critically important freshwater resources.