RiverWatch Water Quality Monitoring Data for 8-29-17
Bacterial Concentrations Low for Second Year in a Row
The North and South Rivers Watershed Association has been sampling water quality at 10 sites along the North and South Rivers for 24 years to evaluate the health of the rivers. This volunteer-driven program monitors the rivers every other week from the beginning of June to the end of August. We monitor for both swimming and shellfishing standards, each of which have specific concentrations of bacteria that are considered safe for humans. In 2017 we switched from testing fecal coliform at all sites to focusing on the areas where shellfish could be harvested (both in conditionally open areas as well as estuarine areas that still support shellfish but are prohibited). We expanded our enterococcus testing to include all ten sites, since that is the current standard for swimming in brackish and marine waters.
This summer, we found concentrations of enterococcus bacteria exceeding the swimming standards on two sampling dates out of seven. Willow Street exceeded the single sample standard of 104 colony forming units (cfu) per 100mL on both June 29th and July 17th, and Washington Street Bridge exceeded the standard on July 17th. On June 29th, a small amount of rain (0.05 inches) had fallen in the previous 48 hours, which may have contributed to the elevated concentration on that date. However, on July 17th the most recent rain was on the morning of the 14th (0.1 inches), which could indicate a longer effect of rainfall on stormwater contributions and therefore bacterial concentrations. That said, 0.41 inches of rain fell in the 48 hours prior to the June 14th sampling date, which elevated concentrations at all sites but not above the swimming standard.
Three sampling sites in our rivers are located within seasonally opened shellfish beds. Currently the shellfish beds in the North and South Rivers are opened for recreational harvest between November 1st and May 31st. Among these three sites, both North River Marine and Damon’s Point exceeded the single sample standard of 14 cfu/100mL on June 14th and July 17th. The former was likely due to stormwater and rainfall. As mentioned above, more analysis is needed to determine if rain in the 48-36 hour preceding period could affect bacteria concentrations in the rivers. This year and last year have had the lowest concentrations of bacteria in these shellfishing areas within the past decade, based on geometric means of fecal coliform data over each summer of sampling. This trend is also reflected in the enterococcus data from these sites.
Over the years bacteria counts have diminished in the rivers due to Title V septic improvements, implementation of town sewerage and improved treatment and minimization of stormwater runoff – all of which the NSRWA has advocated for using these data to make the case for reducing pollution sources.
Thank you to the fourteen dedicated volunteers who helped with this program this year. If you are interested in volunteering next year please contact Sara Grady at firstname.lastname@example.org or (781) 659-8168.
Thank you to the Norwell Women’s Club for sponsoring one week of water quality testing!
NSRWA Executive Director Samantha Woods accepts a $500 donation from Abby Gray, President, and Tracey Cooke, Treasurer, of the Norwell Women’s Club. The donation helps to support the RiverWatch Water Quality Monitoring program and will be used to help pay the costs of water sample analysis. Thank you Norwell Women’s Club! If you would like to sponsor a week of testing, contact Gabriela Silva at email@example.com.