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US Fish & Wildlife Service FieldNotes

Contaminant Assessment Process initiated at Big Stone National Wildlife Refuge, Minnesota

Region 3, August 13, 2012
Granite extracted from Bigstone NWR was tranformed into a fencepost.
Granite extracted from Bigstone NWR was tranformed into a fencepost. - Photo Credit: n/a
A granite outcropping is habitat for the endangered Ball cactus.
A granite outcropping is habitat for the endangered Ball cactus. - Photo Credit: n/a
Bigstone NWR wetland
Bigstone NWR wetland - Photo Credit: n/a
Water control structure
Water control structure - Photo Credit: n/a
Endangered Ball cactus.
Endangered Ball cactus. - Photo Credit: n/a

On August 13-14, 2012, biologists and hydrologists with the Environmental Contaminants Program at the Twin Cities Ecological Services Field Office, Big Stone National Wildlife Refuge, and the Division of Biological Resources in the Midwest Regional Office initiated a Contaminant Assessment Process for the refuge. CAP is a standardized approach to identify sources, pathways and effects of contaminants, and evaluate threats that these contaminants may pose to Service lands. Information from CAPs can be incorporated into Habitat Management Plans, Hydro Geomorphic Models and Comprehensive Conservation Plans.


Big Stone NWR was established in 1975 as part of the Big Stone Lake-Whetstone River project of Minnesota and South Dakota. Project purposes included flood control, and fish and wildlife habitat management. The project lands were set aside to provide feeding, resting and nesting habitat for migratory birds with emphasis on waterfowl, and habitats for other wildlife. The Big Stone is located near the headwaters of the Minnesota River and encompasses 11,586 acres of riverine wetlands and uplands, native prairie and granite outcrops. Big Stone NWR was selected for a CAP because of suspected water quality issues. Tributaries upstream of the refuge have been listed as impaired for mercury, turbidity, low dissolved oxygen and bacteria. Land use practices within the surrounding watershed, as well as stream alterations and dam construction, strongly influence hydrology and water quality within the refuge.

Highly altered hydrology of the surrounding watersheds presents a challenge for water and habitat management because the wetlands become sinks for sediment and other contaminants, which leads to habitat degradation. Water impoundment on the refuge reduces velocity, sediment transport and distribution, creating depositional zones that are prone to sediment and contaminant accumulation. Additionally, alteration of the surrounding landscape (e.g., conversion of prairie and drained wetlands to agriculture) has increased surface runoff, erosion and contaminant concentrations in the nearby rivers. Sedimentation within wetlands increases turbidity, decreases native plant growth, decreases invertebrate abundance and diversity, increases the production of invasive plant species (e.g., hybrid cattail), and decreases wetland volume. In addition to sedimentation, other contaminants, such as high levels of nutrients and heavy metals, are suspected to be impacting the refuge wetlands.

The CAP Project at Big Stone NWR is an opportunity for Refuges, Biological Resources, and the Environmental Contaminants programs to work together to elucidate contaminant dynamics and their impacts to our trust resources and guide management of our trust resources.
By Elissa Buttermore, Kim Bousquet, Alice Hanley, Josh Eash, and Dave Warburton

Contact Info: Elissa Buttermore, 612-725-3548 ext 205, elissa_buttermore@fws.gov