Hydrochemistry and isotopic studies to identify Ganges River and riverbank groundwater interaction, southern Bangladesh
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ORIGINAL PAPER
Hydrochemistry and isotopic studies to identify Ganges River and riverbank groundwater interaction, southern Bangladesh R. K. Majumder & M. A. Halim & J. Shimada & B. B. Saha & A. Zahid & M. Q. Hasan & M. S. Islam
Received: 3 August 2012 / Accepted: 1 November 2012 # Saudi Society for Geosciences 2012
Abstract The Ganges River water and riverbank shallow groundwater were studied during a single wet season using the hydrochemical and isotopic composition of its dissolved load. The dissolved concentrations of major ions (Cl−, SO42−, NO3−, HCO3−, Ca2+, Na+, Mg2+, and K+), trace elements (barium (Ba) and strontium (Sr)) and stable isotopes (O and D) were determined on samples collected from the Ganges River and its riverbank shallow aquifers. In the present study, the shallow groundwater differs significantly from the Ganges River water; it shows distinct high concentrations of Ca2+, Mg2+, HCO3−, Ba, and Sr due to water–rock interaction and this in particular suggests that the Ganges River may not contribute significantly to the riverbank shallow aquifers during wet season. Besides, the sum of the total cationic charge (∑ + , in
milliequivalents per liter) in the groundwater shows high values (2.48 to 13.91 meq/L, average 9.12 meq/L), which is much higher than the sum of the cations observed in the Ganges water (1.36 to 3.10 meq/L, average 1.94 meq/L). Finally, the more depleted stable isotopic (δ18O and δ2H) compositions of the Ganges River water are in contrast to those of the riverbank aquifer having enriched stable isotopic values during the wet season and the riverbank groundwater thus has a purely local origin from precipitation.
R. K. Majumder (*) : M. A. Halim Isotope Hydrology Division, Bangladesh Atomic Energy Commission, Dhaka, Bangladesh e-mail: [email protected]
In Bangladesh, the total number of rivers including tributaries and distributaries is about 700 under the Ganges– Brahmaputra–Meghna (GBM) river system. The GBM river system discharges huge volumes of surface water through Bangladesh, a part of which enters groundwater. About 93 % of the stream flow passing through the country originates from outside the Bangladesh (Khan 1991). Rainfall within the country contributes to the total water available in Bangladesh, a part of which infiltrates the ground to recharge existing groundwater and the remaining rainwater flows as surface runoff. Streams are the terminal points of groundwater flow and the start of the surface water system (Woessner 2000). The fluvial plain is, in fact, a point of complex interaction between streams and the groundwater system (Lambs 2000). Streams play an important role in mixing stream water with groundwater (hyporheic zone). Mixing of surface water and groundwater takes place within the upper layers of the channel sediments. Such near-channel exchange occurs at many scales, from centimeters to tens of meters
J. Shimada Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan B. B. Saha Mechanical Engineering
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