Distribution and Migration of some Metals in the Water-Sediment System Using Radiotracers

The knowledge of heavy metals and related radionuclide distribution, and accumulation among the different components of a fresh water ecosystem, plays a relevant role in environmental studies. In the present study reported here the behaviour of ⁶⁰Co, ¹³⁴Cs and ⁵⁴Mn was investigated in a water-sediment system. Water and sediment samples were obtained from an artificial channel, derived from the Po river near Serafini Island (middle course). It was characterized by a very low water flow.     

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.     

Comparative Toxicities of Polar and Non-Polar Organic Fractions From Sediments Affected By the Exxon Valdez Oil Spill in Prince William Sound, Alaska

Standardized tests were applied to aromatic and polar fractions of sediment extracts to determine whether polar constituents or oxidative degradation products contributed significantly to the toxicity of sediments oiled by the Exxon Valdez spill. Intertidal sediment and pore-water samples were collected in September 1990 from two heavily oiled sites and an unoiled site in Prince William Sound (PWS). Methylene chloride extracts from these samples were fractionated by liquid chromatography into aliphatic, aromatic and polar fractions, and the aromatic and polar fractions were tested for toxicity using the Microtox^R test, bivalve larval mortality and development (Mytilus); several measures of genotoxicity in Mytilus, including SOS Chromotest^R, anaphase aberrations and sister chromatid exchange; and survival, anaphase aberrations and teratogenicity in coho salmon (Onchorhynchus kisutch). Microtox^R and SOS Chromotest^R protocols were applied in a screening mode to all samples, whereas other tests were applied only to selected fractions from two sites. Samples from Bay of Isles (oiled) were consistently more toxic (usually only 2 to 5-fold) than the Mooselips Bay (unoiled) samples, which gave very low responses in all tests. for both sites, however, responses to polar and aromatic fractions were about the same in most tests, suggesting that while the overall toxicity of the oil was low in these samples, at least part of that toxicity was derived from polar constituents. Compared to the parent hydrocarbons, polar oxidation products partition preferentially into pore-water and are more rapidly diluted and dispersed in the water column. These results suggest that polar oxidation products of petroleum hydrocarbons pose little risk to marine organisms, except possibly for infauna continuously exposed to pore-water in heavily oiled sediments. Independent surveys showed that sediment toxicity in PWS declined during 1989-1991 to near background levels, in accord with previous understanding of oil weathering and toxicity.     

Sex ratio and optimal harvest of canvasback ducks,A model

The North American population of canvasback ducks (Aythya valisineria) exhibits extreme distortion of the sex ratio in favor of males. This paper describes a model which accounts for this pattern by relatively heavier female mortality in both the breeding and nonbreeding seasons. The density-dependence of winter mortality leads to the conclusion that the observed sex ratio depresses total population numbers. Variation in nesting success is shown to influence sex ratios and strongly depress population numbers. Because a standard harvest scheme can be demonstrated to severely depress the numbers of ducks, an alternative graduated or weighted harvest procedure is recommended.     

Seven Years of Change Following Liming of Sphagnum Communities in Sector Vii of the Loch Fleet Catchment

In 1986, application of lime within the upper wetland area of sector VII of the Loch Fleet catchment initiated numerous unscheduled small-scale experiments on the vegetation of this heterogeneous terrain. Vegetation changes and erosion were monitored in permanent or relocated plots established in 1987 and 1989 and re-surveyed in 1993, seven years after liming.

The most striking early effect, possibly occurring within a few weeks of lime application, was the death of Sphagnum papillosum carpet in soakways within the 2.5 ha area. Some patches of dead material were washed away, but bare surfaces were generally colonised by vascular plants, notably Juncus bulbosus. Effects in moorland and bog communities with dwarf shurbs were more subtle, involving reduction in Sphagnum cover and expansion of Erica teralix, Molinia caerulea, sedges and Narthecium ossifragum, but little change in the frequency of occurrence of Calluna vulgaris.     

Studies On the Effect of Hexachlorocyclohexane On the Growth and Silk Qualities of Silkworm, Bombyx Mori L

Toxicity of an organochloride insecticide, hexachlorocyclohexane (HCH) on the alterations in the growth and silk qualities of silkworm, Bombyx mori L were investigated. HCH yielded higher growth constants (K), indicating impairment of growth of silkworms and silk gland. the decrement in fibroin content is significant. HCH treatment also resulted in considerable reduction in the cocoon, pupal and shell weights, survival and emergence of pupae and number of eggs laid and deterioration in quality and quantity of silk thread.     

Delayed neurotoxicity in the wild mallard duckling caused by the organophosphorus insecticides cyanofenphos and leptophos

The susceptibility of wild mallard ducklings to the delayed neurotoxic effect of the neurotoxic organophosphorus insecticides cyanofenphos and leptophos was evaluated following a daily dosing regimen. Ducklings were treated daily with either cyanofenphos or with leptophos at different dose levels for 90 days, or until they died, or became paralyzed. A control group of ducklings given corn oil at 1 ml/kg daily for 90 days was used for comparison. All treated birds were observed daily for any clinical signs of neurotoxicity during the course of this study. All of the surviving ducklings that were treated with cyanofenphos at 4 mg/kg/day or leptophos at 10 mg/kg/day developed clinical signs of delayed neurotoxicity after 7 to 11 weeks of intoxication. Symptoms included leg weakness, ataxia, severe ataxia and paralysis. The observed clinical signs were confirmed by histological changes found in the spinal cords of the treated birds. These changes were of the type associated with organophosphorus-induced delayed neuropathy (OPIDN). These results demonstrate that wild mallard ducklings are susceptible to OPIDN and this avian species can be used in screening organophosphorus compounds for such effect.     

Density and Viscosity Measurements of Natural Solutions

Utilizing sophisticated equipment, densimetric and viscosimetric measurements were carried out on samples of ground-waters of Apulia.

Experimental data, utilized to check if simple equations can evaluate the density and the viscosity of multicomponent solutions, confirm the validity of the hypothesis.