October 2021 Water Quality Report (CWMN)

Our October sampling event was a dry one, with no large rain events happening in the 72 hours prior.

CWMN sampling site near Ellis Pond in Norwood. Photo by Meghan Slocombe

This monthly sampling event involved over 50 CWMN volunteers. Some volunteers visited a single site and carefully collected water samples to be analyzed at Deer Island for bacteria and nutrients. Other volunteers visited upwards of five sites, taking dissolved oxygen measurements along the way. All the collected data is used by the Massachusetts Department of Environmental Protection (DEP) to uphold the Clean Water Act. Thanks to our CWMN volunteers for making this work possible!

E. coli

E. coli is a bacterium that lives in the intestines of healthy animals, including humans. Its presence in water is evidence of waste contamination. Typical sources of E. coli include leaking sewer infrastructure and bird or dog feces. High levels of the bacteria associated with this waste can make people sick.

The end of our CWMN season saw a decline in daily temperatures. In addition, our October sampling event was a dry one, with no large rain events happening in the 72 hours prior. Without high water temperatures which allow bacteria to flourish or a large rain event to flush bacteria out of sewer infrastructure, October E. coli levels remained low. Only 8% of our CWMN sites tested unsafe for recreation of any sort. In fact, 75% of our sites were safe to swim in. Although the cold water temperatures might be enough to make some reconsider a dip in the River!

While the October data certainly gives us something to celebrate, it is important to remember our long-term goal of having consistently low E. coli levels throughout the summer sampling period. As a way of measuring seasonal E. coli levels the Massachusetts Department of Environmental Protection states that Class B waters, which the Neponset River Watershed has been designated as, should have a geometric mean (of the five most recent E. coli samples) that does not exceed 126 colonies/100 mL. Unfortunately, the number of sites which do not pass this standard increased from 63% to 71% between 2020 and 2021.

The E. coli results are summarized in the maps and graph below. Note that there was no E. coli data collected for BEB025 in October.


Total Phosphorus

Phosphorus is a key nutrient for proper plant growth. For this reason, fertilizers contain phosphorus and when it is washed off lawns via rain, phosphorous can end up in streams and ponds. Too much phosphorus can lead to harmful algal blooms, cyanobacteria blooms, and fish kills.

Total phosphorus levels were low in October. Only 1 of the stream sampling sites exceeded the lower (.1 mg/L) total phosphorus standard and 63% of flowing water sites even passed the higher (.05 mg/L) total phosphorus threshold. While our flowing water sites saw major improvements from last month, the 5 pond sites we monitor still exceeded the pond threshold of .025 mg/L of total phosphorus.

These low phosphorus measurements were likely due to the lack of extreme precipitation events that occurred in the week preceding the sampling event. Less extreme rain events means that there is a lower likelihood of high amounts of phosphorus entering streams and ponds via runoff.

The phosphorus results are summarized in the graph below. Note that there was no phosphorus data collected for BEB025.

Dissolved Oxygen

The Neponset River Watershed’s critters and plants were breathing easy this past October, with high dissolved oxygen throughout streams and ponds! Dissolved oxygen is important for our aquatic life because dissolved oxygen is how many of these underwater critters access the oxygen they need to respire, or breath. Certain animals, including trout, require more dissolved oxygen than others. Low dissolved oxygen levels are linked to drought conditions and sustained high temperatures.

Nearly 94% of our sites with dissolved oxygen measurements available reached the recommended number of milligrams of oxygen per liter for cold-water fish. Only two of our measured sites had lower than recommended dissolved oxygen results.

The dissolved oxygen results are summarized in the graph below. Note that there were no dissolved oxygen measurements collected at HAB006, WIP003, or PQB040 and we are currently awaiting the results from MIB030, MMB106, NER002, NER040, SMB001, and SPB016.

Thank you to all our CWMN volunteers for an incredible 2021 water quality sampling season! Your dedication to this program allows NepRWA to play a crucial role in upholding important legislation such as the Clean Water Act.

NOTE: All the above data has gone through preliminary quality control, however, please note that a more extensive overview is given to the data before reporting it to DEP.

For comments, questions — or to learn more about becoming a CWMN volunteer — please contact NepRWA’s Environmental Science Fellow, Eleanor Yeomans at yeomans@neponset.org or 781-575-0354 x 302.


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