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Wei-Jun Cai Xianghui Guo Chen-Tung Arthur Chen Minhan Dai Longjun Zhang Weidong Zhai Steven E. Lohrenz Kedong Yin Paul J. Harrison Yongchen Wang 《Continental Shelf Research》2008
In this paper, general relationships of riverine bicarbonate concentrations and fluxes as a function of drainage basin mineral content and runoff are examined using a database of the 25 largest rivers in the world. Specific HCO3− flux normalized to unit basin area, which peaks in the mid latitudes, was found to be strongly correlated with the carbonate mineral content of river basins, while river HCO3− concentration was related to the balance of precipitation and evaporation. Within this global context, the weathering patterns of CO2 in a few large rivers (Changjiang, Huanghe, Pearl, and Mississippi rivers) were examined in further detail. The Zhujiang (Pearl River), especially its largest branch (Xijiang), was characterized by the highest specific weathering rate among all the world's large rivers due to an exceptionally high carbonate mineral content (over 80%) in its drainage basin and its warm and wet environment. It has a moderate level of HCO3− concentration, however, due to dilution by relatively high precipitation in the watershed. In stark contrast, the Huanghe (Yellow River) has one of the lowest specific weathering rates because of low carbonate mineral content and a dry climate. However, it has a high HCO3− concentration due largely to the concentrating effects of high evaporative water loss, as a result of arid weather and the agricultural use of water through irrigation systems, as well as carbonate-containing surficial deposits (i.e., loess). The strong correlation between specific HCO3− fluxes and discharge in all four rivers with different discharge seasonality suggests that higher precipitation in drainage basins promotes higher weathering rates. 相似文献
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Hydrophilic xenobiotics can be eliminated in the UV/H2O2-process. The oxidation in this process is enhanced by the photolytically generated HO radicals. Bicarbonate is able to scavenge HO radicals. So it was expected that the degradation rates of the investigated xenobiotics were affected by the influence of bicarbonate. In contrast to the widely described decrease of the degradation rate, a much more complex situation was found in this investigation. The degradation rates of 2-amino-1-naphthalenesulfonate and diphenyl-4-sulfonate were decreased and reached for high concentrations of bicarbonate the values of the photolytical degradation rate. The degradation of 4,4′-diaminostilbene-2,2′-disulfonate was accelerated significantly in the presence of bicarbonate. The degradation rate of EDTA was increased at small concentrations of bicarbonate and decreased at higher concentrations. 相似文献
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The factors controlling the chemistry of 69 low-order streams in the Blue Ridge and Valley and Ridge physiographic provinces of Virginia and Maryland were studied over a 13-month period. Principal component analysis was used to examine regional patterns in stream chemistry and to examine the degree to which the chemistry of low-order streams is controlled by the bedrock upon which they flow. Streams clustered into regionally isolated groups, strongly related to bedrock type, with SO2?4 and HCO?3 the chemical variables of most importance. Sulphate concentrations appear to be strongly controlled by climate and hydrology, and sorption in the soils within the watershed. Much of the atmospherically derived SO2?4 accumulates in watersheds during the growing season and is later flushed out. Weathering reactions were found to be particularly important in the production of HCO?3, accounting for 91 per cent on an annual basis, and export of divalent cations from these watersheds, accounting for 48–50 per cent on an annual basis. About half of non-anthropogenic Na+ was derived from weathering of silicates, whereas nearly all K+ was identified with leaching by SO2?4. Water chemistry was strongly related to the rock type in the watershed and the weatherability of the component minerals. Rock type is not a randomly distributed function; instead, it is controlled by geologic factors that result in clusters of similar rock types in a given region. When planning large synoptic studies, it is extremely important to consider that a sampling scheme based on random sampling of a non-randomly distributed function May, not provide the most accurate representation of the variables of interest. Instead, a hierarchical sampling scheme May, be indicated. Our results also suggest that, although one sample in time May, be sufficient to characterize the primary geochemical factors controlling stream chemistry throughout the year, it May, not be sufficient to detect subtle, flow-related alterations in chemistry. 相似文献
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