| Nanling-Jing county national commodity grain base is the place where is famous of the Nanling rice produce area,national good quality rice base and national commodity grain base.It is very nessisary to get deep information on the disstribution,variation characters and the protential ecological effect of the beneficial/heavy metal elements which displayed in the farmland top-soil.Aiming at the key scientific issue that the section character,variation and formation mechanism of the feature elements in the farmland topsoil.This paper set the Anhui province,Nanling-Jing county national commodity grain base as the key area,indentified the beneficial/harmful elements in farmland top soil,devided the study area into 5 sections which has different hydrogeological sysytem and calculated the background values.Based on the results of environmental values and section,a series of study about the distribution and fomation mechanism of beneficial/harmful(heavy metal)elements and the potential ecological effects were carry on.On the basis of 1:50000 farmland area hydrogeology and soil quality chemical survey,by adding longitudinal,latitudinal and vertical profile to increase samples idensity,the special experiments and the integrated research,the study identified the feature elements and computed the backgound values of farmland soil,devided the study section scientificly.Meanwhile,the study revealed the section characters,variability of distribution and the formation mechanism of farmland top-soil as well as illustrated the potential ecological effect of heavy metal and put forward corresponding countermeasure.The breakthrough development and new understanding as follows:(1)According to the characteristics of geomorphic unit,surface water drainage basin and groundwater system,as well as referring to the land use condition and crops planted types,deviding the study area into 5 section units.The soil environmental background values of 32 kinds of elements were clarified and computed firstly,which lay the foundation of this study.On the basis of that,the degree of variation of beneficial/harmful elements in the commodity grain base top-soil were recognized and display.(2)Based on semi-variogram theory,541 soil samples and data reliability were argued and proved that the spatial variability is minor.Meanwhile,the cause of spatial variability of beneficial/heavy metal elements in Nanling-Jing county national grain base was clarified.The research conclusion shows that,in study area farmland,the error and random variation which caused by sample collecting and analysing is not remarkable.In the farmland top-soil,most beneficial elements except SOM,N,available Mn and all 7 heavy metal elements show a moderate to strong spatial autocorrelation.The spatial variability of the feature elements(beneficial/heavy metal elements)in farmland top-soil is a integrated impacting consequence which concluding the structural factor(climate,soil parent material and soil types)and random factor(human activity).The natural and structural factor plays an important role to the spatial distribute variation in a large scale,otherwise,in a farmland scale the impact of human-influenced is even more obviously.(3)By using the geoaccumulation index method,the unit character of 9 kinds of heavy metal and the degree of potential risk effect to soil quality in Nanling-Jing county national commodity grain base top-soil were revealed.The conclusion shows that,the section Ⅰ has the largest area of risk range in "minor-medium" degree of heavy metal Hg which has the harmful impact to farmland soil quality,only 13.7 percent area were safety;and about 65.3 percent farmland area were impacted by the heavy metal Cd,the As impacted area is about 14.5 percent.More than 95 percent area of section Ⅱ were safety which had no the potential impact of heavy metal.In the section Ⅲ farmland,the maximum Igeo value of Hg was 3.38 which is also the maximum value in Nanling-Jing county national commodity grain base,and the influencing area reached 90 perncent of the unit Ⅲ total area,the impact range of"slight-medium" degree is about 73.8 percent.In the seciton IV farmland top-soil,the most harmful heavy metals were Hg and Cd,in regional field the Cd potential risk impact on soil quality present "strong" degree,at the same time,the Hg and Mn potential impact present"medium-strong" and "medium" degree respectively.In the section V farmland,however,the potential risk impact on soil quality of heavy metals Hg,Cd and As were all great.More than 30 percent area were affected by "moderate" and above level influence of Hg and Cd,about 18 percent and 4 percent farmland in section V were affected by "medium" and "strong" level risk of As,respectively.(4)With the method of potential ecological risk index,the section-related features and viration characters of potential ecological risk on soil quality at different section units were clarified in Nanling-Jing county national commodity grain base.According to the results,the potential ecological risk index of heavy metals As,Pb,Cr,Cu,Zn,Fe and Mn was betw een 0.74 to 23.86,which presenting "slight" level impact on farmland top-soil.Only the heavy metal Cd and Hg present "medium" and "strong" level potential risk on soil quality at the 5 section units.More than 70 percent area were under the potential ecological risk influence of Hg,which risk level is at strong degree.The level of potential ecological risk of Cd is at moderate degree.At section Ⅰ,the area of moderate degree influence of Cd potential ecological risk is about 75 percent;at section Ⅴ almost 30 persent farmland soil were in strong and above degree potential ecological risk.At section IV and V,the farmland area which were in moderate level potential ecological risk was above 10 percent,however,there is no potential ecological risk in section Ⅰ、Ⅱ、Ⅲ。(5)Proposing targetly,it is necessary to conduct deep survey on the distribution,sources causing and dynamic feature of Hg and carry out 1:10000 scale soil quality geochemical specific investigaion on regional heavy metal anomaly inspection.In addition,the key technique and countermeasures research which will be utilized to control the potential ecological risk of Hg were urgently demanded;What’s more,for the section units Ⅰ and Ⅴ,the mechanism of potential ecological risk cause and sources origin of heavy metal Cd should be further illustrated;for the section units Ⅳ and Ⅴ,the potential ecological risk impacting trends and scales of As should be checked and determinated.Both of these will helpful for forming the report of technical consultation and suggestion as soon as possible,and to the benefit of regional green agriculture,as well as the economic society sustainably develop. |
