| The global CO2concentration continue rising in recent years, many states havepaid a great attention and effort on energy conservation and emission reduction,carbon sink effect of chemical weathering and riverine dissolved carbon transporthave also aroused considerable attention from scholars. In this study we selected theDongjiang River and its tributaries as the research object, grasp the characteristics ofthe water physical and chemical parameters, revealed major ions temporal and spatialvariation characteristics as well as their sources, discussed effects of different factorson the river water chemical characteristics and estimated their relative contribution toriver water composition. We estimated the chemical weathering rate and the annualtotal consumption and flux of atmospheric CO2of chemical weathering in theDongjiang River basin. DIC and DOC conenertation of river water were analyzed toexplore their spatial variation characteristics. Monthly observation of DIC and DOCconenertation in basin outlet was taken to reveal their temporal variationcharacteristics and to calculate their export flux. The results are as follows:①The temperature of the Dongjiang River water ranged from9.10to34.80℃.The pH ranged from5.32to8.93and the river water is neutral to alkalescent. The ECranged from20.14to228.10μs/cm, which was at a low level. The EC of watersamples which were collected in dry and flood season showed little discrepancy, theconstruction of water conservancy facilities within the watershed and human activitiespollution on the water environment caused this phenomenon. The TDS ranged from12.48~150.50mg/L, with an average of59.88mg/L, which was far lower than theglobal median of100mg/L. The ORP of water samples collected in dry season were higher than the counterparts collected in flood season, organic matters decompositiondue to high temperature in flood season consumes dissolved oxygen were responsiblefor this phenomenon.②Cations in the Dongjiang River were dominated by Ca2+and Na+, while thecontents of Mg2+and K+were minor. Anions were dominated by HCO3-, followed byCl-while SO42-and NO3-were minor. The conenertation of Na+, K+, SO42-and HCO3-in Boluo section changed obvious and they showed significant correlations with dailydischarge, which reflects the impact of rock chemical weathering, sea salt depositionand anthropogenic inputs on river water composition.③According to the analysis of Gibbs diagram, most of the sampling points lie inthe rock weathering dominance area for cations and anions, but few of the samplesfell outside of the plot area due to high concentration of Na+and Cl-in these samplescompared to Ca2+and HCO3-, revealing that river water composition were mainlyaffected by rock chemical weathering and precipitation while the effect ofanthropogenic activities was also important. Each end-members contribution to riverwater composition can be arrayed as descending order: silicate, sea salt and carbonate,reflecting the dominative effects of chemical weathering of silicate, atmosphericprecipitation and human activities on the Dongjiang River water composition.④Chemical weathering of silicate in the Dongjiang River basin were mainly inthe supergene environment and the weathering products were between secondary clayminerals and kaolinite. The SWR and CWR in the Dongjiang River basin is calculatedas15.88t/km2/a and1.39t/km2/a, total chemical weathering rate was17.27t/km2/a.Compared to others river basin, the total chemical weathering rate of the DongjiangRiver basin is at a low level. The annual total consumption and flux of atmosphericCO2of chemical weathering in the Dongjiang River basin were (76.46~77.94)×108mol/a and (3.02~3.08)×105mol/km2/a, which was higher than the world average(2.46×105mol/km2/a), revealing that rock chemical weathering in the DongjiangRiver basin constitutes an important component of CO2consumption in the globalrocks chemical weathering.⑤In dry season the DIC content of the Dongjiang River basin ranged from2.23to14.54mg/L, in flood season it ranged from0.60to16.74mg/L, which was at a low level among worldwide rivers. The DIC content in Boluo sampling site changed stably,which was affected by the precipitation leaching and dilution effects as well as soilmicrobial activities. The DOC concentration in the Dongjiang River wasinsignificantly corrected with flood season water temperature and daily discharge(p>0.05), however, it was very significantly corrected with dry season watertemperature and TDS (p<0.01). The annual denudation flux of DIC was calculated as4.16t/km2/a, which is close to the Amazon River basin while lower than the theHuang River and the Xijiang River basin.⑥In dry season the average concentration of DOC in the Dongjiang River basinwas0.87mg/L while in flood season it was1.16mg/L, which was close to the Xijiangand Beijiang River basin and at a low level among worldwide rivers. The DOCcontents in Boluo sampling site fluctuated obvious, the maximum of DOC (2.25mg/L)appeared on the May (flood season) while minimum (0.79mg/L) occurred inSeptember (the end of flood season). The yearly export flux of DOC was2.17×1010g,DOC export was mainly in the flood season, especially in summer, which accountedfor56%and40%of the total yearly transport. Monthly denudation flux of DOC in theDongjiang River was very significantly corrected with runoff depth, and the annualdenudation flux of DOC was calculated as0.86t/km2/a, which is close to the NujiangRiver basin. |
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