Report to the Fund for the Preservation of Wildlife

May 7, 1984

The Fund for Preservation of Wildlife and Natural Areas

1 Boston Place

Boston, MA 02108

Dear Sir:

This report reviews the current conditions and observations at Foster's Pond and suggests programs to improve and maintain the water quality of the pond. The significance of phosphate as a water pollutant and the relationship between phosphorus loads and water quality responses in water bodies is discussed. Physical, Chemical, and Bacteriological data is provided to be used as a baseline for future reference.

In Foster's Pond the euphotic zone reaches the bottom and there is minimal temperature difference throughout the water column. Layers of soft sediment underlie shallow water and there is a high aquatic plant production - an extremely eutrophic pond.

The softness of the sediment suggests that the pond is in the late stages of eutrophication and has been rapidly filling in. In a pond where sediment builds up more slowly one would expect a more compacted sediment with less nutrients available for re-circulation into the water. How rapidly the filling-in will continue is difficult to predict because as the water becomes shallower its flow will be accelerated and the increased speed may help slow further deposition of the soft sediment.

Foster's Pond has no thermocline and no separate, colder, anaerobic bottom layer. This condition seems to add to the problem in the following way:

When a water body becomes so shallow that no thermocline develops in the summer and no stratification develops, a reasonably windy day may start enough water circulation that nutrients (including phosphate) are picked up from the sediment and re-introduced into the productive surface layer of the pond much as in a fall overturn. Friction of the sustained wind blowing across the water surface moves the surface water to one side where it sinks, moves across the bottom, and picks up nutrients from the sediment layer. This condition allows the entire water layer to circulate over a very nutrient-rich sediment layer, and nutrients from the sediment are distributed throughout the pond. This exchange plays a major role in making phosphorus available for algae and contributes, therefore, to eutrophication.

There are several chemical elements needed for plant growth. Most are present at a level more than sufficient to support plant life. Carbon is provided by CO₂ from the atmosphere, and from decaying vegetation. Calcium, magnesium, and sulfate are normally present in abundance from mineral strata in contact with the water. The micronutrients are only required at the parts per billion level. Thus, nutrients likely to be limiting are the fertilizer elements, phosphorous , nitrogen, and potassium.

Apparently, at Foster's Pond phosphorus is the limiting nutrient responsible for the excessive eutrophication. Consequently, the key to the control of the excessive fertilization is control of phosphorus from external and internal loads.

The following program for Foster's Pond water quality is suggested:

1. Evaluate the nutrients in the pond over a period of at least one year. Sample at various locations and depths to establish a correlation between nutrient content and biological productivity.

2. Test of a “jar test” scale the addition of aluminum sulfate to combine with and thus inactivate phosphorus. Careful testing and planning is necessary in this approach.

3. Consider removal of phosphate, the limiting nutrient in the system, by removing the major phosphate reservoir - the sediment, by dredging.

Additional data on orthophosphate and total phosphate is required prior to this type of program.

4. In the summer recreational season, initiate a bacteriological testing program - analyze for Total and Fecal Coliform on a weekly basis.

5. Continue the “Action plan for the Cleanup of Foster's Pond.”

I hope this information helps you.

Cordially,

John J. Pollano