A Gel Probe Equilibrium Sampler for Measuring Arsenic Porewater Profiles and Sorption Gradients in Sediments: II. Field Application to Haiwee Reservoir Sediment
Abstract
Arsenic (As) geochemistry and sorption behavior were measured in As- and iron (Fe)-rich sediments of Haiwee Reservoir by deploying undoped (clear) polyacrylamide gels and hydrous ferric oxide (HFO)-doped gels in a gel probe equilibrium sampler, which is a novel technique for directly measuring the effects of porewater composition on As adsorption to Fe oxides phases in situ. Arsenic is deposited at the sediment surface as As(V) and is reduced to As(III) in the upper layers of the sediment (0–8 cm), but the reduction of As(V) does not cause mobilization into the porewater. Dissolved As and Fe concentrations increased at depth in the sediment column driven by the reductive dissolution of amorphous Fe(III) oxyhydroxides and conversion to a mixed Fe(II, III) green rust-type phase. Adsorption of As and phosphorous (P) onto HFO-doped gels was inhibited at intermediate depths (10–20 cm), possibly due to dissolved organic or inorganic carbon, indicating that dissolved As concentrations were at least partially controlled by porewater composition rather than surface site availability. In sediments that had been recently exposed to air, the region of sorption inhibition was not observed, suggesting that prior exposure to air affected the extent of reductive dissolution, porewater chemistry, and As adsorption behavior. Arsenic adsorption onto the HFO-doped gels increased at depths >20 cm, and the extent of adsorption was most likely controlled by the competitive effects of dissolved phosphate. Sediment As adsorption capacity appeared to be controlled by changes in porewater composition and competitive effects at shallower depths, and by reductive dissolution and availability of sorption sites at greater burial depths.
Additional Information
© 2008 American Chemical Society. Freely available via the ACS AuthorChoice program. Received for review May 13, 2007. Revised manuscript received October 2, 2007. Accepted October 5, 2007. Web Release Date: December 12, 2007. This work was supported by funding from NSF BES-0201888, BES-0201943, and EAR-0525387. We thank the Los Angeles Department of Water and Power (LADWP), particularly Gary Stolarik, Stanley Richardson, and Fred Richardson, for access to Haiwee Reservoir. We also thank Nathan Dalleska for analytical support and Mike Vondrus for gel probe construction. Portions of this research were carried out at the Stanford Synchrotron Radiation Laboratory, a national users facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences. Supporting Information Available: Map of Haiwee reservoir, gel probe schematics, microcosm results, comparison of porewater measurement techniques, correlation between As and Fe (October 2004), amount of As(III) and As(V) in HFO-doped gels, XANES spectra for field gels, XRF bulk sediment composition and solid phase organic carbon data, KD* for competitive phosphate laboratory study. This material is available free of charge via the Internet at http://pubs.acs.org.Attached Files
Published - CAMest08b.pdf
Supplemental Material - CAMest08bsupp.pdf
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Additional details
- Eprint ID
- 11217
- Resolver ID
- CaltechAUTHORS:CAMest08b
- NSF
- BES-0201888
- NSF
- BES-0201943
- NSF
- EAR-0525387
- Created
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2008-07-24Created from EPrint's datestamp field
- Updated
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2021-11-08Created from EPrint's last_modified field