Over the past year, a considerable number of water samples from ponds in the Six Ponds area have been analyzed by EnviroTech Laboratories of Sandwich, MA. These analyses give information about nineteen different chemicals and minerals found in the water. The Town of Plymouth has paid for many of these analyses, the Six Ponds Association has paid for quite a few analyses, and individuals have paid for additional analyses.
The chart below summarizes the results obtained for just one of these indicators of the “health” of these ponds, and some portions of this picture for Total Phosphate levels are very disturbing.
The box plots below show the range of values for half of the water samples from each pond. The line across each box indicates the middle, or median, value of the readings for each pond. Whisker lines extend from the box to the highest and lowest readings with the exception of instances where extreme readings are shown outside of this range.
Total Phosphate (P) mg/L
Twenty-one water samples taken over the past nine months from a variety of Halfway Pond locations have been analyzed by EnviroTech Laboratories. In twenty of these samples, the Total Phosphate (TP) level reached or exceeded a critical eutrophic level of .03 mg/L. The TP levels ranged from slightly higher than the critical level to nearly 5 times the critical level. The median was nearly 3 times the critical level. The causes for such high readings need to be uncovered. The serious pond weed problems and the toxic algae blooms which made the pond largely unusable this past summer are visible signs that there are problems to be solved.
By way of contrast, one sample was taken from the clear spring-fed inlet to Halfway Pond near where the water runs through a pipe under a dirt road around the edge of the pond revealed a remarkably different situation. In this sample the TP level was less than 1/4th the critical level. However, in the cove just on the pond side of this dirt road, the TP level in samples ranged from 1.5 to 3 times the critical level.
Analyses of eight samples taken from Little Long Pond over the past nine months have shown TP to consistently exceed the critical eutrophic level of .03 mg/L. The TP levels ranged from 2 times to 7 times the critical level. The average TP level was more than 3 times the critical level. While the Phosphate situation at Halfway Pond is bad, the situation at Little Long Pond is worse. The algae problem at Little Long Pond is a visible sign that there are problems to be solved.
An autumn Plymouth-wide sampling of nineteen ponds revealed that only one other pond had higher TP levels than Halfway Pond and Little Long Pond. This other pond has been known to have serious pond weed and algae problems for many years.
While the median TP reading for Bloody Pond was nearly 3 times the eutrophic level, several readings were far below the critical level and a few were much higher than the critical level. This situation bears close examination of possible causes for such a wide range of readings. Moreover, it is very likely that problems at Bloody Pond will get worse unless the causes are discovered.
The situations at Gallows Pond, Long Pond and Round Pond were fairly good with respect to TP readings. The median readings were below the critical level, and the ranges of these readings were quite narrow. On the other hand, each of these ponds had at least one TP reading which was 3 to 6 times the critical level. Again, possible causes for a few very high reading need to be investigated further.
Clearly, there are signs that the quality of the water in our ponds is deteriorating. There are signs that the stuff flowing and leaching into the water is getting ahead of Nature’s ability to recover from what we are doing to it.
As we learn more about other aspects of the water quality in our ponds, this information will be brought to your attention.