异龙湖湖泊沉积对流域人类活动的响应

Human Activities Indicated by the Sediments at the Yilong Lake

通过对异龙湖短钻岩芯沉积物粒度、碳酸盐以及有机质含量等环境代用指标研究,结合文献资料和当地气象数据并参考实验室其他项目组137Cs-210Pb方法建立的年代标尺,讨论了异龙湖流域1880年以来的环境变化和人类活动对湖泊沉积环境的影响。结果表明：岩芯35～25 cm段（1880—1936年）碳酸盐含量、中值粒径均值较高,表明这一时期为暖湿气候,TOC含量处于低值且平缓,证实人类活动对周围环境影响较小,湖泊环境变化的影响因素以自然因素为主;至25～15 cm段（1936—1996年）碳酸盐含量明显下降,有机质含量快速增加,指示湖泊沉积环境受人类活动影响强烈,碳酸根离子等其他化合物含量、反应条件、过程及碳酸盐沉淀保存条件发生改变,在此种情况下,指标已不能指示湖泊环境变化;岩芯15～0 cm段（1996—2013年）沉积物粘土含量升高,砂含量降低,应与异龙湖流域防护林工程有关,这一时期的指标特征表明人类活动强度较之前有所减弱,并且开始有意识地恢复流域生态。

The sediment core YLH - 1 from the Yilong lake in Yunnan Province of China was analyzed for grain size,contents of carbonate and organic. Accurate sediment chronology was referred by YL- 1 core＇s 210Pb and 137 Cs. By comparing the grain-size, carbonate and organic proxies with documents and meteorological data, we dis- cussed the environmental evolution and influence of human activities on depositional environment since 1880. Re- suits show that both carbonate and average median grain-size high contents at 35 -25 cm depth （1880--1936 a）, the lake catchment was characterized of increased rainfall and relatively warm climate. During this period, in a low organic content, the lake evolution and the environmental change were mainly influenced by natural factors. At 25 ~ 15 cm depth （1936--1996 a） obviously lower carbonate content and organic content increased rapidly,with im- plied the sedimentary environment of the loke affected by human activities. Some properties of carbonate ions and other compounds, including the content, reaction condition, and the preservation condition of carbonate precipitati- ons can vary. in this case, carbonate content could not be explained by temperature or precipitation change. The lake catchment was shelter forest project implementation and consciously ecological recovery. It may be why grain size in YLH- 1 core became finer at 15 -0 cm depth（ 1996--2013 a）.