『Abstract
The Silicate Weathering Rate (SWR) and associated Carbon dioxide
Consumption Rate (CCR) in tropical silicate terrain is assessed
through a study of the major ion chemistry in a small west flowing
river of Peninsular India, the Nethravati River. The specific
features of the river basin are high mean annual rainfall and
temperature, high runoff and a Precambrian basement composed of
granitic-gneiss, charnockite and minor metasediments. The water
samples (n = 56) were collected from three locations along the
Nethravati River and from two of its tributaries over a period
of twelve months. Chemical Weathering Rate (CWR) for the entire
watershed is calculated by applying rainwater correction using
river chloride as a tracer. Chemical Weathering Rate in the Nethravati
watershed is estimated to 44 t.km-2.y-1
encompassing a SWR of 42 t.km-2.y-1 and
a maximum carbonate contribution of 2 t.km-2.y-1.
This SWR is among the highest reported for granito-gneissic terrains.
The assessed CCR is 2.9・105 mol.km-2.y-1.
The weathering index (Re), calculated from molecular ratios of
dissolved cations and silica in the river, suggests an intense
silicate weathering leading to kaolinite-gibbsite precipitation
in the weathering covers. The intense SWR and CCR could be due
to the combination of high runoff and temperature along with the
thickness and nature of the weathering cover. The comparison of
silicate weathering fluxes with other watersheds reveals that
under similar morpho-climatic settings basalt weathering would
be 2.5 times higher than the granite-gneissic rocks.
Keywords: Silicate weathering; Granitic-gneissic terrain; Tropical;
Nethravati River; CO2 consumption』
1. Introduction
2. Study area
3. Sampling and analysis
4. Results
5. Discussion
5.1. Sources of major ions
5.1.1. Silicate weathering rate in the Nethravati River
5.1.2. Degree of silicate-rock weathering in the Nethravati
watershed
5.1.3. Carbon dioxide consumption during rock weathering
5.2. Factors controlling the intensity of silicate weathering
in the Nethravati watershed
6. Conclusions
Acknowledgment
References