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Type of Document	Dissertation
Author	Campbell, Kate Marie
Author's Email Address	kcampbell AT usgs.gov
URN	etd-12182006-102819
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-12182006-102819
Title	Biogeochemical mechanisms of arsenic mobilization in Haiwee Reservoir sediments
Degree	PhD
Option	Environmental Science and Engineering
Advisory Committee	Advisor Name Title Janet G. Hering Committee Chair Dianne K. Newman Committee Member George Robert Rossman Committee Member Michael R. Hoffmann Committee Member
Keywords	XANES arsenic ESEM bacterial arsenate reduction bacterial iron reduction
Date of Defense	2006-12-05
Availability	unrestricted
Abstract Naturally-occurring arsenic (As) in the Los Angeles Aqueduct, a major drinking water source for the City of Los Angeles, is removed by precipitating an amorphous iron (Fe) oxyhydroxide floc in the aqueduct waters. The floc is removed via sedimentation at Haiwee Reservoir, where the Fe- and As-rich sediments provide a unique field site for studying the mechanisms of As mobilization to sediment porewater. A gel probe equilibrium sampler was developed to measure the porewater concentrations and As sorption behavior in Haiwee Reservoir sediments. The gels consisted of a polyacrylamide polymer matrix and were 92% water. Undoped gels (clear gels) were used to determine porewater composition, and hydrous ferric oxide (HFO)-doped gels were used to measure in situ As adsorption chemistry. Gels were placed in a plastic holder, covered with a membrane filter, and allowed to equilibrate with the sediment porewaters. This study combined data from the gel probe samplers, gravity cores, and laboratory studies, to elucidate the biogeochemical processes governing As partitioning between the solid and aqueous phases. The gel probe device allowed for in situ observation of the effect of porewater chemistry on As adsorption. Arsenic was reduced from As(V) to As(III) in the upper layers of the sediment, but the change in redox state did not cause As to be mobilized into the porewaters. Arsenic mobilization occurred during reductive dissolution of Fe(III) oxides. Arsenate and Fe(III) reduction were probably microbially mediated. Arsenic sorption onto the HFO-doped gels was inhibited at intermediate depths, probably due to dissolved carbonate produced from organic carbon mineralization. The partitioning of As onto the sediment in this region may be primarily controlled by porewater chemistry, rather than sorption site availability. Deeper in the sediment column, the Fe(III) phase was partially transformed to carbonate green rust, possibly sequestering dissolved carbonate. In this region, As adsorption onto HFO-doped gels was controlled by dissolved phosphate. The accumulation of As in the porewater in this region may be due to lack of available surface adsorption sites on the sediment. Arsenic partitioning between solid and aqueous phases depends on microbially driven diagenetic processes, as well as porewater composition.
Files	Filename       Size       Approximate Download Time (Hours:Minutes:Seconds)     28.8 Modem   56K Modem   ISDN (64 Kb)   ISDN (128 Kb)   Higher-speed Access    01_Title_and_acknowledgements.pdf 29.12 Kb 00:00:08 00:00:04 00:00:03 00:00:01 < 00:00:01   02_Abstract.pdf 21.13 Kb 00:00:05 00:00:03 00:00:02 00:00:01 < 00:00:01   03_Table_of_Contents.pdf 49.84 Kb 00:00:13 00:00:07 00:00:06 00:00:03 < 00:00:01   04_Chapter_1.pdf 53.94 Kb 00:00:14 00:00:07 00:00:06 00:00:03 < 00:00:01   05_Chapter_2.pdf 180.98 Kb 00:00:50 00:00:25 00:00:22 00:00:11 < 00:00:01   06_Chapter_3.pdf 132.57 Kb 00:00:36 00:00:18 00:00:16 00:00:08 < 00:00:01   07_Chapter_4.pdf 658.72 Kb 00:03:02 00:01:34 00:01:22 00:00:41 00:00:03   08_Chapter_5.pdf 183.39 Kb 00:00:50 00:00:26 00:00:22 00:00:11 < 00:00:01   09_Chapter_6.pdf 1.45 Mb 00:06:43 00:03:27 00:03:01 00:01:30 00:00:07   10_Chapter_7.pdf 48.08 Kb 00:00:13 00:00:06 00:00:06 00:00:03 < 00:00:01   11_AppendixA_E.pdf 3.08 Mb 00:14:16 00:07:20 00:06:25 00:03:12 00:00:16   12_References.pdf 83.31 Kb 00:00:23 00:00:11 00:00:10 00:00:05 < 00:00:01   Campbell_Thesis_Complete.pdf 5.71 Mb 00:26:25 00:13:35 00:11:53 00:05:56 00:00:30