异龙湖近百年来湖泊沉积物有机碳、氮稳定同位素变化及其环境指示意义

Changes of organic C and N stable isotope and their environmental implication during the past 100 years of Lake Yilong

通过对异龙湖沉积物岩芯(YLH-1)样品有机碳、氮及其稳定同位素、C/N值测定,结合人类活动的阶段性特征,分析了近百年来异龙湖沉积物有机质的来源,探讨受人类活动影响下湖泊的生态环境变化过程。结果表明:异龙湖沉积物中有机质的碳、氮稳定同位素分别为-25.9‰^-22.5‰和0.5‰~4.7‰,C/N值16.4~20.4,表明异龙湖有机质主要受大型水生植物影响,而藻类和陆源有机质贡献较小。δ^13C逐渐偏负的过程反映了异龙湖富营养化加剧的过程,可能与藻类吸收有机质降解产生的CO2有关,而δ^15N的变化则与流域内工业污染物、农业化肥和大气氮沉降有关。异龙湖的生态环境变化可以分为3个阶段:19世纪80年代至20世纪60年代初期,湖泊初级生产力较低,水质好,受人类活动干扰较小;20世纪60年代中后期至20世纪90年代,随着人类活动的加强,湖泊生产力迅速提高,富营养化程度加剧,水质恶化,藻类大量繁殖;20世纪90年代之后,湖泊处于高生产力水平,湖泊富营养化严重。因此,未来管理部门要重视人类活动对湖泊生态环境影响,加强湖泊生态环境治理,改善湖泊生态环境。

Based on the analysis of organic C,N stable isotope,C/N ratio,TOC,and TN from core sediments(YLH-1)in Lake Yilong,combined with the stage features of human activities,we analyzed the origin of organic matter and the stage-based evolution process of lake ecosystem during the past 100 years.The results showed that the organic C and N stable isotope values varied from-25.9‰to-22.5‰and 0.5‰to 4.7‰,respectively,and the range of C/N ratio was between 16.4 and 20.4.Such results suggested that aquatic macrophyte was main origin of organic matter,with relatively little contribution of algae and terrestrial sources.The decline in δ^13C values suggested that the process of intensified eutrophication,which may be related to CO2 produced by algae due to the degradation of organic matter.The increase in δ^15N was attributed to the increasing sewage,the application of fertilizers,and atmospheric nitrogen deposition.The historical evolution of Lake Yilong ecosystem could be divided into three stages.From the 1880 s to the early 1960 s,primary production level was relatively low and water quality was good,with weak human influence.From the mid-1960 s to 1990 s,with the intensified human activities,the lake productivity rapidly increased,eutrophication was aggravated,water quality was deteriorated,and the intensity of algal blooms increased.Since the 1990 s,the lake was at high production level and serious eutrophication state.Future work should pay attention to the impacts of human activities on the lake ecological environment.The management of lake ecosystem should be emphasized to improve the quality of eco-environment.