Monitoring Of Heavy Metals In The Sewage Irrigated Farmlands In Longkou City Using Remote Sensing Technology

Soil,of which the environmental quality has a direct influence on the growth of crops and human health,is an indispensable resource using in the living and producing process.More and more “three wastes” including solid residue,sewage and waste water were discarded into soils and accumulated as the outburst of population and rapid development of industry,leading to the contamination of farmlands.Particularly,the heavy metal pollution caused by waste water irrigation is common worldwide.Domestic sewage generally contains much nutriment made for the improvement of soil fertile and the growth of plants,while it may induce the excessive enrichment of heavy metals in soils and crops since there existed lots of metals and other detrimental substances in the industrial waste water.Heavy metals are hardly removed and therefore the harmful effects on farmlands are durable.Hence,the subject on the rapid and accurate monitoring and evaluation of heavy metals in soils and crops comes into a hot issue for the scholars in China and abroad.Compared with the traditional monitoring methods,remote sensing technique offers a new idea as the advantages of its timeliness,environmental friendliness and widely covered.The study area is located in the north plain of Longkou city.Being supported by the National Natural Science Foundation Project of China “Monitoring of the ecological safety of croplands in Longkou city based on the surface parameters of remote sensing”,Shandong Province Natural Science Foundation Project “Monitoring of the mining area and coastal zone using remote sensing technique”,“Geological survey on the environment of Jiaojia-type gold mine belt using remote sensing”,“Survey on the intrusion of sea/saline water and construction of warning system in the effective ecological economic zone of Yellow River Delta ”,Shandong Province Department of Land and Resources Project “Construction of remote sense spectra library”,Seventy-two soil samples and forty-two corn leaf samples were collected for spectra measurement in the labtorary and content determination of Cr,Cu,N i,Pb,Zn,As,Cd and Hg.Derivate treatment,continuum removal transformation,standard normal variate and multiple scatter correction techniques were used to protrude spectral signals.Quantitative relationship between spectra data and concentrations was established using multiple linear regression(MLR),partial least square regression(PLSR)and stepwise multiple linear regression(SMLR)algorithm.Geostatistics and principal component analysis were used to explore the characteristics of spatial distribution and the possible sources of heavy metals.The contamination situation of soils was assessed with aid of the Nemerow comprehensive pollution index,Pollution Loading Index and Risk Index.Moreover,some advises were put forward with respect to the current status of the farmlands in Longkou city.The main conclusions were listed as followed:(1)Results showed that the modeling effects of Cr,Cu,Zn and Pb in soils were rather outstanding.Except for Cr and Zn,the best spectral parameter was first deviated(RD1)data,and SMLR were more suitable for the concentration estimation of all elements.As shown in the result of corn leaf calibration construction,Zn,Cd and Hg were more ideal,and the first deviate pre-processing can improve the accuracy of modeling to a certain degree.The predictive results of Pb and Cd in soils using the spectra of corn leaves were considerably accepted with R2 values all above 0.5,which suggested that it was feasible to reflect the contamination levels of heavy metals in soils with assistance of the plant reflectance spectra.(2)Apart from Cr and Ni,the spatial distributions of other elements were quite different.But common high concentration areas were mainly located in the industrial zone and densely populated area,which indicated that the content levels of heavy metals were disturbed by anthropic activities.The spatial distributions of the corresponding elements were distinguishing.The hot spot areas of Cd were lay in the south part,which the rest were in the islands of the partial zones in east and north region.The possibilities that the heavy metals in the corn leaves were influenced by some random factors,for example,the application of chemical fertilizer and pesticide,were much higher.(3)The correlations between some heavy metals were significant,indicating the similar pollution sources,and principal component analysis was used to make further judgments about the origins.There were three components extracted from the contents of heavy metals in soils.The first principal component(PC)mainly including Cr and Ni was considered the natural source.PC2 represented the contamination introduced by traffic and industrial ac tivities which contained Cu and Zn elements.Moreover,the third component was regarded as the agricultural and industrial factors,such as the employ of chemical fertilizer and pesticide,combustion of coal or coal washing process,and Cd and Pb were primarily affected by the inducement.The concentrations of As and Hg in soils were controlled by both natural and anthropic factors.Three derivations were also distinguished in respect of the corn leaves.Contents of Cd and As were correlated with the application of fertilizer and pesticide,Cr,N i,Pb and Hg were correlated with industrial activities,while Cu and Zn were mainly come from plants using for the compound of chlorophyll,photosynthesis and respiration.(4)The evaluated results of Nemerow comprehensive index and pollution loading index implied that the soils were moderately contaminated by heavy metals and there existed some point pollution sources.However,the potential ecological risk was slight.The asse ssments were embodied through GIS analysis and the spatial distributions showed that the sites of severe polluted area resembled the high value areas of heavy metals where densely distributed many industrial factories and population.On the whole,the contamination level of the farmlands caused by heavy metals in Longkou city was moderate,but obvious accumulation was detected in this area.Direct at the situations,some advice were advanced in the aspects of soil remediation,soil environmental monitoring,protection and legislation,offering theoretical guidance to the improvement of the ecological environment of croplands.