A Study On The Chemical Weathering, Mechanical Denudation And Transport Of Carbon

As a very important part of the global surface water cycle, River water plays a crucial role in the water chemical cycle of the elements. The geochemical and the hydrological features of the river water transportation are a signature of the surface weathering and denudation. And at the same time, it reveals the hydrology, geology, climate and entironment of the basin-wide scale.Based on the status of the international research topics and the needs of the research topics.In this paper, we take the Longchuan River as the typical climate, geology and ecological background for the research object. To discuss the main source of major ions, mechanism, the quantity and their response to the changes of the river suspended sediment and the puts of different forms of canrbon by interrelated the river area of the weathering with the mechanical of denudation。Main contents and conclusions of this paper include the following three parts:First, in the use of elements composition to trace the chemical weathering reactions occurred in the river basin by mathematical statistical, and discussing the influences of the different rock, atmospheric precipitation,human activities and atmospheric CO2 contribution to the river. Through explore the intensity of chemical weathering of rock basin to estimate the chemical weathering and the elements transportion. The results is, Longchuan Jiang has a high concentration, because of the weathering of carbonate rock, the chemical compostition of the reaches of Longchuan Jiang is dominated by HCO3-,Ca2+,Na++K+ and SO42-. We can know that the atmospheric precipitation and the human activities can be basically ignored, and the river is under the control of "rock weathering type". The relative contribution of Carbonate, silicate, evaporation and atmospheric CO2 to water ions in the Longchuan River Basin are 39.0%,19.0%,6.1% and 34.9%.Second, by using the available data to analyze the relationship between the water body and sediment charateristics, revealed the correlation and the change erosion time of the water and sediment. At last, to characterize the mechanical physical erosion rate and quantitative the strength of the watershed denudation by the use of the river suspended particulate matter or sediment, erosion modulus. By the whole, the relations between the chemical weathering rates or the runoff modulus and the chemical weathering rate to catch the weathering intensity, and evaluate the quantitative analysis in an objective view. Obtained, sediment yield accompany with the water, average more sediment in flood year and less sand in the dry years.The relationship has a consistency of the overall trend still existing between water and sediment in Longchuan Jiang. In these two years, the chemical weathering rates and ion-runoff model were 41.7t.km-2.yr-1, 36.6t.km-2.yr-1and 63.9t.km-2.yr-1, and 56.2t.km-2.yr-1. Both of the two take on a highly significant in positive correlation. To use these seven years'data we can find the physical weathering rate is not relatively high, the maximum and minimum are 152.4t.km-2.yr-1 and 50.4t.km-2.yr-1.Based on the average sediment volume changes obvious, we can see the improvement of the watershed situation than before, the local grovement has made a great achievements.Third, by analyzing the composition of various forms of carbon, we obtained the factors to control the canbon transport, the output with the variation of seasonal and hydrological processes, and to calculate the erosion of various forms of carbon flux. The change of the whole type of carbon accompany with the water and solid. And judge the strength of the chemical weathering rate and physical weathering rate qualitatively. Finally, focus the research on the response to the various forms of carbon in the flood period and comparied whith other river. We drawn, the erosion of organic matter accompany obvious with the seasons and hydrological changes in the overall. The linear relationships between the carbon and the TSS take on significant differences, for example as the POC and TSS with a positive correlation, DOC to the TSS is sometimes shows a positive correlation sometimes shows a negative correlation, DIC and TSS has a certain linear correlation, indicated existed that a certain controlled by the effect of the water dilution. The average DOC to POC is 0.84, in the dry season the transport of the two didn't change significantly, but unexpected heavy rain occurred in the wet period increased the soil erosion, leading the POC flux is greater than DOC flux. Showing the erosion effect responded obviously. By statistics these two years, the water had transported the carbon for 51.8×106g.km-2.yr-1, and in the high-flow period, the inorganic carbon and organic carbon accounted for 90% and 10% respectively. And during the time of November 2008, it removes different carbon accounting for the full-year is 33.3%,34.4% and 59.9%, response to the "erosion effect" significantly.The last, many potential deviations of the above estimated results from true values may retrospect to limited of study level. The consistency and supplement with each other may make sure the whole discussion and demonstrated truly and equitably.