Wujiang River Basin Water Chemical Characteristics, Weathering Processes CO <sub> 2 </ Sub> Consumption Trends And Changes In Water Quality

River plays a crucial role in biogeochemical cycles of elements and water chemistry geography research is one of most important fields of chemistry geography. Based on data of water quality monitoring published on Water Year Book, the major ion chemistry of Wujiang River have been studied in this work. The natural factors that affected on major ion chemistry have been analyzed through statics methods. Based on major chemical composition of river water, the key chemical weathering processes of the basin have been discussed and chemical weathering rate and atmospheric CO₂ consumption have been calculated. In addition, the water quality trend of the Wujiang River during the last 15-30 years has been analyzed as well as its cause. The conclusions reached are as follows:(1) The water chemistry characteristics: The chemical composition of Wujiang River is dominated by Ca²⁺,HCO₃^- and SO₄^2-, and chemical type of water is HCO₃^--Ca²⁺; the total ion consentration of the main stream of Wujiang River shows an increasing trend, and then decreases trend from the upper reaches to the lower reaches of Wujiang River; The middle content of Wujiang River is 273.1mg/l, which is higher than the content of Yangtze River and is 2 double of TDS in the world River.(2) The origin of major ion: according to Gibbs picture and Basic A-CN-K and A-CNK-FMternary, the composition of Wujiang River is dominated by carbonate weathering, which is responsible for 90% of concentration of HCO₃^-, and that of atmosphere CO₂ is 55%.(3) The primary chemical weathering process: the dominating dissolved matters are the calciteand dolomite, and that of secondary dissolution are the silicate and evaporatey..(4) The atmospheric CO₂ comsumption: based on the contribution proportion of atmosphericCO₂ to the HCO₃^- in the river water, the quantity of CO₂ consumption is 657.57×10⁸ mol, the value is 6 times more than quantity of Yellow River and 2/3 quantity of Yangtze River; the quantity of CO₂ consumption of middle reaches of Wujiang River is 482.83×10⁸ mol, which is 63.19-85.32 percent of quantity of CO₂ consumption of total Wujiang River; the quantity of CO₂ consumption of watershed of Hongfeng lake which is tributaries of Wujiang River is 5.14×10⁸ mol; compared to amount(5.15×10⁸mol) in 2005 years, it is less than half of amount in 1980s. (5) The chemical weathering rate: through the factor analysis results of watersheds waterchemistry and the statistical datas from water year book, the annual chemical weathering rates is 86.43 t/km².a, which is close to that of Yangtze River and higher than that of world river and Yellow river; the average chemical weathering rates of the upper and middle reaches of Wujiang River is 73.24 t/km².a, lower than that of Wujiang River.(6) The water quality (major ions) characters: according to "Seasonal Kendall"trend test to dataof all sites, Wujiang River showed a "acidification" trend from 1960s to 1990s with the contents of total ion content,Ca²⁺,SO₄^2-,HCO₃^- and the ratios of total hardness to total alkalinity are all increasing in different degree.(7) The cause of water change: thorough quality change statistics to Wulong site, Shiqian site andGuiyang site, space quality acidification trend was caused by serious acid precipitation and increasing nitrogenous fertilizer ran off from farmland; By analysis to the content of NH₄⁺ about Guiyang site, the result showed that the water qulity in acidification is related to that Guizhou province fired coal mostly and the trend was influenced strongly by discharge of acid wastes.