Boston, MA
Overview
The study area in Boston encompasses the watersheds of three major rivers (Charles, Mystic, and Neponset), with a combined watershed area of approximately 500 sq mi/1300 sq km and a population of nearly 5 million people. Relative to the other study areas, Boston has a colder climate with year-round precipitation. Wastewater and stormwater infrastructure is much older, and contamination from aging sewer pipes and combined sewer overflows is a major concern.
Map showing the main stems of the Mystic, Charles, and Neponset Rivers, with their watersheds outlined in dark gray.
History
Rivers and streams in the Boston area have experienced over 400 years of urban influence, including canals and dams constructed beginning in the 1600s, and infilling of marshes beginning in the 1700s. Cities and towns in the area have a long history of implementing a variety infrastructure approaches to dealing with the domestic and industrial sewage associated with a growing population, as well as flooding associated with replacing vegetation with impervious surfaces. Industrial development lead to the construction of mills and dams and additional dumping.
Beginning in the mid 1830s, combined sewers carried waste and storm water directly into the rivers. In the 1880s, a drainage system was constructed to carry combined waste to an offshore disposal point in Boston Harbor, though combined sewer overflows still drained into the rivers. Many streams were also culverted in the late 1800s and early 1900s.
The first wastewater treatment plants were constructed in 1952 and and 1968. Secondary treatment was added to the Deer Island Treatment plant in 2000, with treated effluent being discharged further out into the ocean to reduce contamination in the harbor. Currently, with the exception of scattered septic systems (mostly in the upper Neponset watershed), all wastewater is routed to the Deer Island Treatment plant in Boston Harbor. The sewer infrastructure includes both combined (stormwater and wastewater) and separated (wastewater only) systems.
More information on the history of infrastructure in the Boston area:
Mystic River History (Mystic River Watershed Association)
Charles River History (Charles River Watershed Association)
Stony Brook: Boston's Stygian River (Universal Hub)
A River Interrupted (Charles River Watershed Association)
Burial of Stony Brook, Boston in the 1880s. Source: Journal of the Association of Engineering Societies
Sewage Contamination
Sewage contamination in the streams and rivers in the Boston area is a result of (1) leaky infrastructure, (2) illicit discharge, and (3) combined sewer overflow events (CSOs). CSOs occur during rainy weather when increased stormwater runoff overwhelms combined sewers, and the combined wastewater and stormwater is released directly into streams and rivers to prevent sewage backup in buildings.
Efforts to remove illicit discharges, close CSO outfalls, and separate combined sewer systems began in the late 1980s and 1990s. Since 1987, CSO discharge has been eliminated from about 40 of 84 outfalls. CSO events still discharge millions of gallons of wastewater into streams and rivers, particularly in years with heavy rainfall events (which are increasing due to climate change). As an example, CSO discharge to the Mystic River increased from 41.5 million gallons in 2020 to 338 million gallons in 2021 due to heavy rain storms in the summer and fall.
Sewage contamination leads to high levels of human bacteria and other pathogens, reflected in E. coli measurements and warnings against contact with water following precipitation events. The organic carbon from sewage contamination also likely impacts overall stream ecology.
More information:
Combined Sewer Overflows (Massachusetts Water Resources Authority)
CSOs on the Mystic 2021 (Mystic River Watershed Association)
CSO outfalls in the Boston area as of May 2020 (source: MWRA). Full size image.
Volume of CSO discharge to Mystic River in 2020 and 2021 (source: MyRWA)
Water Quality Report Cards for the three watersheds in 2020 show that E. coli levels vary between different tributaries and reaches of the river. Higher E. coli levels are associated with sewage contamination from leaky sewer and septic systems, illicit discharge, and combined sewer overflows. For full size images and more information, see the links for the Charles River 2020 Report Card, Mystic River 2020 Report Card, and Neponset River 2020 Report Card.
Additional Environmental Issues
In additional to wastewater contamination, urban development has lead to several other environmental issues, including those outlined on the Project Overview page.
Specifically:
Stormwater runoff brings litter, herbicides and pesticides, road salts, leaves, and excess fertilizer directly into streams and rivers. Excess nutrients, specifically nitrogen and phosphorous, lead to algal blooms, oxygen depletion, and ecosystem disruption. Stormwater runoff is exacerbated by impervious surfaces (roads, parking lots, and buildings) that rapidly route water into streams.
In particular, excess phosphorous pollution leads to the growth of cyanobacteria that release chemicals toxic to wildlife, humans, and pets. These events are known as harmful algal blooms (HABs).
Disconnected habitats and restricted fish migration are the result of numerous dams and culverts.
Legacy toxins from industrial waste are contained in stream and river sediments. As an example, the lower Neponset River was recently designated a Superfund site due to PCBs in river sediments.
More information:
Environmental Issues (Neponset River Watershed Association)
Charles River Challenges (Charles River Watershed Association)
Mystic River Pollution (Mystic River Watershed Association)
Stormwater Runoff into the East Branch River, a tributary to the Neponset River, 2021.
Cyanobacteria and algae bloom on the Mystic River, Medford, 2017. Photo credit: Jack Bitney. (Source: MyRWA)
Synoptic Sampling Sites
To represent the range of urban conditions in the greater Boston area, 100 stream and river sites were selected for synoptic sampling. All of these sites were sampled over a short period of time to capture a "snapshot" of stream biogeochemistry at 4 times over one year:
September 2021 (late summer of a wet year)
November 2021 (during leaf fall)
April 2022 (during greenup)
July 2022 (full canopy cover, mid summer)
The 100 sites include small tributaries and main stem rivers. Based on topography and USGS StreamStats, subwatersheds were delineated for all 100 of the sampling sites. Subwatersheds range from less than 1 to greater than 800 square kilometers.
100 sampling sites in the Boston area. Yellow markers show the locations of 25 sites in the Mystic Watershed, 35 sites in the Neponset Watershed, and 40 sites in the Charles Watershed.
Subwatersheds for the synoptic sampling sites in the Boston area.
The subwatersheds for the synoptic sampling sites (black symbols) include developed (red) and forested (green) areas. From north to south, the Mystic, Charles, and Neponset river watersheds are outlined in black.
Sensor Sites
At three of the sites, sensors were temporarily installed to measure dissolved organic matter, temperature, pH, conductivity, turbidity, and optical brighteners (an indicator of wastewater contamination). Measurements will be logged every 15 minutes for one year, and data will be correlated with discharge measurements from nearby USGS gages to analyze how stream water characteristics change over time in urban watersheds with different properties.
In Boston, sensors were installed in Alewife Brook in Somerville, Beaver Brook in Waltham, and Stony Brook in Weston. These streams drain subwatersheds of similar size (22-29 sq km). The temporal data from these sites provide insight into watersheds with very different land cover, ranging from 14% developed/10% impervious cover in the Stony Brook watershed to 83% developed/45% impervious cover in the Alewife Brook watershed.
The figures below show landcover in the watersheds for the installed sensors. Red colors correspond to developed area, and green colors correspond to forested area.
Sensor in Alewife Brook
For More Information
For questions about this project in the Boston area, please contact the researchers below. Additional information about overall water quality and research in the three major watersheds is available through the local watershed associations.
Postdoctoral Researcher, UMass Amherst
Unit Leader, USGS, Massachusetts Cooperative Fish and Wildlife Research Unit
Research Associate Prof., UMass Amherst
