Response of hydrogeochemical characteristics to land-use modes in exposed karst areas of northwestern Guizhou Province

Land use modes are important to assess the impact of human activity on the earth surface, especially in bare karst areas. The hydrogeochemical characteristics can be used in this assessment. This study was based on geological survey combined with remote sensing and hydrochemical analysis of groundwater. The purpose was to reveal the response of hydrogeochemistry to land-use modes in a typical karst agricultural region of Bijie city, Guizhou Province. The major land-use modes include farmland, woodland, grassland and construction land. It was found that there are differences in the concentrations of major ions of groundwater and SI (Saturation Index) values of dominant minerals for these four different landuse modes. In addition, the contents of water-soluble salts of soil are higher than that of major ions of groundwater in almost all of samples, indicating that under the condition of rainfall infiltration recharge, the leaching of water-soluble salts can affect the concentrations of major ions in groundwater. Moreover, the dominant groundwater types are ofHCO3-Ca, HCO3-Ca-Mg, and HCO3-SO4-Ca in compositions for these four land-use modes. However, due to the influences of natural geographical factors and human activity, there are differences in the compositions and hydrochemical types for these four land-use modes. Based on these results, two conceptual models are established for the evolution of groundwater in the study area.