『Abstract
A detailed geochemical study on river waters of the Australian
Victorian Alps was carried out to determine: (i) the relative
significance of silicate, carbonate, evaporite and sulfide weathering
in controlling the major ion composition and ; (ii) the factors
regulating seasonal and spatial variations of CO2
consumption via silicate weathering in the catchments. Major ion
chemistry implies that solutes are largely derived from evaporation
of precipitation and chemical weathering of carbonate and silicate
lithologies. The input of solutes from rock weathering was determined
by calculating the contribution of halite dissolution and atmospheric
inputs using local rain and snow samples. Despite the lack of
carbonate outcrops in the study area and waters being undersaturated
with respect to calcite, the dissolution of vein calcite accounts
for up to 67% of the total dissolved cations, generating up to
90% of dissolved Ca and 97% of Mg. Dissolved sulfate has δ34S
values of 16 to 20‰CDT, indicating that it
is derived predominantly from atmospheric deposition and minor
gypsum weathering and not from bacterial reduction of FeS2. This militates against sulphuric acid weathering
in Victorian rivers. Ratios of Si vs. the atmospheric corrected
Na and K concentrations range from 〜1.1 to 〜4.3, suggesting incongruent
weathering from plagioclase to smectite, kaolinite and gibbsite.
Estimated long-term average CO2 fluxes from
silicate weathering range from 〜0.012×106 to 0.039×106
mol/km2/yr with the highest values in rivers draining
the basement outcrops rather than sedimentary rocks. This is about
one order of magnitude below the global average which is due to
low relief, and the arid climate in that region. Time series measurements
show that exposure to lithology, high physical erosion and long
water-rock contact times dominate CO2 consumption
fluxes via silicate weathering, while variations in water temperature
are not overriding parameters controlling chemical weathering.
Because the atmospheric corrected concentrations of Na, K and
Mg act non-conservative in Victorian rivers the parameterizations
of weathering processes, and net CO2 consumption
rates in particular, based on major ion abundances, should be
treated with skepticism.
Keywords: Rivers; Geochemistry; Weathering; CO2
consumption』
1. Introduction
2. The Victorian Alps drainage system
2.1. Geologic setting
2.2. Climate and watershed characteristics
3. sampling and analytical methods
3.1. Chemical analysis
4. Hydrochemistry
4.1. General characteristics
5. Sources of major ions in Victorian rivers
5.1. Correction for atmospheric input and halite dissolution
5.2. Evaporation
5.3. Carbonate, sulphate and sulfide weathering
6. Silicate weathering
7. Lithologic controls on CO2 consumption
via chemical weathering in the Victorian Alps
8. Climatic controls on CO2 consumption via
chemical weathering in the Victorian Alps
8.1. The effect of runoff and temperature
8.2. The effect of physical erosion
9. Conclusions and implications
Acknowledgements
Appendix A
References