Massachusetts wetlands have been degraded by many different types of historic impacts. The variety of impacts encountered within degraded wetlands requires that restoration approaches be custom tailored to address the unique problems and conditions of each restoration site. Common types of wetland impacts and restoration actions are reviewed below.
Restoring Tidal Hydrology
All wetlands depend on certain water conditions (hydrology) to maintain healthy habitats for plants, fish, and other forms of life. When these conditions are altered by people, wetlands become degraded or are lost completely. In coastal areas, altered hydrology and wetland changes are frequently caused by tidal restrictions.
Tidal restrictions occur where human infrastructure, such as roads and railroads, have been built across coastal wetlands and waterways and disrupt the natural ebb and flow of the tides within upstream habitats. Most of these crossings were originally built with bridges or pipes too small to pass the full tidal range—picture an hourglass on its side, with the narrow middle acting as a choke point. By disrupting tidal flow, restrictions alter water levels and chemistry, diminish sources of ocean nutrients, and reduce the flushing of pollutants out of upstream areas. They also often block the passage of fish into important upstream habitats. Removing a restriction and restoring tidal flow improves the marsh by returning the hydrologic conditions needed to support healthy marsh habitats.
Addressing a Pollution Source
If a wetland is being degraded by polluted stormwater runoff, for example from an adjacent roadway or a farm field, the remedy is to reduce or remove the pollutants carried by the runoff. This can be accomplished by reducing the amount of pollutants that runoff can carry away (e.g., by regular street sweeping), diverting runoff away from the wetland (e.g., into a settling basin), or treating the polluted runoff before it reaches the wetland.
Removing Fill / Re-grading
Thousands of acres of Massachusetts wetlands have been historically impacted by the placement of fill such as gravel, trash, and dredged material. Restoration of this type of impact requires excavation and removal of the fill material to re-establish appropriate soil and water conditions that can support a healthy wetland system. If the original wetland soils no longer exist beneath the fill, organic soils may need to be spread throughout the area once the fill has been removed.
Re-planting a restoration site with native wetland species is often performed in conjunction with other restoration work (e.g., fill removal). Most of the time it is not enough to only restore wetland soils and hydrology. This is because the highly disturbed conditions favor the growth of invasive species that out-compete native species under those conditions. Thus, native species are planted throughout the restoration site to give them a head start and the ability to cover the wetland surface before invasives can take hold.
Invasive Species Control
Invasive species pose a very serious threat to the health and integrity of all types of ecosystems, including wetlands. They are "invasive" because people have transported them from their native landscapes (where they evolved over thousands of years) to new areas around the globe where they have never existed before and have few natural controls. The lack of natural controls allows them to quickly spread un-checked, replacing native species and degrading natural systems.
One method of addressing invasive species is through the use of bio-controls, whereby natural competitors are imported from the invasive's native landscape to a location where the invasive is growing out of control. For the invasive wetland plant purple loosestrife (Lythrum Salicaria), a certain beetle from Asia (where purple loosestrife is native) is proving to be an effective bio-control. In Massachusetts, several biocontrol pilot projects are now underway to study the beetle's ability to control the spread of this invasive plant. See the Purple Loosestrife Biocontrol Project webpage for more information.