『Abstract
The draw down of CO2 from the atmosphere
during mineral weathering plays a major role in the global budget
of this greenhouse gas. Silicate minerals remove twice the CO2 of carbonate minerals per mole of calcium in
runoff during weathering. Bedrock weathering chemistry was investigated
in the White River watershed of northeastern USA to investigate
whether there are seasonal differences in carbonate and silicate
weathering chemistry. Geographic Information Systems analyses
of bedrock geology were combined with major element concentrations
in river waters to gain an understanding of the consistency of
mineral weathering during three seasons. The percent of carbonate
mineralogy comprising the bedrock in tributaries of the White
River varied from less than 5％ to 45％ by area. A mass balance
calculation using major element concentrations in waters was applied
to estimate the seasonal relationships between bedrock geology
and bicarbonate flux. In all tributaries and the main stem of
the White River the highest calculated percent of bicarbonates
from carbonate mineral weathering was measured in the late fall.
The results suggest that carbonate and silicate bedrock weathering
processes are seasonally controlled. Thus single season sampling
could not accurately represent an entire year's geochemical budget.
In the White River, water samples obtained solely during the simmer
would consistently underestimate the total yearly source of bicarbonate
from carbonate bedrock weathering. The same sample set would also
provide data that would lead to an underestimation of the yearly
atmospheric CO2 draw down by bedrock weathering
in the watershed. For example at four of the seven locations studied
there was an almost two-fold difference between summer and spring
calculated atmospheric CO2 consumption rates.
Keywords: Bedrock weathering; River chemistry; Carbonate system;
Carbon dioxide; Geochemistry』
1. Introduction
2. Sampling and analytical methods
2.1. The White River watershed
2.2. Field and laboratory methods
3. Results
3.1. Geologic classification by GIS
3.2. Major cation and anion chemistry
4. Discussion
4.1. Seasonal influences on river geochemistry
4.2. Bedrock influences on river geochemistry
4.3. Carbonate and silicate weathering as a source of bicarbonate
4.4. Atmospheric CO2 consumption in the
White River watershed
5. Conclusions and implications
Acknowledgements
References