The Remediation Effects Of Litter From Tree And Grass Species On Petroleum Contaminated Soil In Northern Shaanxi Oil Zone

In recent years, environmental pollution and ecological destruction has a worse tendency with the large-scale oil exploitation in northern Shaanxi. Therefore, we are in urgent need of remediation and improvement of petroleum contaminated soil so that reduce the harmful petroleum hydrocarbons, improve soil physicochemical and biological properties, and restore soil structure and function. In the domestic and overseas, the study that utilizing plant to repair petroleum contaminated soils has increased, little research has been done that make use of plant litter to repair. Plant litter, as natural organic matter, especially after decomposition, play important roles in improving soil fertility, promoting the return and release of the nutrients, enhancing soil microbial activity and changing soil enzyme activity. Plant litter is a discarded resources that can be used to repair and improvement of petroleum contaminated soils. Vegetation litter has the affinity with soil microorganism and soil enzyme, and release soluble substances into soil after decomposition, which could adjust C/N ratio of the petroleum contaminated soil and provide metabolic substrate for petroleum hydrocarbon degrading bacteria, and then promote the degradation of petroleum hydrocarbons, reduce the residues of petrolic material, thus to achieve the effect of remediation and improvement. In this paper, we collected petroleum contaminated soil from Yujiaping oilfield in Zichang county, Yan’an city, Shaanxi province. 19 kinds of leaf litter of urban landscaping trees and 21 kinds of leaf litter of afforestation trees in oil polluted area were sprinkled on the contaminated soil, respectively. After a period of 120 d of indoor decomposition mixed culture experiments, we examined the residue of petroleum hydrocarbon, soil microbial quantity and enzyme activity. By comprehensive analysis and evaluation of different vegetation leaf litter on the repair capacity of oil-contaminated soil, we screened out vegetation leaf litter has a better repair capacity. Accordingly, we can take advantage of these litter resources, and reflects its value of ecological restoration. By measuring the correlation properties of the mixed cultured soil, we draw the following conclusions:(1) 19 kinds of leaf litters of urban greening trees has a difference of N, P, K content, and after decomposition, the release of nutrients has a positive correlation to soil remediation. Most of leaf litters has significant complementary effect on the loss of available and micro- nutrients(except for available phosphorus) of petroleum contaminated soil, thus increasing the organic matter content, changing the soil pH value significantly, and promoting the degradation of petroleum hydrocarbons. The majority of leaf litters improved soil enzyme activities, such as catalase, sucrase, urease, dehydrogenase, alkaline phosphatase and protease, but reduced the activity of polyphenol oxidase. Most leaf litter are promoted the growth of actinomyces and fungi, but different leaf litter have a different effects on bacterial growth. According to the results of comprehensive principal components analysis, the species that have the best comprehensive repair effects on contaminated soil among 19 kinds of leaf litter of urban greening trees are Melia azedarach and Prunus persica, following are Morus alba, Sophora japonica, Salix babylonica, Acer mono Maximand Prunus cerasifera, and the effects of other trees litters is not obvious or even worse.(2)Among the soil remediation effects of 21 kinds of afforestation plants, Platycladus orientalis, Populus simonii, Caragana Korshinskii and Periploca sepiumcan significantly increase the number of soil bacteria, fungi, actinomycetes, which has a positive effect on the reproduction of polluted soil microbial. All of leaf litter were significantly increased soil available Zn content, and also added soil available Fe and Mn content except Trifolium repens and Quercus liaotungensis. In addition to Pinus tabulaeformis and Q. liaotungensis, other litter can be significantly increased soil alkaline hydrolysis N, available K content.Larix gmelinii,Zanthoxylum bungeanum, Medicago sativa,Coronilla varia and Bothriochloa ischaemum were significantly increased soil available P content and Trifolium repens showed the most remarkable effect. Similarly, Q. liaotungensis is best plant for increasing soil organic matter content. These litter treatment can enhance the activity of soil urease, protease and dehydrogenase. Nevertheless, Medicago sativahas the most significant effect to increase soil invertase and polyphenol oxidase activity, as well as Ziziphus jujuba to catalase. According to the results of comprehensive principal component analysis, for these 21 kinds of afforestation plants, the species that have the best comprehensive repair effects on contaminated soil are Platycladus orientalis and Trifolium repens, following are Caragana Korshinskii, Medicago sativa, Coronilla varia, Artemisia argyi, Populus simonii, and the effects of Periploca sepium and Ziziphus jujuba is not obvious.Ulmus pumila, Armeniaca sibirica and Bothriochloa ischaemum has weak inhibitory effect on the restoration of petroleum-contaminated soil, plants have stronger inhibitory effect are Pinus tabulaeformis, Hippophae rhamnoides, Q. liaotungensis, Pyrus betulifolia Bunge, Zanthoxylum bungeanum and Robinia pseudoacacia. Larix gmelinii and Amorpha fruticosa present most serious deterioration on the remediation of petroleum-contaminated soil.