2019 RiverWatch Water Quality Summary
Bacterial Concentrations Reflect Influence of Stormwater
The NSRWA has been sampling water quality at 10 sites along the North and South Rivers to evaluate their health for 25 years. RiverWatch, a volunteer-driven program, monitors the rivers every other week from the beginning of June to the end of August. This year we were able to sample the shellfish growing areas weekly thanks to a MassDEP Watershed Monitoring Grant. 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 four of the six full sampling dates. These higher counts were at either Washington Street Bridge or Willow Street Bridge, the two sites highest in the watershed, with the exception of the July 24th sampling round, during which seven out of ten sites exceeded swimming standards after 1.8 inches of rain.
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, North River Marine was above the standard on 4 out of 16 weeks sampled, Damon’s Point was above the standard 5 out of 16 weeks sampled, and the North River Mouth was only above the standard on one date out of six. Counts being over the standard did not correlate with rainfall, although the magnitude of the counts did.
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.
This program was funded by a MassDEP Watershed Monitoring Grant, the Norwell Women’s Club, an anonymous donor, and members like you!
Thank you to the dedicated volunteers who helped with this program this year. If you are interested in volunteering next year please contact Sara Grady at email@example.com or (781) 659-8168.
On July 30th we had another sampling of just the shellfishing growing areas, after having had no rain in the previous 48 hours. Without rain, we expect relatively low bacterial counts compared to a day with lots of rain. A comparison of dry versus wet sampling days shows the impact that stormwater has on bacterial counts. When it rains, surface runoff occurs. This is when the land cannot absorb more water, and that water flows into our streams and rivers, bringing in the bacteria from the surrounding area. On a wet sampling day, we expect to see higher bacteria levels than a dry sampling day.
On July 30th 3 of the 4 sites exceeded the shellfishing threshold for fecal coliform of 14 cfu per 100 mL – Driftway Park (130), Damon’s Point (16), and Julian Street Bridge (25). None of the sites exceeded the Massachusetts limit for swimming. Compared to last week when the sampling occurred after almost 2 inches of rainfall in the previous 48 hours, all 4 of the shellfishing sites saw decreases in both types of bacteria. Please keep in mind that shellfishing for the North River Marine, Damon’s Point, and the North River Mouth are closed until the Fall, while the Driftway Park and Julian Street Bridge sites are closed indefinitely.
The July 24th water quality sampling showed how water quality is influenced by rain bringing pollution into our rivers from the land. After having received about 1.8 inches of rain on July 22rd and into the 23rd, we saw significant increases in bacteria counts at most sites sampled, with the exception of the mouth of rivers (closest to the tidal influence which dilutes and flushes out the bacteria). The last time we sampled with over an inch of rain was June 11th, which had the highest levels of bacteria of the season.
Out of the 10 spots we tested for enterococcus, 7 of them exceeded the Massachusetts swimming standard of 104 cfu (colony forming units) per 100 mL. The swimming symbols in red on the map and the numbers on the chart highlighted in dark grey are those that exceeded the swimming limit on July 24th. Only 3 spots met the swimming standards: the Scituate Wastewater Treatment Plant (which discharges into the Herring River, not that you would want to swim there), the North River Mouth, and Damon’s Point.
We tested 5 sites for fecal coliform, the bacteria used for shellfishing standards, and 4 of them were significantly over the Massachusetts shellfishing standard of 14 cfu per 100 mL. The shellfish sites near the mouth of the rivers on the map are red (closed) because the Division of Marine Fisheries closes the North and South Rivers to shellfishing between May 31st and October 1st annually. They do this because the water quality during this timeframe does not meet the standards frequently enough.
The July 24th samples had the highest bacterial counts we have seen this season by far. Scituate’s Driftway Park’s previous season high for enterococcus was 52 cfu, and increased drastically this week to 500. Similarly, the Norwell Canoe Launch (Union St. Bridge), enterococcus came back at 310 cfu this week, while its previous high was 43.
Can I swim or shellfish?
As we have noted before, shellfishing is closed from May 31st to October 1st regardless of our sampling. As for swimming, we would advise waiting 24–48 hours after a rain event, depending on the tides and where you want to swim on the rivers. Closer to the ocean you can wait a shorter time frame than further upstream. While this sampling event exceeded the standards, this is a “snapshot in time” of the bacteria in the water and doesn’t reflect the regularly clean water in our rivers.
Why are our waters polluted after it rains?
The bacteria in the water increases when the rain falls on developed and paved land, where pollution accumulates from wildlife and domestic animals, and washes into our streams and rivers. This is why it is important to pick up your dog waste, reduce the amount of pavement on your property, and retain water on your land with rain gardens, dry wells and rain barrels. It is also important to support the budgets of our Departments of Public Works to sweep our streets regularly and to clean out stormdrains where bacteria can fester in the heat of the summer.
On July 10th we had another full RiverWatch, and on July 17th we had another sampling of just the shellfishing areas, both of which were on what we consider to be a dry sampling day. Without rain, we expect relatively low bacterial counts compared to a day with lots of rain, like our first week of sampling. A comparison of dry versus wet sampling days shows the impact that stormwater has on bacterial counts. When it rains, surface runoff occurs. This is when the land cannot absorb more water, and that water flows into our streams and rivers, bringing in the bacteria from the surrounding area. This is why on a wet sampling day, we expect to see higher bacteria levels than a dry sampling day.
On July 10th, we visited our normal ten sites listed above, testing for both fecal coliform and enterococcus, the bacteria monitored for shellfish and brackish or marine swimming standards, respectively. For enterococcus, only 2 of the 10 sites exceeded the Massachusetts threshold for swimming. The standard for enterococcus is 104 cfu (colony forming units) per 100 mL; the Washington Street Bridge and Willow Street Bridge had 220 and 120 cfu per 100 mL, respectively. Out of our shellfishing sites of interest, on July 10th 3 of the 5 spots exceeded the Massachusetts shellfishing standard for fecal coliform of 14 cfu per 100 mL. Driftway park (25), Damon’s Point (17), and the Julian Street Bridge (38) all surpassed the threshold, while the North River Marine (12) and North River Mouth (2) were below.
On July 17th, the bacteria levels were the lowest we have seen all summer. Only 1 of the 4 sites, Driftway Park (24), exceeded the shellfishing threshold for fecal coliform of 14 cfu per 100 mL. None of the sites exceeded the Massachusetts limit for swimming. Compared to last week, all 4 of the shellfishing sites saw decreases in both types of bacteria, which was great to see. Please keep in mind that shellfishing for the North River Marine, Damon’s Point, and the North River Mouth are closed until the Fall, while the Driftway Park and Julian Street Bridge sites are closed indefinitely.
This week’s RiverWatch was another dry weather sampling day, so we expected our results to follow a relatively similar pattern to previous dry weeks. Since this week was a reduced RiverWatch, only four sites were sampled, but it was interesting to look at how this week’s data compared to previous weeks. We gather data for these four sites every week, as they are our areas of interest for shellfishing and it is important to monitor them. However, please keep in mind that shellfishing for the North River Marine, Damon’s Point, and the North River Mouth are CLOSED until the Fall, while the Driftway Park and Julian Street Bridge sites are closed indefinitely.
Per usual, we were testing for both fecal coliform and enterococcus bacteria and comparing the results to the Massachusetts standards for both swimming and shellfishing. For the samples collected on July 2nd, 2019, nothing was shocking, but there were a couple points of interest. None of the sites we tested were above the swimming standard for enterococcus. However, three of the four sites were above the fecal coliform standard for shellfishing. Driftway Park, Damon’s Point and Julian Street Bridge came in at, respectively, 63, 15, and 28 cfu (colony forming units) per 100 mL, above the Massachusetts threshold of 14 cfu per 100 mL. Compared to last week’s dry weather sampling, the bacterial count at Damon’s Point was only slightly higher, while Julian Street actually decreased. However, Driftway Park saw a bit of an increase from last week. So far this summer, both the Driftway Park and Julian Street Bridge have been above the acceptable threshold all four times we have sampled them. The higher bacterial counts at these two sites show why they are within the prohibited shellfishing area when compared to the other sites.
By Drew Martin, NSRWA Summer Intern
On June 26, back to our full RiverWatch schedule, we visited the normal 10 sites, again testing for both Fecal Coliform and Enterococcus. For the first time this season, the rain did not join us, nor did it rain in the 48 hours prior. It’s always interesting to look at the relationship between rainfall and bacteria, as, generally speaking, rain leads to higher levels of bacteria. This is not always the case, but it makes sense that when it rains, bacteria is washed into the rivers. The correlation between rain and bacteria is something we will be gathering data on throughout the summer, so it’s very helpful to get days with no rainfall as a comparison.
This week, we had a few spots exceeding the shellfish standard, as well as one spot exceeding the swimming standard. For the sites we test for comparison to the shellfishing standards, Driftway Park, North River Marine, and the Julian Street Bridge all had levels of Fecal Coliform that were higher than the acceptable shellfishing standard threshold of 14 per 100 mL. The Damon’s Point site came in just under the threshold at 13 per 100 mL as did the North River Mouth. Of these sites, only the North River Marine and the North River Mouth site are within the conditionally approved area for shellfishing (Driftway and Julian Street are still classified as prohibited for shellfishing by Mass Division of Marine Fisheries). Please remember that shellfishing is not open again until the fall. For swimming, only the Washington Street Bridge (140 per 100 mL) site just exceeded the Enterococcus limit of 104 per 100 mL. When we see exceedances of the swimming standard, they are typically at the sites farther upstream due to reduced flushing and greater influence of runoff. While the site exceeded the limit it was just over and most likely is safe to swim. This bacteria is likely background wildlife driven. Comparing this week to our last full RiverWatch on June 11th, when it rained a considerable amount, we saw that, in general, less rainfall lead to less bacteria. There were increases in 2 spots, which is interesting, but for the most part, the data for this week’s RiverWatch is typical of a dry weather sampling day.
What a great start to this year’s Riverwatch Water Quality Testing. Accompanied by some wicked rain, a group of seven NSRWA members and volunteers went to ten different sites around the watershed on June 11th. Those ten sites are Washington Street Bridge, Cornhill Lane, Union Street Bridge, the Scituate Wastewater Treatment Plant, Driftway Park, North River Marine, Damon’s Point, North River Mouth, Julian Street Bridge and Willow Street Bridge. At each location, we carefully collected water quality samples that were to be used to gather data on enterococcus and fecal coliform, two common bacterial standards of water quality. At each stop, we used a meter to determine levels of dissolved oxygen, conductivity, salinity, and temperature. These values will be gathered each week throughout the summer, as well as compared to previous year’s numbers, in order to determine the health of our waters. For example, a test like dissolved oxygen will tell us how much breathable oxygen is in the water, which has a direct impact on the health and wellness of the wildlife there.
After almost three hours of gathering data and samples, we dropped off 11 bottles to be analyzed at Morrell Associates in Marshfield. Once they ran their tests and sent us the data, we compared it to the state’s swimming and shellfishing standards. For enterococcus, only one site, the Willow Street Bridge in Marshfield, exceeded the swimming standard. We typically see elevated bacteria at the upper watershed sites after rain due to more impervious surface as well as less flushing from tides. Unfortunately, four out of the four shellfishing sites exceeded the limit for fecal coliform levels, confirming why the state’s Division of Marine Fisheries closes the shellfishing beds in the North and South Rivers every summer from May 31 – November 1st . These results were not surprising given the rainfall that we had previous to and during the testing as stormwater is the number one cause of pollution to our waters. There were no significantly shocking values for any of the dissolved oxygen, conductivity, salinity or temperature tests. We’ve had a great start to our monitoring program and we are looking forward to a very productive summer.