Surface runoffs and the contents of major ions and dissolved silicon were surveyed and analyzed based on weekly sampling for one year in a granite watershed of Zhuhai City, Guangdong Province. The results demonstrated that the slope runoff played an essential role in feeding the rivulet during precipitation, whereas the groundwater was more important for the rivulet in the non-raining stages. Dissolved silicon, Na+, HCO3-, and Clions constituted the major chemical components of the rivulet water. Atmospheric CO2 and H2SO4 sourced from the oxidation of pyrite were the main erosive mediums in the natural chemical weathering. Natural chemical weathering, the wet and dry deposition of sea-salt, and acids precipitation contributed approximately equal shares of anions to the rivulet water. The ratio of NO3- to SO42- was more than 1.0 in the runoff of the studied seashore watershed, whereas it is less than 1.0 in the Xijiang River that is adjacent to the study area. This implied that the chemical composition of runoff is controlled mainly by the differences in atmospheric acid precipitation caused by human activities and lithology within the catchments under the same bio-climate zone. The CO2 flux consumed by the rock chemical weathering processes within the seashore granite watershed in South China was (0.35-1.37)×105 mol km-2 a-1.
GAO QuanZhou & TAO Zhen School of Geography and Planning, Sun Yat-sen University, Guangzhou 510275, China
The fluvial geochemistry of the mainstream and tributaries of the Zengjiang River was investigated,and the mass balance approach and deduction methods were used to estimate the uptake of atmospheric CO2 through rock chemical weathering.The results showed that the chemical runoff mainly consisted of HCO3-,Ca2+,Na+,and dissolved Si,and that silicate mineral weathering was significant,but carbonate mineral weathering was a minor source of dissolved loads in the Zengjiang River basin because of the low amount of interlayered carbonate rock strata in the catchment.The ion composition indicated that atmospheric CO2 was the primary erosive agent for rock chemical weathering in the Zengjiang River basin.The CO2 consumption fluxes caused by rock chemical weathering were(3.50-3.81) × 105 mol km-2 a-1,which is just lower than that in tropical and subtropical basalt and carbonate regions,and is much higher than that in temperate and cold-temperate regions,indicating that surficial chemical weathering processes in the humid and hot monsoon current influencing the low-middle latitude zone of the Northern Hemisphere constitutes a significant carbon sink in the global biogeochemical cycle.
TAO ZhenGAO QuanZhouWANG ZhenGangZHANG ShengHuaXIE ChenJiLIN PeiSongRUAN XiaoBingLI ShuHongMAO HaiRuo
