Date of Award

12-1-2012

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Sciences/Environmental, Earth & Ocean Sciences

First Advisor

Robert F. Chen

Second Advisor

Curtis R. Olsen

Third Advisor

William E. Robinson

Abstract

Two sediment cores and eleven grab samples collected from the Charles River were analyzed to determine changes to the concentration of metals in sediments due to anthropogenic changes in the watershed. The unique aspect of this research was that sediment cores from the same geologic setting, yet having widely different sources, were compared. The findings from that comparison were used to focus the investigation through the remainder of the Charles River. The radionuclides 210Pb, 214Pb, and 137Cs established the year of deposition in the sediment cores. The concentrations of aluminum (Al), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), chromium (Cr), cobalt (Co), lead (Pb), arsenic (As), cadmium (Cd), tin (Sn), scandium (Sc), strontium (Sr), silver (Ag), mercury (Hg) and total organic carbon (TOC) were determined in the sediment cores and surface samples.

The primary findings were that several metals in Charles River sediments exceeded regulatory standards for aquatic organisms and that storm water affected the concentrations of metals such as Cu, Hg, and Pb throughout much of the river. What appeared critical was the retention of metals within the upland areas of a watershed which was controlled by the amount of impervious surface. Storm water runoff from areas with greater amounts of impervious materials, coupled with the retention of sediments behind dams in the Charles River, increased the long-term availability of metals that may affect aquatic organisms. A simple model is presented that determines the concentration of Cu and Hg in sediments based on the percentage of impervious area and the concentration of TOC in the sediment. This model indicates that a potential key to reducing the concentrations of metals in sediments is to either reduce the amount of impervious surfaces in a watershed or decrease the supply of metals and TOC to sediments.

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