Joint application of an empirical and mechanistic model for regional lake acidification

The empirical direct distribution model for lake acidification is calibrated for use in an integrated assessment model which predicts the regional impact of an acid deposition control strategy. The calibration is based on the mechanistic Model of Acidification of Groundwater in Catchments (MAGIC). The models are applied jointly to a set of 33 statistically-selected lakes in the Adirondack region of New York. Calibration of the direct distribution model is based on a step-function application of acid deposition to MAGIC. Comparative evaluations of the resulting model predictions are made using historic deposition estimates and two alternative future deposition scenarios. The predictions of the direct distribution model match well the shapes and patterns of change of the regional distributions of ANC and pH predicted by MAGIC, the short- and medium-term dynamics of these changes, and the effect of including organic acids. However, small, long-term decreases in the fraction of incoming acid deposition neutralized by lakes and their watersheds predicted by MAGIC are not reproduced.     

Floodplain management: Land acquisition versus preservation of historic buildings in Cambridge,Ontario, Canada

Non-structural adjustments in floodplain management are often avoided because they are seen to infringe on personal rights, adversely affect property values and restrict local tax bases. Land acquisition programs in urban areas encounter a further problem when they lead to demolition of buildings and other structures considered to have historical or architectural value. An experience in Cambridge, Ontario demonstrates that the potential conflict between flood damage reduction and historical preservation objectives can be exacerbated as a result of uncoordinated planning efforts, inflexibility in interpreting mandates, unclear roles for participating agencies, and lack of cooperation Many of these dilemmas can be resolved through consultation and discussion early in the planning process as well as through a willingness to be flexible and to search for a compromise     

Modelling and experimental studies on the transfer of radionuclides to fruit

Although fruit is an important component of the diet, the extent to which it contributes to radiological exposure remains unclear, partially as a consequence of uncertainties in models and data used to assess transfer of radionuclides in the food chain. A Fruits Working Group operated as part of the IAEA BIOMASS (BIOsphere Modelling and ASSessment) programme from 1997 to 2000, with the aim of improving the robustness of the models that are used for radiological assessment. The Group completed a number of modelling and experimental activities including: (i) a review of experimental, field and modelling information on the transfer of radionuclides to fruit; (ii) discussion of recently completed or ongoing experimental studies; (iii) development of a database on the transfer of radionuclides to fruit; (iv) development of a conceptual model for fruit and (v) two model intercomparison studies and a model validation study. The Group achieved significant advances in understanding the processes involved in transfer of radionuclides to fruit. The work demonstrated that further experimental and modelling studies are required to ensure that the current generation of models can be applied to a wide range of scenarios.     

Environmental PCB forensics: processes and issues

Environmental Science and Pollution Research - PCB forensic science is the process of identifying the source(s) of polychlorinated biphenyls (PCBs) at a site in the context of a legal proceeding to...     

Shell selection in the hermit crab Pagurus bernhardus

Three shell variables were deemed to be important in the selection of a shell by the hermit crab Pagurus bernhardus (L.). These were the weight, volume and aperture width of a shell. Each of these variables were used in multiple regressions against crab weight for 25 Littorina littorea and 25 Thais lapillus shells chosen when both shell species were together in a tank, and for a further 25 L. littorea and 25 T. lapillus when the two shell species were separate. Principal component analysis was performed on the four groups of 25 shells selected, and multiple-regression equations were calculated using the principal components as the new variables. It was found that crabs chose a shell of suitable general dimensions rather than solely on the basis of one shell variable. The advantages of using statistical techniques developed in this paper over previous approaches to shell selection are discussed.     

The nature and significance of public exposure to arsenic: a review of its relevance to South West England

In South West England, more than two hundred years of intensive exploitation of metalliferous ore deposits, combined with the natural processes of pedogenesis from mineral-rich parent rocks, has resulted in the creation of a aignificant area of arsenic-contaminated wastes and soils. The scale of arsenic dispersion by natural and anthropogenic processes is such that 722 km² of land contains concentrations of arsenic in excess of 110 g g^–1, more than twice the maximum that might be expected in a normal soil.The general rationale for the clean-up of derelict and contaminated mining sites often includes aesthetic factors and the desirability of preventing the dispersion of contaminants beyond the site boundaries. Only in extreme cases is public health directly invoked as justification for remediation. In South West England, if arsenic constitutes a genuine threat to the public, an increased rate of site remediation would be justified. The primary purpose of this review is to establish whether or not widespread arsenic contamination (principally of soils) has any measurable effects on public health in South West England, and how this might affect current contaminated site remediation policy. The review is based on data from previous research in the region, and other relevant international studies of mining and smelting communities, and other populations exposed to elevated arsenic concentrations. The literature reviewed also includes the determination of the extent and sources of contamination, and pathways between source and man.While the contamination of potable waters in some countries has led to measurable health effects, this scenario has not yet been identified in South West England, and there is little reason to believe that significantly contaminated potable water supplies would escape detection for extended periods of time under the current monitoring regime.In relative terms (based on both globaland local data), one of the most significant links between contaminated soils and humans appears to be contaminated food stuffs. In absolute terms, such exposure is low due to the natural constraints on arsenic uptake by herbage, cereal crops and vegetables, and the food chain does not appear to have been significantly compromised in South West England. Chronic health effects are unlikely as excessive arsenic concentrations in locally grown food crops remain rare.With the problems of confounding medical and social factors, it is not surprising that studies in South West England have failed to identify chronic exposure to arsenic at very low concentrations as a significant health risk. Those studies that indicate otherwise do not stand up to close scrutiny. It appears that the number of additional deaths arising from the widespread arsenic contamination in South West England is small. The relative benefits of a costly statistical study to actually determine the number of additional deaths might be considered minimal, but one major area could benefit from further studies: the sensitivity of certain population sub-groups to environmental arsenic exposure. Of particular interest are children, for whom significant exposure to arsenic via soil ingestion may be occurring.Based on available information, there appears to be no justification for a large programme of site remediation. Resources should, however, be expended on enlightening the general public, and private and governmental organisations as regards the gap between the perceived and actual significance of arsenic contamination in South West England.To whom correspondence should be addressed.     

Competitive regimes and female bonding in two species of squirrel monkeys (Saimiri oerstedi and S. sciureus)

Summary Ecological and behavioral data from long-term field studies of known individuals in two closely related squirrel monkey species (Saimiri oerstedi and S. sciureus) were used to examine hypotheses about the source of variation in female bonding among group-living primates. Social relationships in species which live in cohesive groups are thought to depend on the nature of competition for resources. S. oerstedi and S. sciureus both live in large groups and are subject to intense predation. Direct feeding competition both between and within groups is extremely low in S. oerstedi; in this species female relationships are undifferentiated, no female dominance hierarchy is evident and females disperse from their natal group. S. sciureus also experiences very low levels of between-group competition, but within-group direct competition for resources is frequent; this species demonstrates differentiated female relationships, a female dominance hierarchy, and female philopatry. The correlated ecological and social variables found in these two congeners further minimize the minor effects of phylogenetic differences and emphasize the importance of food distribution in determining social characteristics. Offprint requests to: S. Boinski     

Influence of sediment on the fate and toxicity of a polyethoxylated tallowamine surfactant system (MON 0818) in aquatic microcosms

The fate and toxicity of a polyethoxylated tallowamine (POEA) surfactant system, MON 0818, was evaluated in water-sediment microcosms during a 4-d laboratory study. A surfactant solution of 8 mg l(-1) nominal concentration was added to each of nine 72-l aquaria with or without a 3-cm layer of one of two natural sediments (total organic carbon (TOC) 1.5% or 3.0%). Control well water was added to each of nine additional 72-l aquaria with or without sediment. Water samples were collected from the microcosms after 2, 6, 24, 48, 72, and 96 h of aging to conduct 48-h toxicity tests with Daphnia magna and to determine surfactant concentrations. Elevated mortality of D. magna (43-83%) was observed in overlying water sampled from water-only microcosms throughout the 96-h aging period, whereas elevated mortality (23-97%) was only observed in overlying water sampled from water-sediment microcosms during the first 24h of aging. Measured concentrations of MON 0818 in water-only microcosms remained relatively constant (4-6 mg l(-1)) during the 96-h period, whereas the concentrations in overlying water from microcosms containing either of the two types of sediment dissipated rapidly, with half-lives of 13 h in the 3.0% TOC sediment and 18 h in the 1.5% TOC sediment. Both toxicity and the concentration of MON 0818 in overlying water decreased more rapidly in microcosms containing sediment with the higher percent TOC and clay and with a higher microbial biomass. Mortality of D. magna was significantly correlated with surfactant concentrations in the overlying water. These results indicate that the toxicity of the POEA surfactant in water rapidly declines in the presence of sediment due to a reduction in the surfactant concentration in the overlying water above the sediment.