SHAO Mingyu1,2, ZHANG Liankai1,2, LIU Pengyu1,2, SHAO Tianjie3,CAO Jianhua2, QIN Xiaoqun1,2, ZHANG Chunlai2
(1. Institute of Karst Geology, CAGS /Key Laboratory of Karst Ecosystem and Rocky Desertification, Ministry of Natural Resources, Guilin 541004, China;
2. Ministry of Natural Resources, Guangxi Key Laboratory of Karst Dynamics, Guilin 541004, China; 3. College of Tourism and Environment, Shanxi Normal University, Xi'an 710062, China)
Abstract: The loess is a huge carbon pool, the transfer of carbon in the loess has important impacts on regional and even global carbon cycles. In this study, samples were selected in a typical loess basin in the Linxian County, Shanxi Province to investigate the characteristics of water chemistry in loess water, to analyze the dissolution process and carbon sink effect of loess minerals, and to estimate the carbon flux and the proportion of different mineral contributions of the watershed by using forward modeling and water chemistry methods. The results showed that the list of chemical constituents according to their contents in the loess from high to low in the study area is SiO2, Al2O3, CaO, Fe2O3, MgO, K2O and Na2O, showing the characteristics of SiO2 and Fe2O3 depleting and CaO and MgO enriching. It was found that pH values of soil water in the loess (loess water) of the study area ranged from neutral to alkaline, the dominated cation in the loess water was Na+ and the dominated anion was HCO3-, and the water chemistry type of loess water was the HCO3--Na+ type, and the chemical compositions of loess water correlated closely to the chemical compositions of the loess. A chemical budget method was employed to estimate the contribution of different end-member of ion sources in the basin, the results showed that five end-member components, atmospheric precipitation, human input, evaporating salt minerals, silicate minerals and carbonate minerals could be identified and their contributions to the total dissolved mass of the Qingliangsigou watershed water system were 1.66%, 6.32%, 10.38%, 62.23% and 19.31%, respectively, the major contribution from the silicate minerals dissolution might be resulted mainly from the long-term water-mineral reaction in the loess area and partially from cation exchange reaction, soil-salt leaching and evaporation and impacts of human activities. Due to the relatively low temperature and low rainfall in the loess area, the average chemical weathering rate of loess minerals was 9.31 t/(km2？a), lower than the average chemical weathering rate of global rocks, 36 t/(km2？a). However, the consumption rate of atmospheric CO2 was about 6.34 t/(km2？a), which is significantly higher than the carbon sink rate of the Sanchuan River karst Basin in the same latitude (5.28 t/(km2？a)). The atmospheric CO2 consumption of mineral-chemical weathering calculated by the water chemical budget method for the small watershed of Qingliangsigou was 0.18？104 t/a, which provides basic data for the estimation of atmospheric CO2 consumption in the loess area of China.
Key words: loess; carbonate minerals; silicate minerals; water chemistry; carbon sink effect
EARTH AND ENVIRONMENT Vol.47, No.5, Tot No.331, 2019, Page 575-585
