Arsenic and carbon cycling during hydrologically driven soil redox transitions
- Groundwater arsenic contamination affects the health of millions of people worldwide. Although industrial contamination affects localized aquifers, the vast majority of individuals are exposed to arsenic in drinking water that is geogenic in origin. Throughout Asia, geogenic arsenic originates from weathering rocks of the Himalaya and is transported to depositional environments where it is buried during sediment deposition and delta formation. Arsenic comprises only a minor component of these sediments, about 10 ppm, but even such small amounts of arsenic can lead to groundwater concentrations orders of magnitude higher than the World Health Organization drinking water standard of 10 ppb. Once deposited and buried, sediments no longer in contact with the atmosphere are quickly depleted of oxygen, and in the absence of oxygen, microbes utilize alternative electron acceptors such as Mn(IV), Fe(III), As(V), and sulfate to oxidize carbon to gain energy. The result of these reactions is the dissolution of insoluble Fe(III) minerals that are largely responsible for trapping arsenic in the solid phase. The limiting component of these reactions, and thus the key to predicting arsenic concentrations in groundwater, is the supply and fate of microbially reactive organic carbon needed to sustain reducing conditions conducive to arsenic solubilization. In essence, the fate of organic carbon is the determinant of dissolved arsenic concentrations within the groundwater systems (including surface-subsurface exchange) of Asia. In this thesis, I examine how surface and groundwater hydrology control the conditions dictating microbial metabolism of organic carbon and the ensuing impacts on dissolved arsenic concentrations. I use the Yangtze River Basin to illustrate changes in groundwater chemistry arising from surface-groundwater exchange that control arsenic concentrations, and the Mekong Delta of Cambodia to demonstrate how variation in surface hydrology leads to different carbon fates and thus dissolved concentrations of arsenic.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Schaefer, Michael Vernon
|Stanford University, Department of Environmental Earth System Science.
|Statement of responsibility
|Michael Vernon Schaefer.
|Submitted to the Department of Environmental Earth System Science.
|Thesis (Ph.D.)--Stanford University, 2016.
- © 2016 by Michael Schaefer
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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