Restored Wetlands (NRCS 657)

Considerations

• Upon completion, the site shall meet soil, hydrology, vegetation, and habitat conditions of the wetland that previously existed on the site to the extent practicable.
• Sites suspected of containing hazardous material shall be tested to identify appropriate remedial measures. If remedial measures are not possible or practicable, the practice shall not be planned.
• Invasive species, federal/state listed noxious plant species, and nuisance species shall be controlled on the site as necessary.
• Establish vegetative buffers around the wetlands to reduce the movement of sediment and soluble sediment-attached substances carried by runoff.
• The wetland shall not adversely affect adjacent properties or other water users, the capacity of drainage systems on other properties, and shall not back surface water onto an adjoining property or restrict the capacity of adjacent subsurface drainage systems unless agreed to by signed written letter, easement or permit.
• Where practicable, existing subsurface drains (tile) shall be rendered inoperable (blocked or removed) or controlled as needed to meet the goals of the restoration and site conditions.
• Water control structures shall only be used to recreate natural hydrologic patterns or to allow management and maintenance of the desired community.

Soil Considerations

• Add amendments or mechanical tillage, as appropriate, to promote native vegetative growth.

Hydrology Considerations

• Natural drawdown through evapotranspiration is preferred over regulating water levels with water control structures. Drawdown of permanent storage is often necessary or desirable to manage wetlands for certain species or during certain times of year.

Vegetation Considerations

• Vegetative buffers can increase function by trapping sediment, cycling nutrients, and removing pesticides.
• Prescribed burning can restore wetland and adjacent upland plant communities.
• Water levels or topography can be manipulated to control unwanted vegetation.

Fish and Wildlife Habitat Considerations

• When possible, establish vegetated corridors to link the restored wetland to adjacent landscapes, streams, and water bodies and to increase establishment of native vegetation.

Effectiveness 

• Case studies in Maryland, Illinois, and Iowa indicate wetlands can remove 68% of nitrate-nitrogen and 43% of phosphorus can be retained from drainage water. (Woltemade, 2000)
• A Minnesota study on constructed wetlands found a 68% and 73% reduction in nitrate-nitrogen and phosphorus, respectively.
• Crumpton et all. (1993 Iowa) found that constructed wetland mesocosms could reduce N03-N concentrations ranging from 3 to 15 mg/L by >80% during residence times of approximately 1 week.

Costs

• Costs will vary based on the size of the wetland and existing site conditions.
• The highest costs are associated with site planning and design, excavation activities, control structures required, tile drain work, and the opportunity cost of any land removed from agricultural production.
• Cost analyses should take into account the cost of the wetland as well as the acres treated. Estimated life spans of restored wetlands can be 50 years or longer.
• Average 2016 costs (first year costs and per acre per year) of 1-acre constructed wetland located on land with a high Corn Suitability Rating (CSR 80) treating about 100 acres of drainage, would cost just over $10,000 for design and installation, or just under $800 per acre per year when annualized over a 40-year time period; (Tyndall)