Monthly changes in <I>p</I>CO₂ in the Ganges River: implications for carbon release from soil to the atmosphere via inland waters

Abstract

Recent studies have revealed that inland waters, such as rivers, act as an excellent source of soil-derived CO 2 for the atmosphere. This flow is comparable in magnitude to that of anthropogenic CO 2 release, such as fossil fuel use, playing an important part in the global carbon cycle and future climate change. Although one of the most active CO 2 evasions in the world has been reported in Himalayan rivers, data on the partial pressure of CO 2 pCO 2 remains sparse. In this study, we conducted a monthly sampling survey of the Ganges River in Bangladesh during 2011-2014 and measured the chemical composition of the river water. Both chemical weathering and dissolution of soil salt may affect seasonal variations in major ion composition in this river. The pCO 2 values were 377-1,763 μatm, which were higher than the atmospheric level 400 μatm. Higher pCO 2 values were observed during the rainy season, which was likely attributed to active respiration by soil or river biota. We also calculated approximate CO 2 evasion rates from the river into the atmosphere. Our results suggest that water during the rainy season, which has high pCO 2 , temperature, and water current velocity, releases CO 2 into the atmosphere more efficiently 150 mol m-2 yr-1 than that during the dry season 20 mol m-2 yr-1. In addition, we collected groundwater samples in Bangladesh and observed surprisingly high pCO 2 values 4,926-101,610 μatm. Groundwater in this area is likely to transport abundant dissolved inorganic carbon both HCO 3 and CO 2 to the ocean.

Stable Strontium Isotopic Compositions of River Water, Groundwater and Sediments From the Ganges–Brahmaputra–Meghna River System in Bangladesh

“…The concentrations of Sr in our river water and groundwater samples are presented in Table 1, along with major cation and anion data reported by Manaka et al (2015), Manaka et al (2017), and Manaka et al (2019). The water samples from the Ganges and Brahmaputra rivers had greater total dissolved solids, and higher Ca and Mg concentrations than those from the upper Meghna River (Figure 3).…”

“…The variations of δ 88 Sr among our samples collected in dry and wet seasons were within the analytical error, thus the relative inputs from the distinct Sr sources were effectively the same at a given sampling site regardless of season, suggesting δ 88 Sr is insensitive to monsoon weathering. Calcium and carbonate ion concentrations reported in Manaka et al (2019) show that Ω calcite values are notably higher during the dry season, especially for the Ganges river (12.5), whereas the δ 88 Sr values appear to have been unaffected by calcite precipitation, which increases δ 88 Sr values. Here we wish to address the sensitivity of δ 88 Sr to the extent of calcite precipitation using a closed/semi-closed type fractionation.…”

“…Water samples were passed through acetate membrane filters (0.45 µm pore size) and acidified with ultrapure HNO 3 (Tamapure-AA-100, Tama Chemicals, Japan). Ionic concentration, pH, and total alkalinity data were previously reported by Manaka et al (2017) and Manaka et al (2019). Water temperature and pH were measured by 826 pH Mobile Meter (Metrohm, Herisau) immediately at the sampling site.…”

“…The "*" sign for Sr/Ca denotes rain-corrected value. Cation and anion concentrations are from Manaka et al (2015), Manaka et al (2017) and Manaka et al (2019). National Institute of Advanced Industrial Science and Technology.…”

“…"G+B+M" indicates the sample from the lower Meghna River, below its confluence with the Ganges-Brahmaputra river system. Cation and anion concentrations are fromManaka et al (2015),Manaka et al (2017), andManaka et al (2019).…”