Hydrochemistry and weathering processes in the lower Ganges-Brahmaputra-Meghna River system, Bangladesh: Implications for CO2 sequestration and fluxes to the ocean

Description

In this investigation, we examine the major ion compositions for the rivers of lower GBM Basin (Na+, K+, Ca2+, Mg2+, F-, Cl-, SO42-, HCO3-), using original data from December 2019 to January 2020. The high density of sampling and historical data was extensively analyzed, allowing us to (1) show spatial, daily, and vertical variations and long-term trends in major ions, (2) investigate the processes governing the major element chemistry in the basin, (3) evaluate seaward solute fluxes and source apportionment, and (4) estimate the weathering and CO2 sequestration rate in the study site.

Steps to reproduce

Dionex ICS-2000 was used to analyze Na+, K+, Ca2+, and Mg2+ as cations and Cl-, SO42-, and F- as anion; cation eluent was 20 mM methane sulfonic acid and flow rate was 1.0 mL/min, while anion eluent was 25 mM KOH and flow rate was 1.0 mL/min. The sample and eluent were poured into a separator column. IonPac®AS11-HC analytical (4 × 250 mm) was used to separate anions through the ion exchange process, whereas IonPac® CS12A analytical (4 × 250 mm) was used to separate cations. Water samples of 1 mL volume were manually fed into the device via the intake port one after another. The equipment was calibrated using analytical grade anion and cation standard reagents. After every five samples, testing standards were used to determine the instrument's accuracy. The detection limit was roughly 0.01 mg/L (Jiang et al., 2021) and precision for all analysis was below 4%. Nitrate (NO3-) and dissolved silica (SiO2) concentrations were measured using a flow injection system (SKALAR San Plus, Netherlands) (Jiang et al., 2023). The detection limit for these species was around 0.1 μM, with an analytical variability of approximately ±3% (Jiang et al., 2023). Bicarbonate (HCO3-) was measured using the titration method, with diluted hydrochloric acid (HCl) of known concentration employed as a titrant. Color indicators such as phenolphthalein and methyl orange were employed to indicate when the appropriate pH was reached. Each sample was examined two to three times to ensure precise results.

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