By Don Williams

Thanks to the efforts of the Herring Ponds Watershed Association (HPWA), UMass Dartmouth SMAST, and the Plymouth Department of Energy and Environment partners, the Permeable Reactive Barrier (PRB) was installed in the Carters River under the Carters Bridge Road bridge on Wednesday morning, June 26, 2024. The PRB will remain in place for all of July and August to remove some of the phosphorus from the Carters River and stop its entry into Great Herring Pond. The hope is to reduce the phosphorus load thereby reducing the chances of a harmful cyanobacteria bloom.

The UMass Dartmouth team headed by Ed Eichner conducted a Water Quality Study following a devastating 2020 toxic cyanobacteria bloom that shut down Great Herring Pond for 2 summer months, and a less serious 2 week bloom in 2021. The study led to the 2022 report that identified phosphorus as the cause of the blooms, and Little Herring Pond as the single largest source of that phosphorus. The report was funded by your dues and donations and by the Town of Plymouth.

The partnership jointly determined that the innovative experimental installation of a PRB in Carters River was the best short-term solution to remove phosphorus. Wednesday’s installation came only 16 months after the report was issued – a very quick turnaround. UMass Dartmouth will take weekly samples to determine how much phosphorus has been removed.

In addition to helping fund the 2022 report, the Plymouth Department of Energy and Environment, most notably Department Head David Gould, Kim Tower and Mark Brulport, have been instrumental in moving the permitting of this important PRB project forward and subsidizing testing

The active ingredient is polonite which was tested by UMass Dartmouth and found to be very effective in absorbing phosphorus and safe for fish. It was sewn into mesh bags then put inside the black plastic, re-purposed oyster crates seen in the first picture below.  The crates were then fastened to PVC pipes that slid under the bridge as seen in the second and third pictures.  Finally, a fence line was installed to direct the herring to their return route to the sea.  This can be seen in the fourth picture.

The installation is important for 3 reasons:

1. It might significantly reduce the amount of phosphorus in Great Herring Pond.
2. It is the first time that a PRB has been placed in a stream, so we might have a new method for removing phosphorus in our toolbox.
3. If it is effective, it could work for other watersheds with a similar situation.

Thanks to the work of the partnership, we will know how effective this experimental technology will be for removing phosphorus sometime this fall.  Thanks to everyone who participated! 

Additional images of installation provided by Martha Sheldon