云南星云湖表层沉积物粒度空间分布特征及其影响因素

GRAIN-SIZE DISTRIBUTION PATTERNS OF THE SURFACE SEDIMENTS AND THEIR INFLUENTIAL FACTORS IN LAKE XINGYUN

本文以滇中地区星云湖为研究对象,对湖区84个表层沉积物样品进行了粒度测定,并进行了参数计算和空间分布特征分析,进而探讨了星云湖表层沉积物粒度的环境及人类活动指示意义。结果表明:星云湖表层沉积物平均粒径在8.82~57.71μm之间,粉砂为该研究区的优势粒级,平均含量达到62.48%,粘土和砂含量的平均值分别为30.68%和7.04%。研究区北部受入湖河流的影响,砂含量较高;南部由于受到盛行风、湖流和湿地的影响,呈现为舌状细粒沉积为主;在其东部螺蛳铺河入湖区,由于受到湖流的顶托作用和人类农耕和河道改造的影响,粉砂和粘土含量较高。星云湖表层沉积物除海门村附近外普遍较细、整体分选极差,而在北部湖区表现为正偏态。河流入湖口沉积物粒度参数表现出不同特征,其中北部入湖口呈单主峰和多峰态的组合特征,东部入湖口呈双峰态,西南各入湖口呈单、双峰组合特征。星云湖现代沉积物与沉积环境和物源的变化紧密相关,是研究湖泊沉积和环境变化的理想场所。

Lake Xingyun(24°17’~24°23’N,102°45’~102°48’E),one of the nine large lakes in Yunnan Plateau with a lake surface area of 34.5 km2 and drainage area of about 378 km2,is located in south of Kunming of Yunnan Province,southwestern China.The maximum water depth of the lake is ca.10.8 m,with an average water depth of about 6 m.Located in the plateau area near the Tropic of Cancer,Lake Xingyun has the characteristics of subtropical monsoon climate with rainy season lasted from May to October and dry season from December to April of following year.The drainage is dominated by southwestern winds almost yearly,especially during the dry seasons.The annual average temperature is about 15.5℃and the annual average rainfall is about 863 mm that mainly concentrated from May to October.Based on the analysis of 84 surface sediment samples,this paper discussed the relationship between anthropogenic impact and geographical environment reflected by the spatial variation characteristic of grain size in Lake Xingyun.The results show that the average components value of silt,clay and sand in surface sediment are30.68%,62.48%and 7.04%respectively It is revealed that the components of sediments are mainly ranged from silt to clay.The type of grain size of northern lake is mainly sand because of the effect of river input by Longtan River,Dongda River and Xida River.Meanwhile,the southern lake is mainly fine materials due to the impact of prevailing winds,lake flows and wetlands.The sediment in eastern are mainly silt and clay,reflecting the effects of the powerful lake flows,moreover,the grain size is also influenced by the human activities from the surrounding farmlands and Luosi River.The northern part of the lake is characterized by the combination of both main-peak and multi-peak features,and the eastern is characterized by double-peak,and the southwestern is characterized by the combination of both main-peak and double-peak.Generally,except the southern part closed to Gehe,the sorting separation of the grain size in Lake Xingyun is poor which tend to be fine-grained,while the northern area is positive bias.The modern sediments of Lake Xingyun are of great significance to the changes of sedimentary environment and provenances,and can be used as a suitable record to study lake sediments and environmental changes.