EnSafe’s West Tennessee Wetland Mitigation Bank is transforming former farmland into a self-managing, sustainable, and productive wetland using hydrological and ecological design that leverages nature’s unparalleled capacity for ecosystem restoration.
A sea of small orange flags speckling the wintery landscape of West Tennessee is a welcomed sight for EnSafe’s ecological staff.
“Tree planting for habitat restoration is the most rewarding part of my job,” says Biologist Aaron Conti, a Professional Wetland Scientist and Tennessee-Qualified Hydrologic Professional (PWS, TN-QHP) from Memphis, Tennessee. “So, when we planted over 54,000 seedlings last winter, that was a milestone achievement for this wetland restoration project.”
Each of those 54,000 bare-root seedlings is beginning a long journey from survival to maturation. EnSafe’s Jimmy Groton, PWS, TN-QHP oversaw the hardworking crew of Williams Forestry and Associates in planting the seedlings at the recently created wetland mitigation bank along the Loosahatchie River, part of the Mississippi River floodplain. Bald cypress, overcup oak and swamp white oak, cherrybark and willow oak, pin oak, water tupelo, silver and red maple, persimmon – all trees native to the floodplain – are part of EnSafe’s plan to restore wetlands from prior converted cropland.
Draining wetlands for conversion into fertile farmland, such as straightening, channeling, and leveeing rivers, was historically common throughout the U.S. and West Tennessee. This well-intentioned but misguided practice traces its roots back to European hydrologic management and agricultural techniques. The Mississippi River floodplain in particular has suffered some of the heaviest losses from conversion to cropland and timber harvest until 1989, when the “no net loss” of wetlands was first adopted as federal policy.
Conti, Groton, and Velita Thornton (who is a TN-QHP In Training) are part of EnSafe’s crew of wetland and ecological specialists helping clients avoid and reduce adverse impacts to wetlands. They also work to offset unavoidable environmental impacts through constructing and maintaining EnSafe’s new West Tennessee Mitigation Bank (WTWMB).
“Our vision is to nurture this site into a sustainable, self-managing ecosystem,” says Conti. “At this early stage, we are implementing wetland design elements to help facilitate a successful transition from farmland to a healthy bottomland hardwood wetland.”
Restoring a wetland is a complex feat. A multidisciplinary approach involving ecology, hydrology, engineering, water quality, and soil science synthesizes wetland hydrology, vegetation, and hydric soil processes to transform this site into an ecologically-valuable habitat for local and migratory wildlife, especially waterfowl.
To prepare the site for planting the seedlings, EnSafe implemented several improvements to site drainage last winter, with help from GR2 Remediation and Restoration Services. To ensure tree suitability, Groton selected species appropriate for wet and saturated soils and designed a planting scheme that directed the flood-tolerant species to be planted in the lowest-lying areas, with facultative wetland species planted throughout the remainder of the site.
Then, to protect the young seedlings in their first year, EnSafe and GR2 selectively mowed between the rows of the planted seedlings so successional vegetation doesn’t overtop and shade out the first-year seedlings.
“We’re using a patchwork dynamics approach,” explains Groton, “which creates a mosaic of diverse habitats. We’re selectively mowing some areas of volunteer species to give the planted seedlings a better chance to grow and leaving other areas to form thick forested stands. Our goal is to optimize the density, diversity, and productivity of the wetland’s vegetation.”
To monitor and quantify the improvements to site hydrology, EnSafe also installed iron-oxide-coated soil monitoring tubes that register reduction of iron into its soluble form, which is indicative of hydric soil development, and piezometers to monitor and record the shallow water table level below ground surface. “Due to this site’s proximity to the Loosahatchie, we will monitor connectivity between groundwater and biota that will enhance the ecological productivity of this wetland,” adds Conti.
Once the planted seedlings are established, EnSafe will complete a final round of earthwork improvements to further improve hydrology, including ditch plugs to decrease surface water runoff velocities and increase surface water retention and a supplemental wing dike to prevent washout during storm events.
“Now that the site is being managed from an ecological perspective, we are already seeing promising signs of a revitalized wildlife habitat,” reports Conti, who recently recorded over 80 native plant species during a summer 2020 botanical survey.
Sighting of local wildlife are more commonplace now as well: White-tailed deer bounding between the forested tree stands lining the onsite creeks; red-winged blackbirds perching ephemerally on goldenrod in the open fields; indigo buntings, northern parulas, ruby-throated hummingbirds, and yellow-breasted chats flitting along the edges of thicket. Rabbits, field mice, and frogs abound. According to neighboring residents, even a bobcat has been spotted on the move at sunset.
The site’s proximity to the Loosahatchie River provides added ecological benefits. As EnSafe VP of Geological Services Paul Stoddard, PG, points out, “The river’s riparian and floodplain habitat attract migratory waterfowl for use as a resting and feeding area, mitigates flood pulse intensity, and increases availability of phosphorous for biota. It also improves downstream water quality due to the wetland’s capacity for sediment retention and denitrification.”
Mitigation banks, such as EnSafe’s WTWMB, are advantageous tools for overcoming the challenges of compensatory mitigation in a few ways:
- They streamline the mitigation process by establishing the compensatory wetland in advance of future losses.
- The large tract of land provides greater ecologically resource value as compared to smaller, separate and less diverse wetlands.
- Mitigation bank wetlands are protected “in perpetuity” through conservation easements.
- A monitoring period ensures that performance standards meet quantifiable criteria to demonstrate the successful establishment of the wetland.
The WTWMB will provide wetland credits that can be used to offset unavoidable impacts to state- or federally-jurisdictional waters protected under the Clean Water Act, Section 401 and Section 404, among other state and federal regulations. By restoring prior converted cropland into a wetland, EnSafe is playing a critical role in restoring, enhancing, and preserving nearly 250 acres of ecologically-valuable wetland resources that will be legally protected for future generations.
In March of 2019, EnSafe successfully completed requirements for the initial release of 20 percent of the 126.6 total bank credits of the final Mitigation Banking Instrument (MBI) approved by the U.S. Army Corps of Engineers and Interagency Review Team. The wetland mitigation plan is flexible enough to adapt to changing conditions as the site develops during the monitoring period, which is scheduled for at least five years. The long-term goal is to create a self-managing, sustainable hydrological and ecological system that takes advantage of nature’s unparalleled capacity for self-healing and ecosystem restoration.
For more information about EnSafe and the West Tennessee Wetlands Mitigation Bank or to purchase wetlands credits, please contact Paul Stoddard, email@example.com, 901.372.7962.
Posted in Insights/Innovation.