Chemical weathering and carbon dioxide consumption in a small tropical river catchment, southwestern India
Baby Krishnan Nisha, Keshava Balakrishna, H N Udayashankar, B. R. Manjunatha
Abstract
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 CO 2 consumption. Very less studies are reported from these catchments notwithstanding their importance as potential sinks of atmospheric CO 2 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 HCO 3 − contributes ~ 75% of total anions. The average anion concentration in the samples varied in the range HCO 3 − > Cl − > SO 4 2− > NO 3 − > F − , whereas major cation concentration varied in the range Na + > Ca 2+ > Mg 2+ > 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 × 10 5 mol km −2 y −1 and 8.3 × 10 5 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.