Ecolosystem changes and possible mechanisms of Dagze Co in the Tibetan Plateau during the past 1000 years

Abstract

在全球变化的背景下，厘清湖泊生态系统对气候环境以及人类活动的响应机制对制定社会的适应政策非常重要.目前的研究手段如现场观测和围隔实验等可以很好地揭示湖泊生态系统在有观测记录以来的演替和变化过程，但是不能提供历史时期湖泊生态系统的变化及其对气候环境变化和人类活动的响应.古湖沼学可以为探讨湖泊生态系统的长期变化及其对气候环境变化的响应提供重要信息.本文以青藏高原中部无鱼湖泊达则错为研究对象，利用沉积物岩芯西藏拟溞（Daphnia tibetana）残体丰度和总烯酮含量重建该区过去1000年的浮游生物记录；利用总氮、总磷以及总有机碳含量重建过去1000年湖泊营养盐以及有机质变化记录；结合烯酮不饱和度重建的古温度记录，探讨达则错过去1000年生态系统变化及其对气候环境演变的响应机制.研究发现达则错湖泊生态系统尤其是生产力在自然状况和人类活动影响下存在显著变化.在自然状况下，较高的湖泊初级和次级生产力发生在温度较低和湖水营养盐浓度较高时；而在过去150年，达则错湖泊环境受到人类活动影响显著，湖泊生产力发生相应变化，较高的湖泊生产力发生在温度较高时期，其主要受由人类活动带来的营养盐元素浓度控制.研究结果表明达则错湖泊生态系统在人类活动影响下发生了显著的改变.;Understanding the evolution of the lake ecosystem and their response to climate change and human activities on the long-term scale is important for making social adaptation policies. Current research methods, such as in-situ observations and enclosure experiment, can well reveal the succession and change process of lake ecosystem during the past few decades, but cannot provide the change of lake ecosystem or its response to climate change and human activities in the historical period. Paleolimnology can provide valuable information for the study of long-term changes of lake ecosystem and its response to climate and environment changes. Here, we took Dagze Co, a fishless lake in the central Tibetan Plateau as the research object. Firstly, Daphnia tibetana remains abundance, and total alkenone content in the lake sediment cores were analysed to reconstruct the plankton records of the past 1000 years. Then, total nitrogen, total phosphorus and total organic carbon were analysed to reconstruct the nutrients and organic matter records of the lake during the past 1000 years. Lastly, paleotemperature record reconstructed by the unsaturation index of long-chain alkenones in the sediment core of Dagze Co obtained in previous work were combined to study the ecosystem changes and their response mechanisms to the evolution of climate and environment in the past 1000 years. The results show that the lake ecosystem, especially lake productivity, has significant changes under the influence of natural conditions and human activities. Under the natural conditions, the higher primary and secondary productivity of the lake occurs when the temperature is lower, and the nutrient content of the lake is higher. However, in the past 150 years, the lake environment was significantly affected by human activities, and lake productivity changed accordingly. The higher lake productivity occurred in the period of high temperature, which was mainly controlled by the nutrient element content brought by human activities. The results show that the lake ecosystem has changed significantly under the influence of human activities.