Sediment resuspension under variable geochemical conditions and implications for contaminant release
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Resuspension of sediment derived from natural and anthropogenic processes in surface waters may induce the release of metals, nutrients and other undesirable constituents from sediment to the water column. Characterizing the effects of sediment resuspension under variable geochemical conditions is important for predicting and mitigating contaminant releases during potential dredging operations, as metal(loid) transport may differ under oxidizing and reducing conditions.
Materials and methods
Lake sediment core samples containing elevated concentrations of mercury, other metal(loid)s and nutrients were physically and chemically characterized. Speciation analyses using sequential extraction and synchrotron radiation-based X-ray absorption spectroscopy methods were used to investigate the chemical form and distribution of mercury and other metal(loid)s. The sediment samples were subjected to resuspension under oxic and anoxic conditions to isolate the effects of air entrainment on contaminant release.
Results and discussion
Sequential extraction analyses suggested that the mercury was present primarily in moderately to strongly bound forms, such as mercury-organo chelates and mercury sulphides, whereas only trace amounts were found as less bound forms of mercury. Synchrotron-based micro-X-ray absorption near-edge structure (μ-XANES) and micro-X-ray fluorescence (μ-XRF) spectroscopy analyses suggested the presence of mercury oxide, mercury sulphide and copper sulphide phases. Higher aqueous metal(loid) and nutrient releases were observed under oxic resuspension conditions compared to anoxic conditions.
Higher releases of some constituents under oxic mixing conditions potentially were due to the oxidation of organic matter and/or sulphide mineral phases. These results suggest that resuspension tests performed under variably oxygenated conditions may provide a useful analytical tool for isolating the effect of air entrainment on contaminant release.
KeywordsCopper Mercury Oxidation Resuspension Sediment Speciation
This study was made possible by funding through the Natural Science and Engineering Research Council of Canada. Synchrotron-based techniques were performed at GeoSoilEnviroCARS (Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation—Earth Sciences (EAR-0622171) and Department of Energy—Geosciences (DE-FG02-94ER14466) divisions. Use of the Advanced Photon Source was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. We thank Dr. M. Newville and Dr. Y. Choi for their assistance at the beamline, and Melissa Holingham and Alan Fan for their assistance with the experimental work.
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