热带花岗岩海岛的化学风化及其环境效应——以东澳岛为例

Chemical weathering and its environmental effects of tropical granite island: A case study in Dong Ao Island

通过对珠江口花岗岩海岛-东澳岛小流域水体离子的实测分析,揭示海岛小流域的离子来源与贡献量,获得在相对封闭环境下的热带海岛地区花岗岩小流域的化学风化速率及过程对大气CO2的年消耗量.研究表明,东澳岛溪水总体为弱碱性,总溶解固体均值为68.14 mg·L-1,远低于世界河流均值,非汛期溶解固体和电导率均高于汛期.溪水离子组成以Cl-、溶解Si、Na+以及HCO-3为主,体现了海盐沉降和硅酸盐岩化学风化过程对溪水化学组成的共同影响.东澳岛岩石化学风化速率和CO2消耗通量分别为1.09×104kg·km-2·a-1和1.12×105mol·km-2·a-1,均低于世界河流均值,主要是由于花岗岩抗风化能力较强所致.广东省热带花岗岩海岛年碳汇消耗CO2约5218 t,因此保护海岛表层土壤和生态环境对海岛的碳汇作用具有重要意义.

Through measurement and analysis of small watershed water ions from the Granite IslandDong Ao Island,the study revealed the contribution and sources of the island＇s small watershed ions,and obtained the chemical weathering rate and atmospheric CO2 consumption of the weathering processes of a small Granite tropical island regions in a relatively closed environment. The study showed the water was weak alkaline in the stream of Dong Ao Island. The mean dissolved solids was68. 14 mg·L- 1much lower than the average of other rivers. And all dissolved solids and conductivity were high during the non-flood period. The main ions were Cl-,dissolved Si,Na＋and HCO-3in steam waters,which indicated that chemical composition of the stream water was the results of sea salt deposition and silicate rocks＇ chemical weathering. The weathering rate of rock and mineral in Dong Ao Island was 1. 09 × 104kg·km- 2·a- 1,and CO2 consumption flux was 1. 12 × 105mol·km- 2·a- 1. Both were lower than the average of other Rivers,which might be caused by the strong anti weathering ability of granite. About 5218 tons of CO2 were absorbed by chemical weathering of tropical granite islands in Guangdong province per year. Therefore,the protection of ecological environment and surface soil has important significance on the CO2 sink of the island.