The water quality of most of our saltwater ponds has declined noticeably in the last generation as a result of growth on the Vineyard and beyond. About 64% of the Vineyard’s land area is made up of watersheds that drain into nitrogen-sensitive coastal ponds, either through runoff or groundwater flow. Excessive nitrogen over-fertilizes aquatic plants, resulting in odorous, unattractive ponds devoid of eelgrass, fish, and shellfish, adversely affecting the Island's valuable tourist industry and coastal property values. There are three main sources of excessive nitrogen in our coastal ponds:

Atmospheric
Rain deposits nitrogen from polluted air, largely from upwind coal-fired power plants and other industrial sources off-Island. (On average, this represents about 29% of nitrogen pollution, although the proportions vary considerably among watersheds.)

Wastewater
By far the greatest amount of "manageable" (i.e. non-atmospheric) nitrogen pollution in our ponds comes from urine in wastewater. About 90% of Vineyard homes have their own on-site Title 5 septic systems that deal well with pathogens but have little impact on nitrogen. (Accounts for about 62% of nitrogen pollution.)

Fertilizer
Much of the nitrogen-based fertilizer used on lawns, gardens, and farms ends up in the water table where it drains into ponds. (Accounts for about 9% of nitrogen pollution.)

What Can We Do?

The MVC has worked for many years with towns, pond associations, and the MA Department of Environmental Protection (DEP) to gather and analyze data and identify the best ways to deal with this challenge.

The Massachusetts Estuaries Project (MEP) has analyzed most Vineyard coastal ponds in order to establish safe levels of nitrogen loading and identify the most cost-effective ways to meet these levels. DEP then establishes the Total Maximum Daily Load (TMDL) for each pond. Some ponds are already over these limits, others are projected to exceed their limits with future development, and others can accommodate all projected growth without exceeding their limits.

We need to identify the lowest-cost ways to reduce nitrogen-loading so that the ponds meet their TMDLs, and continue implementation. Aside from benefitting the ponds, this will help avoid measures imposed by the DEP or courts that may be more costly or conflict with other community objectives. The following are possible ways to deal with the manageable portion of excessive nitrogen:

Wastewater Treatment
Nitrogen can be reduced at the source with techniques such as composting or urine-separating toilets. Wastewater can also be treated to reduce nitrogen, such as with sewering and centralized treatment that removes about 95% of the nitrogen, or DEP-approved on-site innovative alternative septic systems that remove about 40-50% of the nitrogen, compared to a standard Title 5 system. Both methods are costly to install and maintain.

Tidal Flushing
Improving water circulation to the sea with widened inlets or more pond openings can help dilute nitrogen in a pond.

Landscaping and Fertilizers
A number of landscaping techniques can be used to reduce nitrogen, including reducing the use of fertilizers and designing properties so the effluent from septic systems passes through vegetation where it is converted into gases taken up in the atmosphere.

Aquaculture
Growing oysters and other shellfish can reduce nitrogen in a pond, although this is not yet recognized by DEP as a method for receiving nitrogen credits.

Growth Management and Nitrogen Limits
Board of health and zoning regulations can be used to limit the nitrogen generated in nitrogen-sensitive watersheds in the future, such as by limiting the number of bedrooms or how much nitrogen a new project can generate, and requiring that nitrogen generated in a critical watershed is offset with nitrogen reduction elsewhere in the same watershed. Land acquisition for open space also reduces potential nitrogen sources.