Heavy Metal Pollution History In Fuzhou Area Over The Past 170 Years Inferred From Tree Rings

Tree rings becomes an important carrier for effectively recording the history of heavy metal pollution due to the elements can be enriched in the tree rings.A number of pollution historical studies based on tree rings have been carried out in China,but usually they have a shorter time period of study due to the trees in the urban areas tend to be younger.We provide time series of the concentration of 10 heavy metal(Fe,Mn,Cu,Zn,Ni,Cr,Cd,Pb,Co,Sr)for the Pinus massoniana tree rings from Fuzhou City for the past 170 years,which are to our knowledge the longest heavy metal series in Southeast China.According to the results of correlation analysis,cluster analysis,rotational principal component analysis and autocorrelation analysis,the radial distribution patterns of ten heavy metal elements in the study area tree ring samples can be divided into four types: descending type(Mn,Sr),arched type(Co,Cd,Pb),ascending type(Ni,Cu),wave type(Cr,Fe,Zn),the radial distribution pattern of elements is affected by common pollution sources,elemental properties and radial migration ability,wood characteristics and other factors.The difference in migration ability between different elements is discovered by calculating the autocorrelation coefficient.Cr,Fe,Zn,Ni,and Cu with weak radial migration ability can better reflect the development of tourist areas,traffic pollution history,and environmental events.The elements with strong migration ability such as Co,Cd and Pb can better reflect the wood characteristics of the tree(e.g.the boundary between heartwood and sapwood)and the influence of physiological activities on the radial distribution of elements in tree rings.The climate significantly affects the content of elements in the tree ring.The elements with weaker migration capacity are usually positively correlated with growth season temperature and precipitation.The essential elements for plant growth show a significant consistent correlation with temperature and precipitation,which provides a reference for further understanding of how climate affects the selective absorption of trees.Our results reveal the potential of long-term dendrochemistry studies to reconstruct environmental changes and effects of plant physiological factors and climatic conditions on the reconstruction of environmental history in the region.