PALEOENVIRONMENTAL RECONSTRUCTION BASED ON HYDROCHEMISTRY AND TUFA STABLE ISOTOPES:CASE STUDY OF XIANGSHUI RIVER, LIBO, GUIZHOU
水化学和钙华碳氧稳定同位素在古环境重建中的应用——以贵州荔波小七孔景区响水河为例

It was found by in-situ monitoring that the Xiangshui River has a very low concentration of calcium and bicarbonate, which does not match with the huge tufa deposits in the riverbed and the dense vegetation cover in surrounding area. In fact, there are some erosional features on the surface of the tufa, such as dissolutional notches and pits. It means that the tufa deposits may be remains of the past environment. Analyses on the stable carbon and oxygen isotopic compositions of the tufa revealed that for the past 4 000 years, the general trend in climatic and environmental change is: from 4 000aB.P. to 3 400aB.P., it was warm and humid, and the vegetation grew well, and the ecosystem was in benign cycle; from 3 400aB.P. to 2 000aB.P., in the early stage, it was warmer and drier, and in the later stage, it was getting cooler; from 2 000aB.P. to 900aB.P. the climate fluctuated gently, with alternation of cool and warm, dry and wet. However, from 900aB.P. till now, the value of the stable carbon and oxygen isotopic compositions increased steeply. It reflects that the climate was getting cooler and drier, soil erosion increased, and the ecosystem was in vicious cycle, the latter being intensified by human activity in the recharge area.