Sources of Nitrogen in an estuary such as Sengekontacket

Sources of Nitrogen in an estuary such as Sengekontacket

Old and New Nitrogen

Nitrogen is a common gaseous element that has the symbol N in the periodic table.  Nitrogen comprises about 78% of Earth’s atmosphere. Nitrogen is essential for plant growth and all life.

Nitrogen fixing bacteria in the soil remove free nitrogen from the air and form the nitrogen compounds that plants need to grow. These compounds recycle through plants, animals, water, and soil.  Other kinds of bacteria return the nitrogen to the soil and air.  This circulation of nitrogen is called the nitrogen cycle.

For millennia the amount of fixed or “old nitrogen” was limited to the amount fixed by bacteria in some legumes and other plants and by lightning.  Crops were fertilized with manure or compost.

In the last several decades the amount of fixed “new nitrogen” has nearly doubled.  People learned how to capture atmospheric nitrogen and convert it in an industrial process for use in fertilizers, medicines, and other things. 

Coal, natural gas, petroleum, and other carbon based fuels formed over millions of years from once living things.  When these fossil fuels are burned to generate electricity and in heating, manufacturing, and transportation their nitrogen stored for eons is released to the air with exhaust gases.  These “new nitrogen” compounds are a major cause of global warming, acid rain, and pollution of coastal waters.

Excess nitrogen enters pond waters and stimulates the growth of algae, simple plants that have no roots or flowers.  Algae blooms form dense floating mats  that deplete oxygen in the water and decrease the amount of sunlight reaching submerged aquatic vegetation, such as eelgrass, a nursery for finfish and shellfish.  Water quality is degraded, becomes turbid and smells unpleasant.

Since our founding, the Friends of Sengekontacket has funded extensive research to learn more about nitrogen in the pond. In 2010 the results of the Massachusetts Estuaries Project will be available. The study will determine the extent of nitrogen loading (excess nitrogen) and will recommend the maximum amount of nitrogen that Sengekontacket Pond can safely absorb in order to maintain good water quality (the Total Maximum Daily Load or TMDL).

Studies of Sengekontacket Pond funded by or participated in by Friends of Sengekontacket, Inc.

Studies of Sengekontacket Pond funded by or participated in by Friends of Sengekontacket, Inc.

Sources of Nitrogen

Water Body Surface Area 

This is acid precipitation falling directly into Sengekontacket Pond.  Acid rain is the popular term for wet and dry deposition.  This results from the burning of fossil fuels in power plants, industries, and internal combustion engines.

Impervious Surfaces

Hard surfaces such as paved roads and roofs that are not porous.


The nitrogen in fertilizers promotes plant growth, but some escapes to travel with the ground water to our ponds.

WWTF (Wastewater Treatment Facility)

This is a centralized sewage treatment plant such as the Edgartown Treatment Plant.  This is not in the Sengekontacket watershed.

Natural Surfaces

The natural cycling of nitrogen through vegetated upland as well as the natural cycling of nitrogen through the vegetation.


Agricultural lands.


Water carrying dissolved or suspended solids from homes, farms, businesses, or industries.  Wastewater flows into either an on site system such as a septic system, or by pipe from its origin to a distant centralized sewage treatment plant.

The Sengekontacket watershed

The Sengekontacket watershed is a geographic area of land in which all ground water flows to a common body of water. While Sengekontacket Pond is about 750 acres, the watershed comprises over five thousand acres, or 8.2 square miles! It extends from a narrow point near West Tisbury center to Sengekontacket Pond (see map below).

As water drains over the land it carries vegetation, soil and sediment, dissolved materials and pollutants downstream to recipient water bodies, such as Sengekontacket. This is why the use of land for conservation, housing, commercial, farming, golf courses, roads and other development impacts water quality in different ways. Activities in the remote parts of the watershed can affect the groundwater in a matter of months, but the affected groundwater may take decades to reach Sengekontacket Pond.

What You Can Do To Help

The Friends of Sengekontacket, Inc. appreciate the assistance of William Wilcox, Water Resource Planner, Martha's Vineyard Commission, as we researched the subject of Nitrogen.

Saving Sengekontacket

How do we achieve the Total Maximum Daily Loads for nitrogen in Sengekontacket Pond?  There may be a number of strategies, which will restore water quality.

These are:

Ecological Landscaping

Ecological landscaping refers to landscaping that is not dependent on synthetic fertilizers and other petrochemicals used to suppress weeds and insects. In contrast, organic fertilizers enhance long- term plant viability and eliminate the need for frequent applications of synthetic fertilizers.

Ecological landscaping minimizes turf, utilizes native species, many of which are flowering, promotes wildlife habitat, and emphasizes the understory.  This is equally as prominent as well as the vertical tree canopy and horizontal lawn layer.  Overall ecological landscaping requires less watering and provides more diversity and interest on the land.  Some term this relationship between the built and natural environment that is very different from suburbia a “Vineyard landscape.” 

Native plants thrived on the Vineyard for thousands of years.  Bayberry, huckleberry, sheep laurel, bearberry, shadblow, and sweet pepperbush are just a few examples of those adapted to the Vineyard’s soil and climate conditions and require little costly maintenance.  They also are conducive to greater enjoyment of Vineyard wildlife.  Native plants provide food, water, safety from predators, and breeding and rearing areas beneath the canopy.  These understory and shrub layers attract a myriad of birds, butterflies, colorful moths and damsel and dragonflies.

Buffer zones between the managed landscape and the pond are an important component of ecological landscaping. Native grasses and plants control erosion and filter pollutants before they enter the pond and degrade water quality.  Also smaller areas of green lawn are less attractive to Canada geese whose droppings are a source of nitrogen.

Local Government Initiatives

Towns need to identify their role in protecting Sengekontacket Pond. Actions could include managing potential growth in the watershed.  This could include zoning changes resulting from the development of a comprehensive nitrogen control program that identifies key parcels of land to be conserved in highly nitrogen sensitive areas within the Sengekontacket watershed. New taxes may be needed to support the acquisition of open space and the expansion of sewers in densely populated areas. 

Collaboration between towns such as the recently established Joint Sengekontacket Committee with representatives from Edgartown and Oak Bluffs as well as partnering with federal and state environmental agencies, the Martha’s Vineyard Commission, and non- profit organizations such as the Friends of Sengekontacket, Inc. is essential. Towns can also promote the use of public transportation and alternate energy systems that are not fossil fuel based such as wind turbines and solar panels in public and other buildings.  

Educate residents about the capacity, technology, limitations, and cost relative to nitrogen removal of various kinds of wastewater treatment systems: On site systems, after the effluent has gone through the leaching field and passed through groundwater, remove about 25% of nitrogen. Individual nitrogen management septic systems can remove up to 50% of nitrogen flushed down the drain. The upgraded Edgartown Wastewater Treatment Plant removes between 85% and 95% of nitrogen.

Oyster Aquaculture

A novel biological solution to nitrogen removal in coastal ponds being implemented now in other states may not involve expensive wastewater treatment systems but oyster aquaculture or gardening.  Shellfish are filter feeders.  Adult oysters particularly filter between thirty and fifty gallons a day.  They consume the absorbed nitrogen in the algae and phytoplankton that have proliferated because of the excess nutrient enrichment.  In this way, oysters help to restore water clarity.  More sunlight can then penetrate the water and eelgrass re-colonizes.  Oysters deposit the nitrogen in the bottom sediment where specialized bacteria convert it to a gas and return it to the atmosphere.

The Massachusetts Department of Environmental Protection (DEP) provides constructive advice of individual citizens on ways to improve Sengekontacket water quality.