Chemical denudation in a small mountainous-coastal river in the tropics: Insights from Kali River, Southwestern India

A study was conducted for the first time to understand the geochemical processes controlling the chemistry of the Kali River in tropical southwestern India and to determine its chemical denudation and net carbon dioxide consumption. The samples were collected from the source to the mouth of the river (15 stations) during monsoon (July 2018), post-monsoon (December 2018), and pre-monsoon (May 2019) seasons. The catchment experiences intense chemical weathering on account of heavy rainfall accompanied by runoff during the summer monsoon. Seasonal variations in silicate weathering processes are significantly controlled by runoff, and their rates are proportional to the discharge. The annual chemical denudation rate (CDR) calculated exclusively from the upstream catchment that are dominated by silicate rocks estimated to be 48.2 tons/km 2 /yr with a silicate weathering rate (SWR) of 41.3 tons/km 2 /yr and carbonate weathering rate (CWR) of 6.9 tons/km 2 /yr. The CDR is two times higher than the global mean average rate. The mean CO 2 consumption rate (CCR) for silicate weathering is 2.9 × 10 5 mol. km −2 y −1 , which is three-fold higher than the global average. Silicate rock weathering intensity (Re) values indicate the formation of the gibbsite. The Re does not show variations from upstream to downstream, implying the rapid transport of weathered material from the river catchment area. Intense rain, runoff, and temperature are the dominant climatic factors that accelerate weathering in the study area. This underscores the significance of small mountainous coastal rivers as drivers of intense chemical weathering in humid tropical environments, which removes the atmospheric CO 2 . This study adds to the existing database on chemical weathering and associated fluxes in granitic catchments across the globe. • A small tropical river draining predominantly silicate rocks is studied. • Weathering dominated in the upstream and anthropogenic activities in the downstream. • Rainfall, accompanying runoff and high temperature controlled the weathering. • Silicate weathering rates are one-fold higher than other global granitic watersheds.