Study Of The Ecological Environment Of The Urban Forest Green Features

The thesis studies the important function of urban forest and green space in Nanjing— improvement ecological environment,emphasis on absorbing dustrull and sulphur dioxide capability,standing pooh absorbing heavy metal capacity of forest floor litter, analyzed heavy mental pollution of Nanjing and absorbing characters and affecting factors in different soil based on the investigation of Zn, Cr, Cu and Pb in the soil of different domains in Nanjing,studies the transfer laws of cadmium, chromium, cuprum and plumbum in urban forest soil ecosystem by the means of collecting water samples in different soil depth and analyzing the concentration of different heavy metals in each soil layer after artificial sewaging. The results show:(1)There is difference between the absorbing dustfull capability of different greening species. The law of absorbing dustfull capability of greening tree species in the same spot is :high in Spring,down in summer,higher in Autumn,highest in Winter.The amount of dustfull on the leaves will increase with time extends.There is difference between the absorbing sulphur dioxide capability of different greening species.For evergreen tall tree,amount of sulphur dioxide is the highest in Winter.For bush,amount of sulphur dioxide is the lowest in Spring.The distance between different spot is not large.(2) There exists heavy mental pollution in researching area, especially in industry area. There is no consistent regularity for the total and virtual content of different mental in different layers of soil. Heavy mental in the soil of city area is almost originate from the same pollution source, but the origin of the other three heavy mental is maybe more than one pollution source. The total of heavy mental relates to virtual content of heavy mental, and heavy mental content relates to physicochemical property of soil.(3) Static absorbing Cu and Cd of woodland, farmland and grassland increases with the increasement of Cu²⁺ and Cd²⁺ concentration in equilibrium liquid, which could be described by Langmuir equation and Freunlich equation. The release capacity of the three kind soil increases with the increasement of their absorbing capacity. There is linear positive correlation between them. The absorption character in soil of Cu²⁺ and Cd²⁺ is obviously different: under the same PH in same soil condition, the absorption capacity of Cu²⁺ is larger than that of Cd²⁺; and the absorption rate of Cu²⁺ is higher than that of Cd²⁺. The absorption capacity of Cu²⁺ and Cd²⁺ in every soil relates to PH in soil and increase with the increasement of PH in soil. There is no consistent regularity for citric acid and oxalic acid to absorbing Cu²⁺ and Cd²⁺ in different soil.(4) The heavy metal content of forest floor litter is higher than that of soil background value in Nanjing.The hervy metal cntent of different layers is Y layer>L layer.The order of heavy metal content in different spots is:urban district, outer suburbs>city suburbs.The order of different heavy metal content in forest floor litter is :Zn>Cr>Pb>Cu>Cd.(5) The forest soil has relatively strong percolating ability to the sewage which is polluted by heavy metals, but there is a certain environmental capacity. The ability of adsorbing heavy metals, such as Cr, Cu, Pb etc. is widely different in different depth of soil,the order of which is top layer > middle layer > bottom...