Study Of Chemical Weathering In The Huanghe Drainage Basin And Transportation Character Of The Dissolved Carbon In Summer

Funded by the National Key Basic Research Development Project (2002CB412501) and National Natural Science Foundation of China(40476063),we investigated the hydrology and geochemistry of the Yellow River Basin and inorganic carbon in the main stream of the river from June to July 2007.We study the chemical weathering and its rate in the drainage basin,CO₂ consumption rate(volume) caused by chemical weathering of rocks,and the transport characteristics of inorganic carbon. Preliminary conclusions are presented as follow:1.What dominates in the Huanghe catchments is the chemical weathering of carbonate and the dissolution of evaporate.Carbonate,mainly including calcite and dolomite,dramatically contributes in the upstream while with regard to the downstream evaporate such as halite,Glauber salt,Gypsum,magnesium sulfate offers more.2.The average annual rate of chemical weathering in the Huanghe watershed is estimated as 22.94 t/km²/yr during this investigation.The consumption rate of CO₂ in terms of silicate and carbonate is 12.23×10³ t/km²/yr 55.05×10³ t/km²/yr respectively.The rate of chemical weathering is expected to be 53.41 t/km²/yr,above 36 t/km²/yr,the world' average value,according to the average discharge into the sea from Huanghe River 58.02×10⁹ km²/yr.And the consumption rate of CO₂ in terms of silicate and carbonate is 28.48×10³ mol/km²/yr 55.05×10³ mol/km²/yr respectively.3.PIC transport pattern is significantly controlled by the TSS concentration.PIC value is positively correlated with the erosive degree,and therefore linearly increases with the TSS concentration.While PIC%logarithmically declines along with the increase of the TSS concentration.Due to the chemical weathering,PIC is converted into DIC.TSS is the major factor controlling the DIC/PIC value and so the DIC generally is the main form of inorganic transportation.4.PCO₂ values of the surface water of the Yellow River stays between 646 1649μatm,with an average 1120μatm in summer,and lags behind that for the main rivers in the world.Besides the spatial distribution is uneven,with the value in the mid-stream higher than that in the downstream and upstream. pCO₂ is mainly controlled by the carbonate system resulted from the strong mechanical erosion and chemical weathering.Biological aerobic respiration weakly contributes to pCO₂ w but becomes strong in the static water in the reservoir.In addition,the photosynthesis of phytoplankton consumption on the role of CO₂ has an weak effect on the pCO₂.5.During the survey conducted in the Huanghe watershed,the annual total volume CO₂ consumption caused by rock chemical weathering is estimated as 50.59×10⁹mol,amomg which CO₂ consumption from the process of carbonate and silicate weathering are respectively expected to be 9.20×10⁹mol and 41.39×10⁹mol.The flux of DIC from erosion in the Yellow River surpasses that of PIC in respect to magnitude in summer.Huanghe River serves as a source region for the atmospheric CO₂,water according to our research and analysis.The air interface CO₂ exchange rate is expected to be 2.02×10^-1μmol·m^-2·s^-1,the CO₂ outgassing flux about 1.25×10⁹ mol C,roughly equaling to the annual carbon trapped by 8.25×10³km² grassland or 1.12×10² km² of forest.The CO₂ flux released from the Huanghe River closed to that of the Ottawa River yet much lower than that of the Amazon River.