Distribution and transport of copper and lead in the Blackstone River, Massachusetts

Because of their persistence in the environment (as well as their susceptibility to bioaccumulation and biomagnification processes), heavy metals often pose threats to aquatic life in the environment. The Blackstone River, located in south-central Massachusetts and Rhode Island, is an example of a water body that has been plagued by these problems. Extensive historical contamination in this river has resulted in the bottom sediments with extremely high metals concentrations. However, the sources and processes governing the subsequent mobilization of these metals are still poorly understood.; This dissertation characterizes the sources, distribution, and transport characteristics of metals in the Blackstone River. For this case, copper and lead are selected for in-depth study since these cations demonstrate differing interactions with the sediment. Analyses of sediments in selected reaches of the Blackstone River show that bottom sediments are important sources of heavy metals. Laboratory analyses of catch-basin cleanings from the City of Worcester also reveal high metals concentrations, indicating that sediment-laden runoff from the City of Worcester may also contribute to heavy metal pollution. The role of sedimentation and desorption due to mixing were explored using a sedimentation test and a series of TCLP-based desorption tests. In addition, the relationships between streamflow and heavy metals were examined using long-term daily measurements and short-term hourly measurements during both dry and wet weather flow conditions. Sedimentation is found to be important during low flow conditions, while resuspension (leading to mobilization of the metals) is found to be especially prevalent during higher flow events. The Biotic Ligand Model (BLM) was applied to characterize metal partitioning and transport.; Since the system is relatively well mixed, the heavy metals in the water column also become available to the riverbank and affect vegetation. Therefore, selected plant species were analyzed to assess the concentrations of copper and lead in vegetation adjacent to the river. Total copper and lead concentrations were observed to decrease with respect to the distance from the riverbank. While aquatic species are conventionally used to evaluate toxicity of heavy metals, this investigation indicates that riverbank vegetation samples can also serve as pollution monitoring and evaluation tool.