Chemical weathering and atmospheric carbon dioxide (CO 2 ) consumption in Shanmuganadhi, South India: evidences from groundwater geochemistry

Chemical weathering in a groundwater basin is a key to understanding global climate change for a long-term scale due to its association with carbon sequestration. The present study aims to characterize and to quantify silicate weathering rate (SWR), carbon dioxide consumption rate and carbonate weathering rate (CWR) in hard rock terrain aided by major ion chemistry. The proposed study area Shanmuganadhi is marked with superior rainfall, oscillating temperature and runoff with litho-units encompassing charnockite and hornblende–biotite gneiss. Groundwater samples ( n = 60) were collected from diverse locations and analysed for major chemical constituents. Groundwater geochemistry seems to be influenced by geochemical reactions combining dissolution and precipitation of solids, cation exchange and adsorption along with minor contribution from anthropogenic activities. The SWR calculated for charnockite and hornblende–biotite gneiss was 3.07 tons km −2 year −1 and 5.12 tons km −2 year −1 , respectively. The calculated CWR of charnockite and hornblende–biotite gneiss was 0.079 tons km −2 year −1 and 0.74 tons km −2 year −1 , respectively. The calculated CO 2 consumption rates via silicate weathering were 1.4 × 10 3 mol km −2 year −1 for charnockite and 5.8 × 10 3 mol km −2 year −1 for hornblende–biotite gneiss. Lithology, climate and relief were the key factors isolated to control weathering and CO 2 consumption rates.