桂江主要离子及溶解无机碳的生物地球化学过程

Biogeochemical Processes of the Major Ions and Dissolved Inorganic Carbon in the Guijiang River

河流水体的化学组成记录了流域内各种自然过程与人类活动的信息.对西江一级支流桂江化学径流的分析结果表明,桂江水体的离子组成主要受碳酸盐岩化学风化过程的控制,CO2是这一过程的主要侵蚀介质;H2SO4对碳酸盐岩的风化影响桂江河水的化学组成.大气沉降、人类活动、碳酸盐岩和硅酸盐岩化学风化对桂江水体贡献的溶解物质分别占总溶解物质的2.7%、6.3%、72.8%和18.2%.河流溶解无机碳(DIC)的稳定同位素组成(δ13CDIC)揭示桂江河水中的DIC明显被浮游植物的光合作用所利用.浮游植物初级生产力对桂江颗粒有机碳(POC)的贡献达22.3%~30.9%,这表明岩石风化来源的DIC经浮游植物的光合作用转化为有机碳,并在迁移过程中部分沉积水体底部,进而形成埋藏有机碳.

Within the drainage basin,information about natural processes and human activities can be recorded in the chemical composition of riverine water. The analysis of the Guijiang River,the first level tributary of the Xijiang River,demonstrated that the chemical composition of water in the Guijiang River was mainly influenced by the chemical weathering of carbonate rocks within the drainage basin,in which CO2was the main erosion medium,and that the weathering of carbonate rock by H2SO4had a remarkable impact on the water chemical composition in the Guijiang River. Precipitation,human activities,the weathering of carbonate rocks and silicate rocks accounted for 2. 7%,6. 3%,72. 8% and 18. 2% of the total dissolved load,respectively. The stable isotopic compositions of dissolved inorganic carbon( δ13CDIC) indicated that DIC in the Guijiang River had been assimilated by the phytoplankton in photosynthesis. The primary production of phytoplankton contributed to 22. 3%-30. 9% of particulate organic carbon( POC) in the Guijiang River,which implies that phytoplankton can transform DIC into POC by photosynthesis,and parts of POC will sink into the bottom of the river in transit,which leads into the formation of burial organic carbon.