The Merrimack River was among the top ten most polluted rivers in the country in the 1970’s. After the Clean Water Act was passed in 1972, the point source pollution from factories was tackled, and the river’s water quality dramatically improved. In addition, pathogen (primarily bacteria) and nutrient concentrations (total phosphorus and nitrate-nitrogen) were reduced (DEP, unpublished data; MRWC).
We’ve come a long way, but still have work to do!
Today, the river is classified primarily as B waters, meaning that the water is intended to be both fishable, swimmable, and boatable, but all 50 miles in Massachusetts are still considered non-supporting for Class B waters (EOEA, 2001).
The main environmental problems currently impacting the Merrimack River’s water are the following:
- Nutrients, primarily phosphates;
- Increasing amounts of impervious surfaces;
- Loss of private forested lands in southern NH due to sprawl; and
- Climate change, which will increase both flooding and polluted runoff
The quality of the Merrimack River’s water matters, because it is the only major New England River used as a drinking water supply. Nearly 600,000 people rely on the 125 mile long river for their drinking water, including the environmental justice communities of Lowell and Lawrence, Methuen, Tewksbury, and other towns.
The upper portion of the Merrimack River in New Hampshire courses through heavily forested, rural areas. The forested lands help clean the river water by absorbing nutrient and sediment runoff before it can reach the river. The runoff also infiltrates the forest soil, cooling the water before it reaches the river. In contrast, the lower portion of the Merrimack River, from Manchester to the mouth of the river at Newburyport, has poorer water quality. This part of the river played an important role in industrialization, due to the many textile mills along the river who relied on water power to run the mills. The mills dumped their waste into the river for decades. In 1967, the condition of the water was classified as B or C waters, but its actual condition was considered D in many places (Commonwealth of Massachusetts, 1967). Remnants of that time period include hazardous wastes sites, junkyards, and Superfund sites that can impact water quality.
Pathogens are the main problem, stemming from the Combined Sewer Overflows (CSOs) in Lowell, the Greater Lawrence Sanitary District, Haverhill, Nashua, NH, and Manchester, NH, along with polluted runoff. Both public health and recreational enjoyment of the river are impacted by high bacterial levels in the river.
Pathogens are measured by using the common bacterium E. coli as an indicator of fecal contamination. The pathogen levels are measured against a state standard of 235 counts per The state’s recommendation for the acceptable risk level for swimming for waters with a nonbathing beach is a single sample concentration of 235 counts per fecal unit (cfu) /100 ml or 126 colonies of organisms per 100 milliliters of water (cfu) based on a geometric mean of all samples taken within the most recent six months. The risk of getting sick increases as the numbers of bacterial colonies increase above the standard.
We analyzed our water quality data over the years from 2008 to 2012. The good news is that several regions showed improvement in the average count of E. coli bacteria over the last four years, including Nashua, Tyngsborough, and Lowell. In 2013, the City of Lowell had no days that were considered unsafe for swimming (source: City of Lowell Recreation Department).
Nutrients are a problem because too many nutrients can cause excess algal growth and even fish kills. In freshwater, phosphate is the limiting factor for algal growth; in the ocean, nitrate is.
Urban and agricultural areas provide additional phosphorus or nitrates which can lead algae to grow too much, setting off a chain of events which can lead to excessive algal growth, reduced dissolved oxygen, and fish kills. Excessive phosphorous comes from older wastewater treatment plants (which do not have tertiary treatment to breakdown phosporous), combined sewer overflows, polluted runoff, runoff from lawn fertilization, animal waste, and industrial cleaning operations. Excessive nitrate comes from these sources, along with failing septic systems in rural areas of New Hampshire.
The greatest contributors of phosphate to the Merrimack River come from municipal wastewater (60%), with an additional 21% from developed lands (source: USACOE). The greatest contributors of nitrate to the Merrimack River are developed lands, atmospheric deposition from midwestern coal-fired plants, and municipal wastewater.
The natural baseline levels for total phosphorus in rivers is usually less than 0.03 mg/L. The State of Massachusetts does not have a single numerical standard, but notes that nutrients.. “shall not exceed the site-specific limits necessary to control accelerated or cultural eutrophication.” However, EPA guidelines for phosphorous in streams and rivers not flowing into lakes suggest that phosphates should not exceed 0.1 mg/L to control algal growth (USEPA 1986).
MRWC data from 2010 shows that overall, phosphorous levels are below EPA guidelines. The highest source of phosphorus (.095 mg/L) was observed in Haverhill, near the 0.1 mg EPA guideline.
As development increases in the area, parking lots and other impervious surfaces have increased. These impervious surfaces impact rivers in a number of ways, causing:
- Increasing pollutants from stormwater runoff (oil, grease, brake fluid, animal waste, road salt);
- Thermal stress (heat from impervious surfaces);
- Reduction in water quantity; and
- Flashiness (i.e., changes in river flow speed), leading to bank erosion.
The expanding amounts of parking lots and other impervious surfaces has also led to flooding, a key concern of many residents in Lowell and Lawrence. When it rains or snows, the water has no place to go, but into the storm drains and eventually the Merrimack River.
As the percentage of impervious surfaces increases, water quality and wildlife diversity and abundance suffer. The latest research shows that both water quality and ecology are degraded when impervious cover is above 5-7% (Schiff and Benoit, 2007). The most important areas to protect are the lands bordering the river, or river buffers.
Once degraded, river water quality and its ecology are difficult to restore. This is why it is much cheaper to maintain clean water by land protection than with water treatment. The Trust for Public Land reports that for every dollar spent on land protection, $27 dollars are saved on water treatment costs!
The forests in New Hampshire are critical to the health of the Merrimack, due to their role in filtering pollutants from entering the Merrimack River. If these forests are cut down to make way for suburban housing, the river’s water will suffer. The US Forest Service considers the Merrimack to be the most threatened in the country for loss of private forested lands (USFS, 2009). Due to this threat, the watershed is considered 4th most threatened in the country for impacts to water quality.