Geochemical Characteristics Of River Water During High-Flow Season In The Pearl River Basin, South China

The study of the relationship between chemical weathering and global carbon cycle has been one of the topics of scientists over the years.It is an important link in the study of carbon cycle to determine the source and fate of carbon in large river basins.Hydrochemical investigations were carried out in the Pearl River basin,which flows through the karst area of South China.The major ions,H,O and Sr isotopes were determined from the river water to analyze the spatial variation characteristics in July 2014?wet season?.Based on the chemical characteristics analysis of the Pearl River water,we research the key chemical weathering processes of the river basin and discuss the influences of the difference rock weathering from atmospheric precipitation and human-activities.Then,we estimate the rocks chemical weathering rate and consumption of atmospheric CO₂ in the process of the river basin rocks chemical weathering.The results are showed as follows:?1?The pH values of the Pearl River water varied from 6.36 to 8.43,with an average of 7.7.The EC values were between 90 and 533?S·cm^-1 with an average of 307.7?S·cm^-1.The TDS values were between 70.0 and 415.1 mg·L^-1 with an average value of 241.4 mg·L^-1.The major cation concentrations in river water followed the descending sequence of Ca²⁺>Mg²⁺>Na⁺>K⁺>NH₄⁺and major anions of HCO₃^->SO₄^2->NO₃^->Cl^-.The?¹⁸O values ranged from-10.3‰to-4.8‰with a mean value of-7.6‰and the?²H ranged from-77.1‰to-35.3‰with a mean value of-54.0‰.The concentrations of dissolved Sr were between 0.67 and 7.34?mol·L^-1,with an average value of 2.41?mol·L^-1.The ⁸⁷Sr/⁸⁶Sr ratios ranged between 0.707537 and 0.724847and the mean value was 0.711103.?2?The analysis of water chemistry in the Pearl River basin showed that atmospheric precipitation contributes significantly to K⁺and Ca²⁺,and the contribution to Na⁺and Mg²⁺is very low,which is directly related to the atmospheric acid deposition.The influence of human activities on the dissolved loads of river water is also becoming increasingly serious.?3?The analysis of rock weathering processes showed that the chemical composition of the Pearl River water is mainly controlled by rock weathering,dominated by weathering of carbonate rocks,and is less affected by weathering of silicate rocks and evaporites.It would appear that H₂SO₄ is involved as a proton donor in weathering reactions in the Pearl River basin,and the participation of HNO₃ may also be involved.?4?The total chemical weathering rate of rocks for the Pearl River basin is approximately70.37 t·km^-2·a^-1,which is much higher than the global mean values and controlled by both temperature and runoff.The budgets of CO₂ consumption by carbonate and silicate weathering are estimated to be 197.31×10⁹ mol·a^-1 and 90.07×10⁹ mol·a^-1,accounting for 1.60%and 1.03%of the CO₂ consumption flux in the global carbonate and silicate rocks,respectively.