Leaf litter breakdown in streams receiving treated and untreated metal mine drainage

Rates of alder leaf decomposition were used as an ecosystem-level measure of effects of untreated and treated acid mine drainage on two Colorado mountain streams. Untreated mine effluents had low pH and high concentrations of metals, particularly iron. Deposition of ferric hydroxide on leaf surfaces inhibited colonization by decomposers, such as fungi and aquatic insects, and thus little leaf breakdown occurred. Treated effluents had improved water quality (basic pH, low metal concentrations), but suspended flocs released by the treatment process buried leaves and reduced consumer activity. The rate of leaf breakdown was not significantly different from the rate with untreated effluents; thus improvement in water quality alone was insufficient to restore this important pathway of energy flow in headwater streams.     

Aggregation error in ecological models

Models of complex ecosystems require the representation of a large number of components by a few variables. The exact nature of the limitations imposed by this abstraction process has received surprisingly little treatment. In this study, models with k variables were taken, for the sake of argument, to exactly represent a system. Models with k — n variables were then developed for the same system and differences in output examined. As a result of the study, we suggest some simple rules for minimizing aggregation error, including lumping components with similar turnover times and lumping rare species with common ones.     

Mining disasters caused and controlled by mankind: the case for coal mining and other minerals

In Part I of this two-part paper, the characteristics of mine disasters and their effects are presented with case studies from coal, metal and non-metal mines leading to an amplification of their causes and opportunities for control. The disasters discussed encompass those which threaten the health and the safety of miners and those which affect the general population. In Part 2 of the paper, which will be published in the November 1995 issue of Natural Resources Forum , the approaches to hazard and disaster control are reviewed with particular attention to laws and regulations to promote health and safety at the workplace, and general welfare in mining communities. Further, a systems approach to disaster control is outlined .     

Cadmium-binding proteins in Mytilus edulis: Relation to mode of administration and significance in tissue retention of cadmium

Tissue cadmium levels and the amount of metal associated with the various protein fractions thereof have been determined in specimens of $\text{Mytilus edulis}$ exposed to cadmium in the water and by direct injection. In addition to metallothionein, heavy-molecular weight proteins are involved in cadmium retention.     

Reduction of fecal indicator bacteria in sewage effluent when pumping for crop irrigation.

When sewage effluent was pumped from a lagoon for spray irrigation the pumping process reduced the fecal coliforms (FC) by 66% and the fecal streptococci (FS) by 91%. Bactericidal effects associated with the pumping of effluent were investigated in the laboratory by seeding sterilized effluent with fecal bacteria and repeatedly passing the liquid through a centrifugal impeller type pump at 50 psi pressure. The pumping effect was cumulative, 49 and 90% of FC being killed after two and four passages through the pump, respectively. FC were more susceptible than FS to injury by pressure shock. Very weak chlorination of the effluent increased the destruction of FC but not FS during subsequent pumping. Within the range of experimental conditions used, the percentage of FC killed by pumping was not markedly affected by changes in temperature and pH of the effluent or by differences in the number and age of cells added.     

Overview and definition of risk: Its assessment and management

Risk assessment includes both risk estimation (identifying hazards and estimating their outcomes and probabilities) and risk evaluation (determining the significance or value of risks to those concerned with or affected by the decision). Risk estimation is about situations, and risk evaluation about the effect on people. Few situations are absolutely safe. Risks need to be estimated, and for many kinds of risk (e.g., exposures to potentially toxic substances or to potentially catastrophic situations) an expert view has to be formed, which must take account of associated uncertainties. Different sections of the public perceive risk in different ways, and regard some risks more seriously than the expert estimates. Thus studies of risk perception form a further input into the decision-making process. Another input is the benefit of the activity. A regulatory framework consistent with the reality of risk estimation has been proposed. Since risks and benefits fall on different parts of the community, the decision process is essentially political, though it must be informed scientifically. How the decision is taken will depend on national governmental practices.