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Modeling the Pollution Dynamics of the Blackstone
River Watershed
 Once considered ‘America’s Hardest Working River’ due
to the number of mills utilizing the hydraulic energy produced along
the river, the 475 square mile Blackstone River watershed in central
Massachusetts and northern Rhode Island contributes the majority of
flow and nutrients emptying into Narragansett Bay. Designated an American
Heritage River by EPA in 1998, the Blackstone River is at risk from
pollution from agricultural runoff, public and private municipal water
treatment facilities, and development impairing both the hydrology
and the ecology of the river and bay system.
Paula Rees, Assistant
Professor of Civil and Environmental Engineering and Interim Director
of the MA Water Resources Research Center, has been conducting field
research to monitor, assess, and model the river system since 2001.
The Blackstone River and Narragansett Bay systems
have periodically experienced nutrient-fueled algal blooms. Such blooms
can be detrimental to both fish and shellfish populations due to the
potential for areas of low dissolved oxygen to develop as the algal
die and decay, stressing the watershed ecosystem. As Rees explains, “One
major source of nutrients for these algal blooms is waste water treatment
plant effluent. However, nonpoint sources of nutrients are perhaps
of equal importance but have received only limited attention.”
To address watershed health, Rees has been working with the Upper Blackstone
Wastewater Facility to create a dynamic model to analyze the magnitude
and persistence of point and non-point source pollutants along the
river. “The model provides an opportunity to assess the relative
magnitudes of point and non-point sources, as well as to determine
the nutrient ‘total daily maximum load’, or the load that
the river can safely assimilate before the onset of hydrologic and
ecological degradation,” Rees says. Rees and her graduate students
have collected data on dissolved oxygen levels, pH, conductivity, and
temperature at nine locations along the river continuously between
April and November over the last two years. In addition, they have
monitored nutrient and dissolved metals concentrations along the river
during two dry weather and five wet weather events. These data are
invaluable for calibrating the model of the pollution dynamics of the
watershed. Rees’ team is currently finalizing the model and using
it to better understand the source, persistence and fate of pollution
along the river as well as to consider alternative management schemes
for reducing negative impacts.
To develop an equitable and efficient pollution discharge reduction
program, Rees explains “it is essential to factor in the difference
amongst pollution sources.” Currently, the wastewater facilities
along the river are implementing upgrades to reduce effluent concentrations
of phosphorus and nitrogen. Rees explains, “Further reductions
of nutrient-enriched effluent presents an economic impact that may
not result in the expected benefits to the watershed system, particularly
if non-point source loadings to the system are ignored. To ensure cost-effective
improvement of ecosystem health, it is beneficial to evaluate the impacts
of management schemes for both point and non-point sources prior to
their implementation. The dynamic model we have developed will facilitate
this evaluation.” Continued improvement in the accuracy of the
model through the collection of additional watershed data will help
improve understanding of the watershed’s complex relationships
involving multiple pollution sources. Implementation and refinement
of the model by Rees’ group will assist regulators and stakeholders
in developing a more efficient and equitable pollution control plan
to restore the ecology of the Blackstone River and Narragansett Bay
systems.
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