Chemical weathering and associated CO 2 consumption in the Godavari river basin, India

Abstract

The study gives insight into the source of major ions concentration and their seasonal variability, chemical weathering rates and associated CO 2 consumption in the Godavari River Basin (GRB). The results show that the Godavari river basin water was mildly alkaline, with a wide range of TDS (40 to 550 mgL − 1 ). The most dominant anion was HCO 3 − followed by Cl − and the most dominant cation was Ca 2+ followed by Na + for all three sampling seasons. The average molar ratio of Cl −/Na + was 0.59 in pre-monsoon, 0.51 for post-monsoon and 0.66 in monsoon, which is lower than the values, reported in earlier studies. The range of precipitation corrected molar ratio for (Ca 2+/Na +) was 0.20 to 1.84 in pre-monsoon, 0.59 to 1.59 in post-monsoon and 0.35 to 2.09 in monsoon season, (Mg 2+/Na +) was 0.26 to 1.18, 0.24 to 0.62 and 0.17 to 1.42 in pre-monsoon, post-monsoon and monsoon respectively, while (HCO 3 −/Na +) was 2.08 to 7.0 in pre-monsoon,1.98 to 4.05 in post-monsoon and 1.67 to 5.79 in monsoon, which indicated the influence of basalt weathering on river water chemistry. Factor analysis indicated the vital role of silicate and carbonate weathering along with atmospheric and anthropogenic input that govern the water chemistry of the GRB. The chemical weathering rate of GRB varied from 17.61 to 68.16 tkm − 2 y − 1 with an average of 39.49 tkm − 2 y − 1 in pre-monsoon, from 27.94 to 65.67 with the average of 42.02 tkm − 2 y − 1 in post-monsoon season and from 17.53 to 62.95 tkm − 2 y − 1 with an average value of 34.69 tkm − 2 y − 1 in monsoon. The associated CO 2 consumption rate due to chemical weathering in the GRB was ∼ 0.25 × 10 12 mol y − 1 which is ∼ 1.04% of the annual global CO 2 consumption (24 × 10 12 mol y − 1 ) by chemical weathering of silicate and carbonate rocks. The average annual CO 2 drawdown by Deccan trap (area 5 × 10 5 km 2) based on CO 2 consumption rate due to silicate weathering determined in this study was 0.29 × 10 12 mol y − 1 , ∼ 2.48% of the annual global CO 2 consumption (11.7 × 10 12 mol y − 1 ) by silicate weathering [Gaillardet, J., Dupre, B., Allegre, C.J., 1999. Global silicate weathering and CO 2 consumption rates deduced from the chemistry of large rivers. Chemical Geology 159, 3–30.]. The present study was the first attempt to calculate weathering rate of Deccan trap using major ion chemistry of the Godavari River water, the third largest river in India. The study further provides the inventory for CO 2 consumption on river basin scale, which is an important consideration from the point of view of global warming.