1970s, 1980s and Early 1990s
Phosphorus and Nitrogen Problems
in the Six Ponds Area
In the 1970s the Town of Plymouth commissioned year-long detailed studies of the water, flora and fauna in 41 ponds in Plymouth. In connection with these studies, the investigators constructed a eutrophication index for all of these ponds to evaluate the overall healh of ponds. All of the ponds in the Six Ponds area were included in these studies. There were follow-up studies of a couple of our ponds in the 1990s.
This eutrophication index considered factors such as phosphorus and nitrogen levels, algae growth, aquatic plant growth, dissolved oxygen levels, and other factors.
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Baseline Studies of 2 of the Six Ponds
Full Reports of 2 Baseline Studies from the 70s and 80s
Halfway Pond
Halfway Pond
Two of the Six Ponds stood out as being ultra-eutrophic-- Halfway Pond ranked 38th and Little Long Pond ranked 30th on the index (1 is best and 41 is worst).
A consistently high level of Phosphorus was identified as a major reason for the poor condition of Halfway Pond, and nitrogen was identified as a contributing factor. Both high phosphorus and high nitrogen levels were identified as major reasons for the poor condition of Little Long Pond. In both studies, the authors discussed many different actions that could be taken to improve the health of these ponds.
With respect to Halfway Pond, they argued that stopping nutrients from flowing into the pond from the few year-round homes near the pond (from use of phosphate-rich products and from septic systems that may need replacement) and from the cranberry bogs around the pond were both essential to improving the situation. They also argued that, since the flushing rate was very high (about 39 days), the pond could basically cure its own problems over time.
On the other hand, the authors concluded that it would be far more difficult to improve the health of Little Long Pond even though this pond too was flushed rather quickly. Over a few years prior to 1979, quite a number of homes had been constructed around the pond. In addition, over the preceeding 10 to 15 years, a large number of homes had been built in Plymouth Estates on higher slopes above the pond. The authors stated that the soil surrounding the pond is not able to keep nutrients from flowing into the pond from the septic systems, lawns, driveways and roads associated with homes constructed on the slopes surrounding the pond. They argued for active management of human impacts by instituting extensive measures ranging from water conservation to bans on products containing phosphates to catch basins for runoff to replacement of septic systems with far more advanced technologies to zoning restrictions and laws prohibiting nutrient pollution. They did not seem very hopeful of seeing success in these regards.
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Baseline Studies including the Other 4 of the six ponds
Our other ponds ranked better (1 is best and 41 is worst) on this eutrophication index-- Long Pond 1st; Bloody Pond 5th; Gallows Pond 7th and Round Pond 11th.
It should be noted, however, that the investigators were concerned about the adverse impact of Little Long Pond on Long Pond since it empties billions of gallons of water each year directly into Long Pond.
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Living Lakes Liming Experiments
These studies were conducted for the Conservation Commission of the Town of Plymouth by Living Lakes, Inc.
The lime applications did substantially raise the pH level and alkalinity of the water, and the research indicated some improvements in the viability of the fish populations.
It should be noted, however, that the positive effects of liming last just a few years. Data collected a few years later and data collected more recently confirm that both of these ponds quickly returned to pre-application pH and alkalinity levels consistent with the other ponds in this area.
Since the benefits of liming are rather temporary, it raises questions regarding the efficacy of doing this at all considering that as much as 2 tons of lime per acre may be required depending on depth and the fact that the benefits may be rapidly flushed from spring-fed or inlet-fed ponds with substantial outlets.
It should also be noted that liming may promote the growth of algae by increasing the availability of phosphorus.