The Anthropogenic Characteristics Of Alpine Lake Sedimentary Records In The Monsoon Fringe

Since the industrial revolution,human activities have gradually become an important geological force affecting the change of the global environment.In addition to the global warming caused by the well-known greenhouse gas emissions,the human activities have led to some new environmental changes,for example,the influence of the emission of man-made active nitrogen?Nr?on the global ecological environment,the soil,the lake sediment and the like has become more and more obvious;the new material called the"technical fossil":aluminum,cement,plastic and the like are rapidly deposited in the global range,It has even affected high latitudes,high elevations,far from human settlements,which were previously less directly affected by human activity.According to this,some scholars have put forward a new world that has ended,and today's earth has entered a new era of Anthropocene.Whether the Anthropocene has come,the extent and significance of human activity to the Earth's environment need to find more evidence in more areas.Lacustrine deposition is an important carrier of climate and environment record,and alpine lake,because of its fragile ecological environment and sensitive to environmental change,is an ideal area to study how human activities affect high altitude areas.The climate change background can be reconstructed by analyzing a variety of proxy indicators of alpine lake sediments,and the degree of impact of human activities on the environment can be revealed,and the basic characteristics and laws of climate change and human activities in high altitude areas can be understood.This paper provides a reference for the establishment of the new geological age of the“Anthropocene".In this paper,three small alpine lakes-Donghaizi,Niangniao Tianchi and Yuhuangchi,with different elevation gradients in the marginal area of the monsoon in China,have been selected for precise dating with ²1010 Pb,¹³⁷Cs and AMS¹⁴C,and the age-depth model has been established.The geochemical indicators such as total organic carbon?TOC?,total organic nitrogen?TN?,carbon-nitrogen ratio?C/N?,carbon isotope(?¹³C),and nitrogen isotope(?¹⁵N)were combined to reconstruct the environmental change of the region for more than a thousand years.At the same time,based on the information of human activities such as regional population development,industrial development and nitrogen deposition,the influence of human activities on each geochemical index of lake sediments in the past two hundred years is emphatically discussed.The preliminary results are as follows:1.The source of sediment organic matter in the three lakes is mainly exogenous.The total productivity of the three lakes was consistent with the response of the medieval warm period,the small glacial period and the modern warm period,showing that the total organic carbon and total organic nitrogen content of the three lakes increased significantly during the medieval warm period,and all reached the peak of the entire profile.The vegetation in the basin developed well and the productivity was higher.The content of total organic carbon?TOC?and total organic nitrogen?TN?in the small glacial period was significantly decreased,which was located in the low value section of the whole section.The vegetation growth in the basin was poor and the productivity was low.Due to the influence of human activities and regional climate change,the total organic carbon and total organic nitrogen decreased first and then rose in the modern warm period,and the vegetation in the basin began to recover from 1980 because of the influence of human activities.2.The nitrogen isotopes of the three lakes have changed significantly since the increase of human Nr release in 1950.Due to the direct influence of human Nr solid and liquid produced by people's industrial and agricultural production and daily life,the nitrogen isotope of Donghaizi has been obviously positive since 1950.Niangniang Tianchi and Yuhuangchi are at higher altitudes and are less directly affected by human activities.However,the surrounding large factories and the man-made Nr gas compounds emitted into nature by applying chemical fertilizers have been transported and settled into the lake basin through the atmosphere.The nitrogen isotopes of Niangniang Tianchi and Yuhuangchi sediments show a negative trend since 1950.3.In the three lakes of the study area,the elevation of Donghaizi is relatively low,and the variation of carbon isotope and nitrogen isotope of Donghaizi is different from that of Niangniang Tianchi and Yuhuangchi.The geochemical indexes of alpine lakes at different altitudes are also affected by human activities.The higher altitude is less affected by human activity,but the higher altitude is gradually increasing since1950.