Chemical Erosion rates of Peninsular Indian Rivers: An inversion approach

Abstract

Chemical weathering of silicate minerals act as a major sink for atmospheric CO2 in a geological timescale. These continental weathering processes are higher in tropical regions, mainly due to conducive climate (higher temperature and intense rainfall). The rivers in the peninsular India predominantly drain silicate terrains and hence, weathering in from this region is likely to play an important role in global carbon budget. Recognizing this, appreciable amount of geochemical studies of these Individual rivers have been carried out at basin-wide scale; however, a comprehensive study considering all the Peninsular Indian rivers is still pending. The present study aims to study these rivers, by using the available major element geochemical information from literature, to quantify the chemical weathering in the region, associated CO2 consumption and understand the factors regulating the phenomenon. The river water chemistry of the Peninsular Indian rivers are mainly dominated by Ca and HCO3, hinting at dominant role of carbonate weathering influencing the hydrochemistry. Although the rivers predominantly flow through silicate terrains, the faster dissolution kinetics of carbonates supply significant amount of solutes to these basins. The chemical compositions of these rivers also show strong seasonal variations, mainly due to relative changes in silicate-to-carbonate weathering. The silicate weathering rates (SWR) and hence, the CO2 consumption potential of these rivers are by and large found to be higher when compared to the corresponding rates for the global average for rivers. Two Archean flowing rivers, the Damodar and Subranrekha, are found to have high SWR compared to other Archean drain streams (Mahanadi and Nethravati). The observed higher SWR for Damodar and Subranrekha is mainly due to sulphuric acid-mediated weathering in these basins. Relatively higher SO4/HCO3 ratios observed for these two rivers also support the H2SO4-mediated weathering. The H2SO4, a relatively stronger acid, may form through oxidation of sulphidies and/or anthropogenic supplies from mines present in these basins. Unlike the CO2-mediated weathering, the H2SO4-mediated weathering from these basins can act as an important source of CO2.