西江流域化学风化过程及其CO_(2)消耗通量

Chemical Weathering Process and Its CO_(2) Consumption Flux in the Xijiang River Basin

为深入评估中国南方陆地风化过程及河流物质循环过程,通过测定西江主要干、支流丰水期及枯水期水体主要离子和锶及其同位素比值,结合Galy模型对西江流域化学风化特征及CO_(2)消耗通量进行计算。结果表明:(1)西江流域化学风化受人类活动的影响较小,流域化学风化过程主要受到碳酸的控制。(2)河水阳离子的主要物质来源为硅酸盐岩和碳酸盐岩风化,硅酸盐岩在丰水期和枯水期的阳离子物质来源摩尔占比均为0.04,碳酸盐岩中石灰岩占比分别为0.79和0.78,白云岩分别为0.17和0.18。(3)西江流域在丰水期和枯水期的化学风化过程具有一定的差异性,由于硫酸参与白云岩的风化作用影响碳酸盐岩风化过程中的CO_(2)消耗通量,导致各个化学风化过程所涉及的CO_(2)通量有所差别。(4)碳酸风化碳酸盐岩在丰水期和枯水期所消耗的CO_(2)通量分别为(0.78~244.25)×10^(6) mol/km^(2)/yr和(0.10~49.16)×10^(6) mol/km^(2)/yr,硫酸风化碳酸盐岩所产生的CO_(2)通量分别为(0.25~42.16)×10^(6) mol/km^(2)/yr和(0.01~13.90)×10^(6) mol/km^(2)/yr,碳酸风化硅酸盐岩所消耗CO_(2)通量的分别为(0.05~17.83)×10^(6) mol/km^(2)/yr和(0.02~6.07)×10^(6) mol/km^(2)/yr。

To evaluate the process of terrestrial weathering and river material cycling in south China,the main ions,strontium(Sr)content,and Sr isotopic ratio of river water were measured in the main streams and tributaries of Xijiang River during wet and dry periods.By combining the Galy model,the chemical weathering characteristics and CO_(2) consumption flux of Xijiang River basin were calculated.The results show that:(1)Chemical weathering in the Xijiang River Basin is less influenced by anthropogenic activities and mainly controlled by carbonic acid.(2)The main sources of cations in river water are silicate and carbonate.The molar proportion of cation materials in silicate during the high and low water periods remains at 0.04.Meanwhile,the respective molar proportions of limestones in carbonate are 0.79 and 0.78,while those of dolomites are 0.17 and 0.18.(3)The chemical weathering process of the Xijiang River Basin shows discrepancy during the high and low water periods.The participation of sulfuric acid in dolomite weathering impacts the CO_(2) flux during the carbonate weathering process,causing the CO_(2) flux to be different in each chemical weathering process.(4)The CO_(2) fluxes of the chemical weathering process between carbonate and carbonic acid are(0.78~244.25)×10^(6) and(0.10~49.16)×10^(6) mol/km^(2)/yr during the high and low water periods,respectively.The respective CO_(2) fluxes between carbonate and sulfur acid are(0.25~42.16)×10^(6) and(0.01~13.90)×10^(6) mol/km^(2)/yr,and those between silicate and carbonic acid are(0.05~17.83)×10^(6) and(0.02~6.07)×10^(6) mol/km^(2)/yr.