通过对沙湖41 cm沉积岩芯摇蚊亚化石组合进行分析,结合210Pb测年、长江中下游摇蚊-总磷转换函数模型、降趋势对应分析(Detrended Correspondence Analysis,DCA)方法及武汉市历史资料数据,定量重建湖泊水体总磷浓度,揭示了沙湖自20世纪70年代以来环境演化历史.结果表明:(1)1973—1989年,摇蚊组合以水生植被相关属种Cricotopus sylvestris-type和Dicrotendipes nervosus-type占优势,揭示湖泊水生植被发育;这一时期摇蚊重建水体总磷浓度为47—55μg/L,沉积物总磷维持在700 mg/kg;(2)1989—2002年,沉积物总磷增加近一倍,与此同时水体总磷逐渐上升到100μg/L以上,水生植被相关摇蚊属种相对丰度显著减少,湖泊由此进入富营养态;(3)2002年以来,沉积物总磷持续升高到2000 mg/kg以上,摇蚊组合以富营养属种Tanypus和Propsilocerus akamusi-type占绝对优势,水体总磷浓度维持在150μg/L以上.DCA第一轴解释了摇蚊组合变化的62.1％,且样品点在DCA第一轴得分与沉积物总磷呈显著负相关,表明摇蚊组合主要响应于湖泊营养富集过程,这主要与武汉市城市化发展导致湖泊面积萎缩和入湖污水增加相关.研究表明沙湖水体营养本底值约为50μg/L,减少外源营养盐输入是保护沙湖水环境的重要途径.%This study aimed to reconstruct total phosphorus (TP) concentration in the water column and to reveal the history of environmental changes since the 1970s in Shahu Lake based on subfossil chironomid assemblages analysis of a 41-cm length sediment core, combined with 210Pb dating, chironomid-inferred total phosphorus (CI-TP) transfer func-tion in the middle and lower reaches of the Yangtze River, detrending correspondence analysis (DCA) and documen-tary data of Wuhan City. Three distinct stages were identified in chironomid assemblages. From 1973 to 1989, the domi-nance of macrophyte-related taxa (e.g. Cricotopus sylvestris and Dicrotendipes nervosus-type) indicated that the develop-ment of macrophytes in the lake, with CI-TP fluctuating from 47 to 55 μg/L. Meanwhile, sedimentary TP maintained around 700 mg/kg. From 1989 to 2000, sedimentary TP doubled its concentration and CI-TP increased to above 100μg/L, concurrent with a marked decrease of the relative abundance in macrophyte-related taxa. These lines of evidence revealed that the lake had shifted from a mesotrophic status to a eutrophic condition. After 2002, sedimentary TP in-creased continuously to more than 2000 mg/kg. Concurrently, the chironomid assemblages were dominated by eutrop-hic species (i.e., Tanypus and Propsilocerus akamusi-type), with the CI-TP concentration above 150 μg/L. The first DCA axis captured 62.1％ of total variance in the chironomid data and was significantly correlated with sedimentary TP, suggesting that variations in chironomid assemblages were mainly the consequence of nutrient enrichment. Lake eutrophication was in association with both lake area shrinkage and sewage inputs resulted from the urbanization in Wuhan City. This study revealed that the baseline TP concentration of Shahu Lake was around 50 μg/L and reducing external nutrient inputs is crucial for water environment protection.
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