『Abstract
Concentrations of major ions, Sr and 87Sr/86Sr
have been measured in the Gomti, the Son and the Yamuna, tributaries
of the Ganga draining its peninsular and plain dub-basins to determine
their contribution to the water chemistry of the Ganga and silicate
and carbonate erosion of the Ganga basin. The results show high
concentrations of Na and Sr in the Gomti, the Yamuna and the Ganga
(at Varanasi) with much of the Na in excess of Cl. The use of
this ‘excess Na’ (Na*=Nariv -
Clriv) a common index of silicate weathering
yield values of 〜18 tons km-2 yr-1 for silicate
erosion rate (SER) in the Gomti and the Yamuna basins. There are
however, indications that part of this Na* can be from
saline/alkaline soils abundant in their basins, raising questions
about its use as a proxy to determine SER of the Ganga plain.
Independent estimation of SER based on dissolved Si as a proxy
give an average value of 〜5 tons km-2 yr-1
for the peninsular and the plain drainages, several times lower
than that derived using Na*. The major source of uncertainty
in this estimate is the potential removal of Si from rivers by
biological and chemical processes. The Si based SER and CER (carbonate
erosion rate) are also much lower than that in the Himalayan sub-basin
of the Ganga. The lower relief, runoff and physical erosion in
the peninsular and the plain basins relative to the Himalayan
sub-basin and calcite precipitation in them all could be contributing
to their lower erosion rates.
Budget calculations show that the Yamuna, the Son and Gomti together
account for 〜75% Na, 41% Mg and 〜53% Sr and 87Sr of
their supply to the Ganga from its major tributaries, with the
Yamuna dominating the contribution. The results highlight the
important role of the plain and peninsular sub-basins in determining
the solute and Sr isotope budgets of the Ganga. The study also
shows that the anthropogenic contribution accounts for ≦10% of
the major ion fluxes of the Ganga at Rajmahal during high river
stages (October). The impact of both saline/alkaline soils and
anthropogenic sources on the major ion abundances of the Ganga
is minimum during its peak flow and therefore the SER and CO2 consumption rates of the river is best determined
during this period.』
1. Introduction
2. Geohydrology of the Ganga basin
2.1. Hydrological setting
2.2. Geological setting
3. sampling and analysis
4. Results
5. Discussion
5.1. General observations
5.2. Sources of major ions
5.2.1. Atmospheric contribution to water chemistry
5.2.2. Anthropogenic input
5.2.3. Silicate weathering and solution of saline/alkaline soils
5.2.4. Carbonate weathering
5.3. Impact of alkaline/saline soils on estimates of SERs and
elemental fluxes
5.4. Sr and 87Sr/86Sr budget
6. Conclusions
Acknowledgments
Appendix A. Supplementary data
References