On the evening of Wednesday, July 29, the Vineyard Conservation Society presented a public information forum titled Ponds in Peril. Several speakers analyzed problems in various Island ponds leading to declining water quality and pond health.
Throughout the evening, emphasis was focused on nitrogen excess as a primary cause of eutrophication and the consequences thereof. Sources of nitrogen were identified as resulting principally from human presence and activities.
Residential development with septage is a major source of nitrogen. Probably unknown to some of the audience is the fact that Title V septic systems may remove bacteria but not nitrogen. (Not mentioned is the fact that mutiple enteric viruses are also not removed.)
With this background, strategies for abatement, including regional sewers with denitrification, introduction of several types of shellfish, limiting nitrogen fertilizers, etc,. were discussed.
Perhaps the most controversial were suggestions for limiting land development by new and more stringent zoning regulations.
There was no discussion of better enforcement of existing regulations concerning distance of development from wetlands, although these rules would have little effect on nitrogen in the groundwater that is making its inexorable way to ponds at the rate of one foot per day. These distances are of importance, however, in preserving the buffer effect of natural vegetation in helping with nitrogen removal. So-called “enhanced on-site septic systems” have a disappointing record of effectiveness and acceptance by homeowners.
Overall, it sounds wonderful if these remedial suggestions can be implemented.
Earlier in the afternoon of that same day, the Edgartown conservation commission met to consider a building application for development of property on the immediate shore of Sengekontacket Pond. Plans indicated location of a building and septic field less than 100 feet from the wetland at the edge of the pond. This property on the shore of Sengekontacket is immediately adjacent to Felix Neck preserve, sharing a common ecosystem. Regardless, this application was approved.
In spite of all the good suggestions and advice in the later VCS forum, we have here the reality of a failure to limit nitrogen contribution to groundwater making its way to the pond.
Of course, the expression is “it’s only one more house.” However, this property should never have been classified as a building lot in the first place. But what of the other properties in the community more remote from the pond, and those directly contiguous to the pond shore?
Each of these new “one more house” developments adds its own nitrogen to the groundwater. Clearly, community-wide sewer is indicated. Zoning for larger lot size would also help some to reduce the nitrogen load to either regional or on-site systems, and with surface runoff.
In the case of Sengekontacket, dredging of channels and between bridges can, and perhaps will, improve flushing.
Dr. James A. Riley