Fenton's in-situ reagent chemical oxidation of hydrocarbon contamination in soil and groundwater

Industry and regulatory demands for rapid and cost-effective clean up of hydrocarbon and other contamination in soil and groundwater has prompted development and improvement of in-situ remediation technologies. In-situ technologies offer many advantages over ex-situ treatment alternatives, including lower initial capital and long-term operation and maintenance costs, less site disruption, no Resource Conservation and Recovery Act (RCRA) liability, and shorter treatment time necessary to achieve cleanup objectives. Fenton's reagent, a mixture of hydrogen peroxide and ferrous iron that generates a hydroxyl free radical as an oxidizing agent, is widely accepted for chemical oxidation of organic contaminants in the wastewater industry. In-situ implementation of Fenton's reagent for chemical oxidation of organic contaminants in soil and groundwater continues to grow in acceptance and application to a wide variety of environmental contaminants and hydrogeologic conditions (EPA, 1998).     

Educating the South Pacific about the environment

Summary Environmental education is currently fashionable. However, some educators are viewing it with suspicion as a trendy subject which will disrupt their carefully planned syllabii which are geared largely towards the passing of examinations. In the South Pacific there have been a number of attempts to increase people's awareness of their surroundings and to build up a respect for what is loosely termed our physical environment. These programmes have included, increasing the amount of environmental examples in a range of primary and secondary school subjects, formal courses in environmental planning at the tertiary level, and conservation messages through the media.Dr Jenny Bryant is a Lecturer in Geography at the University of the South Pacific, and recently Secretary, now Acting Chairperson, of the South Pacific Action Committee for Human Ecology and the Environment (SPACHEE).     

Methodological convergence as an issue within environmental cognition research

Two perspectives in the analysis of pointing and mapping tasks as the measure of representations of the large-scale environment are examined. These two perspectives are: (1) an individual difference approach; and (2) a cognitive representational approach. Convergence between methods assessing the same geographical/spatial knowledge is necessary as evidence for the existence of unified cognitive-spatial representations of the environment.Three sets of analyses interrelate performance on pointing and mapping tasks. In the first analysis, a confirmatory factor analytic model is applied to short tests of pointing and mapping accuracy to determine whether one or two factors are needed to account for covariation between the tests. In the second analysis, covariation among errors in pointing and mapping of specific locations is partitioned into general and specific method factors using the Schmid-Leiman procedure. In the third analysis, pointing errors for identical locations within the mapping and pointing tasks are directly compared on the basis of directional errors.The three analyses indicate that: (1) tests of pointing and mapping measure highly related abilities; (2) the targets used in pointing and mapping tasks are of differential importance in identifying general and specific method factors; and (3) there is little or no direct correspondence between directional errors made in pointing tasks and those occurring in mapping tasks for the same locations.When results of the three analyses are examined in relationship to criteria for convergence of pointing and mapping tasks, little evidence is found to suggest that directional errors in these tasks arise from a unified mental representation of the geographical environment. However, substantial predictable individual differences are apparent for both tasks.     

Modelling conflict over natural resources issues

In recent years political instability and economic uncertainty have dominated resources policy issues. As a result, conflicts of interest have arisen in many contexts relating to the control and use of natural resources. A number of methodologies have been developed to study conflict situations in other areas, and this paper seeks to demonstrate the relevance and usefulness of these methodologies in the natural resources field. The resulting models do not always have predictive power but can provide valuable insights into the structure of conflicts.     

Microbial community phylogenetic and trait diversity declines with depth in a marine oxygen minimum zone

Oxygen minimum zones (OMZs) are natural physical features of the world's oceans. They create steep physiochemical gradients in the water column, which most notably include a dramatic draw down in oxygen concentrations over small vertical distances (<100 m). Microbial communities within OMZs play central roles in ocean and global biogeochemical cycles, yet we still lack a fundamental understanding of how microbial biodiversity is distributed across OMZs. Here, we used metagenomic sequencing to investigate microbial diversity across a vertical gradient in the water column during three seasons in the Eastern Tropical South Pacific (ETSP) OMZ. Based on analysis of small subunit ribosomal RNA (SSU rRNA) gene fragments, we found that both taxonomic and phylogenetic diversity declined steeply along the transition from oxygen-rich surface water to the permanent OMZ. We observed similar declines in the diversity of protein-coding gene categories, suggesting a decrease in functional (trait) diversity with depth. Metrics of functional and trait dispersion indicated that microbial communities are phylogenetically and functionally more overdispersed in oxic waters, but clustered within the OMZ. These dispersion patterns suggest that community assembly drivers (e.g., competition, environmental filtering) vary strikingly across the oxygen gradient. To understand the generality of our findings, we compared OMZ results to two marine depth gradients in subtropical oligotrophic sites and found that the oligotrophic sites did not display similar patterns, likely reflecting unique features found in the OMZ. Finally, we discuss how our results may relate to niche theory, diversity-energy relationships and stress gradients.     

An uncertainty analysis of mean flow velocity measurements used to quantify emissions from stationary sources

Point velocity measurements conducted by traversing a Pitot tube across the cross section of a flow conduit continue to be the standard practice for evaluating the accuracy of continuous flow-monitoring devices. Such velocity traverses were conducted in the exhaust duct of a reduced-scale analog of a stationary source, and mean flow velocity was computed using several common integration techniques. Sources of random and systematic measurement uncertainty were identified and applied in the uncertainty analysis. When applicable, the minimum requirements of the standard test methods were used to estimate measurement uncertainty due to random sources. Estimates of the systematic measurement uncertainty due to discretized measurements of the asymmetric flow field were determined by simulating point velocity traverse measurements in a flow distribution generated using computational fluid dynamics. For the evaluated flow system, estimates of relative expanded uncertainty for the mean flow velocity ranged from ±1.4% to ±9.3% and depended on the number of measurement locations and the method of integration.

Implications:Accurate flow measurements in smokestacks are critical for quantifying the levels of greenhouse gas emissions from fossil-fuel-burning power plants, the largest emitters of carbon dioxide. A systematic uncertainty analysis is necessary to evaluate the accuracy of these measurements. This study demonstrates such an analysis and its application to identify specific measurement components and procedures needing focused attention to improve the accuracy of mean flow velocity measurements in smokestacks.     

Effects of limiting access to prey on development of first zoeal stage of the brachyuran crabs Cancer magister and Hemigrapsus oregonensis

We tested the influence of limiting access to prey on larval development of the crabs Cancer magister and Hemigrapsus oregonensis by raising their Stage 1 larvae in the laboratory on different prey densities and with various periods of access to prey. Experiments were conducted in 1995 and 1996 at the Shannon Point Marine Center in Anacortes, Washington, USA. Our results show that crab larvae do not require continuous access to prey for optimal development nor do they appear to require light for prey capture. Survival and duration of Stage 1 C. magister fed continuously on only one-fourth the amount of the control density of prey and those fed at the control density for only 6 h per day were the same as for larvae fed continuously at the control density (20 ml⁻¹). Larvae with cyclic access to prey at the control density for 24 h and then starved for 72 h showed significantly lower survival and longer instar duration to Stage 2. Experiments on Stage 1 H. oregonensis which investigated a combination of prey density, period of access to prey and light/dark conditions during feeding revealed that survival decreased with decreasing prey density or with decreasing feeding period, but no differences were observed during periods of limited prey availability as a function of light or dark conditions. Stage duration was not affected by reduced prey density nor by the light/dark condition at the time of feeding, but it was prolonged when the period of access to prey was limited. The period of access to prey did not affect the weight of Day 1 Stage 2 larvae. Larvae fed high densities of prey for 4 h followed by 20 h of reduced-density diet exhibited the same survival and stage duration as controls that were continuously fed high-density prey. Our results define sub-optimal diets that can be used experimentally to determine the nutritional contributions made by naturally-occurring prey organisms during larval development in the two species. In nature, larvae may satisfy nutritional requirements through periodic encounters with dense prey patches during vertical migrations by day or night. Received: 12 August 1997 / Accepted: 5 February 1998