Chemical Weathering, Atmospheric Carbon Fluxes and River Geochemistry of Sandstone of Nanjing Purple Mountain River System, China

Carbon is the essential element of life on Earth. Weathering of silicate rocks acts as a net carbon sink of the integrated global carbon cycle in the geological time scale. The chemical composition of river can provide us sources of major ions, chemical weathering rates of watershed and the consuming rate of atmospheric carbon dioxide. Accordingly, we choose Nanjing Purple Mountain River System to analyze chemical characteristics of the river water, the consuming rate of atmospheric carbon dioxide and some representative characteristics of rocks and soils. We have got Sodium normalized value for major elements of sandstone weathering, which can provide basis for calculating different endmenbers for large river systems in the world. We found the variation between river water samples, rock samples and soil samples by using several measurement methods and analysis methods. We conclude that: (1) The weathering of sandstone is weak. The contributes of sandstone for river are that Ca/Na:1.5-3, Mg/Na:0.5-1.5, K/Na:0.02-0.1(after sodium normalized). (2) We suggest that there is interference from atmospheric dust input by analyzing those rock samples and soil samples. (3)The rates of chemical weathering are controlled by both temperature and humidity. (4) The consuming rate of atmospheric carbon dioxide is 1.40×105mol/yr. (5) Strontium isotope provides that n(87Sr)/n(86Sr) is between 0.710557×7 and 0.710955×2. Moreover, the concentration of strontium is over 1μmol/L, and the average value is 2.29μmol/L, which suggests that relatively high concentration and isotope ratio.