| Soil heavy metal pollution poses an increasingly serious threat to the ecological environment and people’s health.The source of soil pollution in the suburbs is complex and affects a wide range of the resident population.Traditional soil heavy metal detection methods are time-consuming and laborious.Based on hyperspectral data,this paper studies the pollution monitoring,spatial distribution,pollution status and source analysis of heavy metals in suburban xi ’an.The main conclusions are as follows:(1)As affected by soil organic matter,clay minerals,the adsorption effect of aluminum and iron oxide,Cr and Ni by organic matter,iron,aluminum,silicon manganese oxide and clay minerals content of adsorption concentration effect is stronger,Cu is mainly influenced by organic matter,aluminum oxide,iron,manganese oxide adsorption agglomeration effect,the content of Pb in soil mainly by organic matter,iron,manganese oxide,the adsorption effect of aluminium oxide,zinc mainly by organic matter and clay minerals content,iron,manganese oxide concentration adsorption.The moving average method is used to smooth the original spectral data and improve the signal-to-noise ratio of the spectrum.The trend of the soil spectral curve in the study area is a gentle oblique parabola with convex top.At 400nm,the reflectivity reaches the lowest point,and then the slope of the reflectivity curve is large.The reflectivity value increases rapidly within the range of 400-600nm,while the reflectivity value tends to be flat within the range of 600-1024nm,and the curve generally shows an upward trend.(2)The sensitive bands of As are 388-420nm,480-490nm,570-590nm,640nm-670nm,700-7 10nm and 980-1020nm.The sensitive bands of Cr were 406-440nm,630-670nm,920-930nm,and 980-1020nm.The sensitive band range of Cu is 388-1024nm.The sensitive bands of Ni are 392-510nm,650-700nm,740-750nm,920-960nm and 1000-101 Onm.The sensitive band range of Pb is 440-480nm and 510-1020nm.The sensitive band range of Zn is 430-1020nm.In addition to As,the partial least square regression model has a higher estimation accuracy for the content of heavy metal elements in soil.The optimal spectral index of As,Ni and Pb is reciprocal,and the optimal spectral index of Cr,Cu and Zn is first-order differential.The reciprocal transformation and first-order differential transformation of spectral reflectivity can effectively improve the precision of inversion modeling.(3)The range of As content in soil is 3.0-21.2 mg/kg,the range of Cr content is 42.4-94.2 mg/kg,the range of Cu content is 11.0-50.1 mg/kg,the range of Ni content is 16.2-45.9 mg/kg,the range of Pb content is 20.0-87.4 mg/kg,and the range of Zn content is 30.9-166.1 mg/kg.Compared with the background value of soil elements in Shaanxi Province,there is a certain enrichment phenomenon.The variation coefficients of the six heavy metals were 10%<CV<100%,which belonged to the moderate degree of variation.As,Cr,Cu and Ni present normal distribution,while Pb and Zn present lognormal distribution.The content of As is higher in the soil of fruit park,farmland and public service area(park,green space);the content of Cu is higher in the soil of industrial area;the distribution characteristics of Pb and Zn are similar in different functional areas,and the content of As is higher in the soil of traffic area.As,Cr,Cu,Ni and Zn all show the distribution characteristics of higher content in new accumulated soil and loess soil and lower content in Chao soil.The content of Pb in four types of soils is basically the same.The contents of Cr,Ni,Pb and Zn fluctuate greatly in Loess diet soil,and the contents of Cu fluctuate greatly in Chao soil.(4)As,Cr,Cu and Ni conform to the Gauss model,Pb to the exponential model and Zn to the spherical model.The nugget effects of Cr and Ni are 22.51%and 24.42%respectively,which have strong spatial autocorrelation and are mainly influenced by the structure of natural factors;the nugget effects of As,Cu and Zn are 45.08%,26.79%and 52.78%respectively,with moderate spatial correlation;and the nugget effect of Pb is 78.94%,with weak spatial correlation,which is greatly influenced by human factors.The ranges of As,Cr,Cu,Ni,Pb and Zn are 4.85 km,3.04 km,3.32 km,3.60 km,4.82 km and 3.28 km respectively,which are larger than the sampling interval of 2.5 km.The content of As in the northern part of Gaoling District is higher than 12 mg/kg.In addition.Dizhai Street and Hongqing Street in Baqiao District also have some accumulation phenomenon.The content of As in Weiyang District is lower;Dizhai Street,Baqiao Street and Hongqing Street in Baqiao District,Weiyang Palace Street.Tongyuan Town and Luyuan Street in Gaoling District are all higher than 75 mg/kg in Weiyang District;the high content of Cu is mainly distributed in southern streets of Weiyang District,southwest of Baqiao District and Yaohui Administration Committee in Gaoling District,with the content of Ni over 33 mg/kg;The content of Pb in the southern streets of Weiyang District is higher than 48 mg/kg.The high value area of Zn is mainly located in the southern streets of Weiyang District and the southwestern streets of Baqiao District,with the content above 106 mg/kg.(5)The order of cumulative pollution degree of heavy metals in soil in the study area is Pb>Cu>Ni>As>Cr>Zn,in which Pb and Cu are heavily affected by human factors,and the comprehensive pollution index is 1.444.The pollution situation in the study area is in a light pollution state as a whole.As mainly comes from agricultural pollution sources,Cr and Ni mainly comes from parent materials of soil formation,Cu mainly comes from industrial pollution sources,and Pb and Zn mainly comes from traffic pollution sources.The contribution rate of each pollution source is as follows:the total contribution rate of agricultural pollution source is 21.3%,the contribution rate of natural parent material is 30.7%,the industrial pollution source is 26.7%,and the traffic pollution source is 21.4%.The contribution rate of anthropogenic sources is greater than that of natural sources in the study area. |
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