Adsorption and clay-catalyzed degradation of erythromycin A on homoionic clays

Erythromycin has been widely used in food-producing animals and in humans, and is frequently detected as an organic pollutant in U.S. streams. In batch experiments with homoionic clays, the Freundlich isotherms were determined at 10 and 25 degrees C. The adsorption of erythromycin A was strongly influenced by clay type, exchanged cations, the pH of the bulk solutions, and the acidity of clay surfaces. The formation of clay-erythromycin A complexes was thermodynamically favorable except for K+- and Fe3+-exchanged montmorillonites, since the reactions were exothermic (deltaH(o) > 0) and the systems became stable (deltaS(o) > 0). Clays catalyzed the erythromycin A degradation by the hydrolysis of the neutral sugar and the multiple dehydrations. The surface acidity of clay surface enhanced the rate of clay-catalyzed degradation of erythromycin A. In addition, the Fe3+-exchanged clay minerals seemed to have an electrostatic interaction with the erythromycin A molecule, by which the hydrolysis of the neutral sugar was influenced.     

Resilience and sustainable development: building adaptive capacity in a world of transformations

Emerging recognition of two fundamental errors underpinning past polices for natural resource issues heralds awareness of the need for a worldwide fundamental change in thinking and in practice of environmental management. The first error has been an implicit assumption that ecosystem responses to human use are linear, predictable and controllable. The second has been an assumption that human and natural systems can be treated independently. However, evidence that has been accumulating in diverse regions all over the world suggests that natural and social systems behave in nonlinear ways, exhibit marked thresholds in their dynamics, and that social-ecological systems act as strongly coupled, complex and evolving integrated systems. This article is a summary of a report prepared on behalf of the Environmental Advisory Council to the Swedish Government, as input to the process of the World Summit on Sustainable Development (WSSD) in Johannesburg, South Africa in 26 August 4 September 2002. We use the concept of resilience--the capacity to buffer change, learn and develop--as a framework for understanding how to sustain and enhance adaptive capacity in a complex world of rapid transformations. Two useful tools for resilience-building in social-ecological systems are structured scenarios and active adaptive management. These tools require and facilitate a social context with flexible and open institutions and multi-level governance systems that allow for learning and increase adaptive capacity without foreclosing future development options.     

Geographic information systems and environmental impact assessment

The analytical structure of environmental impact assessment is continually changing as the applicability of established techniques from other fields and the development of novel methods become known. This paper illustrates the applicability of using existing data bases, through a geographic information system, for theex ante evaluation of land use disruption. More specifically, the Canada Geographic Information System was employed to retrieve, to analyze, and to produce land capability statistics and land use maps for the proposed Glengowan dam and reservoir.     

Computer simulation of barren-ground caribou dynamics

This paper describes a simulation model of a Canadian caribou population. The model was constructed by an interdisciplinary team of field biologists, managers, and systems ecologists. Population dynamics are represented in terms of age structure, with age-dependent survival and fecundity. Biomass dynamics of the major food species are also simulated, and the food dynamics interact with the caribou population through a foraging submodel that explicitly considers snow depth, seasonal migrations, and total area of useable winter habitat. The model was used to examine two hypotheses regarding the abundance of barren-ground caribou. It was shown that there is no reason to suspect that food supply currently limits the population size; instead, hunting pressure appears to be the critical variable. The implications of this finding for population management are discussed.     

Modeling negative affectivity and job stress: a contingency‐based approach

Understanding the role of negative affectivity (NA) in relations between job stressors and resultant strains has been a major source of research interest in the organizational literature for almost two decades. In this study, we propose a contingency approach, whereby the role of NA depends on the nature of the strain construct under investigation. Specifically, we predicted that perceived job stressors would fully mediate the relationship between NA and turnover intentions, while job stressors would only partially mediate the relationship between NA and job and life satisfaction, and job stressors would be unrelated to depression once NA was taken into account. The relative fit of these four models is tested utilizing data from two divergent samples (sales representatives and managers) employing both self‐ and informant reports of strain measures where feasible. Hypotheses regarding the specified nature of the NA → stressor → strain relationship generally were supported and replicated across samples. In addition, an alternate model specifying that NA moderates the relationship between stressors and strains was not supported for any strain variable. Copyright © 2004 John Wiley & Sons, Ltd.     

Ecological limitations and appropriation of ecosystem support by shrimp farming in Colombia

Shrimp farming in mangrove areas has grown dramatically in Asia and Latin America over the past decade. As a result, demand for resources required for farming, such as feed, seed, and clean water, has increased substantially. This study focuses on semiintensive shrimp culture as practiced on the Caribbean coast of Colombia. We estimated the spatial ecosystem support that is required to produce the food inputs, nursery areas, and clean water to the shrimp farms, as well as to process wastes. We also made an estimate of the natural and human-made resources necessary to run a typical semiintensive shrimp farm. The results show that a semiintensive shrimp farm needs a spatial ecosystem support—the ecological footprint—that is 35–190 times larger than the surface area of the farm. A typical such shrimp farm appropriates about 295 J of ecological work for each joule of edible shrimp protein produced. The corresponding figure for industrial energy is 40:1. More than 80% of the ecological primary production required to feed the shrimps is derived from external ecosystems. In 1990 an area of 874–2300 km² of mangrove was required to supply shrimp postlarvae to the farms in Colombia, corresponding to a total area equivalent to about 20–50% of the country’s total mangrove area. The results were compared with similar estimates for other food production systems, particularly aquacultural ones. The comparison indicates that shrimp farming ranks as one of the most resource-intensive food production systems, characterizing it as an ecologically unsustainable throughput system. Based on the results, we discuss local, national, and regional appropriation of ecological support by the semiintensive shrimp farms. Suggestions are made for how shrimp farming could be transformed into a food production system that is less environmentally degrading and less dependent on external support areas.     

Automatic safety belt use in Michigan: A two-year follow-up

The use of automatic safety belts among motorists throughout the state of Michigan was examined as part of a broader direct observation survey to measure compliance with the state's mandatory belt use law. Use of the most common types of automatic belt systems were measured: the nonmotorized detachable three-point lap and shoulder belt system, and the two-belt system with either a motorized shoulder belt and manual lap belt or a nonmotorized shoulder belt and manual lap belt. Belt use rates in vehicles with and without air bags were also compared. A total of 1,367 drivers and front-right passengers were observed with automatic belt systems between June 1 and July 11, 1992. Use of nonmotorized detachable three-point lap and shoulder belt systems was 72.3%. Lap belt use of motorized shoulder and manual lap belt systems was 70.5%. Lap belt use of nonmotorized shoulder and manual lap belt systems was 60.2%. Of all motorized and nonmotorized shoulder belt and manual lap belt systems observed, 94.5% had the shoulder belts connected.