Wetlands of Weymouth

The Town of Weymouth is a developed urban area located just south of Boston. In addition to its mainland territory, Weymouth also owns several islands in Boston Harbor. It has a population of nearly 58,000 people and hosts a variety of businesses, industries, and municipalities. Of the 21.6 square miles of property, 17 square miles is land and 4.6 square miles consists of water. Weymouth contains multiple river systems and water bodies as well as parks and natural coastal areas including Bare Cove Park and Great Esker Park.

The town is part of a larger watershed composed of at least 6 other towns covering 215 square miles that ultimately empties into the Boston Harbor. The town's drinking water supply comes from two limited sources: the Great Pond and the Mill River basin. The water is treated before being distributed to the community.

Several different types of wetlands exist within this town, including coastal marshes, vernal pools, emergent swamps, but dominantly forested swamps. The study area of interest includes a portion of the forested swamp that feeds into Weymouth Great Pond by a pipe running under the street. This spot is part of a larger wetland ecosystem existing around the pond that has been severed by roads, neighborhoods, and other infrastructure. The Great Pond then flows into Mill River which empties in Whitman's Pond before discharging into the bay.

The study area lies in a notable depression as indicated in gray from the terrain elevation map. The edges of the wetland are sloped resulting in residential homes located at the top of the hills surrounding the wetland. Although the larger wetland is separated by Weymouth Street, a pipe installed under the elevated road connects the northern part of the wetland to the south, ultimately reaching Weymouth Great Pond.

The most obvious indication of wetland presence is inundation. The area is often flooded and has a hydroperiod possibly year round. Moving water indicates the presence of an inlet (rivers/streams) and outlet (the great pond).

Few trees thrive in standing water and certain adaptations help the vegetation survive. Therefore, micro-topography is prevalent in this area. A collection of mounds and pools exists as plants have engineered the habitat around them. Plants become raised up over time on top of mounds due to the deposition of organic matter beneath the plants, the formation of soil beneath, and the further extension of roots. As mounds form, subsequent pools form around them.

Hydrophytic vegetation, aka hydrophytes, are plants specifically adapted to tolerate living in saturated soil conditions.

Soils are extremely valuable in properly identifying and delineating wetlands. An understanding of how inundated conditions affect soils can help distinguish between the two.

Here is an example of upland soils. This profile is about 8 inches deep and reflects a thin organic layer of decomposed plant material in the top inch or two. Below the organic layer, the A soil horizon begins which is a mineral soil layer. The depth of the organic layer is the main distinction between wetlands and non-wetlands. Below the A horizon, serval inches down which may not be apparent in this sample, lies the B horizon, another mineral layer. These A and B layers are rich in metals and other nutrients that play a part in pedogenesis, or the formation of soil, which takes several hundreds if not thousands of years. This soil is fairly bright in color indicating the presence of oxidized iron which contributes a warm brown/orange hue. The texture is fairly coarse with lots of rocks and gravel. This soil is likely a loam or sandy loam

Conversely, wetland soils exist under anaerobic conditions due to the presence of water and soils of a different composition and texture form. The lack of oxygen prevents proper decomposition of organic material which simply accumulates at the surface in the organic (O) layer. To be considered a wetland the organic layer must be several inches thick before reaching the A layer. The organic layer is typically dark, smooth, mucky, and almost greasy in texture. It is typical to find partially decomposed plant matter here, which provides some texture. Other redoximorphic features can be found such as a gleyed matrix, seen in the picture to the left. In the absence of oxygen, many compounds become reduced to a different state. In the case of iron, the oxygen gets stripped by the water producing these washed-out gray pockets. You can see along the water table there are some pockets of bright orange oxidized ferric ion that has reduced to a dull gray ferrous ion. These are important indicators of wetland soils.

The greater wetland area around Weymouth Great Pond is predominantly surrounded by medium to high density residential as well as significant commercial, industrial, transportation, and urban development. Of particular importance is the utility infrastructure that runs directly through the wetland, depicted in dark gray.

Integrating the information from the elevation and land use map, it can be concluded that a significant amount of urban runoff ends up in this large interconnected wetland. There is substantial residential development along the wetland perimeter not only around the study area, but all the wetlands surrounding the pond, and the actions of the homeowners may directly impact the quality of this forested swamp and water body. More concerning, however, are the areas of commercial, industrial, and urban public/institutional development in close vicinity. There is even a large utility power station right across the street from the study area and adjacent to the Great Pond. These highly developed areas are high in impervious surfaces due to roads and building with heavy traffic that risk directing pollutant runoff towards this complex wetland, ultimately affecting the health and quality of the drinking water and any other downstream riparian systems. The ecosystem is also at the edge of its watershed boundary implying that pollutants have a long distance to travel and accumulate before discharging into the bay at the location of Great Esker Park and Bare Cove Park. These precious coastal marsh habitats provide an integral habitat for a variety of fish, invertebrates, and birds. These parks are valued areas of recreation for the community and greater awareness must be spread about the upstream activities that may affect the few natural areas remaining among the urban sprawl.

The health of a watershed begins at the source. Actions can be taken by members of the community to improve not only the quality of the drinking water but also the aesthetic and recreation of wetlands and water bodies.

On an individual level, citizens can avoid using fertilizer, herbicide, and pesticides on their lawns especially along the slope of the wetland. Animal waste should be picked up even in your own yard and littering/dumping trash should be refrained from. (It was sad how much litter I found during my survey). These actions prevent the quantity of synthetic nutrients from entering the waterway which can lead to eutrophication events and harmful algae blooms, making it more laborious to treat. Homeowners can also plant more vegetation to serve as a riparian buffer for stormwater to filter through.

On a community level, a combined effort can pressure local government to create stricter emission/pollutions guidelines for businesses and industry. Furthermore, local government can provide incentives like subsidies or tax breaks for those who follow guidelines and best management practices. Littering and dumping trash should be penalized and more strictly enforced.

With a greater understanding of the interconnectivity of the water cycle, citizens may gain a greater appreciation for their resources and a greater sense of care to preserve them. By taking actions to aid in the health and quality of overlooked wetland ecosystems like this forested swamp, the community can only benefit from cleaner water, lower cost of water treatment, and healthier open spaces.

Thank you.