The baseline monitoring program, which is the longest running program at the Mystic River Watershed Association, includes 20 years of data about the water quality along the Mystic River and its tributaries. Fueled by the work of 40 volunteers who go out every month to collect data at 15 sites--it is used by the EPA to calculate the annual Water Quality Report Card for the Mystic River.
The data shows some great news:
A- grade for the Mystic Lakes and mainstem of the river--for the fifth year in a row;
Infrastructure improvements downstream at the Island End River between Everett and Chelsea--and the resulting improvement in the grade from an F to a C+ in three short years.
Though we always want to focus on the good news, that isn’t the whole story.
This year we saw a dip in the grade up in the Aberjona River. Because they grade went down, our watershed scientist, Andy Hrycyna, has been investigating why. .
What seems to have driven the decline were three or four days of very high bacteria levels at three different sites on the Aberjona river in 2018. We average the past three years of data in calculating any given year’s grade, so these bad days brought the averages--and the grade-- down for 2018.
Figure 1. Baseline results for Aberjona River from 3 sites in Woburn and Winchester, 2016-2018. The red dashed line shows the state water quality standard for boating; the yellow dashed line is the water quality standard for swimming.
High bacteria levels in urbanized areas are the result of wastewater contamination of the stormwater system that carries rain to rivers and lakes. (Yes, it’s as yucky as it sounds.)
Does the grade going down mean that the infrastructure around the Aberjona is getting worse?
Not necessarily. The days with the worst bacteria results were days when it rained a lot. 1-2+ inches of rain in the previous 48 hours. Rain makes all the processes that lead to wastewater getting to the river (leaky and broken pipes, etc.) more active. This is very common in urbanized areas with old infrastructure.
In fact, if you look back not just at three years of baseline data, but at all 20 years we have (thanks to our amazing volunteer samplers!), you see that in general when it rains more, E. coli concentrations in the Aberjona get higher:
Figure 2. 20 years of baseline data on the Aberjona River. When it rains more (x-axis), bacteria levels go up (y-axis). A classic pattern in urban watersheds with old infrastructure.
So what made the grade go down in 2018 was really the fact that we happened to sample on some really rainy days, when conditions were at their worst. (The report card actually uses a weighting system for dry and wet weather days, meant to cancel out the effect of different precipitation patterns in different years. But these last three years had a frequency of really high rainfall events that inched the grade down, nonetheless.)
We hope to work with local municipalities to help find the sources of the contamination that wet weather brings. Next step: go out in rainy weather and sample from some of the many pipes that empty stormwater into the Aberjona!
The data we shared today would only be possible thanks to our baseline monitoring program. Every data point you see above we have only because volunteers went out in all weather to acquire samples from the river for testing.
That is why for #GivingTuesday, the Mystic River Watershed Association is raising money to fund water quality testing at 4 of our 15 sites for a full year. This includes purchasing water testing kits, paying for lab services, as well as analyzing and publishing the results.
All gifts will be matched 1:1 up to $3,534.05-between now and #GivingTuesday on Tuesday, December 3rd, 2019. Please join the movement with a gift today so we can keep monitoring water quality and making change!
