泸沽湖近代沉积环境时空变化特征及原因分析

发布时间：2018-03-29 22:17

本文选题：泸沽湖　切入点：沉积特征　出处：《湖泊科学》2017年01期

【摘要】：通过对泸沽湖沉积岩芯粒度、磁化率(χ_(lf))、化学蚀变指数(CIA)等沉积指标的分析,结合~(210)Pb和~(137)Cs定年结果以及区域降水和人类活动等资料,研究了近150年来泸沽湖沉积环境的时空变化特征与主要影响因素.泸沽湖沉积物粒度组成以黏土与细粉砂为主(80%),细颗粒组分(如黏土)含量与χ_(lf)、CIA之间具有显著相关性.各岩芯沉积指标垂向变化规律相似,1920s之前,沉积指标较为稳定,为人类活动影响较弱的准自然沉积阶段;1920s以来,χ_(lf)、CIA值与黏土含量逐渐升高,反映了风化与成壤作用较强的细颗粒表土物质侵蚀开始加强,可能与流域农业发展及森林砍伐等人类活动影响有关;约1970年以来,χ_(lf)、CIA值与黏土含量进一步升高,指示了流域内表土侵蚀与上述人类活动影响的进一步增强,与文献记录的1970s—1980s两次大规模的森林砍伐吻合;约2002年以来,χ_(lf)、CIA值与黏土含量降低,反映了表土侵蚀减弱,与近年来流域植被逐渐恢复及降水减少有关.与器测资料对比研究表明,降水等气候因素对近代泸沽湖沉积环境演变的影响相对较弱.空间上,各沉积指标表现出一定的异质性.黏土含量在南部和北部湖区两侧靠近洪积扇及冲积平原的湖区沉积物中较高;近50年以来,各沉积岩芯所反映的平均沉积通量为0.020~0.043 g/(cm~2·a),南部湖区高于北部湖区,主要受入湖水系分布及流域南部地区高强度人类活动导致的土壤侵蚀的影响.
[Abstract]:Based on the analysis of grain size, magnetic susceptibility and chemical alteration index (CIAs) of sedimentary cores in Lugu Lake, the dating results of Pb and 137Cs, regional precipitation and human activities were analyzed. The temporal and spatial variation of sedimentary environment in Lugu Lake and its main influencing factors were studied in the last 150 years. The grain size composition of sediment in Lugu Lake was mainly composed of clay and fine silt. The vertical variation law of each core sedimentation index is similar before 1920s, The sedimentation index is relatively stable. Since 1920s, 蠂 ~ (lfU) CIA value and clay content have gradually increased, which indicates that the erosion of fine grain topsoil with strong weathering and soil formation is beginning to strengthen. It may be related to the impact of human activities such as watershed agricultural development and deforestation. Since 1970, the CIA value and clay content have increased further, indicating that the erosion of the topsoil in the basin and the impact of the above-mentioned human activities are further enhanced. It coincides with the two large-scale deforestation of 1970s-1980s recorded in the literature, and since about 2002, the value of 蠂 ~ + -lflfche and the clay content have decreased, which reflects the weakening of surface soil erosion, which is related to the gradual restoration of vegetation and the decrease of precipitation in recent years. The influence of precipitation and other climatic factors on the evolution of sedimentary environment of Lugu Lake in modern times is relatively weak. The clay content was higher in the lake area near the alluvial fan and alluvial plain on both sides of the southern and northern lakes, and in the last 50 years, The average sediment flux reflected by each sedimentary core is 0.020 ~ 0.043 g/(cm~2 / a, which is higher in the southern lake area than in the northern lake area, and is mainly affected by soil erosion caused by high intensity human activities in the southern part of the basin.
【作者单位】：中国科学院南京地理与湖泊研究所湖泊与环境国家重点实验室;中国科学院大学;南京信息工程大学环境科学与工程学院;
【基金】：科技部基础性工作专项(2014FY110400) 国家重点基础研究发展计划项目(2012CB956104) 国家自然科学基金项目(41271214)联合资助
【分类号】：P512.2

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