The hydrogeochemistry of pond and rice field recharge : implications for the arsenic contaminated aquifers in Bangladesh

The shallow aquifers in Bangladesh, which provide drinking water for millions and irrigation water for innumerable rice fields, are severely contaminated with geogenic arsenic. Water mass balance calculations show that groundwater-irrigated rice fields and man-made ponds are the primary sources of recharge to the contaminated aquifers. We studied the hydrology and chemistry of these anthropogenic recharge sources to determine the impact they have on groundwater arsenic concentrations. Our hydrogeochemical investigation involved fieldwork, laboratory analyses, and modeling. The field research spanned three years and included the deployment of a sensor network to continually monitor soil moisture and water potential, tracer tests to visualize flow patterns, soil cores to determine soil properties, and soil and water samples to ascertain chemical characteristics. The large amount of generated data were synthesized with hydrologic, geochemical and mass-balance models. The study showed that physical and chemical differences between rice fields and ponds explain the spatial patterns of arsenic in the Bangladeshi aquifers. Recharge from rice fields is both temporally and spatially heterogeneous. It is focused through bunds (the raised boundaries around the perimeter of fields) and depends on irrigation intervals. Flow from ponds is constant and uniform through the pond sediments. These distinct hydrologic behaviors produce different water chemistries. Ponds contribute anoxic recharge elevated in labile organic carbon, while rice fields contribute semi-oxic recharge that lacks labile organic carbon.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Civil and Environmental Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2010

Author dc:creator

• Neumann, Rebecca B

Advisor dc:contributor.advisor

• Charles F. Harvey.

• Civil and Environmental Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/57548

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/57548