Why eco-restoration of the retired bog?
As we explore an eco-restoration future for the 31-acre property at the corner of Headwaters Drive and Pleasant Lake Ave., let’s review why ecological restoration of retired bogs benefits the environment.
A New Chapter of Ecological Restoration
Looking statewide, Massachusetts has lost more than 28% of its wetlands between the 1780s and 1980s (Dahl, 1990) and continues to lose wetlands every year (Massachusetts Department of Environmental Protection [MassDEP]). In addition, the Massachusetts Division of Ecological Restoration (DER) estimates that more than 3,000 dams are currently located in the state. These dams, and the related flow-control barriers associated with cranberry farming, result in decreased water quality, are a barrier to the movement of diadromous fish and other aquatic organisms, and can be costly to maintain.
Pro-active ecological restoration of retired cranberry bogs and the removal of flow-control structures has been an increasingly common method for farmers to transition their bogs and leave a legacy of improved ecosystem function and services.
The Eel River headwaters restoration project in Plymouth was the first project to restore retired cranberry bogs to more naturally-functioning stream and wetland ecosystems. Construction was completed in 2009 with the project partners winning the Coastal America Partnership Award from the United States Department of the Interior. In 2016, construction was completed on the largest freshwater wetland restoration project in the state at Tidmarsh Farms, a >200-acre former cranberry bog, in Plymouth. This award-winning project was featured in the New York Times and in Landscape Architecture Magazine.
Construction on three bogs along the Coonamessett River in Falmouth was completed in the spring of 2020, including the construction of multiple boardwalks for pedestrian access and recreation.
Construction is currently ongoing at the Foothills Preserve on ~50 acres of retired bog in Plymouth, and along the Childs River on ~12 acres of former bog in Falmouth and Mashpee. Inter-Fluve has completed the designs and construction observation for all of these projects, working with the Towns, private landowners, DER, and other state and federal entities to achieve the project goals.
In Harwich Port on Bank Street, partners including the Town Selectmen, Harwich Conservation Trust (HCT), DER, U.S. Fish & Wildlife Service, and Inter-Fluve are in the design phase of the Cold Brook Ecological Restoration Project for a set of retired bogs. With Cold Brook as well as groundwater flowing through HCT’s Robert F. Smith Cold Brook Preserve to Saquatucket Harbor on Nantucket Sound, there is the added benefit of naturally removing nitrogen, which will reduce sewering needs in the watershed.
To improve the health of the impaired Saquatucket Harbor, Town Meeting voters in 2017 approved $2 million for ecological restoration of the retired Cold Brook bogs upstream. Reduced sewering results in reduced road construction disruption and reduced long-term sewer expenses for taxpayers. By restoring natural habitats and water flow as well as reducing nitrogen heading to the harbor, the HCT-Town eco-restoration partnership is estimated to save taxpayers up to $6 million according to section 13.5.1 of the Town of Harwich Comprehensive Wastewater Management Plan.
Pro-active Ecological Restoration can include a number of techniques
Removal of dams and flow-control structures:
Dams and flow-control structures are fish passage barriers and also restrict the flow of water and sediment. By removing these structures, fish are able to move and migrate freely, sediment can move through alluvial systems, and other aquatic organisms can move freely up and downstream. In addition, removal of the impoundments that result from this infrastructure can reduce water temperatures by reducing the surface area of water exposed to high summer air temperatures.
Removal of sand:
The sand that has been placed on the pre-farming wetland surface typically builds up to 1.5-2 feet of thickness over the last 100-150 years. This separates the surface of the bog from the groundwater and the wetland soils. Restoration action can include the removal of this sand to bring the restored wetland surface closer to the water table and the former wetland (or peatland) soils. Another restoration action has included select areas of sand removal to expose the underlying peat and create a lower-elevation area that fills with groundwater and rainwater, thus providing off-channel open-water habitat and feeding opportunities for a variety of dabbling and diving ducks, geese, and swans as well as habitat for turtles, frogs, salamanders, and other wildlife.
On restoration sites that include flow-through river channels, these channels were typically straightened and widened to convey flows efficiently. Restoration actions have included the reconstruction of the channel into a more sinuous planform with a narrower and deeper channel cross-section and large wood installations for habitat and channel bank stability.
Large wood installation:
Large wood, including logs, logs with root wads, and slash (smaller woody material), is beneficial for river channel bank stability, aquatic habitat, and terrestrial habitat. Along the proposed channel alignment, large wood is placed on the outside meander bends where deeper pools will be constructed. These deep pools and cover provided by the root wads of the large wood provide necessary habitat and protection from predators for fish, turtles, and other aquatic organisms. Large wood placed on the margins of ponds and other off-channel open water areas can provide sunning habitat for turtles. Large wood on the wetland surface can provide additional habitat for terrestrial organisms that need large wood for cover.
Constructed microtopography provides a range of soil moisture conditions which in turn increases the diversity of wetland vegetation species. A wetland with a more varied topography and vegetation structure will provide a wider range of nesting/denning, rearing, feeding, and cover habitat. This varied topography also provides robust resiliency to climate change and changes in precipitation levels and thus groundwater levels.
We have observed that native seeds within the sand and underlying peat provide a rapid revegetation response once exposed to the appropriate moisture and sunlight conditions for each species. On recently-constructed restoration sites, researchers have found dozens of species of native plants growing within ~10×10-foot study plots, none of which were actively planted during construction. We often encourage spreading native transitional seed along the margins of the bogs where the bogs slope up to the roads to enhance growth in these areas. We also encourage the active planting of trees and shrubs in certain locations to move those areas along the trajectory of the proposed ecosystem. The trees and shrubs planted will mature to create a forested wetland, providing flood storage and important riparian habitat for mammals, birds, reptiles, and amphibians.
Many restoration sites are also important open spaces for public enjoyment. While many farmers allowed neighbors and residents to walk around their bogs, and many others did so without permission, many restoration projects provide the opportunity to formalize this recreation and provide maintained trails. These trails may include wheelchair-accessible options, boardwalks across the wetland and river channels, overlooks, educational and, interpretive opportunities, or other amenities.