九寨沟世界自然遗产地湖泊沉积速率及其影响因素

Lake Sedimentation Rate and Its Influencing Factors in Jiuzhaigou World Natural Heritage Site

选择“8.8”大地震后(2020年6月)震损物源输入程度有差异的箭竹海和犀牛海,基于同位素定年法分析湖泊沉积速率,通过分析沉积物环境指标的垂直变化特征及其与自然灾害和人类活动的关系,阐明影响九寨沟湖泊沉积的长期因素和短期因素。结果表明,从1900年左右至2020年,箭竹海和犀牛海的沉积速率分别约为0.32和0.44cm/a。环境指标(粒度组成、总碳、总氮、总磷和碳酸盐含量)在沉积物表层(0~10cm)的垂直分布特征表现为210Pbex比活度显著增加,沉积物粒径偏大,总碳、总氮和碳酸钙富集,且垂直变动剧烈。同时,受震损物源影响明显的箭竹海表层沉积物扰动深度更大。研究结果揭示,“8.8”大地震导致的地灾松散物源大量入湖,短期内迅速加剧湖泊泥沙淤积,其深层垂直分布特征记录了森林砍伐、不合理排放以及环境保护等人类活动对湖泊沉积长期缓慢的影响。

After the“8.8”earthquake(June 2020),Arrow Bamboo Lake and Rhino Lake,with different input degrees of earthquake damage sources,were selected to analyze the lake sedimentation rates by isotope dating method.Moreover,vertical distribution characteristics of grain size composition,total carbon(TC),total nitrogen(TN),total phosphorus(TP),and carbonate content were analyzed.By analyzing the vertical variation characteristics of sediment environmental indicators and their relationship with natural disasters and human activities,the long-term and short-term factors affecting lake sedimentation were explored.The results showed that the sedimentation rates of the Arrow Bamboo Lake and Rhino Lake from 1900 to 2020 were about 0.32 and 0.44 cm/a,respectively.The vertical distribution characteristics of the environmental indicators on the surface(0–10 cm)were as follows:the specific activity of 210Pbex significantly increased,the sediment particle size was relatively large,TC,TN and calcium carbonate were enriched,and the vertical variation was violent.Meanwhile,the disturbance depth of surface sediment in the Arrow Bamboo Lake,which was obviously affected by seismic damage sources,was greater.These revealed that a large number of loose material sources of land disasters caused by the“8.8”earthquake entered the lake,rapidly intensifying the lake sediment deposition in the short time.The deep vertical distribution features recorded the long-term slow impact of human activities such as deforestation,unreasonable discharge and environmental protection on lake sediment.