A Study On The Chemical Weathering, Mechanical Denudation Correlative With River Water And Sediment Geochemistry And CO₂ Consumption Budget And Controlling Factors In The Major Drainage Basins Of China

The atmospheric CO₂ consumed by rock weathering is long been recognized as providing a major loss of carbon and decreasing atmospheric CO₂. The 0.28xl0^<sub>9t carbon derived from atmospheric CO₂ is transferred from atmosphere and biosphere to the ocean by surface rock weathering processes. In order to monitor the quality of the river, it is also important to understand the natural flux of dissolved ions. So far, most studies on water chemistry in China had focused on water quality and dissolved flux, scarce literatures could be used to understand the sources of solute load and CO₂ consumption budget in China. However, many scholars had attempted to fill in the gap in our knowledge of atmospheric CO₂ wastage by rock weathering and tried to link water chemistry with weathering reactions in the major world watersheds.In fact, as a very important part of material geochemistry cycle, chemical weathering and mechanical denudation plays a crucial role in affecting and changing the surface continent deeply. The global rivers transported the dissolved loads of about 4.0X10⁹t and solid fluxes of 15.5X10⁹t mainly derived from chemical weathering and mechanical denudation into the ocean yearly. In addition, the water and soil lost correlative with weathering and erosion had threatened seriously the production and living along the valleys at present.In this paper, newly compiled data on the major rivers of China were used to calculate the relative contribution rates of precipitation, main lithologies and atmospheric CO₂ according to the dissolved loads by principal components and correlative analysis. New estimates of carbonate and silicate weathering fluxes and associated with CO₂ consumption budget were given in the major drainage basins of China where previous information was indeed limited. An attempt was also made to calculate chemical weathering rates of silicates and carbonates per unit area. The paper focused on consumption of atmospheric CO₂ through rock weathering and weathering reactions what were attributable for dissolved loads in the major basins ofChina.Generally, dissolved loads were preferentially considered to evaluate chemical weathering relative to river-borne particulate/sediment because they are directly from source rock weathering. However, local differences in lithlology and human activities or precipitation might participate in and disturb the processes. Many studies had attempted to characterize chemical weathering process by focusing on geochemisty of river particulate and sediment.The sediment geochemistry may reflect and compare with the carbonates and silicates weathering degree by introducing the chemical index of alteration (CIA) and new sediment index of variation (SIV) and elemental molar abundance ratio of the sediment. The one main objective of this study would provide and compare the relative weathering intensities of silicates and carbonates with the different basins. For the mass balance equations, the average mechanical denudation rates would be estimated based on chemical weathering rates for the major basins of China.Finally, the first detailed compilation on fluvial transport model of solid was established based on data from a variety of sources for the typical major rivers of China. The relationship between the chemical weathering and physical denudation rates and possible controlling parameters were also explored. A combined effect of climate, relief, integrated lithology, vegetation and cultivated area seemed to explain the variability of modern chemical weathering and mechanical denudation rates.Samples and analysis methodsHundreds of water samples from the upper reaches to lower reaches of the rivers were collected and stored in acid-washed polypropylene bottles from 1997 to 2001 in major watersheds of China. After collection, all samples were filtered in time through 0.45 um acetate fibrous filters. The analytical procedure for water analysis included conventional flame atomic absorption spectrophotometry (AAS) for Ca,...