Effects Of Climate And The Other Factors On Soil Heavy Metals In The Raohe-Puer Transect

Soil heavy metal concentration is one of the environmental quality indicators that affect ecological safety and human health.However,the spatial distribution characteristics of heavy metal concentrations at a large scale and their key influencing factors are still unclear.In this study,the spatial distribution characteristics of total and fractional soil heavy metal concentrations were investigated in the Raohe – Puer transect,an environmentally complex area with a length of more than 4000 km.The relationship between environmental factors and soil physicochemical properties and heavy metal concentrations was discussed using regression analysis and variance analysis.The key influencing factors of various heavy metals in soil were selected through RDA,and different climate change scenarios were simulated through field observation data and indoor incubation experiments under different climatic conditions to determine the potential effects of climate change on heavy metal fractions.The main conclusions are as follows:(1)Soil heavy metal concentrations exhibit various spatial distribution patterns at a large scale.With the exception of cadmium and zinc,the total concentrations of other heavy metals linearly increase(p < 0.05)from northeast to southwest.The different forms of heavy metals exhibit four significant distribution patterns:(1)The content of cadmium,lead,chromium,and copper in iron-manganese oxide-bound form,as well as copper,cobalt,nickel,and vanadium in residual form,linearly increase(p < 0.05)from northeast to southwest,except for the exchangeable form of vanadium and cobalt.(2)The exchangeable form of vanadium,ironmanganese oxide-bound form of cobalt and vanadium,and the organic-bound form of copper,zinc,nickel,and vanadium significantly decrease(p < 0.05).(3)The carbonate-bound form of eight heavy metals,as well as the iron-manganese oxide-bound form of zinc and nickel,exhibits a trend of increasing and then decreasing(p < 0.05).(4)The organic-bound form of chromium and cobalt,as well as the residual form of chromium and zinc,exhibits a trend of decreasing and then increasing(p < 0.05).(2)Climate significantly influences both the total content and forms of soil heavy metals.The annual mean temperature,annual mean precipitation,and humidity index are significantly positively correlated with the total content of six heavy metals except for cadmium and zinc(p< 0.05),while drought index is significantly negatively related with the total content of all heavy metals except for cadmium(p < 0.05).Among the various forms of the elements,the exchangeable form of cadmium,lead,zinc,and nickel,the iron-manganese oxide-bound form of cadmium and lead,and the residual form of all heavy metals except for cadmium,lead,and zinc,are prominently affected by the four climatic factors(p < 0.05).However,the organicbound and residual forms of cadmium,the residual form of lead,the iron-manganese oxidebound form of zinc and cobalt,are least affected by climate,and their relationships with the four climatic factors are all not significant(p > 0.05).The other forms of each element are significantly affected by one to three climatic factors(p < 0.05).(3)This passage discusses the results of a comprehensive analysis using RDA to determine the dominant factors influencing the distribution of eight forms of heavy metals in soils,including climate,parent material,and vegetation.These factors were found to contribute 55%-65.5% of the variation in heavy metal forms(p < 0.05),and the study identified the specific effects of climate(primarily mean annual temperature and precipitation)on these forms of heavy metals.Specifically,an increase in mean annual temperature and precipitation was found to promote the exchangeable form of cadmium,lead,chromium,and nickel,as well as the ironmanganese oxide and organic matter-bound forms of cadmium,lead,and chromium,and the residual forms of heavy metals except for cadmium and lead.On the other hand,it was found to reduce the exchangeable form of vanadium,the carbonate-bound form of vanadium,chromium,zinc,nickel,and vanadium,the iron-manganese oxide-bound form of zinc,cobalt,nickel,and vanadium,and the organic matter-bound form of copper,cobalt,nickel,and vanadium,as well as the residual forms of cadmium and lead.(4)Field observations and indoor simulation experiments have jointly shown that climate has a significant influence on the distribution of heavy metal forms in soils.The comparison between the two indicates that a single warming can lead to a remarkable decrease of 12.77%(p < 0.05)in the content of organic-bound chromium,while warming and reduced humidity can result in a significant raise of 20.58%(p < 0.05)in the content of carbonate-bound cadmium.Warming and increased humidity can cause a prominent decline(p < 0.05)in the content of carbonate-bound lead and nickel.Overall,this study,which selected an ultra-long scale transect,showed that the distribution of heavy metal total content and forms exhibits linear and quadratic characteristics,and that climate and the other factors jointly shape the total content and forms of heavy metals in the soil transect.