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91.
挥发性氯代烃(Volatile chlorinated hydrocarbons,VCHs)是工业污染场地的常见污染物,在非饱和带存在于土壤气相、水相、固相或以高密度非水相液体(Dense non-aqueous phase liquids,DNAPL)的形式存在,形成一个动态平衡系统。土壤对VCHs的吸附不仅影响土壤中的污染物浓度,而且极大地影响VCHs的迁移转化行为。根据VCHs在土壤中的吸附机制,可以对土壤中的VCHs浓度进行预测,优化各种模型参数,指导污染修复及管理工作。本文总结了VCHs在非饱和带土壤中的相间分配特征,吸附机制及其影响因素,特别探讨了土壤有机碳、矿物及水分对吸附的影响,提出了当前研究中存在的问题,并对将来研究进行了展望。 相似文献
92.
Systems analysis of wheat stripe rust epidemics in China 总被引:1,自引:0,他引:1
S.-M. Zeng Y. Luo 《European journal of plant pathology / European Foundation for Plant Pathology》2008,121(4):425-438
Stripe rust is the most destructive disease of wheat in China and shows long-distance spread with interregional epidemics.
Systems analysis had been implemented by the epidemiology group at the China Agricultural University to study the epidemiology
of this disease from field to regional levels. This paper reviews major achievements by this group from the 1970s to the present
in this pathosystem in China. Field experiments were conducted to obtain necessary parameters for constructing various simulation
models. Field-level models were generated to study the spatial and temporal disease developments, while region-level models
were developed to study the disease long-distance spread, interregional epidemics and strategies for disease management. Interactions
between host, pathogen and environment were also studied with modelling approaches to generate information on deployment of
resistance for regional disease management. 相似文献
93.
Given the extent of biological invasions in industrialized countries, our understanding of the determinants of overall patterns of biological invasions could gain most from consideration of why exotic species are absent from some areas, rather than from distribution patterns of exotic species. Fish communities were sampled at 381 sites representing 221 rivers in the Adour-Garonne stream system (116 000 km2, SW France). Very few rivers were not colonized by exotic fish species, however, on a local basis, only 33% of the sampling sites hosted exotics. Using General Linear Modelling, we found that patterns of exotic fish (occurrence, number of species, proportion within assemblage) responded to both land-use and physical variables, whereas patterns of native fish only responded to the local meso-scale characteristics of each stream reach from headwaters to mouth. All fish communities were susceptible to invasion regardless of native species richness, and higher native species richness did not decrease the opportunity for establishment by exotic species. The likelihood that exotic fish are absent primarily increased with elevation and with lower human influence upon the land cover, while human-impacted landscapes (agricultural and urban areas) were more likely to host exotic fish and higher numbers of exotic species. In light of urban and agricultural development, our ability to detect responses of exotic species to landscape alterations using a combination of simple physical and land cover variables exemplifies a cost-effective technique for assessing areas at greater invasion risk in large stream systems. 相似文献
94.
Caroline Lejars Pierre-Yves Le Gal Sandrine Auzoux 《Computers and Electronics in Agriculture》2008,60(2):239-249
Increased competition between agri-food supply chains has strained relationships between farmers and processing factories while reducing individual profit margins. Decisions at different levels of the supply chain can no longer be considered independently, since they may influence profitability throughout the supply chain. This paper presents a decision support approach based on the MAGI® simulation tool, which aims to facilitate discussion and negotiation between stakeholders while collectively exploring satisfactory solutions.The simulation tool helps sugarcane growers and millers in designing and assessing new ways of organizing cane supply management within a mill area. It addresses key issues such as restructuring mill areas or changing cane delivery allocation rules in order to increase total sugar production and total net revenue at the mill area level. This approach has been implemented for two mills in Réunion and one mill in South Africa. Simulations showed that sugar gains may be obtained by rearranging supply scheduling according to quality-based zoning within a mill area. Discussions led to further studies regarding the practicality of the best scenarios. MAGI® is now available as freeware for testing in different settings. 相似文献
95.
农田土壤中生物质炭的老化及其对有机污染物吸附-解吸影响的研究进展 总被引:1,自引:1,他引:0
生物质炭独特的表面性质、形貌结构及丰富而离散的孔隙系统使其对有机污染物具有良好的持留与吸附作用,可望用于土壤污染控制与修复。在田间条件下,进入土壤的生物质炭自身不稳定组分会发生转化、淋溶,并与土壤发生相互作用出现老化现象,导致生物质炭的化学与物理性质发生显著变化。生物质炭在土壤中的老化过程具有复杂性和多样性,主要包括:生物质炭化学性质的变化,如无机元素的流失、表面官能团组成的变化以及部分矿化反应;生物质炭物理性质的改变,主要是土壤有机质和矿物质对生物质炭的包覆作用造成生物质炭的孔隙特征发生改变。生物质炭在土壤中的老化可能会导致有机污染物的吸附-解吸行为发生改变,且受土壤、生物质炭以及污染物性质的影响较大。本文综述了生物质炭在农田土壤中的老化机理及主要影响因素研究方面的进展,总结了生物质炭在土壤中的老化对有机污染物吸附-解吸行为的影响,提出了尚待解决的相关前沿科学问题。 相似文献
96.
Moisture sorption isotherms of raw bamboo shoot were determined by static gravimetric technique based on isopiestic transfer of water vapor at 20, 30 and 35 °C. Inorganic saturated salt solutions in the range of 11.2-97.2% were used to create the required controlled humidity environment in a closed chamber. In the study, the sorption isotherms obtained were of sigmoid shape and of BET II type classification. Out of three sorption models i.e., BET, Caurie and GAB, fitted to the experimental data, Caurie model was found superior in interpreting the moisture sorption characteristics of bamboo shoot at three temperatures. The monolayer moisture content Mm as estimated by the best fitted Caurie's model for the sorption processes were 6.012%, 5.801%, 5.014%, and 5.987%, 5.816%, 4.998% (dry basis) at 20, 30, and 35 °C, respectively. The isosteric heats of sorption for both the adsorption and desorption process of bamboo shoots were found to increase with decrease in moisture content suggesting endothermic reaction at lower moisture content and it approached the value of heat of vaporization of free water at higher moisture content. 相似文献
97.
Koen Kramer Bernd Degen Jutta Buschbom Thomas Hickler Wilfried Thuiller Martin T. Sykes Wim de Winter 《Forest Ecology and Management》2010
We explored impacts of climate change on the geographic distribution of European beech by applying state of the art statistical and process-based models, and assessed possible climate change impacts on both adaptive capacity in the centre of its distribution and adaptive responses of functional traits at the leading and trailing edge of the current distribution. The species area models agree that beech has the potential to expand its northern edge and loose habitat at the southern edge of its distribution in a future climate. The change in local population size in the centre of the distribution of beech has a small effect on the genetic diversity of beech, which is projected to maintain its current population size or to increase in population size. Thus, an adaptive response of functional traits of small populations at the leading and trailing edges of the distribution is possible based on genetic diversity available in the local population, even within a period of 2–3 generations. 相似文献
98.
[目的]研究莠去津在原状土柱中的运移,判断其在土壤中的移动性及其对地下水的危害性。[方法]在相隔依次为6.5、8.5和6.5m的A、B、C、D4个地点的20~73cm深处,采集直径为25cm的原状土柱。土柱上端用马氏瓶供水,进水水头稳定保持在土柱土壤表面上2cm处。土柱底部以透水金属盘承托,金属盘中心为出水口。用量为大约10倍孔隙容积的去离子水饱和土柱,随后向其投放含不同质量浓度的莠去津和溴化钾溶液,用溴化钾作示踪剂来标记土柱中水分的运动。用CXTFIT软件模拟莠去津的穿透曲线、率定吸附和降解参数,并与批次试验所得相应参数进行比较。[结果]莠去津到达约53cm深土柱底部的浓度可达到初始浓度的20%~42%,说明其弱吸附和弱降解使得其污染浅层地下水的可能性很大。土壤的渗透性影响土壤水分运动,是影响莠去津运移的重要因素。CXTFIT的两区和两点模型均能较好地模拟莠去津的穿透曲线,4个原状土柱中平均不可动水体含量约为7%。两点模型拟合效果更好,主要表现在穿透曲线的尾部。据此推测莠去津的非平衡运移部分可描述为化学非平衡。[结论]土柱试验和批次试验得到的吸附参数和降解参数都存在空间差异,但是基本处于同一数量级。因此,如果试验条件控制得当,可以结合土柱试验和批次试验的结果进行大尺度莠去津运移模拟和预报。 相似文献
99.
Wojciech Mrozik Christian Jungnickel Tomasz Ciborowski William Robert Pitner Jolanta Kumirska Zbigniew Kaczyński Piotr Stepnowski 《Journal of Soils and Sediments》2009,9(3):237-245
Background, aim, and scope Ionic liquids (ILs) are a new class of alternative solvents that make ideal non-volatile media for a variety of industrial
processes such as organic synthesis and biocatalysis, as alternative electrolytes, as phases and phase modifications in separation
techniques, and as alternative lubricants. Once the large-scale implementation of ILs begins, the industrial application will
follow. In view of their great stability, they could slip through classical treatment systems to become persistent components
of the environment, where the long-term consequences of their presence are still unknown. Sorption on soils has a critical
effect on the transport, reactivity, and bioavailability of organic compounds in the environment. So far, the IL sorption
mechanism was investigated solely on the basis of batch experiments, which precluded any assessment of the dynamics of the
process. An understanding of the mobility of ILs in soil columns is crucial for an accurate prediction of their fate in the
soil. The aim of this study therefore was to investigate in detail the mobility of selected imidazolium ILs on three soil
types. Moreover, it was decided to study these processes in soils from the coastal region (Gdańsk, Poland), which usually
constitute a very important geochemical compartment, participating in the transport of contaminants on their way to the sea.
Materials and methods The mobility of alkylimidazolium ILs was investigated in columns containing soils from the coastal area. In addition, the
sorption processes in all the soil systems studied were described isothermally and the equilibrium sorption coefficient was
evaluated. The sorption capacities were determined according to OECD guidelines. Sorption dynamics was studied with use of
polypropylene columns (diameter—10 mm, height—100 mm) packed with 10 g of soil. The ionic liquid solution was then injected
into the soil column and left for 24 h to equilibrate. After this, a solution of 0.01 mM CaCl2 was pumped through the column at a rate of 0.3 ml min–1. Effluents were collected from the bottom of the column and analyzed by HPLC.
Results Sorption was strongest on the Miocene silt and the alluvial agricultural soil and weakest on the podsolic soil and Warthanian
glacial till. The K
d value of long-chain ILs was far higher than that of the short-chain ones. Among the substances tested, hydroxylated ILs were
usually more weakly sorbed. Desorption of ILs is inversely correlated with sorption intensity. The experimental results of
the column tests correlate well with those from batch experiments. In the cases of weakly binding soils, ILs were detected
almost immediately in the eluent. The elution profiles of long-chain ILs indicate that these compounds are very strongly sorbed
onto most soils, although certain amounts were transported through the soil. ILs exhibit a certain mobility in soils: in particular,
salts with short and/or hydroxylated side chains are extremely mobile.
Discussion The results indicate a stronger binding of ILs in the first sorption layer; once the first layer is saturated, there are no
more active sites on the soil surface (no free charged groups); hence, there are no more strong electrostatic binding sites,
and dispersive interaction becomes the dominant interaction potential. The influence of the structure of the ILs, especially
the side-chain length was also confirmed: The K
d value of long-chain ILs was far higher than that of the short-chain ones. The long alkyl side chain facilitates dispersive
interactions with soil organic matter and intermolecular binding, and the build-up of a second layer becomes possible. Among
the substances tested, hydroxylated ILs were usually more weakly sorbed. The hydroxyl group in the side chain can alter the
polarity of the compound so strongly that interaction with organic matter hardly occurs; these salts then remain in the aqueous
phase. The experimental results from the column tests correlate well with those from batch tests. In the weakly binding soils
(with low organic matter), the only binding to the soil surface must be via electrostatic interactions, although intermolecular
van der Waals (ionic liquid–ionic liquid) interactions could also be taking place. The elution profile maxima for organic
rich soils are far smaller than for the other soils. In the former, hydrogen bonding, dispersive and π…π interactions play
a more important part than electrostatic interactions. The rapidly “disappearing” maxima of the elution peaks may indicate
that, after elution of ILs from the second layer, it is difficult to extract further sorbed ILs. In the first layer, the ILs
are bound by much stronger electrostatic interactions. To break these bonds, a greater energy is required than that sufficient
to extract ILs from double sorption layers. Results indicate, moreover, that hydrophobic ILs will be sorbed in the first few
centimeters of the soil; migration into the soil will therefore be almost negligible.
Conclusions Sorption of ILs was the strongest in soils with the highest cation exchange capacities and a high organic content. ILs were
also more strongly bound to the first sorption layer. The sorption coefficients of long-chain ILs were far higher than those
of short-chain ones; usually, hydroxylated derivatives were the least strongly sorbed. Results of soil column experiments
to investigate the mobility of ILs in soils correlated well with those from batch tests, and the elution profiles were also
well correlated with organic matter content. The observed rapidly disappearing elution peak maxima probably indicate that,
after elution of the ILs from the second layer, it is difficult to extract further sorbed compounds.
Recommendations and perspectives Obtained results gave an interesting insight into mobility of ionic liquids in soil columns. However, several questions are
now opened. It is therefore necessary to undertake further studies focused on total cycle of ionic liquids in the soil environment.
This should include their evapotrasporation (lysimeter test), bioaccumulation by plants as well as degradation and transformation
processes (chemical, biological, and physical) typically occurring in soils. Moreover, a further risk assessment of ILs is
desirable since this study has indicated that these compounds, especially those with low lipophilicities, are generally mobile
in the soil matrix. It is already known that short-chain ILs are characterized by low toxicities; should they enter the environment,
they will probably migrate within the soil and pose a risk of contamination of surface and ground waters. This topic is relevant
to the audience. Environmental threat of short-chain ionic liquids is currently unknown. From the predictive point of view,
judging on known low acute toxic effects or high polarities of these compounds seems to be not enough to confirm their “environmental
friendliness”. If we are to fully understand the potential environmental effects, one should also have an insight into long-term
biological consequences of these ionic liquids, including chronic toxicity tests, bioaccumulation, and biotransformation rates
as well as stability against natural elimination mechanisms. 相似文献
100.
Adsorption of dissolved organic carbon to mineral soils: A comparison of four isotherm approaches 总被引:1,自引:0,他引:1
The partitioning of dissolved organic carbon (DOC) within mineral soils is primarily controlled by adsorption to soil particle surfaces. We compare the theoretical limitations and modeling accuracy of four isotherm approaches to describe DOC partitioning to soil surfaces. We use 52 mineral soil samples to create linear initial mass (IM), non-linear, and Langmuir isotherms, all relating the initial solution concentration (Xi) to the amount of DOC adsorbed or released from soil surfaces. The Langmuir isotherm is also used with final concentration (Xf). The IM isotherm failed to meet theoretical assumptions and provided poor fits to experimental data. The non-linear and Langmuir Xi approaches had good fits to experimental data, and the Langmuir Xi approach had the most robust estimates of desorption capacity. Both Langmuir Xi and Xf isotherms hold the advantage of estimating the maximum adsorption capacity, yet the Xf isotherm is a better reflection of adsorption processes. 相似文献