Wetlands

Six methods of floating roadway widening sections over a peat swamp were designed and constructed on a two-lane roadway in 1976. The project location was on T.H. 53 between International Falls and Ray. Peat depths ranged from 8 to 15 feet. The investigation to date has shown that widenings can be floated on peat when fill height and loading rates are controlled. Performance of the sections will be monitored for a period of at least three years.

This Technical Summary pertains to Report 2023-25, “Stormwater Pond Maintenance and Wetland Management for Phosphorus Retention,” published June 2023.

Reduction in phosphorus is critical because phosphate, a dissolved form of phosphorus, sustains algal and cyanobacteria growth and causes a wide range of water-quality impairments in the ponds and downstream waters including algal blooms, excess floating plants, taste, and odor problems. Many stormwater ponds and wetlands that treat stormwater appear to be less effective than expected or originally intended in phosphorus retention, a key function of these ponds in urban environments. There is evidence that many old ponds are releasing phosphorus from bottom sediments at high rates and likely exporting phosphorus to downstream surface water bodies. A major outcome of this project is a pond Assessment Tool to assess the risk of high phosphorus concentrations in ponds and sediment release of phosphorus. The tool is based on 20 ponds with detailed water quality and phosphorus release measurements and a meta-analysis of 230 ponds in the Twin Cities metro area. Other outcomes included a working definition of a constructed stormwater pond and a wetland treating stormwater in the framework of water-body regulations, the development of recommendations for stormwater pond maintenance and wetland management, and an update to the sections on the constructed stormwater ponds section of the 2009 Stormwater Maintenance BMP Guide.

This report presents the results of a four-year study on techniques for revegetation of native sedges in created basins. Although often the dominant genus in shallow wetlands, sedges (Carex spp.) do not readily recolonize after restoration or creation of the water table. It is unlikely that sedges will naturally establish in created wetlands. The results of seed germination studies on five Carex species suggest the highest germination rates in fresh seeds - with one exception. Wet/cold storage also can prolong seed viability for at least two-and-a-half years. Dry storage is not recommended for wetland sedge seeds. Short-term wet/cold treatment after prolonged dry storage does not improve germination rates. Sensitive to deep water, rising water levels, and competition during the establishment year, seedlings grew well across a wide range of water depths in subsequent growing seasons. Both species outcompeted annual weeds within two to three growing seasons, but not Phalaris arundinacea (reed canary grass). The study recommends weed control during the establishment year to prevent the invasion of P. arundinacea. Wetland soil promotes seedling growth relative to other soils, but does not affect germination rates. Because of the potential for the introduction of undesirable weeds, the study does not recommend the use of donor wetland soil. Instead, study results suggest the potential for the use of organic top-dressings.

This report describes a long-term study to monitor and evaluate the ecosystem recovery of seven wetland restorations in south central Minnesota. The study looks at the impact of planting on wetland restoration success in inland wetlands and develops a methodology to assess wetland restoration success. The study focused on the following question: To what extent can revegetation stimulate overall biological recovery in isolated restoration sites? Researchers used aspects of ecosystem function and structure to characterize recovery rates in planted and unplanted restored sites relative to one another and to reference wetlands, as well as indices of biotic integrity for plants, invertebrates, birds, and amphibians in addition to other indicators of ecosystem structure, such as soil organic matter and water chemistry. Researchers developed field protocols, created biotic indices, and established baseline monitoring on each site including an as-built topographic survey, installation of groundwater and surface water stations, characterization of soils, vegetation, and vertebrates. A long-term monitoring system is now in place that will allow for the assessment of ecosystem recovery of seven restored wetlands relative to four reference wetlands.

In this project, researchers studied mycorrhizal and vegetational characteristics at prairie and wetland restoration areas. Study objectives included the following: * quantifying the effect of fungal inoculum on plant communities at a Minnesota Department of Transportation (Mn/DOT) prairie restoration site near Cambridge, Minn. * evaluating the prairie forb germination rates * monitoring revegetation at prairie and wetland restoration sites * characterizing mycorrhizal status of native wetland and prairie areas for comparison to the restored sites * producing fungal inoculum for incorporation into further reclamation areas. Findings indicated that 15 months after planting, fungal inoculation resulted in significantly greater cover by native plant species than seen in control plots. At this site, mycorrhizal inoculation benefited the prairie restoration effort by encouraging earlier, more extensive establishment of the planted species. Ongoing studies at this site will determine the long-term effects of mycorrhizal inoculation on the plant community. The report also presents specific recommendations for future restoration efforts. The studies of mycorrhizae in native prairies and wetlands provide further data for a baseline against which to compare restored areas. In addition, fungal inoculum produced in this project has been incorporated into restoration plots at another Mn/DOT site.

The three objectives of this project were as follows: (1.) to survey the arbuscular mycorrhizal fungi from the prairies, wetlands, and Mn/DOT experimental sites in anticipation of using data as indicators of the sites' health, (2.) to produce mycorrhizal inocula by different methods and (3.) to incorporate the inoculum into a Mn/DOT restoration site. This project was the first year of a three year study that seeks to define the variability in the mycorrhizal spores and other structures present in different ecosystems and determine if these fungi can be used as indicator species. All phases of the project were successful. The preliminary results suggest the mycorrhizal fungal spore numbers will be useful health indicators of restoration sites. General and single spore mycorrhizal inocula were generated using primarily native grasses and forbs as plant hosts. The general inoculum was then incorporated into a Mn/DOT experimental site. Future evaluations of this site will help to answer long-term questions regarding the possible benefits of amending disturbed roadway plantings or other prairie restorations with mycorrhizal inoculum.

This Technical Summary pertains to Report 2016-11, “Validation of Wetland Mitigation in Abandoned Borrow Areas—Phase II,” published March 2016.

This Technical Summary pertains to Report 2010-11, “Wetland Mitigation in Abandoned Gravel Pits,” published March 2010.

Mn/DOT has long recognized the importance of preserving and protecting the state’s many wetlands. These marshes, swamps and bogs provide habitat to a wide diversity of plants and animals that could not otherwise thrive. Sustaining this ecosystem requires a minimum water quality, which is influenced by the runoff from upland areas. Runoff that contains sediments and chemicals from human activities such as farming, forestry and land development can negatively affect wetland ecosystems and reduce biodiversity.