OPET Designs and Conducts Study of Oyster Pond
By Peter ValtinAt the August 3 meeting of the Board of Directors it was decided that OPET should conduct a study of salinity, dissolved oxygen and vegetation density of Oyster Pond, focused on clarifying basic information about the pond during the annual alewife reproductive cycle.
The spring and summer of 2003 were notably wet. At the same time, the profile of Trunk River, Oyster Pond's outlet to Vineyard Sound appears to have risen. Also, the Falmouth Shellfish Warden, Paul Montague, raised the level of the pond's control weir, during the alewife in-run, from about March to some time in June. As a likely consequence of some or all of these factors (and more - the pond has a nitrogen loading problem), the volume of fresh-water vegetation increased dramatically this summer over what it had been in recent years.
The Board is concerned about the quantity of fresh-water vegetation for a number of reasons. In the not very distant past, this vegeation overwhelmed the pond, creating a eutrophic environment hostile to all kinds of verteberates, including herring and Homo Sapiens. In 1982 for instance, the pond literally stank as large quantities of vegetation and algae died off, leading to very low dissolved oxygen and high hydrogen-sulfide levels. And it is again the case, right now, that hydrogen-sulfide off-gassing is apparent when sediments in the north end of the pond are disturbed. Also the smell of sulfur has been noticeable this fall at the Trunk River pedestrian bridge during any low tide.
Despite the Board's concern, it is not altogether clear what to do about the situation. Discussions about how to manage the pond to a preferable level of vegetation quickly bog down in questions like, "How saline is the pond during the alewife run?" and, "to what extent is the vegetation in the pond affected by salinity?" The Falmouth Pond Watchers, among others, have been sampling Oyster Pond for years - but not during the alewife run!
To begin to address the lack of data on these qustions, the Board asked Bill Kerfoot to design a study, which he graciousuly volunteered his time to do.
Bills' design calls for a triangular sampling grid in the north end of the pond, with the corners of the triangle located at the Treetops dock, Mosquito Creek inlet, and a point somewhat south of the center of the north basin of the pond. [See Fig. 1] Samples will be taken monthly throughout the year. Salinity and dissoved oxygen measurements will be taken at various depths at each sampling point. At each sampling point, a vegetation density sample will be taken. The vegetation density will be measured by (a) estimating the number of strands of vegetation per square meter visible form the surface and (b) using a Secchi disk to measure turbity. Each set of ...