Removing the boundary influence on negatively buoyant jets

A comprehensive laboratory study of negatively buoyant discharges is presented. Unlike previous studies, here the focus is on generating data sets where influences of the bottom boundary have been eliminated. There are significant discrepancies in the published dilution data for these flows and a contributing factor is the large variation in the bottom boundary condition. A Laser-induced Fluorescence system is employed to gather flow spread, peak concentration (minimum dilution) and trajectory data for a wide range of densimetric Froude numbers and initial discharge angles. Data from these experiments are compared with previously published data, along with predictions from integral models and a revised form of the previously published semi-analytical solutions. The new data sets are not distorted by mixing processes associated with the bottom boundary and therefore provide the basis for more meaningful assessments of the predictive capabilities of existing models, given that the influences of the bottom boundary on contaminant mixing are not incorporated into these models. In general the models assessed are able to predict key geometric quantities with reasonable accuracy, but their minimum dilution predictions are conservative. Importantly dilution at the return point shows a strong dependence on the initial discharge angle and this could have important implications for the design of discharge systems.     

The effect of selection treatments on <Emphasis Type=Italic>Mytilus edulis</Emphasis>, modifications of genetic and physiological characteristics

This study examined the effects of two selection treatments (elevated water temperature and air exposure) on the genetic and physiological characteristics of the juvenile marine mussel, Mytilus edulis (<10 mm). Genetic effects were measured on five allozymes and fitness assessed using physiological tests to estimate energy balance (scope for growth) as well as size, growth and survival. The in vitro treatments resulted in 48% mortality from an air exposure of 11 h at 27°C and 76% mortality from a 6-h exposure to 33°C water. Survivors (n = 1,152) of each treatment along with controls (n = 2,304) were measured and randomly placed in compartmentalized cages. Mussels were deployed to three bays in Prince Edward Island, Canada and monitored over a 10-month period. Initially, both of the treatments had an effect on mussel size and increased the heterozygosity of the surviving mussels. Physiological analyses after 3 months in the field showed that the two treated mussels showed lower metabolic rate that the control group. After 10 months in the field, the treated mussels were larger and had lower mortality than the untreated control mussels. Unexplained environmental interaction in each of the bays had an effect on allelic frequencies and heterozygosity. Overall, the results demonstrate that simple husbandry techniques can be used to increase the productivity of mussel seed and heterozygosity measures can be used to assess fitness. However, more field data is needed to determine the consistency of the increased productivity and if the increased productivity justifies the costs of a selective treatment. Furthermore, because the level of heterozygosity in juvenile mussel populations can vary considerably, both spatially and temporally, it may be effective as a warning of future natural mass mortality when overall heterozygosity levels are found to be low.     

Hindcasting nitrogen deposition to determine an ecological critical load.

Using an estimated background nitrogen (N) deposition value of 0.5 kg N x ha(-1) x yr(-1) in 1900, and a 19-year record of measured values from Loch Vale (Colorado, USA; NADP site CO98), I reconstructed an N-deposition history using exponential equations that correlated well with EPA-reported NO(x) emissions from Colorado and from the sum of emissions of 11 western states. The mean wet N-deposition values for the period 1950-1964 was approximately 1.5 kg N x ha(-1) x yr(-1), corresponding to the reported time of alteration of diatom assemblages attributed to N deposition in alpine lakes in Rocky Mountain National Park (USA). This value becomes the critical load defining the threshold for ecological change from eutrophication. Thus if an N-deposition threshold for ecological change can be identified, and the date at which that threshold was crossed is known, hindcasting can derive the amount of atmospheric deposition at the time of change, at least for alpine lakes. Independent support for the technique and the deposition amount comes from experimental studies, ecosystem modeling, and paleolimnological records from northern Wyoming (USA).     

Citizenship and sustainability in dependent island communities: the case of the Huon Valley region in southern Tasmania

In Western democracies, rising levels of political alienation have prompted concerned political authorities to improve the quality of citizenship by such means as civic education. As well, the several international conventions underpinning the sustainable development discourse mandate participation to empower people in their own development. Active citizenship and the participation fundamental to it can be problematic for island communities with a history of economic and political dependence, since there exist a number of structural and agentic barriers to its practice and to the exercise of ecological responsibility through participation. Both the barriers to and the prospects for ecological sustainability are elaborated in this study of aspects of community, participation, citizenship and ecological literacy among the communities of the Huon Valley region of southern Tasmania.     

Perspective and trends in the environmental remediation industry

The approach to management and execution of remediation projects has changed drastically over the past decade, as remedial project managers have begun to understand and accept the numerous environmental regulations developed in the mid-1980s. For example, the adversarial relationship that once existed between regulators and owners has become more cooperative. This article documents trends over time in remediation project practices and quantifies the impact these trends have had on the cost and schedule performance of projects. Proven successful practices are highlighted, and those with the potential for improving project performance further are also discussed.     

Warning variables affecting personal protective equipment use

This paper describes two studies conducted to test selected warning variables for their influence on the use of personal protective equipment. Both of the studies were field demonstrations; one conducted in a recreational setting and the other as part of a consumer product scenario. Each of the studies involved manipulations that could be practically implemented in many warning situations. Both studies showed that cost strongly influenced the use of personal protective equipment. “Cost” was shown to include parameters of time and difficulty with obtaining the equipment. The results indicate that a small increase in cost can devastate equipment use rates. Additional factors that were shown to positively influence equipment use under at least some circumstances include: (1) the addition of “specific consequence” information, including accident frequency and severity data, to standard warning signs/labels; and (2) product labels requiring physical manipulation by the consumer for product use.