Sediment studies in the Assabet River, central Massachusetts, 2003

Abstract

From its headwaters in Westborough, Massachusetts, to its confluence with the Sudbury River, the 53-kilometer-long Assabet River passes through a series of small towns and mixed land-use areas. Along the way, wastewater-treatment plants release nutrient-rich effluents that contribute to the eutrophic state of this waterway. This condition is most obvious where the river is impounded by a series of dams that have sequestered large amounts of sediment and support rooted and floating macrophytes and epiphytic algae. The water in parts of these impoundments may also have low concentrations of dissolved oxygen, another symptom of eutrophication. All of the impoundments had relatively shallow maximum water depths, which ranged from approximately 2.4 to 3.4 meters, and all had extensive shallow areas. Sediment volumes estimated for the six impoundments ranged from approximately 380 cubic meters in the Aluminum City impoundment to 580,000 cubic meters in the Ben Smith impoundment. The other impoundments had sediment volumes of 120,000 cubic meters (Powdermill), 67,000 cubic meters (Gleasondale), 55,000 cubic meters (Hudson), and 42,000 cubic meters (Allen Street). The principal objective of this study was the determination of sediment volume, extent, and chemistry, in particular, the characterization of toxic inorganic and organic chemicals in the sediments. To determine the bulk-sediment chemicalconstituent concentrations, more than one hundred sediment cores were collected in pairs from the six impoundments. One core from each pair was sampled for inorganic constituents and the other for organic constituents. Most of the cores analyzed for inorganics were sectioned to provide information on the vertical distribution of analytes; a subset of the cores analyzed for organics was also sectioned. Approximately 200 samples were analyzed for inorganic constituents and 100 for organics; more than 10 percent were quality-control replicate or blank samples. Maximum bulk-sediment phosphorus concentrations in surface samples from the impoundments increased along a downstream gradient, with the exception of samples from the last impoundment, where the concentrations decreased. In addition, the highest phosphorus concentrations were generally in the surface samples; this finding may prove helpful if surface dredging is selected as a means to control phosphorus release from sediments. There is no known relation, however, between bulk-sediment concentration of phosphorus and the concentrations of phosphorus available to biota. Potentially toxic metals, including arsenic, cadmium, chromium, copper, nickel, lead, and zinc were frequently measured at concentrations that exceeded U.S. Environmental Protection Agency sediment-quality guidelines for the protection of aquatic life and that occasionally exceeded Massachusetts Department of Environmental Protection guidelines governing landfill disposal (reuse). Due to the effects of matrix interference and sample dilution on laboratory analyses, neither pesticides nor volatile organic compoun...

Monitoring to assess progress toward meeting the Assabet River, Massachusetts, phosphorus total maximum daily load - Aquatic macrophyte biomass and sediment-phosphorus flux

“…This dissolved phosphorus and any phosphorus associated with ferric oxyhydroxides would serve as a dissolved-phosphorus reservoir that could be released into the water column if anoxic conditions develop and could break down the oxidized microzone at the sediment-water interface. (Although the existence of iron-rich, oxidized microzones in the Assabet River impoundments was not investigated here, Zimmerman and Sorenson (2005) found that surficial-sediment samples in the impoundments generally had iron concentrations higher than 1 percent by mass. In all likelihood, a substantial portion of this iron would have been in the oxidized form.)…”

“…Parker and others (2004) found that the high proportion of tolerant generalist fish species among the fish communities in the Assabet River Basin indicated a degraded aquatic ecosystem. Zimmerman and Sorenson (2005) reported the results of sediment sampling in six Assabet impoundments and of their investigation of phosphorus dynamics in the Hudson impoundment. Sediment cores from a predetermined number of randomly selected sites in each impoundment were analyzed for bulk chemical properties, including TP, trace metals, volatile organic compounds, organochlorine pesticides, polycyclic aromatic compounds, polychlorinated biphenyls, and extractable petroleum hydrocarbons.…”

“…Site numbers and their locations in the Hudson and Ben Smith impoundments are the same as previously used inZimmerman and Sorenson (2005); the Hudson impoundment site numbers were those used in the phosphorus dynamics part of the study, and the Ben Smith site numbers were used to identify sediment-sampling sites.…”

Long-term effects of land-use change on water resources in urbanizing watersheds

“…The SuAsCo watershed encompasses many impoundments, and anaerobic conditions in deep water provide a conducive environment for phosphorus to unbind. This dissolved phosphorus is then taken up by aquatic plants [57], and these floating plants further reduce dissolved oxygen and create eutrophic conditions in the water. Changes in phosphorus over the LTM scenarios are more strongly related to increasing phosphorus outputs from urban rather than agricultural sources (Table 7).…”

“…In addition, the rivers in the SuAsCo watershed were designated for five "outstandingly remarkable values": history, scenery, recreation, ecology, and place in American literature. However, because of impairment caused by sediments and nutrients, the Assabet, Sudbury, and Concord rivers no longer met the criteria for Class B (fishable and swimmable) in 2001 [57]. Now, these rivers are on the State's List of Impaired Waters (303d) under the Clean Water Act [58].…”