Chemical weathering and carbon dioxide consumption in a small tropical river catchment, southwestern India

Abstract

Studies done on small tropical west-flowing river catchments located in the Western Ghats in southwestern India have suggested very intense chemical weathering rates and associated CO2 consumption. Very less studies are reported from these catchments notwithstanding their importance as potential sinks of atmospheric CO2 at the global scale. A total of 156 samples were collected from a small river catchment in the southwestern India, the Payaswini–Chandragiri river Basin, during pre-monsoon, monsoon and post-monsoon seasons in 2016 and 2017, respectively. This river system comprises two small rivers originating at an elevation of 1350 m in the Western Ghats in peninsular India. The catchment area is dominated by biotite sillimanite gneiss. Sodium is the dominant cation, contributing ~ 50% of the total cations, whereas HCO3− contributes ~ 75% of total anions. The average anion concentration in the samples varied in the range HCO3− > Cl− > SO42− > NO3− > F−, whereas major cation concentration varied in the range Na+ > Ca2+ > Mg2+ > K+. The average silicate weathering rate (SWR) was 42 t km−2 y−1 in the year 2016 and 36 t km−2 y−1 in 2017. The average annual carbon dioxide consumption rate (CCR) due to silicate rock weathering was 9.6 × 105 mol km−2y−1 and 8.3 × 105 mol km−2 y−1 for 2016 and 2017, respectively. The CCR in the study area is higher than other large tropical river catchments like Amazon, Congo-Zaire, Orinoco, Parana and Indus because of its unique topography, hot and humid climate and intense rainfall.

Major Ion Chemistry of the Bheri (Snow-Fed) and the Babai (Rain-Fed) River Systems in Western Nepal: Implication on Water Quality

“…The (Na + +K + )/Tz + ratio in the Bheri and the Babai River systems (Figure 9) with the regression line having a slope value of 0.046 and 0.096, respectively, further confirms carbonate weathering indicating that there is no significant contribution of cations to the river waters from of alumino-silicate weathering. Little ionic contribution from silicate weathering has been reported in several water bodies from Nepal for instance, from Dudh Koshi and Indrawati Rivers (Paudyal et al, 2016), lakes of Pokhara (Khadka and Ramanathan, 2012;Khadka and Ramanathan, 2021;Kafle et al, 2023), Chandragiri-Payaswini River system in India (Nisha et al, 2021), and Teesta River in Sikkim, India (Tsering et al, 2019). Ca 2+ and HCO 3 − are the most dominant cation and anion in both the river systems.…”

“…The low level of K + relative to Ca 2+ , Mg 2+ , and Na + may be due to the fact that it can easily be fixed by clay minerals (Shakeri and Abtahi, 2020). Dominance of HCO 3 − indicates chemical weathering inferred from silicate and carbonate weathering rocks present in the river basin (Nisha et al, 2021). Dissolution of CO 2 in the surface water through natural gas exchange from atmosphere, respiration of riparian plants, and microbial activity in sediments results into the formation of CO 3 − and HCO 3 − , which in turn are mainly accountable for rock weathering, particularly carbonate rocks and aluminosilicate minerals (Gupta et al, 2022).…”

Mechanisms controlling major ion chemistry and its suitability for irrigation of Narmada River, India

“…As the pH of the Narmada was in the range of 7.2-8.8 (Figure 2(b)) i.e., slight alkaline, HCO 3 À concentration might have influenced its pH level. The high concentration of HCO 3 À indicates chemical weathering inferred from silicate and carbonate weathering rocks present in the river basin (Nisha et al 2021). In river catchment area CO 2 dissolves in the surface water through natural gas exchange from atmosphere, respiration of riparian plants and microbial activity in sediments.…”

Hydrogeochemistry of low agricultural soil yield in Sahelian and sub-tropical watersheds, Northern Cameroon

“…As a basis for this study, it is assumed that persistent poor agricultural outputs in the SDLSW and TBIW, reported by farmers and agriculture stakeholders to Cameroon's Institute for Agricultural and Rural Development (IRAD, 2018) is due to soil nutrients deficiency (Forth, 1984). Carbonic acid resulting from the dissolution of atmospheric carbon dioxide in rainwater and from biological respiration of organic carbon, into water bodies, makes water a potent geological solvent (Nisha et al, 2021). As a result, congruent and/or incongruent dissolution of primary and secondary rock minerals occurs and has been identified as an important geochemical mechanism by which elements are released to soil horizons through water-rock interaction (Forth, 1984).…”