| Contamination of heavy metal has become one of the important environmental issues.The content,distribution,existence forms,migration,biological effects and countermeasures of heavy metal pollutants in the environment were paid more attention.On the basis of an ecosystem,the ecological process of heavy metals has become one of the hot topics researchrs in recent years.Thorough understanding of a system on input or output of internal migration and qualitative and quantitative change rule of all kinds of heavy metals due to the biogeochemical process was necessary for knowing bearing capacity of ecosystem and thus maintaining sustainable and healthy development.Therefore,low hilly land in the upper Yangtze river valley(Wutongqiao district)in the typical catchment was used as a study object to investigate atmospheric deposition,throughfall,stemflow and litter layer in different stand types,different soil layers of different land use types and runoff on trunk of concentration of heavy metals by sampling.We also analyzed heavy metal contents in atmospheric dry and wet deposition,dynamic change and its input and output,compared with the filtration of heavy metal in different stand types to calculate the reserves of heavy metals in the study area and to reveal the effect of interception and filtration of heavy metals in catchment compound ecosystem.These results are of significance for protecting the regional ecological environment,providing the scientific basis and optimization measures for in-depth development of Sichuan province,restorating main area polluted by non-point source pollution,and building ecological restoration experiment and demonstration research.Our main results are as follows:(1)The annual precipitation in catchment was 1202.42 mm.The order was summer>spring>autumn>winter.The total of heavy metal contents in dry sedimentation was always higher than that in wet sedimentation.There was a significant negative correlation relationship between heavy metal contents in atmosph,eric rainfall and rainfall.Total input of heavy metals was16.44 kg·hm-2·a-1,of which atmospheric deposition was 13.84kg·hm-2·a-1,pesticides and fertilizers accounted for 2.60 kg·hm-2·a-1.As,Cd,Cu,Pb and Zn input was 0.17 kg·hm-2·a-1,0.09 kg·hm-2·a-1,0.95 kg·hm·2·a-1,0.94 kg·hm·2·a-1,14.29 kg·hm-2·a-1,respectively.(2)There was a significant negative correlation relationship of heavy metal contents between throughfall and stemflow and rainfall in different forest types.The interception of canopy in Metasequoia glyptostroboides plantation was 226.38 mm,account for 18.83%of precipitation.The interception of canopy in Cunninghamia lanceolata plantation was 168.51mm,account for 14.01%of precipitation.The interception of canopy in Eucalyptus grandis plantation was 250.84mm,account for 20.86%of precipitation.The interception of canopy in broad-leaved mixed forest was 288.00mm.account for 23.95%of precipitation.The total heavy metal in annual intercept of forest canopy in Metasequoia glyptostroboides plantation was 5.34kg,account for 70.18%of the total atmosphere deposition.The total heavymetal in annual intercept of forest canopy in Cunninghamia lanceolata plantation was 2.07kg,account for 69.46%of the total atmosphere deposition.The total heavy metal in annual intercept of forest canopy in Eucalyptus grandis plantation was 3.54kg,account for 71.13%of the total atmosphere deposition.The total heavy metal in annual intercept of forest canopy in broad-leaved mixed forest was2.50kg,account for 73.06%of the total atmosphere deposition.The canopy intercept rate of heavy metals As and Cd were the highest in Eucalyptus grandis plantation.There was a strongest adsorption and absorption of As and Cd with atmospheric deposition for this plantation.The canopy intercept rate of heavy metals Cu,Pb and Zn were the highest in broad-leaved mixed forest,indicated that there was a strongest adsorption and absorption of Cu,Pb and Zn by atmospheric deposition.(3)Standing crop of litter in M.glyptostroboides plantation was 6.32 t·hm-2,the annual output was3.02t·hm-2,the reserves of heavy metals was 0.80kg·hm-2.Standing crop of litter in C.lanceolata plantation was 3.58 t·hm-2,the annual output was 2.46t·hm-2,the reserves of heavy metals was 0.49kg·hm-2?Standing crop of litter in E.grandis plantation was 1.86t·hm-2,the annual output was 3.24t·hm-2,the reserves of heavy metals was 0.45kg.hm-2.Standing crop of litter in broad-leaved mixed forest was 9.63 t·hm-2,the annual output was 6.40t·hm-2.the reserves of heavy metals was 2.42kg.hm-2.The interception order of litter was broad-leaved mixed forest 0.98 kg·hm-2)>E.grandis plantation(0.41 kg·hm-2)>M.glyptostroboides plantation(0.25 kg·hm-2)>C..lanceolata plantation(0.14 kg·hm-2).The interception rate order of litter was M.glyptostroboides plantation(42.56%)>C.lanceolata plantation(36.96%)>E.grandis plantation(36.740%)>broad-leaved mixed forest(36.72%).The order of heavy metal contents in different stand types was winter>autumn>spring>summer.The order of heavy metal output of litter drainage in different stand types was C.lanceolata plantation(1.82kg·hm-2)>E.grandis plantation(1.57kg·hm-2)>M.glyptostroboides plantation(1.34kg·hm-2)>broad-leaved mixed forest(1.25kg·hm-2).The order of total intercept of litter was E.grandis plantation>broad-leaved mixed forest>M.glyptostroboides plantation>C..lanceolata plantation,and the interception rate order was M.glyptostroboides plantation(19.78%)>broad-leaved mixed forest(17.89%)>C.lunceolcta plantation(1 7.51%)>E.grandis plantation(17.41%).the litter interception rate of As,Cd,Pb and Zn in M.glyptostroboides plantation and Cu in broad-leaved mixed forest were the highest,indicated that there was a strongest adsorption and absorption of As,Cd,Pb,Zn and Cu in input stand.(4)There was an extremely significant relationship among the 5 heavy metal concentrations in different land use types.There was a significant relationship between pH and As or Cd concentrations in soil of different land use types.There was an extremely significant positive relationship between organic matter and 5 heavy metal concentrations.Compared with the data of 1 year ago,5 heavy metal contents in paddy increased,whereas Cd and Pb contents in dry land soil.Total storage capacity of heavy metals in soil was 3771.54kg,and the total storage capacity in M.glyptostroboides plantation,C.lanceolata plantation,E.grandis plantation,broad-leaved mixed forest,dry land,paddy was 496.02kg,542.39kg,900.38kg,507.66kg,513.45kg,811.64kg,respectively.The interception rate order of soils was dry land(45.46%)>C.lanceoIata plantation(16.54%)>broad-leaved mixed forest(13.67%)>E.grandis plantation(13.22%)>M.glyptostroboides plantation(12.69%).The order of heavy metal output of surface flow in different stand types was dry land(1.39kg·hm-2)>M.glyptostroboides plantation(0.47kg·hm-2)>C.lanceolata plantation(0.45kg·hm"2)>E.grandis plantation(0.44kg-hm"2)>broad-leaved mixed forest(0.25kg-hm"2).The interception rate order was dry land(89.94%)>E.grandis plantation(16.97%)>broad-leaved mixed forest(16.12%)>C.lanceolata plantation(15.12%)>M.glyptostroboides plantation(14.35%).The dry land had the highest interception rate of As,Cd,Cu,Pb,Zn.(5)The enrichment coefficients of As,Cd and Pb in Sassafras tzumu,Cu in Alnus cremastogyne and Zn in Styrax tonkinensis were the highest;the translation coefficients of As,Cd and Zn in Cyclobalanopsis glauca,Cu in Platycarya strobilacea and Pb in Phoebe zhennan were the highest.Two or more enrichment coefficients and translation coefficients of heavy metals in Emilia sonchifolia,Dicranopteris dichotoma,Pteris vittata,Scirpus planiculmis,Lophatherum gracile,Lygodium yunnanense,Oxalis corniculata,Ophiopogon Japonicus,Clematis montana and Rhododendron simsii were more than 1.Such results indicated that these plants exhibited some important characteristics of hyper-accumulators,thus had the potential to rehabilitate polluted soils,but further research is needed.The heavymetals storage capacity of plants was 15.12kg.The heavy metal storage capacity of Metasequoia glyptostroboides plantation was 8.47 kg·hm-2.The heavy metal storage capacity of Cunninghamia lanceolata plantation was 5.04 kg·hm-2.The heavy metal storage capacity of Eucalyptus grandis plantation was 0.32 kg·hm-2.The heavy metal storage capacity of broad-leaved mixed forest was 0.79kg·hm-2.(6)Total storage capacity of heavy metals in water was 1.86kg.Total runoff of two outlet in the catchment was 8075.16 m3,the annual output of heavy metals was 2.17kg·a-1.The order of output rate was As(3.39%)>Zn(3.27%)>Cd(2.92%)>Pb(2.05%)>Cu(0.89%)?(7)Total storage capacity of heavy metals in the catchment was 3791.28kg,and the total storage capacity in soils,plants,litters and water were 3771.54kg,15.12kg,2.76kg,1.86kg,respectively.Total accumulation of heavy metals in the catchment was 64.89kg,and the rate of reservoir filtration was 91.57%.The total storage capacity of As was 0.69kg,and the rate of reservoir filtration was 93.23%.The total storage capacity of Cd was 0.37kg,and the rate of reservoir filtration was 91.36%.The total storage capacity of Cu was 4.01kg,and the rate of reservoir filtration was 98.02%.The total storage capacity of Pb was 3.75kg,and the rate of reservoir filtration was 93.02%.The total storage capacity of Zn was 56.07kg,and the rate of reservoir filtration was 91.03%.The order of interception and filtration in different land use types was broad-leaved mixed forest>E.grandis plantation>C.lanceolata plantation>M.glyptostroboides plantation>dry land.The order of interception and filtration in canopy was broad-leaved mixed forest>E.grandis plantation>M.glyptostroboides plantation>C.lanceolata plantation.The order of interception and filtration in litter was M.glyptostroboides plantation>broad-leaved mixed forest>C.lanceolata plantation>E.grandis plantation.(8)Heavy metals of water were under the surface water environmental quality standard class III in the catchment of agroforestry ecosystem,to drinking water sources protection of two standard.But the heavy metal pollution in the atmosphere was more serious than other cities in the country.The soils were not polluted by Pb,Cu and As,only slightly polluted by Zn,but Cd was seriously polluted in the catchment.The potential ecological hazard of Cd was the highest,the potential ecological hazard of surface soil of dry land and paddy soil were stronger,and the potential ecological hazard of forest soils were moderate.The filtration effect of heavy metals in forest land were significantly higher than that in dry land,and the filter effect of broad leaved forest were higher than that of coniferous forest.In summary,in order to reduce the regional ecological risk,control non-point source pollution,improve environmental quality,on the one hand,we can governance the environmental from thesource,such as appropriate to reduce the use of pesticides and fertilizers,on the other hand,we can increase the forest area(preferably broad-leaved forest),increase the uptake and fixation effect of plant,reduce the migration of heavy metals in the region,provide support for the ecological restoration of pollution. |
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