The effect of a biofilm on solute diffusion in fractured porous media

At sites in fractured rock where contamination has been exposed to the rock matrix for extended periods of time, the amount of contaminant mass residing in the matrix can be considerable. Even though it may be possible to diminish concentrations by the advection of clean water through the fracture features, back diffusion from mass held in the matrix will lead to a continuing source of contamination. In such an event, the development of a biofilm (a thin film of microbial mass) on the wall of the fractures may act to limit or prevent the back diffusion process. The objective of this preliminary study is to explore the influence imparted by the presence of a biofilm on the process of matrix diffusion. The investigation was conducted using radial diffusion cells constructed from rock core in which biofilm growth was stimulated in a central reservoir. Once biofilms were developed, forward diffusion experiments were conducted in which a conservative solute migrated from the central reservoir into the intact rock sample. Diffusion experiments were performed in a total of 11 diffusion cell pairs where biofilm growth was stimulated in one member of the pair and inhibited in the other. The effect of the presence of a biofilm on tracer diffusion was determined by comparison of the diffusion curves produced by each cell pair. A semi-analytical model that accounts for the presence of a biofilm was used to investigate the effect of the biofilm on mass transfer due to changes in the effective porosity, effective diffusion coefficient, and the depth of penetration of the biofilm into the intact rock. The results show that the biofilm acted to plug the rock matrix, rather than forming a discrete layer on the reservoir surface. The reduction in effective porosity due to the biofilm ranged from 6% to 52% with the majority of the samples in the 30% to 50% range. Based on the present results, with more efficient biofilm stimulation, it is reasonable to assume that a more complete plugging of the microcrack porosity might be possible, leaving a much thicker and efficient barrier than could be achieved via a surface biofilm.     

Towards improved understanding of injury prevention program sustainability

As policy makers and funders have become more concerned with allocating scarce resources effectively, attention to the sustainability of health intervention programs has increased. However, the empirical knowledge base about factors facilitating or working against sustainability remains at an early stage. The aim of this study was to contribute to improved understanding of the conditions under which community-based injury prevention programs are most likely to attain sustainability. Ten Swedish community-based injury prevention programs were analysed with respect to factors that contribute to or detract from program sustainability. All the programs are integrated within existing municipality structures. Data were collected by means of semi-structured telephone interviews with key informants.The results suggested that different factors are interrelated, with no one factor being either primary or by itself sufficient for program sustainability. Financial, human, and relational resources lay the groundwork for the long-term operation of a program. The “integrated” program model appears to facilitate sustainability, but program intensity is vulnerable to changes in the financial status of the municipality and the priority-setting by municipality political decision makers. Sustainability may be compromised if a program becomes too dependent on a few key individuals. In contrast to financial, human, and relational resources, structural resources (e.g., injury surveillance and goals) appeared to have limited influence on sustainability. The programs were sustained with little evidence of effectiveness, resulting in limited feedback about how to improve a program in order to achieve and maintain long-term effectiveness.     

Effects of Exploitation and Park Boundaries on Legume Trees in the Sonoran Desert

Abstract: Legume trees have been harvested in the Sonoyta Valley since 1975. We estimated the effects of this woodcutting along the border between Organ Pipe Cactus National Monument (U.S.A.) and Sonora, Mexico. We placed 10 × 100 m transects in ephemeral watercourses and uplands on both sides of the international boundary at different distances from the border. Mesquite and ironwood trees exhibited significantly higher damage in the Mexican sites than in the protected uplands in the United States. Damage for all the species significantly decreased 500 m from the border, with the exception of ironwood, for which damage remained high within ephemeral watercourses.     

‘Short Cut’ Techniques to Incorporate Environmental Considerations into Project Appraisal: An Exploration Using Case Studies

Incorporating environmental and natural resource impacts into the benefit-cost analysis of projects in the developing world now relies on a solid body of theory and recommended techniques, but there remain concerns with how this is done in practice. One aspect arises when time and resource constraints make highly sophisticated analysis difficult or impossible. This paper discusses situations where analyses can be improved using relatively simple ‘short cut’ techniques that substitute for more formal analysis that cannot be undertaken realistically or provide an added perspective on project viability. Case studies are employed to illustrate the techniques, based upon the author's experience with appraisals at the World Bank, Food and Agriculture Organization (FAO) and the International Fund for Agricultural Development (IFAD). It is shown that short cut techniques can dramatically alter the outcome of an appraisal at relatively little cost. However, caution is advised since such techniques can be misused, so that the development of suitable protocols is desirable.     

The Impact of a Change in Collection Frequency on Kerbside Recycling Behaviours

The research monitors the changes in recycling performance indicators arising from halving the collection frequency of a kerbside newspaper collection scheme. The changes in the performance parameters are explained in terms of the underlying behavioural changes that could have occurred within the community. This interpretation is aided by a computer simulation of the kerbside recycling activity of the community. Moving from a 2-week collection to a 4-week collection did not substantially affect the number of households recycling, nor the overall weights collected. A small weight loss, however, may have occurred, from a small minority of households, unable to accommodate the extra storage demand of the new regime. Model predictions were consistent with the observed performance data. It is postulated that the scheme could withstand considerable intervention before significant behavioural changes are induced. It demonstrates that cost-cutting interventions can be undertaken without significantly compromising individual participations. The case-study also highlights the caution needed in the interpretation of the recycling performance indicators themselves.     

A synthesis of current knowledge on forests and carbon storage in the United States

Using forests to mitigate climate change has gained much interest in science and policy discussions. We examine the evidence for carbon benefits, environmental and monetary costs, risks and trade-offs for a variety of activities in three general strategies: (1) land use change to increase forest area (afforestation) and avoid deforestation; (2) carbon management in existing forests; and (3) the use of wood as biomass energy, in place of other building materials, or in wood products for carbon storage. We found that many strategies can increase forest sector carbon mitigation above the current 162-256 Tg C/yr, and that many strategies have co-benefits such as biodiversity, water, and economic opportunities. Each strategy also has trade-offs, risks, and uncertainties including possible leakage, permanence, disturbances, and climate change effects. Because approximately 60% of the carbon lost through deforestation and harvesting from 1700 to 1935 has not yet been recovered and because some strategies store carbon in forest products or use biomass energy, the biological potential for forest sector carbon mitigation is large. Several studies suggest that using these strategies could offset as much as 10-20% of current U.S. fossil fuel emissions. To obtain such large offsets in the United States would require a combination of afforesting up to one-third of cropland or pastureland, using the equivalent of about one-half of the gross annual forest growth for biomass energy, or implementing more intensive management to increase forest growth on one-third of forestland. Such large offsets would require substantial trade-offs, such as lower agricultural production and non-carbon ecosystem services from forests. The effectiveness of activities could be diluted by negative leakage effects and increasing disturbance regimes. Because forest carbon loss contributes to increasing climate risk and because climate change may impede regeneration following disturbance, avoiding deforestation and promoting regeneration after disturbance should receive high priority as policy considerations. Policies to encourage programs or projects that influence forest carbon sequestration and offset fossil fuel emissions should also consider major items such as leakage, the cyclical nature of forest growth and regrowth, and the extensive demand for and movement of forest products globally, and other greenhouse gas effects, such as methane and nitrous oxide emissions, and recognize other environmental benefits of forests, such as biodiversity, nutrient management, and watershed protection. Activities that contribute to helping forests adapt to the effects of climate change, and which also complement forest carbon storage strategies, would be prudent.     

The Economics of Household Solid Waste Generation and Disposal

We develop a household production model of waste management that explicitly incorporates many of the technical and behavioral elements germane to current regulatory and non-regulatory solid waste policy initiatives. Examination of first-order conditions shows the interaction among household preferences, these production options, and external prices and fees. A simplified simulation of our model illustrates these relationships, showing that household response elasticities can vary widely over common price ranges and that relatively large household welfare gains may be obtained by adopting curbside recycling and unit pricing programs.     

Veränderung von Biokonzentration und Wirkung vom PSM in Anwesenheit von Huminstoffen

Humic substances, in aqueous bodies primarily fulvic acids, may demonstrate an inhibitory as well as an activating influence on organisms. We present evidence with bacteria-containing algal cultures and with cultures of the nematodeCaenorhabditis elegans. Structural elements of the fulvic acids which may be responsible for such effects are not yet known. Furthermore, the presence of fulvic acids may lead to increases in bioconcentration of xenobiotics. Increase in the toxicity of xenobiotics in the presence of humic substances have also been described. We present studies applying lethal as well as sublethal toxicity endpoints.     

Ethylenediurea (EDU) pretreatment alleviated the adverse effects of elevated O3 on Populus alba “Berolinensis” in an urban area

Ethylenediurea(EDU)has been used as a chemical protectant against ozone(03).However,its protective effect and physiological mechanisms are still uncertain.The present study aimed to investigate the changes of foliar visible injury,physiological characteristics and emission rates of volatile organic compounds(VOCs)in one-year-old Populus alba"Berolinensis"saplings pretreated with EDU and exposed to elevated O_3(EO,120μg/m~3).The results showed that foliar visible injury symptoms under EO were significantly alleviated in plants with EDU application(p0.05).Under EO,net photosynthetic rate,the maximum photochemical efficiency of PSII and the photochemical efficiency of PSII of plants pretreated with 300 and600 mg/L EDU were similar to unexposed controls and significantly higher compared to EOstressed plants without EDU pretreatment,respectively.Malondialdehyde content was highest in EO without EDU and decreased significantly by 14.9%and 21.3%with 300 and600 mg/L EDU pretreatment,respectively.EDU pretreatment alone increased superoxide dismutase activity by 10-fold in unexposed plants with further increases of 88.4%and 37.5%in EO plants pretreated with 300 and 600 mg/L EDU pretreatment,respectively(p0.05).Abscisic acid content declined under EO relative to unexposed controls with the effect partially reversed by EDU pretreatments.Similarly,VOCs emission rate declined under EO relative to unexposed plants with a recovery of emission rate observed with 300 and 600 mg/L EDU pretreatment.These findings provided significant evidence that EDU exerted a beneficial effect and protection on the tested plants against 03 stress.