HR: 1340h
AN: H13G-1672    [Abstracts]
TI: Depth Transects of Sediment Age, Reflectance, and Aquifer Arsenic in the Bac Bo Plain, Vietnam: Implications for Groundwater Arsenic Heterogeneity in the Red River Delta
AU: * Weinman, B
EM: beth.weinman@vanderbilt.edu
AF: Vanderbilt University, Dept. of Earth and Environmental Sciences 2301 Vanderbilt Place Station B#35-1805, Nashville, TN 37235, United States
AU: Goodbred, S L
EM: steven.goodbred@vanderbilt.edu
AF: Vanderbilt University, Dept. of Earth and Environmental Sciences 2301 Vanderbilt Place Station B#35-1805, Nashville, TN 37235, United States
AU: Radloff, K
EM: kar2108@columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W PO Box 1000, Pallisades, NY 10964, United States
AU: Aziz, Z
EM: aziz@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W PO Box 1000, Pallisades, NY 10964, United States
AU: Jung, H
EM: yan.zheng@qc.cuny.edu
AF: Queens College, CUNY, School of Earth and Environmental Sciences 65-30 Kissena Blvd, Flushing, NY 11367, United States
AU: Frei, F
EM: felix.frei@eawag.ch
AF: Swiss Federal Institute for Environmental Science and Technology (EAWAG), Überlandstrasse 133, Zurich, 8600, Switzerland
AU: Berg, M
EM: michael.berg@eawag.ch
AF: Swiss Federal Institute for Environmental Science and Technology (EAWAG), Überlandstrasse 133, Zurich, 8600, Switzerland
AU: Trang, P K
EM: vietph@hn.vnn.vn
AF: Research Centre for Environmental Technology and Sustainable Development (CETASD), 334 Nguyen Trai, Thanh Xuan, Hanoi, 0000, Viet Nam
AU: Singhvi, A
EM: singhvi@prl.res.in
AF: Physical Research Laboratory, Navrangpura, Ahmedabad, 380 009, India
AU: van Geen, A
EM: avangeen@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W PO Box 1000, Pallisades, NY 10964, United States
AB: Shallow aquifer groundwater arsenic heterogeneity is well documented in many of the fluvial regions of Asia. To this day, the cause for the heterogeneity remains poorly understood in part because of the heterogeneity of sediment properties inherent to a young floodplain depositional environment. In April 2006, a needle-sampler device was used to obtain depth transects of both sediment and porewater samples as the first step towards understanding the heterogeneous subsurface environment. Depth transects were taken between sites with opposing trends in tube-well arsenic, e.g. low As cluster to high As cluster, in a stable, fault controlled river bend in Van Phuc, Vietnam, to determine how sediment properties such as grainsize and reflectance relate to dissolved arsenic. Luminescence dating of aquifer sands and He³/H³ dating of the groundwater was conducted to investigate how aquifer redox conditions and groundwater arsenic evolve in Van Phuc's river-bend over time. Results indicate that localized zones of sediments enriched in leachable arsenic exist at depth within the aquifer and provide a mostly local source of arsenic. It also appears that groundwater flow encountering sediments of different ages can account for some of the observed spatial patterns of groundwater heterogeneity. Compiled with observations that reducing groundwaters with both low dissolved and extractable arsenic exist in the upper deltaic region, it appears that heterogeneities in shallow floodplain arsenic can be driven by magnitude differences in sediment-labile arsenic. Finally, given that these localized packages of arsenic enrichment correspond to a particular in-filling type of facies, it appears that fluvial cycling along the delta is the underlying cause of arsenic heterogeneity in the shallow floodplain.
DE: 1051 Sedimentary geochemistry
DE: 1105 Quaternary geochronology
DE: 1165 Sedimentary geochronology
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: 2007 Fall Meeting