Abstract: 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.

Key words: granite, chemical weathering extent, chemical weathering rate, CO₂ consumption rate