 |
Asia's arsenic affected regions, depicted in a map from Saunders et al., 2005, "Natural arsenic contamination of Holocene alluvial aquifers by linked tectonic, weathering, and microbial processes," G-cubed, 6(4), 1525-2027.
Sedimentology and groundwater arsenic heterogeneity in Asian deltas
Discovered in the mid 1990s, elevated groundwater arsenic in the deltas draining the Himalayas has proven to be somewhat of an enigmatic problem. In countries like Bangladesh, Nepal, Vietnam, and the West Bengal portion of India, it is not unusual for wells spaced several meters apart and drilled to the same depth to have dramatically different concentrations of arsenic. This heterogeneity in groundwater arsenic is a major obstacle to locating clean water, which has left more than 50 million people at risk of arsenic exposure in the most populous and impoverished reaches of the world (see World Health Organization report).
My research focuses on understanding how aquifers develop heterogeneity by exploring the relationships between near-surface geology and groundwater chemistry. By applying new luminescence dating techniques (OSL) along with more traditional sedimentological and geochemical studies, we can clarify how fluvial processes control the types of deposits and the amounts of dissolved arsenic within the shallow aquifer. Work is currently underway in several affected locations--a moribund floodplain in
Araihazar, Bangladesh; a hyperavulsive portion of the Terai in Parasi, Nepal; and a stable, fault controlled river bend in Van Phuc, Vietnam--to reconstruct aquifer history in order to understand how these areas evolve geologically as well as geochemically. In particular, we aid in understanding the dependence of arsenic on fluvial geomorphology and resolving the conditions responsible for arsenic heterogeneity over spatial scales relevant to mitigation and human concern.
Bangladesh
Araihazar village in the floodplains of central Bangladesh showing the small scale variability of groundwater arsenic (van Geen et al., 2003). Tube-wells are denoted by symbols graduated in color and size to depict the nature of groundwater arsenic heterogeneity. Small blue circles correlate to wells with <10 ug/L arsenic and large red circles correlate to wells in excess of 300ug/L arsenic. Groundwater >10ug/L arsenic is noncompliant with the provisional standard of the WHO.
Collaborators:
Steven Goodbred, Vanderbilt University, Nashville, TN
Lex van Geen, Lamont Doherty Earth Observatory of Columbia University, Palisades, NY
Yan Zheng, Queens College, CUNY, Flushing, NY
Ashok Singhvi, Physical Research Laboratory, Ahmedabad, India
Zahid Aziz, Lamont Doherty Earth Observatory of Columbia University, Palisades, NY
A location along the Red River delta plain with heterogeneous distributions of groundwater arsenic (bottom insert from Berg et al., 2001). To investigate how small scale changes in deposition affect arsenic, geochemical and geochronological studies are underway in Van Phuc, a village located in a meander bend of the Red River.
Collaborators:
Steven Goodbred, Vanderbilt University, Nashville, TN
Lex van Geen, Karrie Radloff, and Zahid Aziz, Lamont Doherty Earth Observatory of Columbia University, Palisades, NY
Michael Berg and Felix Frei, Swiss EAWAG
Zsolt Berner and Elisabeth Eich, University of Karlsruhe, Germany
Yan Zheng and Hun Bok Jung, Queens College, CUNY, Flushing, NY
Pham Kim Trang, Vi Mai Lan, and Bui Hong Nhat, CETASD and Hanoi University of Science
Ashok Singhvi, Physical Research Laboratory, Ahmedabad, India
Arsenic heterogeneity in the Nawalparasi district of Nepal's Terai. The groundwater arsenic map was made by Nepal's Dept. of Water Supply and USGS. Our study site traverses a distance of ~1km between Unwach and Sunwach villages, in order to capture how depositional differences can account for the differences in arsenic. The map scale is ~5km across and pink symbols represent arsenic >200 ppb, orange >50, green >10, and blue <10.
Collaborators:
Steven Goodbred, Vanderbilt University, Nashville, TN
Lex van Geen and Karrie Radloff, Lamont Doherty Earth Observatory of Columbia University, Palisades, NY
Laurent Charlet and Stephane Gulliot, University of Grenoble, France
Bishal Nath Upreti and Ananta Prasad Gajurel, Tribhuvan University, Kathmandu, Nepal
Linda Smith, Filters for Families, Nepal
Mohammad Rezaul Huq and Kazi Matin Ahmed, Dhaka University, Bangladesh
Ashok Singhvi, Physical Research Laboratory, Ahmedabad, India
Jennifer Pickering and Warner Cribb, Middle Tennessee State University, Murfreesboro, TN
|
|
