Wetland Mitigation in Abandoned Gravel Pits

Project summary:

It is becoming increasingly difficult to provide mitigation for wetland impacts due to road construction in northeastern Minnesota counties, which retain more than 80 percent of their pre-settlement wetlands. Abandoned gravel pits, defined as those which have been depleted of usable material and that have no further value for borrow, are one of the few remaining areas which can serve as wetland mitigation sites. The main goal of this project was to determine if viable mitigation wetlands can be created on abandoned gravel pit sites to compensate for wetland impacts due to road construction in northeastern Minnesota. To achieve this goal, a wetland creation demonstration site was established in an abandoned gravel pit within the U.S. Trunk Highway 53 reconstruction corridor. The site allowed research and evaluation of hydrologic controls, soil amendments, direct seeding, mulch, and other techniques for wetland establishment. Soil and plant materials displaced by the TH 53 reconstruction were also evaluated for use in wetland creation. The completed demonstration site consisted of a complex of several wetland types most likely to be impacted in northeast Minnesota (Types 2, 6, 7, and 8). The final report contains preliminary recommendations for creating wetlands in abandoned gravel pits based on information acquired during the funding period.