Salvaged-Wetland Soil as a Technique to Improve Aquatic Vegetation at Created Wetlands in Wyoming,USA

Aquatic plants usually establish following wetland creation from a variety of mechanisms including animal transport, inflows from nearby wetlands, wind dispersal, and seed banks if they are available. However, at created wetlands that are isolated from natural wetlands, aquatic plant communities may not establish even after 10 or more years. One method of improving the establishment of aquatic plants is through the use of salvaged-marsh soils. Using this method, wetland soil from a donor site is collected and spread across the basin of the created wetland. When the proper hydrologic regime is reached at the created site, the seed bank from the donor soil is then present to take advantage of the uncolonized site. Over 1500 wetlands have been created in northeast Wyoming, USA from bentonite mining and most of them have not developed submersed and emergent plant communities due to isolation from plant sources. Our goal was to evaluate the effectiveness of using salvaged-wetland soil as a tool for improving plant growth at created wetlands. Our study took place at 12 newly created wetlands that were isolated from other wetlands by >5 km. Six wetlands were treated as reference wetlands, with no introductions of seeds or propagules. At the other six wetlands we spread ≈10–15 cm of salvaged soil from a donor wetland during the winter of 1999–2000. To identify the potential plants in donor soil, we collected 10 random samples from the donor wetlands and placed them within wetland microcosms in a greenhouse where they were treated to either moist-soil conditions (water at or just below the soil line) or submersed conditions (water levels maintained at 15–30 cm). Treatment wetlands were evaluated for plant growth during the fall of 2000 and 2001, whereas the greenhouse samples were grown for two growing seasons then harvested. Our results show that using salvaged wetland soil increases: (1) the number of plant species present at a wetland over time, (2) the total vegetation coverage in a treated wetland over time, and (3) the total plant biomass in a treated wetland. The species pool available in the salvaged wetland soil was limited to 10 obligate wetland species, but several of them are considered valuable to waterfowl and other wildlife. Furthermore, salvaged-wetland soil could be useful for ameliorating poor substrate conditions (i.e., bentonite) and improving conditions for the establishment of additional species. One concern with this technique is the introduction of invasive or exotic species that could form monocultures of undesirable plants (e.g., cattail Typha spp.]); introducing more desirable species during the application of salvaged soil could reduce this probability. We believe incorporating salvaged-wetland soil during basin construction could be used to increase the value and productivity of created wetlands in this region.