Comprehensive Ecological Restoration
Tidmarsh Farms offers an opportunity to create an in-depth case study of a process-based fresh-water wetland restoration. The restoration seeks to remove landscape-scale stressors introduced through farming, restore form and function to landscape hydrology and soils, and jump start a self sustaining naturalized wetland.
Farming Creates Stressors
Most farms are built to maximize production of a monoculture; favoring one species over all others, farm construction unwittingly can create landscape-scale stress. Cranberry production at Tidmarsh highlights this problem. Constructed on swamp-land at the turn of the 20th century, the natural topography of Tidmarsh was re-designed for maximum cranberry production. Flattened bog surfaces soon replaced forested swamp. Berms and water control structures separated these bogs, and impounded the headwaters to provide a reservoir for winter floods and later for water harvest. The bogs were hatched with drainage ditches and covered with a sand layer that was periodically refreshed. These farm practices create limitations to the natural hydrology and soils of the wetland, and impede free passage of wildlife.
In 2011, the Tidmarsh Farms Restoration Project formed a design team to identify the landscape-scale stressors at Tidmarsh East and propose a suite of actions that, when implemented, would jump start the formation of a natural self-sustaining wetland, and provide ecological and community benefits to the entire watershed.
With the decision in 2010 to stop farming cranberries, Tidmarsh and our partners faced the question of how best to restore natural form and function to this landscape. To begin, we conducted a preliminary site assessment that would help scientifically ground restoration design. Typical concerns of this phase of work include conservation status, accessibility (ownership and community support); potential for hydrologic connectivity; existence of toxic materials. As far as possible, the assessment articulates possible potential actions that will help overcome limitations, and articulates how these actions provide ecological and community benefits.
- Fill perimeter irrigation ditches
- Plug interior (lateral) irrigation ditches
- In-stream subsurface grade controls
Why? This increases soil moisture and establishes conditions for self-sustaining wetlands.
1. Anthropogenic sand layer that separates plants from the water table
- Remove berms and dams
- Remove interior water control structures and cell-spanning dikes
Why? To free movement of aquatic and terrestrial organisms, as well as the water, sediment, and organic matter.
2. Barriers to free movement of fish, wildlife, and water
- Rebuild degraded channels
- Add large wood and expose peat in select locations for isolated wetlands
- Roughen surfaces
Why? To jumpstart improved habitat conditions across the site, and set the stage for future natural evolution; creation of a stream form that works with the site, not against it.
3. Physical Simplification
- Gently create preliminary micro-topography
- Add the site to 'self-roughen' over time
- Eliminate bog 'ripping' as an approach to avoid unintended OC pesticide mobilization
- Increase hydro-residence time
Why? So that legacy pesticides stay on site, increase nutrient uptake and other biochemical processes, and to reduce nutrient export.
4. Legacy Pesticides (sand layer) and nutrients
- Site is already self-healing and will continue to be
- Control invasives
- Selective planting over time
- 'Head start' threatened and endangered species
Why? To diversify and allow for self-sustaining biota, and facilitate growth of rare, threatened, and endangered species on site.