结合抚仙湖浮游植物、水生植物等样品,对野生植食性草鱼(Ctenopharyngodon idellus)31个组织和野生肉食性鱇浪白鱼(Anabarilius grahami)17个组织样品碳、氮元素含量和稳定同位素比值(δ13C、δ15N)进行了对比分析.结果显示,鱼类不同组织的碳稳定同位素分馏效应显著,草鱼不同组织δ13C分布范围为-20.66‰～-11.62‰,极差为9.04‰,鱇浪白鱼为-27.55％o～-19.71‰,极差为7.84‰.而氮稳定同位素分馏较小,草鱼δ15N分布范围为9.09‰～10.97‰,极差为1.88‰,鱇浪白鱼为7.91‰～12.51‰,极差为4.60‰.同时,草鱼和鱇浪白鱼不同组织δ13C值与对应C元素含量呈极显著的负相关关系,C含量每升高10％其δ13C值分别减少1.83‰和1.35‰,反映了不同组织对C元素吸收及合成过程伴随着碳稳定同位素的明显分馏.不同组织在δ15N值与N元素含量的相关关系上不显著.进一步开展草鱼不同组织与肠含物的同位素对比分析显示,草鱼背部肌肉组织与肠含物中苦草的碳、氮同位素分馏系数分别为0.40‰和2.66‰,表明背部肌肉组织的碳、氮同位素组成对识别鱼类食性和确定营养级水平的可靠性.研究结果显示,植食性草鱼和肉食性鱇浪白鱼具有较为稳定的食性特征,可以用黏液的 δ13C值和校正后的鳞片的δ15N值替代背部肌肉作为食性分析和确定营养级的类比指标.该研究表明,鱼类组织碳、氮元素组成与同位素分馏特征可为识别云南高原湖泊的食物网结构和营养转移路径提供可靠的分析手段,其中黏液、鳞片等非致命组织的替代性取样与同位素分析对于濒危鱼类的研究与保护具有较好的应用意义.

浮游生物是湖泊食物网的重要组成,其碳、氮稳定同位素能够反映元素地球化学循环和食物来源的波动,是了解水域生态系统结构变化的重要手段之一.本文选取云南4个不同类型湖泊,开展浮游生物碳、氮稳定同位素组成(δ 13 C、δ 15 N)的季节变化与湖泊对比研究.大型深水湖泊（抚仙湖和阳宗海）中,浮游植物δ 13 C值在夏、秋季（-20.34‰±1.98‰）显著高于冬、春季（-28.00‰±2.51‰）,反映夏秋季藻类生长速率较高、HCO 3 - 无机碳源利用增多等的影响.而小型浅水湖泊（长桥海和大屯海）中浮游植物δ 13 C值在夏季最高（-21.24‰±0.88‰）,可能与雨季流域输入增强、陆源有机质占比增加有关.4个湖泊浮游生物δ 15 N值具有一致的变化特征,春季显著高于其他季节.分析表明,云南地区雨季以面源污染为主向旱季以点源污染为主的转变,导致氮素营养盐季节性来源差异,并通过生物吸收作用影响了浮游生物δ 15 N值的季节变化.在浮游动物与浮游植物的稳定同位素差值（即富集度）方面,营养水平高的小型浅水湖泊中δ 13 C富集度为1.61‰±0.90‰、δ 15 N富集度为2.71‰±1.22‰,显著小于营养水平低的大型深水湖泊（分别为2.60‰±0.98‰和4.19‰±1.25‰）,表明随着湖泊营养水平的增加,浮游动物更多地以浮游植物为食,导致有机碳在不同营养级之间的传输过程中具有更强的耦合作用,且相邻营养级之间具有更低的δ 15 N富集度特征.

In the context of catchment development and climate change, anthropogenic activities have significantly altered the succession and functioning of freshwater ecosystems. Combining the sedimentary records and modern survey data, we reconstructed a 250-year history of ecological changes in Chenghai Lake, aiming to assess the long-term ecological changes in Changhai Lake in response to multiple environmental stresses, such as eutrophication and hydrological fluctuation.Three stages were identified for the process of nutrient enrichment leading to a long-term increase in primary production. Nutrient level was relatively low before 1970, increased gradually between 1970 and 2000, with an accelerating increase after 2000. The water regulation project enhanced water turbulence and river flux during 1993-2000, which promoted the growth of turbulence-tolerant Aulacoseira and influx of benthic Nitzschia. The organic carbon cycling in Chenghai Lake was mainly driven by the autogenetic inputs. The eutrophication process dominated the long-term shifts of diatom assemblages followed by hydrological fluctuation. Our results illustrated that ecological restoration and catchment management of Chenghai Lake not only need to focus on the control of nutrient enrichment and pollutant input, but also should consider hydrological regulation and water level fluctuation.