Role and influence of mycorrhizal fungi on radiocesium accumulation by plants

This review summarizes current knowledge on the contribution of mycorrhizal fungi to radiocesium immobilization and plant accumulation. These root symbionts develop extended hyphae in soils and readily contribute to the soil-to-plant transfer of some nutrients. Available data show that ecto-mycorrhizal (ECM) fungi can accumulate high concentration of radiocesium in their extraradical phase while radiocesium uptake and accumulation by arbuscular mycorrhizal (AM) fungi is limited. Yet, both ECM and AM fungi can transport radiocesium to their host plants, but this transport is low. In addition, mycorrhizal fungi could thus either store radiocesium in their intraradical phase or limit its root-to-shoot translocation. The review discusses the impact of soil characteristics, and fungal and plant transporters on radiocesium uptake and accumulation in plants, as well as the potential role of mycorrhizal fungi in phytoremediation strategies.     

Biodiversity on Swedish pastures: estimating biodiversity production costs

This paper estimates the costs of producing biological diversity on Swedish permanent grasslands. A simple model is introduced where biodiversity on pastures is produced using grazing animals. On the pastures, the grazing animals create a sufficient grazing pressure to lead to an environment that suits many rare and red-listed species. Two types of pastures are investigated: semi-natural and cultivated. Biological diversity produced on a pasture is estimated by combining a biodiversity indicator, which measures the quality of the land, with the size of the pasture. Biodiversity is, in this context, a quantitative measure where a given quantity can be produced either by small area with high quality or a larger area with lower quality. Two areas in different parts of Sweden are investigated. Box-Cox transformations, which provide flexible functional forms, are used in the empirical analysis and the results indicate that the biodiversity production costs differ between the regions. The major contribution of this paper is that it develops and tests a method of estimating biodiversity production costs on permanent pastures when biodiversity quality differs between pastures. If the method were to be used with cost data, that were more thoroughly collected and covered additional production areas, biodiversity cost functions could be estimated and used in applied policy work.     

Transaction costs and agri-environmental policy measures: are preferences influencing policy implementation?

This paper investigates whether the level of transaction costs of a Swedish agri-environmental policy measure is attributable to technical factors or whether political factors, such as lobby groups and political majorities at the county level, influence the costs. A previous study indicated that political factors may influence the level of transaction costs, but the extreme bounds analysis performed in this paper reveals that those results are fragile. It shows that three of the technical variables are robust with respect to model specifications but that none of the political variables are. Thus, no evidence can be found that political factors influence the level of transaction costs.     

Presentation and analysis of a model simulating epilimnetic and hypolimnetic temperatures in lakes

An important factor in aquatic modelling is water temperature. This is especially true for dimictic lakes where stratification and mixing influence many processes and variables, such as oxygen conditions, lake water retention time, etc. This paper evaluates and improves an existing method to predict water temperatures developed by Håkanson ,1996 (Ecol. Model., 88:157–181). The method is incorporated in a model simulating water temperatures in epilimnion and hypolimnion. The model is calibrated and validated against an extensive set of empirical data. It is driven by readily available parameters, e.g. latitude, continentality and altitude. The predictive power, especially for the epilimnetic temperature, is such that the model could be used as a sub-model in many models concerning lake ecosystems. However, the model has only been tested for Swedish lakes covering a relatively narrow range in terms of latitude, longitude and altitude and it would be interesting to investigate if this approach also holds for other parts of the world. As an example of how the model can be used in practise, a simulation of retention of caesium in lake water, using the temperature model as a sub-model, is presented.     

Costs and consequences of variation in the size of ruff leks

Summary We studied 13 ruff leks in a small region on the island of Gotland (Sweden) to investigate the effect of lek size on the costs and benefits of lekking for individual males. Male ruffs occur in two behaviourally and morphologically distinct forms, independents (residents plus marginals) and satellites, whose costs and benefits we have assessed separately. These ruff leks had from 1–10 resident (territory-holding) males and were visited daily by satellites, marginals and females from 5–25 May, when most copulations occurred. We used the average number of independent males, counted during censuses taken every 5 min during 2-h observation periods at each lek, as an index of mean lek size. Per independent male, the numbers of both satellites and females increased significantly with mean lek size. Female arrival rate and attendance (total female-minutes) also increased significantly with mean lek size as did the average per capita rate of mating success for resident males (that of satellites was not quite significant). Thus, the dispersion of both of these male categories did not appear to fit an ideal free distribution with respect to mating success. In addition, the number of independent-independent fights per independent and the rate of satellite-resident dyad formation per resident increased significantly with mean lek size. These results suggest that ruffs on larger leks enjoy higher mating success than those on smaller leks but also that costs increase with lek size. We suggest that independent males distribute themselves so as to maximize their own net benefits and that this factor can account for both the occurrence of ruff leks and the variation in their size. Correspondence to: J. Höglund     

Desorption kinetics studies on PAH-contaminated soil under varying temperatures

The purpose of this study was to investigate the effect of temperature on the release of polycyclic aromatic hydrocarbons (PAHs) from aged contaminated soil. The release of fluorene, phenanthrene, anthracene, fluoranthene and pyrene at 7, 15, 18 and 23 degrees C was studied using a column leaching method with a hydraulic retention time of 0.5 h. As the temperature declined from 23 to 7 degrees C the concentrations decreased by a factor of 11-12 for all the studied compounds except for anthracene, which only decreased by a factor 7. Rate constants at maximum release rate at the four studied temperatures were assessed. From temperature dependence studies, apparent activation energies of desorption, E*(des), were calculated. E*(des)-values appeared to be in the range of 105-137 kJ mol(-1) for the studied PAHs and increased with the LeBas molar volume of the compounds. The increase of E*(des) with increased molecular size indicates stronger sorption with increased hydrophobicity of the compounds.     

Recent trends of biocides in pikes of the Lake Päijänne

Pikes were sampled in May 1980 from three areas of the Lake Päijänne, Finland and analyzed for their contents of total mercury, methyl mercury, hexachlorobenzene (HCB), DDE, PCB and chlorophenolic residues. An improved method for methyl mercury determination was applied and 82–84 % methylation of mercury in pikes regardless of area or biological variation was observed. Statistical analysis with previous results from the same areas gave a very significant decreasing trend of mercury levels at all three areas from 1970 to 1980. Future levels of mercury in fish to be consumed as food could be estimated from the trend regression. The very low levels of DDE and PCB showed some increasing trend when the influence of fat contents was eliminated by covariance analysis. General appearance of HCB at sub-ppb level was observed. Also pentachlorophenol occured at 10–70 ppb (fresh weight) levels at all areas, but the other chlorophenols were abundant only at Tiirinselkä which is most contaminated by pulp bleaching effluents.     

Impact of arbuscular mycorrhizal fungi on uranium accumulation by plants

Contamination by uranium (U) occurs principally at U mining and processing sites. Uranium can have tremendous environmental consequences, as it is highly toxic to a broad range of organisms and can be dispersed in both terrestrial and aquatic environments. Remediation strategies of U-contaminated soils have included physical and chemical procedures, which may be beneficial, but are costly and can lead to further environmental damage. Phytoremediation has been proposed as a promising alternative, which relies on the capacity of plants and their associated microorganisms to stabilize or extract contaminants from soils. In this paper, we review the role of a group of plant symbiotic fungi, i.e. arbuscular mycorrhizal fungi, which constitute an essential link between the soil and the roots. These fungi participate in U immobilization in soils and within plant roots and they can reduce root-to-shoot translocation of U. However, there is a need to evaluate these observations in terms of their importance for phytostabilization strategies.     

A column method for determination of leaching of polycyclic aromatic hydrocarbons from aged contaminated soil

In this study a column leaching method for investigation of hydrophobic organic contaminants (HOCs) leaching from soil was developed. The method set-up is based on a recycled flow of sterile water through a soil column with a sedimentation chamber mounted on top of the column, in connection with on-line filtration. The combination of a sedimentation chamber and an on-line filtration enables the measurement of leaching concentrations from contaminated materials consisting of very fine particle fractions. In addition, by using on-line solid phase extraction, minute amounts of leaching HOCs may be captured and quantified with high accuracy and reproducibility. The method was applied successfully on a contaminated aged soil sample and the leaching behavior of seven PAHs, with three to six aromatic rings, was monitored for more than 1600 h under saturated conditions. The tested PAHs were fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)pyrene and benzo(ghi)perylene. The method proved to be reliable and capable of providing data on leachable amounts of the PAHs under field-like conditions and over a longer period of time. The results indicated low availability of the studied contaminants since only a minor fraction (0.3%) of the initial amount of PAHs in the soil was removed during the experiment (liquid/solid-ratio of 700 l/kg). Thus PAHs in aged contaminated soil are not to be expected to be released to any great extent only by leaching with water.