Climate And Environmental Changes And Human Activities Recorded In Lake Sediments Of Xiaonanhai, Chongqing Over The Past 160 Year

Lake is one of the most important components of terrestrial ecosystem,which is of important research significance and application value for regional climate change,ecosystem security and economic development.Based on the study of geochemical parameters such as particle size,radionuclide,organic matter,macro-trace elements,heavy metals,etc.of columnar and surface sediments in Xiaonanhai Lake（XNH）,the provenanc and the spatio-temporal transport process of XNH sediments and theassociated climate change,response to human activities were discussed.（1）The change of radionuclide²¹⁰Pb shows that the sedimentary age of the core（86cm）of XNH is about 160 years.In the past 160 years,the sedimentation rate of sediments in XNH has been divided into two distinct stages,namely,the low sedimentation rate of 0.29cm/a before 1980（40cm）and the high sedimentation rate of0.62cm/a after that,which is closely related to human activities such as lake dam construction and tourism development in recent period.（2）27 surface sediments in XNH are mainly composed of silt（2-63μm）.The spatial distribution characteristics of silt decreasing from west（estuary）to east.The relatively coarser particle entering the lake and the thinner tend of particle size with the increase of water depth indicate that the sedimentation of sediments in XNH is mainly controlled by hydrodynamic force of river.（3）TN in the surface sediments of XNH is generally slightly polluted,mainly imported from external sources,and its topographic characteristics promote the increase of TN load in sediments;TP in sediments is moderately polluted as a whole,which is more likely to be disturbed by human activities.The C/N ratio of sediments indicates that the origin of organic matter is endogenous for most part of XNH,whereas that of the estuary is exogenous.（4）The reconstructed climate,productivity and lake level indicated by organic matter,carbonate,elements and element ratios can be divided into four stages:stage 1:wet and cold climate,declining lake productivity,rising lake water level and decreased salinity from 1856 to 1900;stage 2:warm and dry climate,rising lake productivity,declining lake water level and rising salinity from 1900 to 1942;stage3:wet and cold climate,rising lake productivity,rising lake water level and declining salinity from 1942 to 1962;stage 4:warm and dry climate,rising lake productivity,rising lake water level and declining salinity from 1962 to 2020.（5）XNH is mainly polluted by heavy metals such as Ni,Zn and Cr,but the overall polluted area is small with slight degree.Spatially,the pollution is mainly concentrated in the east edge of lake where human activities are relatively intensive.The pronounced pollution of Cu,Zn,Cr and Ni is likely to be mainly affected by tourism and dam construction.Cr,Cu and Ni peaked in 1980,happened to correspond to dam construction,and the pollution of Zn and Cu began in 1995 and 2005respectively,which may be affected by the development of local agriculture,the increase of fertilizer use,the rise of tourism and the fuel of cruise ships.