Wisconsin lost 50% of its original wetlands in the last 150 years of settlement. There are many agricultural fields, which were former wetlands that were drained to create farmland. Draining was so pervasive that it is rare to find a wetland in southeast Wisconsin that has not had some alteration of its original hydrology through ditching, diversions, berms, drain tiles, and other subtler land alterations.
Another pervasive impact on wetlands is the erosion of upland soils and the deposition of these soils onto wetlands because they are at the low point of the landscape. In the agricultural regions of Wisconsin, it is common to find one foot or more of upland soil washed down onto wetlands, creating a change in hydrology, loading the wetland with nutrients, and increasing the elevation. This deposition of sediment usually leads to a change in the wetland plant community to more exotic invasive plants and even to upland plants.
Wetlands can be restored on farmland and pastureland that was formally wetland. Because the wetland soils persist, bringing the hydrology back on the land and re-wetting the soils may involve filling ditches, removing drain tiles, or removing sediment. In addition, many sites are controlled for invasive species and planted with native seed. Upland un-mowed buffers are often created to protect the newly restored wetland from further degradation.
The Pike River Restoration Project is a multi-year restoration of over 5 miles of the Pike River in Mt. Pleasant, Wisconsin. Thompson and Associates participated in all phases of design, construction oversight, planting, and management. The paths winding through the restored river corridor provide passive recreation while the wetland and prairie restoration in the newly constructed river floodplain filter the water, buffer floods, and provide wildlife and fish habitat.
Wetland mitigation was adopted by the state of Wisconsin in 2002 and modified since then. The process of mitigation is to require newly restored wetlands to replace impacted or filled wetlands. The Wisconsin DNR permitting process, under NR 103, requires every effort be made to avoid wetlands on site. If wetlands cannot be avoided, then the impact to wetlands must be minimized. Minimization includes actions such as narrowing or moving a road, putting in a retaining wall, and/or moving structures to impact the least amount of wetland.
The very minor wetland impacts permitted by a WI DNR General Permit do not require Mitigation (less than 10,000 square feet), but mitigation is now mandatory for any wetland impact with a Wisconsin DNR Individual Permit. The DNR has developed Guidelines for Mitigation, and have many criteria for approving a mitigation plan. Currently, the preferred method of mitigation is for the permittee (the entity responsible for the project) to purchase credit at a state-approved wetland mitigation bank. If no wetland mitigation bank is available with credits to purchase, then the permittee may purchase credits that are termed “in-lieu fee” compensation. Finally, a small number of projects may be eligible for what used to be called on-site mitigation—a restoration project that compensates for wetland loss locally.