东北镜泊湖硅藻对近现代气候变化和人类干扰的响应过程

摘要

全球气候变暖和人类活动加剧已经导致中国大量湖泊生态系统功能退化,而目前对东北地区湖泊生态系统变化的认识主要源于短期的监测.以东北镜泊湖为例,通过沉积记录和现代监测资料,分析一个多世纪以来以硅藻群落为代表的湖泊生态系统对气候波动和区域人类活动的响应过程.研究结果表明,在人类干扰显著加强之前,风力扰动是镜泊湖硅藻群落变化的一个重要因子,表现为Aulacoseira属种取代小型浮游种(Cyclostephanos、Stephanodiscus和Discostella)成为优势种.20世纪70年代以来,Asterionella formosa、Nitzschia palea和Fragilaria crotonensis的相继增加则反映了流域农业活动加剧、农业化肥大量施用以及污水排放导致的湖泊营养水平升高.温度的持续上升已经引起东北地区一些湖泊硅藻群落结构发生显著变化,但镜泊湖的硅藻记录却未显示这一气候变化的信号.考虑湖泊-流域形态和人类活动的不同,研究认为近几十年气候变化对镜泊湖硅藻群落结构的影响被强烈的人类干扰所掩盖而未显现出来.%Climate warming and intensified human activities have led to the deterioration of lake environments and the degradation of lake ecological services in China over the past few decades.In northeast (NE) China,up to now,information about lake ecological changes responding to climate changes and human activities has derived mainly from shortterm observations.In the present study,we choose Jingpo Lake in NE China as the study area.Sediment records and paleolimnological methods,in combination with long-term meteorological observations,were used to determine the patterns of diatom community responses to climate changes and anthropogenic disturbances.The history of diatom assemblage changes over the past 130 years was reconstructed from the sediment of Jingpo Lake.The result was then compared with other diatom records from NE China to evaluate the impacts of climate changes and human activities on diatom community shifts.Our diatom records show a distinct shift from small-type planktonic species (e.g.,Cyclostephanos dubius,Cyclostephanos tholiformis,Stephanodiscus parvus,Stephanodiscus invisitatus,Discostella pseudostelligera) to a genus of heavy frustules (Aulacoseira),implying that wind strength played an important role in diatom assemblage changes before the expansion of human activities.Since the end of the 1960s,successive increases in the abundance of Asterionella formosa,Nitzschia palea,and Fragilaria crotonensis have reflected intensified agricultural activities,fertilizer usage,and sewage discharge,which have resulted in a trend to eutrophication.The meteorological observations of the past 60 years reveal obvious climate warming in NE China,especially since the mid-1970s.Previous studies have shown that diatom communities in Lake Xiaolongwan and Erlongwan (NE China) have clearly responded to climate warming,while diatoms in Jingpo Lake have not responded in a similar way.Lake Xiaolongwan and Erlongwan have similar climate conditions to those at Jingpo Lake but much smaller basins and catchments.Additionally,human activities in the catchments of Lake Xiaolongwan and Erlongwan are much less intense.Therefore,it can be speculated that the impacts of climate warming on the diatom community shift in Jingpo Lake have been obscured by intense human disturbances.Additionally,intensified human activity has become the dominant factor leading to the ecological threshold being crossed in Jingpo Lake.