The Relationship Between Environmental Evolution And Human Activities In Modern Of Yamzhog Yumco Lake And Huguangyan Maar Lake

Since the industrial revolution,the impact of human activities on climate and environment has gradually exceeded that of natural forces.Since modern times,human activities have become an important driving force affecting the lake environment.The accumulation of carbon,nitrogen,phosphorus and other nutrients in sediments and their rapid circulation in water body caused by human activities have an important impact on the lake water environment and significantly accelerated the process of lake eutrophication.Lake sediment is an important carrier to study environmental changes and human activities.In this thesis,we selected Yamzhog Yumco Lake in the Qinghai-Tibet Plateau and Huguangyan Maar Lake in the eastern plain as the research objects.The accurate"Depth-Age"model of the two lakes was established by means of dating.The contents and deposition fluxes of carbon,nitrogen and phosphorus in the sediment cores of the two lakes,the isotopic compositions(?¹³C,?¹⁵N and?¹⁸O_P)were analyzed.Through the comparative study of economic and social conditions and meteorological factors,the relationship between modern environmental changes and human activities in the two lakes was analyzed,and the utilization of phosphoric acid was discussed.The main conclusions are as follows:(1)The sedimentary age span of Yamzhog Yumco Lake is about 286 years(1-9cm above the core),and Huguangyan Maar Lake core is about 120 years(1-40 cm).The cores of the two lakes contain the most intense human activities in modern times,which is conducive to further analysis of the relationship between lake sedimentary records and environmental changes and human activities.According to the changes of carbon,nitrogen,phosphorus and their isotopes in lake sediments,it is judged that the key period for human activities to affect the environmental change of Yamzhog Yumco Lake is from the end of the 20th century,while the key period for the environmental change of Huguangyan Maar Lake is from the 1980s.(2)According to the changes of carbon,nitrogen,phosphorus and their isotopes in the lake sediments,the sedimentation rate of Yamzhog Yumco Lake has changed greatly since the middle of the 20th century,and the primary productivity of the lake is unstable.The main source of organic matter is lake endogenous,but the influence of terrestrial input is also increased.The deposition process of Huguangyan Maar Lake from the end of the 20th century to the beginning of the 21st century is relatively unstable,which may be due to the influence of external input(terrigenous and atmospheric deposition).At the same time,the primary productivity of the lake increased rapidly.Organic matter comes from the mixed source of Lake authigenic and terrestrial input,and the external source of organic matter in Huguangyan Maar Lake has increased since the end of the20th century.(3)The accumulation of carbon,nitrogen and phosphorus in the lake sediments is obviously affected by human economic activities,especially in Huguangyan Maar Lake.The nutrient level of Yamzhog Yumco Lake and Huguangyan Maar Lake is restricted by phosphorus,and the content of endogenous phosphorus in sediments is increasing.In particular,when the bottom of Huguangyan Maar Lake is anoxic,the deep-water area has a high potential of endogenous phosphorus release.We should pay attention to the potential eutrophication risk caused by the continuous release of endogenous phosphorus.Moreover,we should not ignore the process of nutrient input from atmospheric deposition.(4)Human activities have obviously influenced the environmental changes of Yamzhog Yumco Lake and Huguangyan Maar Lake in modern times.However,the phosphate oxygen isotopes of various forms of phosphorus in lake sediments do not reflect the modern climate changes(such as temperature,precipitation and evaporation),but play an important role in determining the phosphorus sources in the sediments.The role of phosphate oxygen isotope of inorganic phosphorus in reflecting modern climate change and human activities still needs further study and discussion.In addition,further evidence should be provided to clarify the relationship between atmospheric dry and wet deposition and nutrient changes in Huguangyan Maar Lake.