Groundwater flow system in Bengal Delta,Bangladesh revealed by environmental isotopes |
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| Authors: | Ratan K Majumder M A Halim B B Saha Reo Ikawa Toshio Nakamura Makoto Kagabu Jun Shimada |
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| Institution: | (1) Isotope Hydrology Division, Atomic Energy Research Establishment, Ganakbari, Savar, Dhaka, 1000, Bangladesh;(2) Department of Mechanical Engineering, Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan;(3) Geological Survey of Japan, AIST Tsukuba Central 7, Tsukuba Ibaraki, 305-8567, Japan;(4) Tandetron AMS 14C dating Laboratory, Center for Chronological Research, Nagoya University, Chikusa Nagoya, 464-8602, Japan;(5) Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan |
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| Abstract: | A total number of 328 groundwater samples are analysed to evaluate the groundwater flow systems in Bengal Delta aquifers,
Bangladesh using environmental isotope (2H, 18O, 13C, 3H, and 14C) techniques. A well-defined Local Meteoric Water Line (LMWL) δ2H = 7.7 δ18O + 10.7 ‰ is constructed applying linear correlation analyses to the monthly weighted rainfall isotopic compositions (δ18O and δ2H). The δ18O and δ2H concentrations of all groundwater samples in the study area are plotted more or less over the LMWL, which provides compelling
evidence that all groundwaters are derived from rainfall and floodwater with a minor localized evaporation effects for the
shallow groundwaters. Tritium concentration is observed in 40 samples out of 41 with values varying between 0.3 and 5.0 TU,
which represents an evidence of young water recharge to the shallow and intermediate aquifers. A decreasing trend of 14C activity is associated with the heavier δ13C values, which indicates the presence of geochemical reactions affecting the 14C concentration along the groundwater flow system. Both vertical and lateral decrease of 14C activity toward down gradient show the presence of regional groundwater flow commencing from the unconfined aquifers, which
discharges along the coastal regions. Finally, shallow, intermediate, and deep groundwater flow dynamics has revealed in the
Bengal Delta aquifers, Bangladesh. |
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