亚热带小流域花岗岩化学风化及CO2消耗速率研究

文章选择深圳市的亚热带典型小流域作为研究对象，通过定期采集流域内降水、泉水、岩石及风化残积土样品，分析所有样品的常量元素和微量元素，探讨流域水体的化学成分组成和主要成分来源以及岩石化学风化程度和风化趋势，结合流域水文气象数据估算了花岗岩化学风化速率及CO₂消耗速率。结果表明，研究区地下水化学类型为HCO₃-Na型，主要受控于硅酸盐矿物的风化溶解作用和阳离子交换作用。花岗岩的化学蚀变指数（CIA）为47.15~57.47，残积土的CIA为59.24~82.71。A-CN-K三角图指示风化初期Na，Ca活泼性元素流失，风化中后期K元素流失，Al元素逐渐富集。花岗岩的平均化学风化速率为14.40 m/Myr。岩性、离子径流通量和气候条件的不同可能是造成化学风化速率差异的主要原因。大气酸沉降对岩石风化的贡献约占总化学风化量的11.73%。研究区平均CO₂消耗速率为0.59×106 mol/(km2 yr)，酸雨使得岩石在风化过程中对大气/土壤中CO₂的消耗减少。

Study of Chemical Weathering and CO2 Consumption Rate ofGranite in a Small Subtropical Watershed

A small subtropical watershed in Shenzhen was selected to investigate granite weathering process and its CO₂ consumption rate. The rainwater, springs, runoff, granite, and saprolite in the watershed were sampled regularly and their major ions and trace elements were analyzed in the lab. Hydrochemical compositions and their sources of the water samples were explored along with the weathering extent and weathering trends of rock and saprolite samples. The chemical weathering rate and CO2 consumption rate of the granite were estimated based on the hydrometeorological data. The results showed that the spring and runoff were HCO₃-Na type, mainly owing to the silicate weathering and cation exchange reaction. The Chemical Index of Alteration (CIA) values of the rock samples were 47.15-57.47, while the saprolite samples have a stronger weathering extent with CIA values of 59.24-82.71. The A-CN-K diagram shows that Na, Ca was leached first in the early weathering, then was K leached, and Al was accumulated as the weathering strength increased. The average weathering rate of the granite is 14.40 m/Myr, and is mainly controlled by lithology, ion flux, and climate conditions. The rock weathering from atmospheric acid deposition accounts for 11.73% of the total weathering amount. The average CO₂ consumption rate is 0.59×106 mol/(km2 yr). The acid precipitation in the study area may weaken the consumption of atmospheric and soil CO₂ by the chemical weathering process.