Cladoceran community succession and identification of anthropogenic signals since 1950s in Lake Tianchi in Yunlong County, northwest Yunnan

Abstract

从1950s开始, 云南地区部分湖泊受到了水文调控(如筑坝)和鱼类引入等流域开发活动的直接影响, 湖泊水环境与生态系统结构已出现明显改变. 开展浮游动物群落的长期生态响应评价有助于认识气候波动和人为胁迫的影响模式. 本文选取云龙天池进行了沉积物记录分析, 在重建过去100年环境变化历史的基础上开展了枝角类群落的多指标分析(物种组成、个体大小、生物量等), 进一步结合多变量分析识别了枝角类群落构建的关键驱动因子. 结果显示, 云龙天池在过去100年间经历了明显的水位波动, 约1962年以前水位较低, 1950s起的水文调控(筑坝)导致湖泊水位波动上升, 2006年以来略有下降. 枝角类群落随水位波动呈现由底栖种向浮游种占优转变的模式, 并在2006年以来底栖种略有增加. 总体上, 低水位时期底栖枝角类占优, 高水位时期浮游枝角类占优. 水体营养水平也对枝角类群落产生了较为显著的影响. 在沉积物总氮和有机质通量上升时, 长额象鼻溞(Bosmina longirostris)相对丰度和枝角类浓度都明显上升. 枝角类象鼻溞个体大小表明, 1969年鱼类引入后象鼻溞的壳长、壳刺长度、触角长度显著减小, 反映了鱼类捕食压力上升的影响. 本研究进一步揭示了水文调控和鱼类引入对湖泊环境和生物群落结构的驱动影响. 其中, 1960s以前云龙天池处于自然波动的状态, 湖泊环境和枝角类群落变化主要受气候(如降水、气温)的影响; 1960s以来人类活动的影响强度已经掩盖了气候变化的信号, 成为影响湖泊生态演化轨迹的主要因素. 为了开展有效的湖泊保护与生态治理, 有必要综合评估水文调控、鱼类引入等人类活动对湖泊生态健康的长期影响.;Since the 1950s, many lakes in Yunnan have been directly impacted by watershed development activities such as hydrological regulation (such as damming) and fish introduction, and thus lake environment and ecosystem structure have changed significantly. Investigation on the long-term response of zooplankton communities to limnological changes is vital for understanding the effects of climate change and anthropogenic stresses on lakes. In this study, Lake Tianchi from Yunlong County, northwest Yunnan, was selected for reconstructing environmental change history over the past 100 years, with a focus on the succession of the cladoceran community and the identification of its environmental drivers. The results showed that Lake Tianchi has experienced significant fluctuations in water level over the past 100 years, which was relatively low before about 1962, gradually rose during 1962-2006 due to hydrological regulation (damming), and slightly declined from about 2006 onward. The dominant taxa of cladoceran community shifted from littoral species to planktonic ones while benthic taxa slightly increased after 2006. In brief, benthic cladocerans were generally dominant during the low water-level period, while planktonic taxa predominated when water level rose. The percentage of Bosmina longirostris and the cladoceran concentration were both increased when the sedimentary TN and LOI₅₅₀ increased since the 1960s, suggesting that the influence of nutrients on the compositional change and production of cladocerans. After planktivorous fish was introduced in 1969, the carapace, carapace mucro and antennule lengths of Bosmina were all significantly decreased, suggesting the influence of increasing predation pressure by zooplanktivorous fish. This study highlights the long-term impacts of hydrological regulation and fish introduction on the lake environment and biological community structure. Before the 1960s, the lake was generally in natural conditions, lake environment and cladoceran communities were mainly affected by climate (precipitation, temperature), while, after the 1960s, the influence of human activities has overridden the role of climate change and become the main factor in affecting the ecological structure of Lake Tianchi. For lake protection and ecological remediation, it is necessary to comprehensively assess the impact of multiple human activities (i.e. hydrological regulation and fish introduction) on lake ecosystem health for generating appropriate restoration strategies.