Analysis of a Farquhar-von Caemmerer-Berry leaf-level photosynthetic rate model for Populus tremuloides in the context of modeling and measurement limitations

The balance of mechanistic detail with mathematical simplicity contributes to the broad use of the Farquhar, von Caemmerer and Berry (FvCB) photosynthetic rate model. Here the FvCB model was coupled with a stomatal conductance model to form an [A,g_s] model, and parameterized for mature Populus tremuloides leaves under varying CO₂ and temperature levels. Data were selected to be within typical forest light, CO₂ and temperature ranges, reducing artifacts associated with data collected at extreme values. The error between model-predicted photosynthetic rate (A) and A data was measured in three ways and found to be up to three times greater for each of two independent data sets than for a base-line evaluation using parameterization data. The evaluation methods used here apply to comparisons of model validation results among data sets varying in number and distribution of data, as well as to performance comparisons of [A,g_s] models differing in internal-process components.     

Tracking nitrogen losses in a greenhouse crop rotation experiment in North China using the EU-Rotate_N simulation model

Vegetable production in China is associated with high inputs of nitrogen, posing a risk of losses to the environment. Organic matter mineralisation is a considerable source of nitrogen (N) which is hard to quantify. In a two-year greenhouse cucumber experiment with different N treatments in North China, non-observed pathways of the N cycle were estimated using the EU-Rotate_N simulation model. EU-Rotate_N was calibrated against crop dry matter and soil moisture data to predict crop N uptake, soil mineral N contents, N mineralisation and N loss. Crop N uptake (Modelling Efficiencies (ME) between 0.80 and 0.92) and soil mineral N contents in different soil layers (ME between 0.24 and 0.74) were satisfactorily simulated by the model for all N treatments except for the traditional N management. The model predicted high N mineralisation rates and N leaching losses, suggesting that previously published estimates of N leaching for these production systems strongly underestimated the mineralisation of N from organic matter.     

我国城市居民健康状况及影响因素研究

随着中国城市化、工业化快速推进,城市居民的健康日益受到环境、外部压力等因素的影响,加上生活方式和健康观念方面的原因,城市居民健康状况的改善缓慢.利用2006年中国健康与营养调查(CHNS)截面数据,描述了我国城市居民的健康及其分布状况,利用Ordered Probit模型分析了影响城市居民的健康状况的各类因素.结果发现:家庭状况、生活习惯、就医决策、医疗保险等因素均影响城市居民的健康水平;尤其是在收入、工作等经济因素之外,健康观念、就医决策和保险覆盖等社会和制度因素亦对城市居民个人健康产生影响.同时,通过逐步回归控制相关变量的方法,检验了Grossman模型的适用性,同时也检验了影响因素作用机制的稳定性.在总结研究结论与不足的基础上,提出了应从经济,社会和制度三个层面全面促进城市居民健康的综合改革框架.     

Quantification of nitrate leaching from German forest ecosystems by use of a process oriented biogeochemical model

Simulations with the process oriented Forest-DNDC model showed reasonable to good agreement with observations of soil water contents of different soil layers, annual amounts of seepage water and approximated rates of nitrate leaching at 79 sites across Germany. Following site evaluation, Forest-DNDC was coupled to a GIS to assess nitrate leaching from German forest ecosystems for the year 2000. At national scale leaching rates varied in a range of 0–>80 kg NO₃–N ha⁻¹ yr⁻¹ (mean 5.5 kg NO₃–N ha⁻¹ yr⁻¹). A comparison of regional simulations with the results of a nitrate inventory study for Bavaria showed that measured and simulated percentages for different nitrate leaching classes (0–5 kg N ha⁻¹ yr⁻¹:66% vs. 74%, 5–15 kg N ha⁻¹ yr⁻¹:20% vs. 20%, >15 kg N ha⁻¹ yr⁻¹:14% vs. 6%) were in good agreement. Mean nitrate concentrations in seepage water ranged between 0 and 23 mg NO₃–N l⁻¹.     

香溪河流域土地利用格局演变对非点源污染的影响研究

以分布式模型SWAT为研究工具,在气候、土壤等因素不变的情况下,模拟了三峡库区香溪河流域土地利用格局演变对于非点源污染的影响.研究结果表明,自20世纪80年代至2007年,研究区由土地利用所造成的非点源污染TN总体呈减少趋势,4种土地利用情景下模拟得到的年均非点源污染TN分别为1 841.60、824.86、1 790...     

Spectral estimation of global levels of atmospheric pollutants

Underlying levels of atmospheric pollutants, assumed to be governed by smoothing mechanisms due to atmospheric dispersion, can be estimated from global emissions source databases on greenhouse gases and ozone-depleting compounds. However, spatial data may be contaminated with noise or even missing or zero-valued at many locations. Therefore, a problem that arises is how to extract the underlying smooth levels. This paper sets out a structural spatial model that assumes data evolve across a global grid constrained by second-order smoothing restrictions. The frequency-domain approach is particularly suitable for global datasets, reduces the computational burden associated with two-dimensional models and avoids cumbersome zero-inflated skewed distributions. Confidence intervals of the underlying levels are also obtained. An application to the estimation of global levels of atmospheric pollutants from anthropogenic emissions illustrates the technique which may also be useful in the analysis of other environmental datasets of similar characteristics.     

Developing Mechanism of Rubber-tea-chicken Agro-forestry Model in Tropical Area of China

As a typical tropical agro-forestry ecosystem in Wenchang,Hainan Province,China,rational mechanisms of the rubber-tea-chicken eco-agricultural model were studied with the Solow technological level index,stability indicator,harmonizing coefficient,grey correlation coefficient and production dominance.This study focused on rational hierarchical structure,the limiting factors and optimal strategies of the model development based on model structure,resource conditions and external market demands.Results showed that rational mechanism of the rubber-tea-chicken ecosystem model mainly included technological contributions,leverage function of dominance component(livestock husbandry),stability of the model structure and harmony of its components,the model dominant product’s market demand and government’s supporting policies.The contributions of fund,technology,information and talent resources played an important role in improving sustainability and productivity of the agro-forestry model.     

基于产业链的区域环境污染物排放的产业贡献

区域经济增长与环境质量之间的关系研究是目前学者们探讨的重要学术议题之一.其中较多的是对EKC曲线的验证,近几年部分学者从国民经济各部门中的产业自身特征、产业结构、技术进步、FDI效应等方面考察产业发展对污染物排放的影响.然而以上研究议题中学者均没有讨论污染物的发生主体-各产业部门与排污的直接关系.故本文将从宏观尺度下的综合水平测度区域经济发展与环境质量关系、中观尺度下的产业属性特征与排污关系的研究视角转移至分析具体产业部门的污染物排放效应,同时将产业置于产业链的结构形式中,研究产业链上产业发展与污染物排放的关系.发现:第一,通过借助复杂网络思想的社区划分方法,将山东省39个产业部门分为3个社团.其中社团I主要由制造业部门组成,共有18个产业部门,社团II包括了15个部门,主要是第三产业,杜团III由6个产业部门组成且内部异质性高.第二,选择其中以制造业为主的社团I,并在社团I内识别出一条彼此间联系最为紧密的产业链,包括农林牧渔业、食品制造及烟草加工业、化学工业、纺织工业、服装皮革羽绒及其制品业、通用/专用设备制造业和交通运输设备制造业.以一种定量的方法获取了通过价值流传递而串在一起的产业链条.该产业链的经济规模、污染物规模在山东省均有重要地位.第三,采用岭回归分析方法,构建了6个制造业与产业链工业废水、固体废弃物排放的关系模型,6个制造业中对工业废水、固体废弃物排放相对贡献度最大的部门分别为服装皮革羽绒及其制品业、食品制造及烟草加工业.这是由于上游产业排污的链式传递效应与产业自身污染物排放效应的共同叠加作用.     

中国ESDPM模型及其在交通需求预测中的应用

交通运输是国民经济的基础部门.未来随着国民经济的快速发展和人均收入水平的不断提高,交通运输部门的能源消费量将会以较高的速度增长,在决定我国终端能耗的局面中占据着非常重要的地位.本文应用集合模型方法建立了中国能源服务需求预测模型( Energy service demand projection model,ESDPM),在对未来经济和社会发展进行合理假设的基础上,预测了中国未来一直到2050年的客运和货运周转量以及小汽车保有量,并进行了国家和地区间的比较.结果显示,2005-2050年中国的客运和货运周转量将分别以年均增长率5.9%和5.1%的速度增长,2050年客运和货运周转量将分别达到23.1万亿人·km和74.7万亿t·km.小汽车将随着人均GDP的快速增加呈现出明显的"S"型增长关系,在小汽车拥有率饱和水平选取为0.4时,小汽车保有量将稳定在5.8亿辆左右.     

城乡二元制度对农民工市民化影响的实证分析

将影响农民工市民化的制度因素归结为城乡分割、城市偏向的城乡二元制度,分析了这一制度的内涵和基本特征,并运用Logistic回归模型和入户调查数据对这一制度对农民工市民化意愿、市民化能力和市民化进程的影响进行实证分析,结果发现,虽然农民工具有比较强烈的市民化愿望,但由于受到市民化能力的制约,绝大多数农民工无法转化为市民,因此尽快提离农民工的市民化能力成为促进农民工市民化的关键;在城乡二元制度中,除了城乡二元户籍制度之外,城乡二元就业制度、城乡二元社会保障制度、城乡二元土地制度和城乡二元教育制度对农民工市民化意愿和市民化能力,进而对农民工的市民化进程具有明显的阻碍作用:因此,未来城乡二元制度的创新重点不能再继续停留在形式化的城乡二元户籍制度层面,而应该尽快切换到对农民工的预期和收入等权利和待遇具有实质性影响的城乡二元就业制度、城乡二元社会保障制度、城乡二元土地制度和城乡二元教育制度上来.