It is a common belief that the water quality of the Charles River and other lakes, streams and rivers is at its worst after a large rainfall because of pollutants carried by runoff. However, a recent study completed by researchers at Northeastern University in Boston found high concentrations of E. coli bacteria in the Charles River after a long period of no rain. Ferdi Hellweger, Ph.D., Assistant Professor of Civil and Environmental Engineering and Acting Director of the Center for Urban Environmental Studies, both at Northeastern, used high-resolution monitoring and modeling to understand the fate and transport of E. coli bacteria in the lower section of the Charles River to determine what factors may lead to the increased concentration.
The results, which were published in the April issue of the Journal of the American Water Resources Association, go above and beyond the current data available about the water quality in the Charles and have the potential to impact the location of future beaches and their management.
Because current monitoring programs do not resolve the small-scale patterns of E. coli, Hellweger and his team carried out a high-resolution monitoring program. Using spatial and temporal surveys at different intervals and locations, Hellweger and his team gathered 757 samples along transects across and along the river, and over time at a fixed location. The results indicated an increased concentration of E. coli after a period of little rainfall. To make sense of these results, they developed a mathematical model of the river. The model accounts for various drivers, including upstream and downstream flow, wind, combined sewer overflow (CSO) and non-CSO flow from two major tributaries, the Muddy River and the Stony Brook. Based on hydrodynamics and die-off kinetics, the model reproduced the general patterns of E. coli in the water over space and time.
“Our analysis suggests that the Stony Brook and Muddy River are the predominant sources of E. coli in the lower Charles River,” said Hellweger, whose interest in urban hydrology drove this research project. “However, it is important to determine where the bacteria go and their concentration at different times and locations.”
One surprising finding was the effect of the New Charles River Dam, which when open, allows the Charles River to flow downstream and empty into the Boston Harbor. When it is closed, however, the Charles River acts more like a lake or a reservoir, creating a static environment. Thus, in addition to rainfall, the Dam operation cycle does affect the level of bacteria in the Charles River.
“Our study results show that water quality in the Charles River is impacted by several factors, including the New Charles River Dam,” added Hellweger. “While the primary focus of the Dam is to control flooding and navigation, I think that taking water quality issues into account could help reduce public health risk to present boaters and future beachgoers in the Charles,” added Hellweger.
Their model can be used to predict water quality in the lower Charles River, which can be used to evaluate various management scenarios and assess public health risk to swimmers at different times and locations.
In a 2002 study, 25% of surveyed beaches had at least one advisory or area closed, mostly due to unsafe levels of certain forms of bacteria. Exposure to unsafe levels of bacterial can sometimes result in recreational water illnesses (RWI), causing diarrhea, respiratory, skin, ear and eye infections.
Water pollution continues to be a public health threat, and because the Summer is quickly approaching, there will be a heightened interest in protecting people who spend time in the water. “My goal is to help make the Charles River a place where people can swim safely,” said Hellweger.
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