|Alternative Title||Soil Ecological Characteristics and its Influencing Factors in Built - up Areas in Beijing|
|Thesis Advisor||陈卫平 ; 王美娥|
|Place of Conferral||北京|
|Keyword||城市生态,Gis,分类回归树,等级分解,生态系统服务功能指数 Urban Ecology, Gis, Cart, Hierarchical Partitioning, Ecosystem-service Performance Index|
（1）北京市建成区土壤呈现出显著的压实现象，超过63%的土壤样品容重超过1.4 g cm-3，即超出粉砂壤土（silt loam）根系生长的限制值。容重较高的区域主要位于西部、北部；研究区内土壤含有较高比例的砂粒，并且接近一半的样品的土壤含水量低于有利于树木生长的最低含水量11.44%；土壤pH值范围为7.44至8.90，为碱性土壤，商业用地的土壤pH值最高，而农业用地最低。
（2）北京市建成区土壤有机碳密度变化范围为1.08-5.62 kg m-2，土壤有机碳储量不以凋落物等为来源的有机碳的变化而变化，其空间分布与土壤的压实、有机质来源有密切关系，在工业用地土壤中浓度显著高于其他类型的土壤；土壤有机碳具有较高的矿化比例，矿化率变化范围为0.67-21.78%，因此可以认为建成区土壤累积碳的能力有限；基于土壤有机碳指土壤固碳能力指数计算结果发现，研究区内近70%的土壤固碳能力指数等于或低于“中等”水平，表明研究区内大部分区域土壤的固碳能力相对较差。通过相关性分析筛选出土壤碳循环的主要影响因素包括人口密度及增长率、景观指数、住宅、绿地及农业用地的面积。采用动力学模型拟合发现，除了微生物量碳和矿化碳，其他有机碳指标均能与城市化因子有一定的定量关系，因此可以进一步认为城市化因子对土壤碳循环的影响。
（3）北京市建成区土壤总氮的浓度变化范围为243-1731 mg kg-1，土壤无机氮净矿化率的变化范围为-10.6-21.8 mg kg-1 d-1，接近10%的样点土壤无机氮的矿化率为负，说明这些样点土壤的无机氮处于被消耗的状态；等级分解分析结果表明土壤性质、景观指数和土地利用类型对建成区土壤总氮、硝态氮、铵态氮和氮矿化率综合影响显著性分别为88%、44%、20%和22%，以土壤理化性质的影响为主。
In recent decades, the world is experiencing an unprecedented process of urbanization. The ecosystem productivity, biodiversity, hydrological processes in watersheds and biogeochemical cycles have been directly or indirectly changed by human activities, and thereby affecting the composition, structure, process and function of the ecosystem. As an important part of urban ecosystem, soil is the key "source" and "sink" of the elemental geochemical cycle. Soil is strongly disturbed by human activities in the process of urbanization. The soil carbon and nitrogen cycling as well as the accumulation of heavy metal elements have also been severely affected by human activities. However, due to the complexity of soil composition and soil ecological processes, the impacts of rapid urbanization on the ecological functions and ecological processes of soils have not been thoroughly studied. Beijing has now experienced the phase of rapid urbanization since 2000, and land-use types have also undergone rapid changes. In this study, we focus on the green space soils in the built-up areas of Beijing. The distribution characteristics of carbon, nitrogen and heavy metal elements in urban soils as well as their influencing factors were studied thorough the analysis of sampling sites collected in the built-up area of Beijing. Our research can reveal the mechanism of the impact of urbanization process on soil ecological functions, explain the relationships between economy, society and nature in urban ecology, and provide theoretical basis for urban planning and urban ecological environment management.
(1) The soil in Beijing built-up area showed significant compaction. The soil bulk density of more than 63% exceeded 1.4 g cm-3. The areas with higher bulk density and exceeding the limit of root growth of silty loamy soil were mainly located in the western and northern locations. With a higher proportion of sand, nearly half of the samples showed a soil moisture content of 11.44%, which is less than the lowest water content favoring the tree growth. The soil pH value ranged from 7.44 to 8.90, which was alkaline soil. In addition, the highest pH value was found in the commercial soil, while the lowest pH value was in the agricultural land.
(2) Soil organic carbon (SOC) density in the built-up areas in Beijing varied from 1.08 to 5.62 kg m-2. Soil organic carbon storage did not vary with the source of SOC like the litters. The spatial distribution of SOC shows significant relations with the soil compaction and organic matter sources. The concentrations of SOC in industrial lands are also significantly higher than those of the other types of land. There were high percent of organic carbon mineralized. The ratio of mineralized organic carbon to total organic carbon varies from 0.67 to 21.78%, which indicates that the carbon accumulation ability of the study area is limited. Based on the ecosystem-service performance index, the capacity of soil carbon sequestration (CSC) index was calculated. Nearly 70% of the sampling sites showed the CSC indexes equal to or lower than the medium level, which revealed that CSC in most areas of the study area is relatively poor. The further correlation analysis showed that the main factors affecting soil carbon cycling include the population densities and growth rates, landscape metrics, residentials, green spaces as well as agricultural land areas. The fitting results of kinetic model show that, the SOC indicators, except for microbial biomass and mineralized carbon, can establish a quantitative relationship with urbanization factors, which further confirms the impact of urbanization factors on soil carbon cycling.
(3) The range of soil total nitrogen (TN) concentration in the built-up areas of Beijing was 243?1731 mg kg-1, and the range of soil inorganic nitrogen mineralization (MNR) ranged from -10.58 to 21.81 mg kg-1 d-1. Nearly 10% of sampling sites showed negative nitrogen mineralization rate. Based on the level decomposition method, effects of the soil properties, landscape metrics and land use types on TN, NO3-N, NH4-N and MNR were 88%, 44%, 20% and 22%, respectively, the effects were dominated by soil physical and chemical properties.
(4) The analysis results of Igeo show that the pollution level of heavy metals in urban soils of the study area was relatively low. Specifically, Zn showed the most widely polluted range, and more than one quarter of the built-up areas reach the first level of mild pollution. Cu showed the highest degree of pollution, and the sampling sites reaching the second and the above level are the highest. The analyse of Classification and Regression Trees (CART) showed that the main influencing factors of soil heavy metal accumulation included organic carbon, population growth rate, cation exchange capacity. In addition, landscape metrics and wind speed also had a significant effect on the accumulation of heavy metals in soils. Soil heavy metal accumulation showed positive relations with the physical and chemical properties of soils, organic carbon and cation exchange capacity, which also showed negative relations with the average annual growth rate of population, but positive relations with population density. The accumulated risks of heavy metals in built-up areas in Beijing were also analyzed. It showed that the high-risk areas are mainly distributed in the center, east and west of the study area, while the low-value areas are mainly located in the south. In addition to the degree of urbanization, the risks of multiple heavy metal accumulation were also related to the intensity of the transportation network.
|刘睿. 北京市建成区土壤生态特征与影响因素研究[D]. 北京. 中国科学院生态环境研究中心,2017.|
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