过渡金属离子改性MCM-41对乙烯吸附的影响

为了提高吸附剂对乙烯气体的吸附量,对常见的MCM-41分子筛进行了过渡金属离子改性研究。通过镍离子交换实验,确定了改性条件,改性后的样品对乙烯的吸附行为发生改变。使用镍离子改性后的MCM-41在常温常压下对乙烯的最大吸附量为可达416cm3／g,约为商用颗粒活性炭的6倍,远高于其他文献的报道。吸附质的检测结果说明乙烯在其吸附过程中发生多聚反应,高碳数的直链烯烃为最终产物。CO原位红外吸附的引人证实经过热处理后,一价镍能在镍离子改性后的MCM-41样品中形成并成为乙烯聚合反应的活性中心。     

Simulating uptake and transport of TNT by plants using STELLA

Understanding the uptake and transport of soil organic contaminants by plants is crucial to a successful application of phytoremediation technique. This study investigated the removal of 2,4,6-trinitrotoluene (TNT) from a contaminated sandy soil by a poplar tree (Populus fastigiata) through the examinations of temporal variations of xylem water potential, leaf water transpiration, and root water and TNT uptake. A dynamic model for Uptake and Translocation of Contaminants from a Soil-Plant ecosystem (UTCSP), developed using the STELLA software package, was modified for the purpose of this study. The model was calibrated using laboratory measurements prior to its application. Simulation results showed that about 25% of TNT was removed from the soil by the poplar tree in 90 days. Simulations further revealed that the rates of water and TNT up taken by roots had a typical diurnal variation pattern: increasing during the day and decreasing during the night, resulting from daily variations of xylem water potentials that were caused by leaf water transpiration. In general, the storage of TNT mass in the roots decreased with time and occurred partially because of the low availability of soil TNT as time elapsed and partially because of the biodegradation of TNT in the plant tissues. This study suggests that the UTCSP model could be a useful tool for estimating phytoremediation of soil TNT by a plant.     

The composition, trend and impact of urban solid waste in Beijing

This paper provides an overview of the trend of generation, composition, and management of municipal solid waste, and estimates the carbon emissions arising from municipal solid waste management in Beijing. The correlation analysis conducted shows that the generation of municipal solid waste in Beijing has been growing steadily, showing high correlations (r > 0.9) to the total GDP, per capita income, and the population. Food waste showed an increasing trend since 1990. Compared with the results of an investigation in 1990, ash and woodchips content in 2003 declined from 56% to 17%, while the percentage of paper and plastic increased from 10% to 29% over the same period. The calorific value of the municipal waste also increased, from 2,686 kJ/kg in 1990 to 4,667 kJ/kg in 2003, indicating that the waste is suitable for incineration. Currently, the source separation ratio of municipal waste is approximately 15%. About 94% of all the collected solid waste goes to the landfill while 4% is composted and 2% is incinerated. A moderate garbage collection fee is applied to both permanent and temporary residents in Beijing, but the willingness to pay for solid waste collection and treatment is still low. Under current treatment mode, the total amounts of carbon emission from waste disposal sites and incineration increased with the increase of municipal solid waste, from 29.8 Gg in 1990 to 84.5 Gg in 2003, including 83.3 Gg of CH₄ and 22.0 Gg of CO₂. The data availability and methodological challenges in monitoring the quantity and characteristics of municipal solid waste are discussed.     

Comparison of a diurnal vs steady-state ozone exposure profile on growth and yield of oilseed rape (Brassica napus L.) in open-top chambers in the Yangtze Delta, China

Most available exposure-response relationships for assessing crop loss due to elevated ozone (O₃) have been established using data from chamber and open-top chamber experiments, using a simulated constant O₃ concentration exposure (square wave), which is not consistent with the diurnal variation of O₃ concentration that occurs in nature. We investigated the response of oilseed rape (Brassica napus L.) to O₃ as affected by two exposure regimes: one with a diurnal variation (CF100D) and another with a constant concentration (CF100). Although the two exposure regimes have the same mean O₃ concentration and accumulated O₃ concentration above 40 ppb (AOT40), our results show that O₃ at CF100D reduced biomass and number of pods/plant more than O₃ at CF100. Both O₃ exposures resulted in larger seed weights/100 pods compared to CF. Numbers of seeds/100 pods were reduced by CF100, while numbers of seeds/100 pods in the CF100D chambers were comparable to those in CF. Our results suggest that chamber experiments that use a constant O₃ exposure may underestimate O₃ effects on biomass and yields.     

Modeling the mechanisms for uptake and translocation of dioxane in a soil-plant ecosystem with STELLA

Knowledge of mechanisms for uptake, translocation, and accumulation of soil contaminants in plants is essential to successful applications of the phytoremediation technique. Analysis and evaluation of these mechanisms would be greatly facilitated by the availability of a dynamic model that can predict soil contaminant uptake by roots, transport from roots through stems to leaves, and accumulation in plant during the transport process. In this study, a dynamic model for uptake and translocation of contaminants from a soil-plant ecosystem (UTCSP) was developed using the STELLA modeling tool. The structure of UTCSP consists of time-dependent simultaneous upward transport, accumulation, and transpiration of water and contaminants in the soil-plant-atmosphere continuum, which was driven by water potential gradients among soils, roots, stems, leaves, and atmosphere. The UTCSP model was calibrated using the experimental measurements and applied to predict phytoremediation of 1,4-dioxane from a sandy soil by a poplar tree. Simulation results showed that about 20% of 1,4-dioxane was removed from the soil by the poplar tree in 90 days. The simulations further revealed that while the mass of 1,4-dioxane in the poplar tree increased consecutively with time, the rates of water and 1,4-dioxane uptake and translocation in the roots, stems, and leaves have a typical diurnal distribution pattern: increasing during the day and decreasing during the night, resulting from daily variations of plant water potentials that were caused by leaf water transpiration. This study suggests that the UTCSP model is a useful tool for estimating phytoremediation of contaminants in the soil-plant ecosystems.     

Distribution of Economic Benefits from Ecotourism: A Case Study of Wolong Nature Reserve for Giant Pandas in China

Ecotourism is widely promoted as a conservation tool and actively practiced in protected areas worldwide. Theoretically, support for conservation from the various types of stakeholder inside and outside protected areas is maximized if stakeholders benefit proportionally to the opportunity costs they bear. The disproportional benefit distribution among stakeholders can erode their support for or lead to the failure of ecotourism and conservation. Using Wolong Nature Reserve for Giant Pandas (China) as an example, we demonstrate two types of uneven distribution of economic benefits among four major groups of stakeholders. First, a significant inequality exists between the local rural residents and the other types of stakeholder. The rural residents are the primary bearers of the cost of conservation, but the majority of economic benefits (investment, employment, and goods) in three key ecotourism sectors (infrastructural construction, hotels/restaurants, and souvenir sales) go to other stakeholders. Second, results show that the distribution of economic benefits is unequal among the rural residents inside the reserve. Most rural households that benefit from ecotourism are located near the main road and potentially have less impact on panda habitat than households far from the road and closer to panda habitats. This distribution gap is likely to discourage conservation support from the latter households, whose activities are the main forces degrading panda habitats. We suggest that the unequal distribution of the benefits from ecotourism can be lessened by enhancing local participation, increasing the use of local goods, and encouraging relocation of rural households closer to ecotourism facilities.     

隧道侧部集中排烟模式下排烟速率对烟气层吸穿的影响研究

排烟速率是公路隧道侧部集中排烟模式下烟气层发生吸穿现象最为直接的影响因素.为研究隧道侧部集中排烟模式下烟气层发生吸穿现象的临界条件,分析了隧道侧部集中排烟过程中排烟口处烟气层的受力情况以及不同排烟速率对烟气层吸穿的影响,并结合前人相关的研究成果,进一步分析得到隧道侧部集中排烟模式下排烟口下方烟气层发生吸穿时的临界弗洛德...     

Impacts of sewage irrigation on heavy metal distribution and contamination in Beijing, China

A potential hazard to Beijing was revealed due to the accumulation trend of heavy metals in agricultural soils with sewage irrigation, which results in metal contamination and human exposure risk. Samples including soils and plants were collected to assess the impacts of sewage irrigation on the irrigated farming area of Beijing. Concentrations of the five elements Cd, Cr, Cu, Zn, and Pb were determined in samples to calculate the accumulation factor and to establish a basis for environmental protection and the suitability of sewage irrigation for particular land use in the urban-rural interaction area of Beijing. Using reference values provided by the Beijing Background Research Cooperative Group in the 1970s, the pollution load index (PLI), enrichment factor (EF), and contamination factor (CF) of these metals were calculated. The pollution load indices (sewage irrigation land 3.49) of soils indicated that metal contamination occurred in these sites. The metal enrichment (EF of Cd 1.8, Cr 1.7, Cu 2.3, Zn 2.0, Pb 1.9) and the metal contamination (CF of Cd 2.6, Cr 1.5, Cu 2.0, Zn 1.7, Pb 1.6) showed that the accumulation trend of the five toxic metals increased during the sewage irrigation as compared with the lower reference values than other region in China and world average, and that pollution with Cd, Cu, Zn, and Pb was exacerbated in soils. The distributions of these metals were homogeneous in the irrigation area, but small-scale heterogeneous spatial distribution was observed. Irrigation sources were found to affect heavy metal distributions in soils. It was suggested that heavy metal transfer from soils to plants was a key pathway to human health exposure to metal contamination. However, with the expansion of urban areas in Beijing, soil inhalation and ingestion may become important pathways of human exposure to metal contamination.     

河口区水质标准问题的探讨

介绍了目前河口区执行水质标准的相关规定,针对福建省一些重要河口区,分析了其在执行地表水环境质量标准或海水水质标准的过程中存在的河海划界不确定、标准无法衔接和河口混合区确定较难等问题,提出了加强河口区适用水质标准研究的建议.     

Soil temperature and moisture sensitivities of soil CO2 efflux before and after tillage in a wheat field of Loess Plateau, China

As a conventional farming practice,tillage has lasted for thousands of years in Loess Plateau,China.Although recent studies show that tillage is a prominent culprit to soil carbon loss in croplands,few studies have investigated the influences of tillage on the responses of soil CO2 efflux(SCE) to soil temperature and moisture.Using a multi-channel automated CO2 efflux chamber system,we measured SCE in situ continuously before and after the conventional tillage in a rain fed wheat field of Loess Plateau,Chin...