HR: 0800h
AN: H31B-1305    [Abstracts]
TI: Stable Isotope (18O, 2H) and Arsenic Distribution in the Shallow Aquifers in Araihazar, Bangladesh
AU: Zheng, Y
EM: yan_zheng@qc.edu
AF: Queens College, City University of New York, Flushing, NY 11367 United States
AU: Zheng, Y
EM: yan_zheng@qc.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964 United States
AU: Datta, S
EM: saugata.datta@gcsu.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964 United States
AU: Datta, S
EM: saugata.datta@gcsu.edu
AF: Department of Biological and Environmental Sciences, Georgia College and State University, Milledgeville, GA 31061 United States
AU: * Stute, M
EM: martins@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964 United States
AU: Dhar, R
EM: RDhar@gc.cuny.edu
AF: Queens College, City University of New York, Flushing, NY 11367 United States
AU: Hoque, M A
EM: hoque0001@yahoo.com
AF: Department of Geology, Dhaka University, Dhaka, 1000 Bangladesh
AU: Rahman, M W
EM: mwrahman2002@yahoo.com
AF: Department of Geology, Dhaka University, Dhaka, 1000 Bangladesh
AU: Ahmed, K M
EM: kmahmed@udhaka.net
AF: Department of Geology, Dhaka University, Dhaka, 1000 Bangladesh
AU: Schlosser, P
EM: schlosser@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964 United States
AU: van Geen, A
EM: avangeen@ldeo.clolumbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964 United States
AB: Recent estimates indicate that in Bangladesh alone, an estimated 50 million people have been exposed to Arsenic levels that exceed the WHO guideline of 10 μgL^-1 for drinking water by up to two orders of magnitude. There is still debate on what processes control the spatial heterogeneity of dissolved As concentrations. One recent suggestion has been that surface waters enriched in labile organic matter and transferred to greater depths by irrigation pumping may be an important factor. We have monitored for a year the oxygen and hydrogen isotopic composition of precipitation in Dhaka, Bangladesh, and of surface waters and groundwaters in a 25 km² study area in Araihazar, 20 km east of Dhaka. The data show a large spatial and temporal heterogeneity, with δ¹⁸O covering a range of up to 12 ‰. The isotopic composition of precipitation falls on the global meteoric water line (GMWL), while most surface waters collected from rivers, ponds and irrigated rice fields plot below and to the right of the meteoric water line, suggesting that evaporation is an important mechanism in this system. Surface waters show a strong evaporative enrichment during the dry season of up to 10 ‰ in δ¹⁸O and then show increased mixing with precipitation during the wet season. The groundwater isotopic composition obtained at 6 multi level well sites covers the range between the GMWL and moderately evaporated surface waters. These data indicate that some groundwaters are recharged directly by precipitation while others show evidence of recharge from evaporated surface waters during the wet and at the beginning of the dry season. For several well nests, the sources of groundwater vary in a systematic way as a function of depth. Highly evaporated irrigation water from rice fields in the dry season does not seem to contribute much to groundwater recharge. The degree of evaporation expressed as deuterium excess does not correlate with As concentrations in the groundwater samples. This finding suggests that whether the source of groundwater is direct recharge from precipitation or from surface waters, which presumably have a higher reducing capacity, is not an important factor in Arsenic mobilization in this area.
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1834 Human impacts
SC: Hydrology [H]
MN: Fall Meeting 2005