漓江流域中下游无机碳通量动态变化及影响因素

为讨论岩溶地表河中等流域尺度无机碳通量的动态变化过程及其影响因素,于2014年1月至12月对漓江流域桂林断面及阳朔断面河水进行为期一个水文年的采样观测,每月定期采样分析.结果表明,这个过程主要受水循环过程控制,除岩溶水化学特征沿途发生变化之外,水体SIc和SId值也逐渐偏正,溶蚀能力逐渐降低,所产生的无机碳通量仍然不断增加,且呈现出旱季低雨季高的特征.通过计算,桂林断面无机碳通量为7.42×107kgCO2·a-1,阳朔断面为27.9×107 kgCO2·a-1,其中桂林断面碳酸盐岩风化所产生的无机碳通量和硅酸盐岩风化所产生的无机碳通量分别占总通量的72.67%和5.21%,阳朔断面分别占87.51%和2.89%,表明硅酸盐岩风化的贡献率沿途不断减小,碳酸盐岩风化的贡献率不断增加.桂林断面以上流域碳汇强度为2.69×104 kgCO2·km-2·a-1,桂林到阳朔断面流域碳汇强度为9.89×104 kgCO2·km-2·a-1,相差近5倍,除沿途大气降水、支流补给、水生生物可能产生的有机碳埋藏等原因外,外源水补给所形成的混合溶蚀作用对岩溶区无机碳通量的增加起着不可忽视的作用.

Variation of inorganic carbon flux in the middle and downstream of the Lijiang river

Water samples of the Lijiang river were collected every month from January 2014 to December 2014 at Guilin and Yangshuo hydrological sections to study the dynamic response process of inorganic carbon flux and its influencing factors in the karst surface river. The results show that the hydrochemical characteristics of the karst river change downstream and the SIc and SId values are increasing as well. Meanwhile, the inorganic carbon flux also increased, with the higher in the wet season and the lower in the dry season, indicating the process was controlled by the hydrological cycle. The inorganic carbon flux was calculated to be 7.42×107 kgCO2·a-1 in Guilin section and 27.9×107 kgCO2·a-1 in Yangshuo section, respectively. The inorganic carbon flux formed by the weathering of carbonate and silicate rocks accounts for 72.67% and 5.21% of the total inorganic carbon flux, respectively, at Guilin section, while it accounts for 87.51% and 2.89% at Yangshuo section, indicating that the proportion of silicate rock weathering is decreasing along the river course while that of carbonate rock increases. The carbon sink intensity of Guilin section is 2.69×104 kgCO2·km-2·a-1 while it is 9.89×104 kgCO2·km-2·a-1 at Yangshuo section, which is 5 times that of Guilin section. Besides precipitation, branch river recharge and the organic carbon accumulation of aquatic organisms, the mixed corrosion of allogenic recharge is also a major reason for the increase of inorganic carbon flux in the karst areas.