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

文章报道了响水河河水的现场监测结果,得到响水河河水的Ca²+和HCO^-₃非常低,这明显与河床中大规模钙华的存在和景区内发育的茂密植被不匹配;并仔细观察发现,钙华表面有被侵蚀的痕迹,如溶蚀槽和溶蚀坑等,这说明目前所见钙华可能是过去环境条件下的产物。根据钙华碳氧稳定同位素组成特征的分析得出:近4000年来,该地区总的气候环境变化趋势是4000～3400aB.P.为相对温暖湿润期,植被生长好,为良性生态期;3400～2000aB.P.前期仍比较温暖但干燥,后期到2000aB.P.左右变得比较凉爽,从这一冷期到大致900aB.P.前后,气候有些波动,但幅度较小,夹有冷暖干湿的交替;而900aB.P.至今,钙华碳氧稳定同位素值的急剧增加,反映出气候的冷干和源区人类活动加剧造成的水土流失增加,岩溶石漠化加重,生态朝恶化方向发展

PALEOENVIRONMENTAL RECONSTRUCTION BASED ON HYDROCHEMISTRY AND TUFA STABLE ISOTOPES:CASE STUDY OF XIANGSHUI RIVER, LIBO, GUIZHOU

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.