Spatial Variation Analysis Of Soil Nutrient Elements And Heavy Metals In The Plain Area Of North Zhejiang Province

The northern Zhejiang plain area is located in the Yangtze River Delta,which is densely populated and rich in natural resources.Since ancient times,it has been known as the land of honey and milk.A correct and comprehensive understanding of the spatial distribution characteristics and variation patterns of nutrients and heavy metals in the soil can provide a theoretical basis for rational planning of land use,adjustment of industrial layout,and prevention and control of pollution in northern Zhejiang.Based on date of multi-purpose regional geochemical survey in northern Zhejiang(1:250000),this paper systematically analyzed the spatial variation of soil nutrient elements and heavy metals in the northern Zhejiang plain area in combination with theory of geostatistical methods,ecology,soil science,and geochemistry.At the same time,some opinions and attempts have been made on the methods of geoststistics and several meaningful results have been obtained.The main findings are as follows:(1)The average content of nutrients,such as organic matter,N,S,in the topsoil of the northern Zhejiang Plain is relatively abundant,which is 3.9,3.2,and 2 times of the surface soil abundance in eastern China respectively.The average content of Hg is 9.2 times of the eastern surface soil,but the spatial distribution uniformity is poor.In some areas,the Hg content in the soil may exceed the standard.(2)Research discussed the spatial structure characteristics of each element by geostatistical methods,and obtained the spatial variation of soil elements in the study area by interpolation of samples in the whole region by Universial Kriging.Studies have shown that the major elements of soil nutrients,such as CaO,Fe2O3,K2O,and Mg0,have strong spatial autocorrelation,and structural factors,such as parent material and particle size composition,play a leading role in spatial variation.The spatial autocorrelation of macronutrients required for plants,such as organic matter,N,P,S,is relatively low,which is mainly formed by structural factors such as parent material and sedmentary environment,and random factors such as artificial fertilization and organic pollutant emissions.The content of Hg exceeded the standard in some parts of soil,and the content of other elements was far below the limit value in Environmental Quality Standard for Soil(GB15618-1995).Hg in soil mainly comes from coal dust pollution and municipal solid waste,but it mainly exists in the form of residual fraction,and the ecological risk is low.The content of the Cd elements varies in the different area,and its spatial variability is greatly affected by human activities.The enrichment rules of Cr and Ni may be related to the adsorbent Fe2O3 in the soil.The spatial variability of other heavy metal elements formed of synergies of multiple factors.(3)The combination of trend surface and variation function(or covariance function)can effectively verify the stability of geostatistical variables.After testing,it was found that soil nutrient elements and heavy metals in the study area could not satisfy the stationarity condition.For this kind of non-stationary data,this paper first attempt to eliminates the drift(or trend)of each point,and then performs the variogram calculation and Kriging interpolation.This method can effectively avoid the distortion of the calculation result caused by non-stationarity of the data,and can also keep the authenticity of original data..