Chemical weathering and associated CO2 consumption in the Mahanadi river basin, India

Chemical weathering of continents is one of the major geochemical processes which consumes atmospheric CO2 and exerts a strong impact on the global climate. The major ion chemistry of the Mahanadi river basin, one of the largest river basins in India, is determined to investigate the sources of major ions and their spatio-temporal variability, chemical weathering rates and associated CO2 consumption in the basin. The results reveal that the ions in the basin are dominated by Ca and HCO3. The total dissolved solids (215 mg L-1 in monsoon and 270 mg L-1 in pre-monsoon) and total cation concentration (2367 mu Eq in monsoon and 3214 mu Eq in pre-monsoon) in the basin are relatively higher than the global average. The dissolved loads in the basin are dominantly controlled by rock weathering particularly chemical weathering of silicates and carbonates. The estimated chemical weathering rates based on the forward model are 44.94 t km(-2) yr(-1) in monsoon and 2.45 t km(-2) yr(-1) in pre-monsoon with annual average chemical weathering rate of 23.7 t km(-2) yr(-1). The contribution of silicate weathering rates in the basin is 32 and 1.55 t km(-2) y(-1) during monsoon and pre-monsoon period respectively. The estimated CO2 consumption rate associated with chemical weathering in the basin is 13.3 x 10(5) mol km(-2) yr(-1) during monsoon and 0.66 x 10(5) mol km-2 yr(-1) during pre-monsoon period with an average annual rate of 6.9 x 10(5) mol km(-2) yr(-1) which is higher than the global average. The net rate of CO2 consumption by silicate weathering is estimated to be approximately 4.78 x 10(5) mol km(-2) yr(-1). It is observed that the runoff and lithology are the major factors influencing chemical weathering in the basin. However, the basin elevation has a good negative correlation with chemical weathering rate.