『Abstract
　Rates of chemical and silicate weathering of the Deccan Trap basalts, India, have been determined through major ion measurements in the headwaters of the Krishna and the Bhima rivers, their tributaries, and the west flowing streams of the Western Ghats, all of which flow almost entirely through the Deccan basalts.
　Samples (n = 63) for this study were collected from 23 rivers during two consecutive monsoon seasons of 2001 and 2002. The Total dissolved solid (TDS) in the samples range from 27 to 640 mg l^-1. The rivers draining the Western Ghats that flow through patches of cation deficient lateritic soils have lower TDS (average: 74 mg l^-1), whereas the Bhima (except at origin) and its tributaries that seem to receive Na, Cl, and SO4 from saline soils and anthropogenic inputs have values in excess of 170 mg l^-1. Many of the rivers sampled are supersaturated with respect to calcite. The chemical weathering rates (CWR) of “selected” basins, which exclude rivers supersaturated in calcite and which have high Cl and SO4, are in range of 〜3 to 〜60 t km^-2 y^-1. This yields an area-weighted average CWR of 〜16 t km^-2 y^-1 for the Deccan Traps. This is a factor of 〜2 lower than that reported for the Narmada-Tapti-Wainganga (NTW) systems draining the more northern regions of the Deccan. The difference can be because of (i) natural variations in CWR among the different basins of the Deccan, (ii) “selection” of river basin for CWR calculation in this study, and (iii) possible contribution of major ions from sources, in addition to basalts, to rivers of the northern Deccan Traps.
　Silicate　weathering rates (SWR) in the selected basins calculated using dissolved Mg as an index varies between 〜3 to 〜60 t km^-2 y^-1, nearly identical to their CWR. The Ca/Mg and Na/Mg in these rivers, after correcting for rain input, are quite similar to those in average basalts of the region, suggesting near congruent release of Ca, Mg, and Na from basalts to rivers. Comparison of calculated and measured silicate-Ca in these rivers indicates that at most 〜30％ of Ca can be of nonsilicate origin, a likely source being carbonates in basalts and sediments.
　The chemical and silicate weathering rates of the west flowing rivers of the Deccan are 〜4 times higher than the east flowing rivers. This difference is due to the correspondingly higher rainfall and runoff in the western region and thus reemphasises the dominant role of runoff in regulating weathering rates. The silicon weathering rate (SWR) in the Krishna Basin is 〜15 t km^-2 y^-1, within a factor of 〜2 to those in the Yamuna, Bhagirathi, and Alaknanda basins of the Himalaya, suggesting that under favourable conditions (intense physical weathering, high runoff) granites and the other silicates in the Himalaya weather at rates similar to those of Deccan basalts. The CO2 consumption rate for the Deccan is deduced to be 〜3.6×10⁵ moles km^-2 y^-1 based on the SWR. The rate, though, is two to three times lower than reported for the NTW rivers system; it still reinforces the earlier findings that, in general, basalts weather more rapidly than other silicates and that they significantly influence the atmospheric CO2 budget on long-term scales.』

1. Introduction
2. Materials and methods
　2.1. Hydrogeology of the region
　2.2. Sampling and analyses
3. Results
　3.1. General observations
　3.2. Spatial and interannual variation in TDS and major ions
4. Discussion
　4.1. Sources of major ions
　　4.1.1. Atmospheric supply
　　4.1.2. Other sources for Na, Cl and SO4
　4.2. Chemical weathering rates
　　4.2.1. Variability in CWRs among different Deccan Trap regions
　　4.2.2. Silicate weathering rates
　　4.2.3. Role of carbonates in Ca budget
　　4.2.4. Comparison of silicate weathering rates
　4.3. CO2 consumption rates
5. Summary and conclusion

Table 6. Silicate weathering rates in the Deccan Traps and in the Himalaya
River basin	Location	Runoff (mm y-1)	TDS(s) (mg l-1)	SWR (t km-2 y-1)	References
Deccan Traps
Krishna (KRS-2)	Alamatti	463	30	14	This work
West flowing rivers@	Western Deccan	1690	32	53	This work
Krishna system (east flowing)	Deccan	463	28	13	This work
Narmada-Tapti-Godavari	Northern Deccan	463	81	37*	Dessert et al.(2001)
Himalaya
Yamuna	Batamandi	1125	25	28	Dalai et al.(2002)
Bhagirathi	Devprayag	1064	14	15	Krishnaswami et al.(1999)
Alaknanda	Bhagwan	1195	9	10	Krishnaswami et al.(1999)
TDS(s) = Σ(Na + K + Mg + Ca)sil + SiO2; TDS(s) and SWR are rounded off. * Chemical weathering rate. @ Sukh, Shashtri, Vashishthi, Gad, Kajli, and Arjuna.

Acknowledgments
References
Appendix

• Dalai,T.K., Krishnaswami,S. and Sarin,M.M.(2002): Major ion chemistry in the headwaters of the Yamuna river system: chemical weathering, its temperature dependence and CO2 consumption rates. Geochim.Cosmochim.Acta, 66, 3397-3416.
• Dessert,C., Dupre,B., Francois,L.M., Schott,J., Gaillardet,J., Chakrapani,G. and Bajpai,S.(2001): Erosion of Deccan Traps determined by river geochemistry: impact on the global climate and the ⁸⁷Sr/⁸⁶Sr ratio of sea water. Earth Planet.Sci.Lett., 188, 459-474.
• Krishnaswami,S., Singh,S.K. and Dalai,T.K.(1999): Silicate weathering in the Himalaya: Role in contributing to major ions and radiogenic Sr to the Bay of Bengal. In Ocean Science, Trends and Future Directions (ed. B.L.K.Somayajulu), pp.23-51. Indian National Science Academy and Akademia International.