Zinc processing in the USA : An analysis of a declining industry

The purpose of this paper is to analyse the recent behaviour of the US zinc processing industry and the impact of US government policies on it. The first section of the paper is a discussion on the basic structure and conditions of the US zinc processing industry since 1950 and how they have changed. The discussion contains a general presentation of the US zinc market, a detailed look at the behaviour of individual primary zinc processing plants in the USA, Canada, Japan and Western Europe and an analysis of US government policies and their impacts on the US zinc industry. The second section of the paper is a discussion of the factors that have contributed to the decline in US zinc processing capacity and the type of government policy that should be followed in response.     

The case for variable density: a new perspective on activated sludge settling.

A new, simple method for directly measuring activated sludge density was developed and applied, and the effects of biomass density on activated sludge settling in full-scale systems were evaluated. The driving force of sedimentation is the physical weight of the biological solids, but the role of biomass density in sedimentation has been largely ignored. Biomass density varied amongst treatment systems and this variability was correlated with settleability. Floc densities were approximately normally distributed within individual samples. Nonsoluble phosphorus content was a major contributor to density, and plants with enhanced biological phosphorus removal (EBPR) configurations generally had higher densities and better settleability than non-EBPR plants with similar filament contents. These results suggest that future work may benefit from consideration of density as a factor affecting activated sludge settling.     

Epidemiologic Analysis of Factors Associated with Local Disappearances of Native Ranid Frogs in Arizona

Abstract:  We examined factors that may independently or synergistically contribute to amphibian population declines. We used epidemiologic case–control methodology to sample and analyze a large database developed and maintained by the Arizona Game and Fish Department that describes historical and currently known ranid frog localities in Arizona, U.S.A. Sites with historical documentation of target ranid species ( n = 324) were evaluated to identify locations where frogs had disappeared during the study period (case sites) and locations where frog populations persisted (control sites). Between 1986 and 2003, 117 (36%) of the 324 sites became case sites, of which 105 were used in the analyses. An equal number of control sites were sampled to control for the effects of time. Risk factors, or predictor variables, were defined from environmental data summarized during site surveys and geographic information system data layers. We evaluated risk factors with univariate and multifactorial logistic-regression analyses to derive odds ratios (OR). Odds for local population disappearance were significantly related to 4 factors in the multifactorial model. Disappearance of frog populations increased with increasing elevation (OR = 2.7 for every 500 m, p < 0.01). Sites where disappearances occurred were 4.3 times more likely to have other nearby sites that also experienced disappearances (OR = 4.3, p < 0.01), whereas the odds of disappearance were 6.7 times less (OR = 0.15, p < 0.01) when there was a source population nearby. Sites with disappearances were 2.6 times more likely to have introduced crayfish than were control sites (OR = 2.6, p = 0.04). The identification of factors associated with frog disappearances increases understanding of declines occurring in natural populations and aids in conservation efforts to reestablish and protect native ranids by identifying and prioritizing implicated threats.     

Distribution of Zooplankton along the Longitudinal Profile of Two Disturbed Small Rivers of the Upper Volga Basin

The abundance and trophic structure of zooplankton along the longitudinal profile of two typical rivers in the Yaroslavl sector of the Volga region are determined by anthropogenic and zoogenic factors. The distribution of zooplankton under the influence of these factors is described by the concept of patch dynamics. The abundance of zooplankton reaches the highest values in the ameliorated upper reaches of rivers and in beaver ponds.