The Comparative Studies On Heavy Metals Pollution And Ecological Risks Between The Kandelia Cande1 Natural Forest And Plantations In The North Of Fujian

Mangrove ecosystem located at the dynamic interface between ocean and land,its features was neither the terrestrial ecosystem nor the marine ecosystem on the structures and function.Fuding city with the special significance of mangrove ecological studies was located on the northern tip of Fujian,which was the mono-dominant community of Kandelia candel mangrove.In this paper,studied on distribution of Zn,Pb,Cd and Cu in Kandelia cande1 mangrove community of Fuding were investigated between the natural forest and the monoculture plantations(The investigation places were situated at Qianqi Town Anren Village and Diantou Town Diantou Village).Base on this,with the case comparative analysis with respect to the traits of transportation,accumulation and circulation of heavy metals,the enriched characteristics,the spatial distribution of heavy metals,the pollution character and the potential ecological risk assessment and the eco-environment service function assessment by comparing the natural forest with the monoculture plantations,this paper discussed transportation,accumulation and circulation of heavy metals in sediments which had different origins of Kandelia candel mangrove community.The results showed that:(1)The respective element average contents in different parts of the Kandelia cande1 natural forest plant were 19.21,28.40,1.30(mg·kg^-1)of Zn,Pb and Cd;While their contents in different parts of the Kandelia cande1 monoculture plantations were 15.06,17.65,1.12 mgkg^-1 of Zn,Pb and Cd (mg·kg^-1),being as much 1.28 times,1.61 times and 1.16 times as that from the natural forest to the monoculture plantations.(2)The pool amounts of Zn,Pb,Cd and Cu elements in the the Kandelia cande1 natural forest plant l(0～30cm depth) were 49.84,84.67,2.55,20.14 mg·kg^-1 and storages were 3353.32,14070.65,540.708,2901.36 (mg·m^-2 )whose variation were in the order of Pb>Zn>Cu>Cd;What's more,The pool amounts of Zn,Pb,Cd and Cu elements in the monoculture plantations (0～30cm depth) were 68.15,127.87,3.61,36.66 mg·kg^-1 and storages were 10778.33,15714.07,719.93,5289.77 (mg·m^-2 )whose variation were in the order of Pb>Zn>Cu>Cd.(3)In the the Kandelia cande1 natural forest,the accumulation indexes of plant to soil were 0.767,0.284,0.339,1.464 of Zn,Pb,Cd and Cu.To different parts of the Kandelia cande1 plant,their indexes ranged from 0.348～1.860,0.074～1.134,0.190～1.015 and 0.508～4.722 of Zn,Pb,Cd and Cu.Furthermore,the accumulating ability of plant to soil heavy metal were in the order of Cu>Zn>Cd>Pb: On the other hand,the accumulation indexes of plant to soil were 0.166,0.133,0.234,1.127 of Zn,Pb,Cd and Cu in the the Kandelia cande1 monoculture plantations.To different parts of the Kandelia cande1 plant,their indexes ranged from 0.049～0.557,0.038～0.439,0.111～0.515 and 0.313～1.272 of Zn,Pb,Cd and Cu.Furthermore,the accumulating ability of plant to soil heavy metal were in the order of Cu>Cd>Zn>Pb.(4)The storages in the community of the the Kandelia cande1 natural forest were 304.33,400.48,21.78,396.86 mg·m^-2,besides the storages of the aerial portion were 179.30,250.78,14.96,327.40 mg·m^-2that occupied respectively 58.9%,62.6%,68.7%,82.5% of total amount,while the storages of the underground part were 125.03,149.7,6.82,69.46 (mg·m^-2)that occupied respectively 41.1%,37.4%,31.3%,17.5% of total amount;What's more,The storages in the community of the monoculture plantations were 63.73,107.88,10.55,251.30mg·m^-2, besides the storages of the aerial portion were36.72,64.14,8.58,179.57 (mg·m^-2)that occupied respectively 57.6%,59.5%,81.3%,71.5% of total amount,while the storages of the underground part were 27.01,43.74,1.97,71.73 (mg·m^-2)that occupied respectively 42.4%,40.5%,18.7%,28.5% of total amount.(5)Based on the studies on horizontal distribution of Zn,Pb,Cd and Cu between the the Kandelia cande1 natural forest and the monoculture plantations , some conclusions were obtained.High contents of Zn and Pb were found in the sediments, while the contents of Cd and Cu were relatively lower.With regard to Cross-section distribution of heavy metals,the concentrations of Pb,Cd and Cu increased across the tidal flat to the mangrove forest edge,while decreased across the forest edge to inside.In addition that Vertical profiles of Zn,Pb,Cd,Cu heavy metals,their average contents decreased with the increasing of soil depth at the 15m inside-forest and the 50m inside-forest sites while the result was different at 100m outside-forest site.(6)On correlation coefficient of various heavy metal and soil character between the the Kandelia cande1 natural forest and the monoculture plantations,the correlation was higher from the 15m inside-forest and the 50m inside-forest to 100m outside-forest site.(7)Studied on pollution characteristic and ecological risk assessment of heavy metals,Concentrations,distribution and accumulation of heavy metals in the sediments were investigated.When the highest values for heavy metals concentrations in sediments before the modern industrialization of the world were taken as references , the accumulating order for these heavy metals was:Cd>Pb>Cu>Zn and the order of pollution level was:Cd>Pb>Cu>Zn.When the environmental background values of mangrove worked as references,the accumulating order was: Pb>Cd>Cu>Zn,and the order of pollution level was:Cd>Pb>Cu>Zn.(8)In the Kandelia candel mangrove forest of Fuding,Zn was absorbed 13871760g, on the one hand,it was 1507800g of the the Kandelia cande1 natural forest;on the other hand,it was 12,363,960g of the monoculture plantations.Employing the replacing and shadow engineering methods,the function value of mangrove soil on absorbing heavy metals was evaluated ,which indicated that the value of the natural mangrove soil to absorb heavy metals in Fuding mangrove ecosystem was about 5.133 million yuan.(9)The total value of the mangrove wetland ecosystem services in the Kandelia candel mangrove forest of Fuding was 16,589,234 yuan RMB per year.based on the economical background of the region in 2009.Among them the value of production of goods was1,031,959 yuan RMB per year,the value of protection against floods was 7950,000 yuan RMB per year,the value of biodiversity was 6,000,000 yuan RMB per year,the value of purification was 635,075 yuan RMB per year,the value of ecotourism was 644,000 yuan RMB per year,the value of the educational research functions was 328,200 yuan RMB per year.