Variation of the distribution coefficient (Kd) of selenium in soils under various microbial states

This study aimed to (i) evaluate whether the K(d) value of selenium is dependent upon the soil microbial activity and (ii) define the limitation of the use of the K(d) concept to describe selenium behaviour in soils when assessing the long-term radiological waste disposal risk. K(d) coefficients, as well as information on selenite speciation in the soil-solution, were derived from short- and long-term batch experiments with a calcareous silty clay soil in various microbial states. Soil microbial activity induced (i) an increase of the K(d) value from 16 l kg(-1) in sterile conditions to 130 l kg(-1) when the soil was amended with glucose and nitrate, and (ii) changes in selenium speciation both in the solution (presence of seleno-species other than free Se(IV)) and in the solid phase (Se linked to microorganisms). Although the K(d) coefficient adequately reflects the initial fractionation between soil-solid and soil-solution, it does not allow for speciation and microbial processes, which could affect reversibility, mobility and the long-term accumulation and uptake into crops.     

Muskox status,recent variation,and uncertain future

Ambio - Muskoxen (Ovibos moschatus) are an integral component of Arctic biodiversity. Given low genetic diversity, their ability to respond to future and rapid Arctic change is unknown, although...     

The role of analogues in radioecology

If no data are available for a specific radionuclide its analogue could be used in radioecological models. They might be used not only in the frame of screening modelling. Relevant processes and features have to be known, such as time scales of these processes, physical, chemical and biological properties of the environment and relevant media. An analogue could only be proven to be valid by comparing its behaviour in the conditions of interest, while confidence in the validity of an analogue will increase as the quality of the justification increases, there will always be some residual uncertainty. Several main types of analogy can be used when measured or recommended values are not available: the same parameter obtained for another isotope of the same element; the same parameter obtained for another element; a different parameter obtained for the same element. There are several cases, when analogues might be applied as indicators of the determining processes in the radioecological studies.     

Bioaccessibility of trace elements as affected by soil parameters in smelter-contaminated agricultural soils: a statistical modeling approach

An investigation was undertaken to identify the most significant soil parameters that can be used to predict Cd, Pb, and Zn bioaccessibility in smelter-contaminated agricultural soils. A robust model was established from an extended database of soils by using: (i) a training set of 280 samples to select the main soil parameters, to define the best population to be taken into account for the model elaboration, and to construct multivariate regression models, and (ii) a test set of 110 samples to validate the ability of the regression models. Total carbonate, organic matter, sand, P(2)O(5), free Fe-Mn oxide, and pseudototal Al and trace element (TE) contents appeared as the main variables governing TE bioaccessibility. The statistical modeling approach was reasonably successful, indicating that the main soil factors influencing the bioaccessibility of TEs were taken into account and the predictions could be applicable for further risk evaluation in the studied area.     

Availability of 99Tc in undisturbed soil cores

Models for safety assessment of radioactive waste repositories need accurate values of the soil-to-plant transfer of radionuclides. In oxidizing environments, (99)Tc is expected to occur as pertechnetate ((99)TcO(4)(-)). Due to its high mobility, leaching of this element in the field might be important, potentially affecting the reliability of estimated transfer parameters of (99)Tc as measured in closed experimental systems such as hydroponics or pot experiments. The aim of this experiment was to measure the leaching of (99)Tc in undisturbed irrigated soil cores under cultivation as well as plant uptake and to study the possible competition between the two transfer pathways. Undisturbed soil cores (50 x 50 cm) were sampled from a Rendzic Leptosol (R), a colluvial Fluvic Cambisol (F) and a Dystric Cambisol (D) using PVC tubes (three cores sampled per soil type). Each core was equipped with a leachate collector at the bottom, allowing the monitoring of (99)Tc leaching through the cores. Cores were placed in a greenhouse and maize (Zea mays L., cv. DEA, Pioneer) was sown. After 135 d, maize was harvested and radioactivity determined in both plant and water samples. Results showed that during the growing period, leaching of (99)Tc was limited, due to the high evapotranspiration rate of maize. After harvest, leaching of (99)Tc went on because of the absence of evapotranspiration. Effective uptake (EU) of (99)Tc in leaves and grains was calculated. EU reached 70% of the input in the leaves and was not significantly different among soils. These results confirmed those obtained from pot experiments, even though leaching was allowed to occur in close-to-reality hydraulical conditions. As a consequence, it was concluded that pot experiments are an adequate surrogate for more complex "close-to-reality" experimental systems for measuring transfer factors.     

Effets de l'ablation de l'organe axial sur l'activité respiratoire chez Asterina gibbosa (échinodermes,astérides)

The removal of the axial organ from the sea-star Asterina gibbosa Penn is followed by disturbances in respiratory activity. Decrease in oxygen uptake occurs from 1/2 to 2 h after which continues from 4 h to 2–3 days. Oxygen uptake then decreases and the test individuals die. These results are compared with those obtained with certain echinids. Since survival after removal of the axial organ is observed in certain other animals, it is concluded that, although the axial organ may partake in respiratory mechanisms, it is nevertheless not indispensable.     

A harvest failure approach to assess the threat from an invasive species

We present the idea of using potential infringements on annual allowable harvest targets as an approach to estimate threats from invasive species to the forest products sector. The approach uses present-day harvest levels as a reference level to estimate when and where the impact of a nonnative forest pest could become economically damaging. We use a generic model that simulates spread and damage by nonnative invasive species, basic harvest and forest growth through time. The concept is illustrated with a case study of a new nonnative invasive pest, Sirex noctilio Fabricius on pine resources in eastern Canada. Impacts of invasion on wood supply, in particular, the point at which present-day harvest levels are not attainable, were identified for 77 non-overlapping geographical regions that delimit the primary wood supply areas around large mills and wood processing facilities in eastern Canada. The results identify the minimum area of a pest outbreak that could trigger harvest shortages (approximately 12.5–14 M ha of pine forests in Ontario and Quebec). Beyond this level, the amount of host resource available for harvesting in any given year declines rapidly. The failure to sustain broad-scale harvest targets may be an attractive and intuitive indicator for policy makers and regulators interested in developing control and “slow-the-spread” programs for non-native forest pests.     

Effect of temperature on the molting,growth and maturation of the antarctic krill Euphausia superba (Crustacea: Euphausiacea) under laboratory conditions

The effect of temperature on molting, growth, and maturation rates was studied on laboratory-maintained Euphausia superba. The length of intermolt periods (IMP's) was inversely proportional to temperature (20.10 d, SD=1.60, at 0.12°C; 16.87 d, SD=1.68, at 0.97°C; and 12.48 d, SD=0.90, at 4.48°C), and directly proportional to krill size at 0.12°C and 0.97°C. For individually maintained krill the maximum growth rate at 4.48°C (0.068 mm d^-1) was nearly twice that at 0.68°C (0.037 mm d^-1). There was no observable temperature effect on maturation rates. The maturation changes of juveniles at all temperatures indicated that more than two years are probably required to reach maturity. Mature males and females regressed to immature forms, suggesting that E. superba may reproduce in successive years. These results and previously reported field and laboratory data for E. superba and other euphausiid species suggest a 4+ year life span for this species.This work was supported by NSF grant DPP 76-23437     

Mapping forest composition from the Canadian National Forest Inventory and land cover classification maps

Canada's National Forest Inventory (CanFI) provides coarse-grained, aggregated information on a large number of forest attributes. Though reasonably well suited for summary reporting on national forest resources, the coarse spatial nature of this data limits its usefulness in modeling applications that require information on forest composition at finer spatial resolutions. An alternative source of information is the land cover classification produced by the Canadian Forest Service as part of its Earth Observation for Sustainable Development of Forests (EOSD) initiative. This product, which is derived from Landsat satellite imagery, provides relatively high resolution coverage, but only very general information on forest composition (such as conifer, mixedwood, and deciduous). Here we link the CanFI and EOSD products using a spatial randomization technique to distribute the forest composition information in CanFI to the forest cover classes in EOSD. The resultant geospatial coverages provide randomized predictions of forest composition, which incorporate the fine-scale spatial detail of the EOSD product and agree in general terms with the species composition summaries from the original CanFI estimates. We describe the approach and provide illustrative results for selected major commercial tree species in Canada.