Estimates of total polychlorinated biphenyl (PCB) compounds in soils/sediments by hydrogenolysis to dicyclohexyl

A method to determine the total PCB content by hydrogenolysis (hydrodechlorination and hydrogenation) of chlorinated biphenyl compounds was extended to natural particulate matrices (soil and sediment). The contaminated soil was suspended in hexane in the presence of Pd/gamma-Al2O3 in a hydrogen atmosphere then permitted to react for one hour at 65 degrees C. Dicyclohexyl, recovered in the hexane, was quantified by gas chromatography mass spectrometry. The reaction was very efficient for soil/sediment in hexane suspension and virtually complete provided that excess catalyst was added to samples that were burdened with higher PCB loadings prior to reaction otherwise some partial hydrogenation of biphenyl was also observed. The proposed method was validated with the analysis of five certified reference materials.     

Predicting arsenic concentrations in groundwater of San Luis Valley,Colorado: implications for individual-level lifetime exposure assessment

Consumption of inorganic arsenic in drinking water at high levels has been associated with chronic diseases. Risk is less clear at lower levels of arsenic, in part due to difficulties in estimating exposure. Herein we characterize spatial and temporal variability of arsenic concentrations and develop models for predicting aquifer arsenic concentrations in the San Luis Valley, Colorado, an area of moderately elevated arsenic in groundwater. This study included historical water samples with total arsenic concentrations from 595 unique well locations. A longitudinal analysis established temporal stability in arsenic levels in individual wells. The mean arsenic levels for a random sample of 535 wells were incorporated into five kriging models to predict groundwater arsenic concentrations at any point in time. A separate validation dataset (n = 60 wells) was used to identify the model with strongest predictability. Findings indicate that arsenic concentrations are temporally stable (r = 0.88; 95 % CI 0.83–0.92 for samples collected from the same well 15–25 years apart) and the spatial model created using ordinary kriging best predicted arsenic concentrations (ρ = 0.72 between predicted and observed validation data). These findings illustrate the value of geostatistical modeling of arsenic and suggest the San Luis Valley is a good region for conducting epidemiologic studies of groundwater metals because of the ability to accurately predict variation in groundwater arsenic concentrations.     

Mapping socio-economic scenarios of land cover change: a GIS method to enable ecosystem service modelling

We present a GIS method to interpret qualitatively expressed socio-economic scenarios in quantitative map-based terms. (i) We built scenarios using local stakeholders and experts to define how major land cover classes may change under different sets of drivers; (ii) we formalized these as spatially explicit rules, for example agriculture can only occur on certain soil types; (iii) we created a future land cover map which can then be used to model ecosystem services. We illustrate this for carbon storage in the Eastern Arc Mountains of Tanzania using two scenarios: the first based on sustainable development, the second based on 'business as usual' with continued forest-woodland degradation and poor protection of existing forest reserves. Between 2000 and 2025 4% of carbon stocks were lost under the first scenario compared to a loss of 41% of carbon stocks under the second scenario. Quantifying the impacts of differing future scenarios using the method we document here will be important if payments for ecosystem services are to be used to change policy in order to maintain critical ecosystem services.     

Spatio-temporal patterns in county-level incidence and reporting of Lyme disease in the northeastern United States, 1990–2000

We present an exploratory analysis of reported county-specific incidence of Lyme disease in the northeastern United States for the years 1990–2000. We briefly review the disease ecology of Lyme disease and the use of risk maps to describe local incidence as estimates of local risk of disease. We place the relevant elements of local environmental and ecological variables, local disease incidence, and (importantly) local disease reporting in a conceptual context to frame our analysis. We then apply hierarchical linear models of increasing complexity to summarize observed patterns in reported incidence, borrowing information across counties to improve local precision. We find areas of increasing incidence in the central northeastern Atlantic coast counties, increasing incidence branching to the north and west, and an area of fairly stable and slightly decreasing reported incidence in western New York.     

Geographical gradients in diet affect population dynamics of Canada lynx

Geographical gradients in the stability of cyclic populations of herbivores and their predators may relate to the degree of specialization of predators. However, such changes are usually associated with transition from specialist to generalist predator species, rather than from geographical variation in dietary breadth of specialist predators. Canada lynx (Lynx canadensis) and snowshoe hare (Lepus americanus) populations undergo cyclic fluctuations in northern parts of their range, but cycles are either greatly attenuated or lost altogether in the southern boreal forest where prey diversity is higher. We tested the influence of prey specialization on population cycles by measuring the stable carbon and nitrogen isotope ratios in lynx and their prey, estimating the contribution of hares to lynx diet across their range, and correlating this degree of specialization to the strength of their population cycles. Hares dominated the lynx diet across their range, but specialization on hares decreased in southern and western populations. The degree of specialization correlated with cyclic signal strength indicated by spectral analysis of lynx harvest data, but overall variability of lynx harvest (the standard deviation of natural-log-transformed harvest numbers) did not change significantly with dietary specialization. Thus, as alternative prey became more important in the lynx diet, the fluctuations became decoupled from a regular cycle but did not become less variable. Our results support the hypothesis that alternative prey decrease population cycle regularity but emphasize that such changes may be driven by dietary shifts among dominant specialist predators rather than exclusively through changes in the predator community.     

The Links Between Resource Dependency and Attitude of Commercial Fishers to Coral Reef Conservation in the Red Sea

The imperative to further constrain extractive uses of natural resources will strengthen as resources degrade through over-use or exposure to climate changes. Here, we explore an approach to increase the support for marine conservation among coral reef fishers. We explore the proposition that resource dependency in the Egyptian Red Sea can act as a barrier to conservation. We administered face-to-face surveys to 49% of the fishing industry to: (i) identify the level of compliance to the local marine protected area (MPA), (ii) assess the level of dependency on marine resources in the region and (iii) examine the relationship between resource dependency and conservation attitudes. Only 11.4% of fishers were aware of the MPA. Fishers were mostly limited in their social flexibility and livelihood options. Results suggest that resource dependency is highly and negatively correlated with conservation attitudes suggesting that management efforts need to seriously focus on reducing dependency if conservation goals are to be met.     

Preliminary comparison of alternative designs for soil remediation by bioventilation

Computer simulation provides a powerful tool for comparing alternative designs of remediation processes. The software package FLUENT copes successfully with subsurface three-dimensional flow fields, multiple and directional permeabilities, wide spatial variations in subsurface gas velocities, and the presence of surface structures. FLUENT can provide an invaluable method for comparing remediation efficiencies among competing design alternatives. This article features case studies to illustrate the benefits that simulation studies provide before and during the initiation of remedial actions using bioventing.     

Toxicant-induced fecundity compensation: A model of population responses

A mathematical model widely applied in population studies and in assessment of the impact of exploitation on fish populations was applied to assess cadmium toxicity in laboratory populations ofDaphnia galeata mendotae. Over a range of toxicant concentrations, the birth rate of the population increased to balance the death rate and the population compensated for the increased mortality. The model describes the relation between toxicant concentration, toxicant-induced mortality, and equilibrium population size. Compensation for increased mortality is described in terms of the decrease in population size necessary to produce an increase in the birth rate that will balance the increased death rate. The relative capacity of different aquatic organisms to compensate for toxicant-induced mortality is examined and a relation between compensatory capacity and the innate capacity for increase is developed.     

The acid rain debate in North America “Where you stand depends on where you sit”

Summary An analysis of the recent acid rain debate in North America reveals that the policies and priorities of the various interested bodies with regard to this issue directly reflect their vested interests and in many instances their geographical location.Dr Marshall E. Wilcher is Assistant Professor in Political Science at the New Kensington Campus of Pennsylvania State University.     

Quaternized agricultural by-products as anion exchange resins

The objectives of this study were the chemical modification of readily available, low-cost agricultural by-products to anion exchange resins and the selection of the best modified by-product for further use in anion removal. Resins were prepared through the quaternization of a series of 12 agricultural by-products with N-(3-chloro-2-hydroxypropyl) trimethylammonium chloride (CHMAC). Phosphate ion adsorption assays were conducted at pH 7 in order to compare adsorption properties among the by-products. Quaternized corn stover showed the highest phosphorus adsorption at 0.66 mmole/g. Since corn stover exhibited the best uptake of phosphate ion, it was compared to a commercially available, cellulose-based anion exchange resin. Additionally, adsorption capacities of quaternized corn stover for arsenate, chromate, and selenate were evaluated and adsorption efficiencies were determined in simulated wastewater samples. Our results indicate that modified corn stover demonstrates good adsorption uptake for arsenate and selenate and especially for chromate.