『Abstract
The dissolved concentrations of major ions and Sr isotopes (87Sr/86Sr)
were measured in the headwaters of the Chambal river and its tributaries
draining the Deccan Trap basalts and the Vindhyan sediments of
peninsular India. The total dissolved solids (TDS) ranged from
181 to 547 mg L-1; much higher than the global “mean”
river water. A significant fraction of solute abundance in the
Chambal river is derived from sodium salts, unlike the Himalayan
rivers which exhibit dominance of (Ca+Mg) salts. It is estimated
that the Chambal river supplies about one-third of sodium via
the Yamuna to the Ganga at Rajshahi (Bangladesh), with only 〜6.5％
of water discharge. The presence of Na salts not associated with
chloride in the Chambal headwaters constraints the application
of Na* (Na corrected for Cl) as an index of silicate
derived component. This finding brings out the need to revisit
the estimates of silicate erosion rate (SER) and associated CO2 consumption in the Ganga basin, downstream Allahabad,
based on Na* as an index.
The Sr concentration in the Chambal tributaries varied from 1.9μM
to 5.9μM and 87Sr/86Sr ratio from 0.70923
to 0.71219. Unlike the Himalayan Rivers, Sr isotope composition
in the Chambal river is far less radiogenic as the major sources
of Sr to the Chambal are the Deccan Trap basalts and the Vindhyan
sediments, which are low in 87Sr/86Sr. The
Sr isotope budget of the Ganga, based on available data of the
Chambal, Betwa, Ken, Yamuna and the Ganga shows that, weathering
of the Deccan Trap basalts and the Vindhyan sediments (the drainage
basin of the Chambal, Betwa and the Ken) contribute 〜70％ of the
dissolved Sr to the Ganga at Varanasi. This study highlights the
key role of peninsular rivers draining the Deccan and the Vindhyan
regions in the major ion and Sr budget of the Ganga.
Keywords: Chambal River; Major ion chemistry; Silicate erosion;
Saline/alkaline soils; Sr-isotopes』
1. Introduction
2. Geologic setting of the Chambal river system
3. Sample collection and analytical methods
4. Results
5. Discussion
5.1. Ca, Mg distribution
5.2. Contribution of major ions from different sources to the
Chambal river system
5.2.1. Atmospheric deposition
5.2.2. Chemical weathering of the drainage basin
5.2.2.1. Solution of alkaline/saline soils
5.2.2.2. Silicate weathering
5.3. Erosion rates and CO2 consumption rates
5.3.1. Sr and 87Sr/86Sr isotope ratio
in the Chambal system
5.3.2. Impact of the Chambal on dissolved Sr flux and 87Sr/86Sr
isotope ratio of the Ganga
6. Flux of Na from the Peninsular Rivers to the Ganga: implication
to SER of the Ganga
7. conclusions
Acknowledgements
Appendix A
References