Mapping and Protecting Vulnerable Wetlands and Stormwater Management Planning Project

As part of a Wetland Program Development Grant through the U.S. Environmental Protection Agency (EPA), MassDEP developed a project that defined, identified, and mapped vulnerable wetlands in Upper Charles River and Upper Neponset River communities. This projected helped provide stormwater management planning tools for towns subject to the Municipal Separate Storm and Sewer System (MS4) General Permit and provided technical assistance to better protect vulnerable wetlands from stormwater pollution. MassDEP developed a set of unique vulnerable wetlands GIS maps for each community, and provided technical training and outreach on how to use the maps for stormwater management planning. In addition to illustrating impaired waters, these maps identified the location of vulnerable wetlands in the community's developed areas and stormwater outfalls. Communities can determine potential sources of impairment and plan the appropriate placement for, and type of, stormwater control practices that are best for protecting these resources and reducing phosphorus loading to the Charles and Neponset Rivers.

Some types of wetland ecosystems are larger and more visible, and their role in safeguarding critical public interests is more apparent: e.g., buffering property from floods and storms, or providing important wildlife habitat. All wetland types are susceptible to changes in hydrology and water quality resulting from increased impervious surfaces and the impacts of stormwater pollution. Vulnerable wetlands are considered to be particularly sensitive because they respond quickly to small changes in hydrology and to adverse water quality impacts.

Degradation of vulnerable wetlands can occur very rapidly with changes in pH, dissolved oxygen, temperature, and turbidity in receiving waters; increased flows containing excess nutrients and other pollutants; and reductions in groundwater discharges resulting in decreased base flows. These degradations affect the water quality for some or all of the public benefits that these resources provide, including protection of drinking water; swimming; boating and other recreational uses; pollution prevention; wildlife, fish and shellfish habitat; storm damage; flood prevention; and filtering pollutants. In general, MassDEP has determined that the maintenance of an undisturbed, naturally-vegetated buffer around wetland resources is one of the best methods to protect vulnerable wetlands from degradation and to improve or maintain water quality in the resources.

Using recent scientific literature, MassDEP has defined vulnerable wetlands to be:

• Headwater Streams;
• Certified and Potential Vernal Pools;
• Vernal Pool Clusters; and
• Critical Areas, as defined by the Massachusetts Wetlands Regulations' Stormwater Standards

Each resource, and its significance to the health of our natural ecosystem and to the public's health and protection, is described below.

Intermittent headwater streams can be as small as seeps or springs, representing an interface between groundwater and surface flows that is critical to sustain stream flows and public water supplies.

Headwater streams are up-gradient of the first order streams depicted on the 1:24,000 scale USGS maps. They may include ephemeral streams that flow only in response to storm events and lack base flow, or small intermittent streams that are unmapped and up-gradient of bogs, swamps, wet meadows and marshes, and may fail to meet the Massachusetts regulatory definition of a stream (310 CMR 10.04). These streams can be defined by topography or digital elevation landscape models and do not include stormwater conveyances. The MassDEP Wetland data layer represents an expansion of the number of streams and hydrologic connections shown on the USGS Topographic Quadrangles, and as such highlights headwater streams.

Why are headwater streams important?

Drinking Water:

• Headwater streams represent a groundwater-to-surface-water flow interface, which facilitates natural water discharge and recharge processes that are critical to sustaining public and private water supplies.
• Based on recent U.S EPA estimates, 53% - 59% of the total stream miles in the contiguous U.S can be considered headwater streams.
• 20% - 30% of all wetlands could be considered geographically isolated.
• Massachusetts is the most populous state in New England, and 98% of our state's population is served by drinking water supply systems that rely on isolated waters, including ephemeral, intermittent, and headwater.
• Only about one-half of these isolated waters are protected as Source Protection Areas or are safeguarded by the Wetlands Protection Act (WPA) or the federal Clean Water Act (CWA), meaning that not only are these wetlands vulnerable, but so is our drinking water supply.

Water Quality:

Headwater streams and isolated wetlands retain and transform excess phosphorus and over 50% of nitrogen inputs in a watershed. The extensive land/water exchanges serve as natural filters to improve water quality to downstream resources.

Small wetland depressions, such as vernal pools, may be considered vulnerable wetlands. They are topographically isolated from other surface water bodies, making them inaccessible to predatory aquatic organisms (e.g. fish) dependent on streams. As such, they provide critical habitat for breeding amphibians.

The Massachusetts Natural Heritage and Endangered Species Program (NHESP) has certified over 3100 vernal pools (CVPs) and identified nearly 30,000 potential vernal pools (PVP) across the state. The potential vernal pools have not been extensively field-validated, but their locations are relevant to town planners contemplating preservation actions and undertaking stormwater remediation. The CVPs and PVPs referenced as sensitive wetlands are those mapped by the NHESP. Vernal pools that have been certified are afforded protection under the WPA regulations (310 CMR 10.00) if they are located within a jurisdictional wetland-resource area. Vernal pools that are not yet certified, but are documented during the wetland permit application review process, are also protected if they are within a jurisdictional wetland resource area. Certified vernal pools are protected under the Massachusetts 401 Water Quality regulations (314 CMR 9.00) as Outstanding Resource Waters (ORWs) independent of other resource areas.

The importance of protecting undisturbed upland habitat adjacent to and between vernal pools is widely recognized in scientific literature. Projects altering wetland resource areas can disrupt existing migration routes of amphibians and reptiles between vernal pools, or between vernal pool habitat and other wetlands or upland nesting areas. The wetland regulations limit jurisdiction to vernal pools and the 100-foot habitat zone around the vernal pool that is within a wetland resource area. Studies have documented, however, that areas beyond the 100-foot habitat zone are biologically important for breeding amphibians and other vernal-pool-using species. Studies demonstrate the importance of preserving habitat connectivity between pools to support viable populations of amphibians. Habitat surrounding vernal pools contribute to the maintenance of the vernal pool hydro period and the quality of the aquatic habitat to ensure successful breeding. Avoiding new stormwater impacts, remediating existing stormwater impacts to vernal pools, and preserving undisturbed habitat around clusters of vernal pools will foster the continued viability of these ecosystems. Knowing the location of vernal pools and vernal pool clusters in the community can help ensure that municipal land-use planning efforts incorporate appropriate stormwater management designs, consistent with TMDL requirements, that can best preserve, protect, and restore these essential ecosystems. The criteria used to define vernal pool clusters on MassDEP's maps include:

• The presence of two or more vernal pools (certified or mapped by NHESP);
• Good connectivity between pools with few obstacles to amphibian migration (i.e. roadways, buildings, etc.); and
• A requirement that the pools be within 400 meters of each other to protect migratory and dispersal distances for juvenile and adult pool breeding amphibians.

Important Wildlife Habitat

Vernal pools are important ecosystems for maintaining biodiversity. Many species of birds and mammals also use these pools as a source of water. Healthy vernal pools support a varied number of amphibians, which compete with and prey on mosquitoes, potentially reducing their numbers. Furthermore, research suggests that the total mass of vernal pool amphibians in a forest exceeds the combined mass of all the breeding birds and small mammals in that forest, suggesting that vernal pools play an important role in the food web of our forests.

Vernal pools provide critical habitat for wildlife and certain species cannot complete their lifecycle without them. Many of these species require an environment free of fish to avoid predation and since vernal pools dry up for parts of the year, fish cannot breed in them. The loss of vernal pools and their associated upland habitat areas would result in the loss of vernal-pool-dependent species.

Critical areas are defined in MassDEP's wetland regulations (310 CMR 10.04) as Outstanding Resource Waters (314 CMR 4.00), Special Resource Waters (314 CMR 4.00), recharge areas for public water supplies (310 CMR 22.02 - Zone Is, Zone IIs and Interim Wellhead Protection Areas for groundwater sources and Zone As for surface water sources), bathing beaches (105 CMR 445.000), cold-water fisheries (310 CMR 10.04 and 314 CMR 9.02), and shellfish growing areas (310 CMR 10.04 and 314 CMR 9.02). Critical areas are included as vulnerable wetlands since they are areas that merit special protection or where restoration efforts would be most beneficial.

Critical Areas are important for drinking water protection, preserving recreational use, and maintaining the fishing and shellfish economy and industry in Massachusetts.

The vulnerable wetland maps for stormwater management planning have proven to be valuable planning tools for MS4 Towns. The maps can be used to identify areas in each of the six pilot communities where phosphorus reduction efforts in the Charles River and pathogen reduction efforts in the Neponset River can be most effective. They help to visualize the location of sub-watersheds with impaired waters; problem areas and the potential sources of pollutants of concern; and more suitable sites for stormwater treatment and infiltration BMPs. These maps also identify which vulnerable wetlands might benefit from protective action by the town and which would benefit from restoration by mitigating stormwater impacts. Protection and restoration can be natural outcomes of the compliance process when consideration of vulnerable wetlands is incorporated into planning efforts to upgrade stormwater management and delivery systems.