Should foliar cadmium concentrations be expressed on a dry weight or dry ash weight basis?

Foliar analysis is a valuable tool for evaluating the pollution status of forests. However, the use of foliar diagnosis in large-scale surveys is a complicated process owing to the high variability within the crown. The method used to express foliar concentrations has often been found to diminish the variability. The effect of the method used to express element concentrations on the spatial variability of cadmium (Cd) in the leaves of crack willow (Salix fragilis L.) was investigated by sampling the leaves of one willow at 292 locations in the crown, each sampling location having a volume of 0.027 m3 (0.3 m x 0.3 m x 0.3 m). Cadmium showed a distinct spatial trend in the crown of the tree. Concentrations as low as 2.4 mg kg(-1) dry weight (DW) or 23.1 mg kg(-1) dry ash weight (DAW) were obtained in the top of the crown, and 10.6 mg kg(-1) DW or 73.0 mg kg(-1) DAW in the bottom of the crown. The lower relative standard deviation and weaker correlation with the sampling height support the use of DAW in large-scale surveys especially. The lower variability of the DAW Cd concentration makes this variable less sensitive to fluctuations caused by differences in growing conditions and sampling methodology. However, the majority of publications in this field report metal concentrations on a DW basis. Therefore, the restrictions set on the use of results expressed on a DAW basis in large-scale surveys of foliar metal concentrations have to be offset against the advantages offered by a reduction of the variability in metal concentrations.     

Monod kinetics rather than a first-order degradation model explains atrazine fate in soil mini-columns: Implications for pesticide fate modelling

Pesticide transport models commonly assume first-order pesticide degradation kinetics for describing reactive transport in soil. This assumption was assessed in mini-column studies with associated batch degradation tests. Soil mini-columns were irrigated with atrazine in two intermittent steps of about 30 days separated by 161 days application of artificial rain water. Atrazine concentration in the effluent peaked to that of the influent concentration after initial break-through but sharply decreased while influx was sustained, suggesting a degradation lag phase. The same pattern was displayed in the second step but peak height and percentage of atrazine recovered in the effluent were lower. A Monod model with biomass decay was successfully calibrated to this data. The model was successfully evaluated against batch degradation data and mini-column experiments at lower flow rate. The study suggested that first-order degradation models may underestimate risk of pesticide leaching if the pesticide degradation potential needs amplification during degradation.     

Effect of vegetation type on throughfall deposition and seepage flux

This paper compares different vegetation types (coniferous and deciduous forest, grassed and pure heathland) in terms of input (throughfall deposition) and output (seepage flux) in a region with intermediate nitrogen load (+/-20kg Nha(-1)y(-1) via bulk precipitation) in comparable conditions in north Belgium. Coniferous forest (two plots Pinus sylvestris and two plots Pinus nigra) received significantly higher nitrogen and sulphur throughfall deposition than deciduous forest and heathland. Grassed and pure heathland had significantly highest throughfall quantities of Ca(2+) and Mg(2+), respectively. The observed differences in throughfall deposition between the different vegetation types were not univocally reflected in the ion seepage flux. Considerable seepage fluxes of NO(3)(-), SO(4)(2-), Ca(2+) and Al(III) were only found under the P. nigra plots. We discuss our hypothesis that the P. nigra forests already evolved to a situation of N saturation, while the other vegetation types did not.     

A multi-objective optimization framework for surfactant-enhanced remediation of DNAPL contaminations

The occurrence of Dense Non-Aqueous Phase Liquid (DNAPL) contaminations in the subsurface is a threat for drinkwater resources in the western world. Surfactant-Enhanced Aquifer Remediation (SEAR) is widely considered as one of the most promising techniques to remediate DNAPL contaminations in-situ, be it with considerable additional costs compared to classical pump-and-treat remediations. A cost-effective design of the remediation set-up is therefore essential. In this work, a pilot SEAR test is executed at a DNAPL contaminated site in Belgium in order to collect data for the calibration of a multi-phase multi-component model. The calibrated model is used to assess a series of scenario-analyses for the full-scale remediation of the site. The remediation variables that were varied were the injection and extraction rate, the injection and extraction duration, and the surfactant injection concentrations. A constrained multi-objective optimization of the model was applied to obtain a Pareto set of optimal remediation strategies with different weights for the two objectives of the remediation: (i) the maximal removal of DNAPL and (ii) a total minimal cost. These Pareto curves can help decision makers to select an optimal remediation strategy in terms of cost and remediation efficiency. The Pareto front shows a considerable trade-off between the total remediation cost and the removed DNAPL mass.     

Dynamic preservation of the coastline in the Netherlands

In 1990, the Government and Parliament of the Netherlands decided on a new national policy for coastal defence. To ensure the enduring safety of the low-lying polders as well as the sustainable preservation of the coastal dunes, it was decided to maintain the coastline in its 1990 position. The main method for coastline preservation in the Netherlands is beach nourishment. Since 1991, approximately 7 million m³ of sand is added to the Dutch beaches annually. From an evaluation study of sand nourishment projects it is concluded that nourishment is an effective and efficient method to preserve the coastline. The evaluation study also proves that nourishment projects should be ‘tailor-made’, taking the local morphological and hydraulic conditions into account. The first results of an experimental shoreface nourishment are discussed. The choice for nourishment as the principal method to combat erosion is well in line with the intention to restore the natural dynamics of the dune-coast in the Netherlands. The key probably is a less strict policy with regard to the maintenance of the foredunes. Plans for the development of typical coastal features such as slufters^*, wash-overs, blow-outs and mobile dunes are currently under discussion. A slufter is a breakthrough in the first dune-ridge whereby the sea invades former dune slacks or beach plains situated behind the duneridge. In this way a tidal marsh is formed within the dune zone.     

Ergonomic analysis of working postures using OWAS in semi-trailer assembly,applying an individual sampling strategy

In semi-trailer assembly, workers are exposed to several physical risk factors. Awkward working postures have not yet been investigated in semi-trailer assembly, although they are known to be a major risk factor for musculoskeletal disorders. We therefore conducted a comprehensive ergonomic analysis of working postures using the Ovako working posture analysing system (OWAS), with an individual sampling strategy. The postural load in semi-trailer assembly was assessed on the basis of 20,601 observations of 63 workers executing a representative set of nine work tasks. According to the OWAS, the postural load of various working postures and body part positions may have a harmful effect on the musculoskeletal system. We therefore give examples of corrective measures that could improve awkward working postures. Applying an individual sampling strategy was revealed to have advantages over a collective strategy, so this is recommended for future ergonomic analyses.     

Uncertainty propagation in vegetation distribution models based on ensemble classifiers

Ensemble learning techniques are increasingly applied for species and vegetation distribution modelling, often resulting in more accurate predictions. At the same time, uncertainty assessment of distribution models is gaining attention. In this study, Random Forests, an ensemble learning technique, is selected for vegetation distribution modelling based on environmental variables. The impact of two important sources of uncertainty, that is the uncertainty on spatial interpolation of environmental variables and the uncertainty on species clustering into vegetation types, is quantified based on sequential Gaussian simulation and pseudo-randomization tests, respectively. An empirical assessment of the uncertainty propagation to the distribution modelling results indicated a gradual decrease in performance with increasing input uncertainty. The test set error ranged from 30.83% to 52.63% and from 30.83% to 83.62%, when the uncertainty ranges on spatial interpolation and on vegetation clustering, respectively, were fully covered. Shannon’s entropy, which is proposed as a measure for uncertainty of ensemble predictions, revealed a similar increasing trend in prediction uncertainty. The implications of these results in an empirical distribution modelling framework are further discussed with respect to monitoring setup, spatial interpolation and species clustering.     

Preparation and certification of a reference material on PCBs in pig fat and its application in quality control in monitoring laboratories during the Belgian "PCB-crisis"

In this article, the production and validation of a new certified reference material "PCBs in animal fat" for the control of the maximum level of 200 ng/g setup by the European Communities for veterinary products from Belgium is described. Three materials are established: a blank, one material with about 100 ng/g and one with about 200 ng/g (sum of seven PCBs). Data on the production and certification are given. Additionally, this material was used as an unknown test material in the quality assurance program of the Belgium meat monitoring system (before the certification of the material). While the certification was performed with an uncertainty of less than 10%, the round robin exhibited larger deviations. However, these deviations were less than 20% for most of the 30 participating laboratories. Only two had significantly higher deviations.     

Transient population dynamics in periodic matrix models: methodology and effects of cyclic permutations

Many biological populations are subject to periodically changing environments such as years with or without fire, or rotation of crop types. The dynamics and management options for such populations are frequently investigated using periodic matrix models. However the analysis is usually limited to long-term results (asymptotic population growth rate and its sensitivity to perturbations of vital rates). In non-periodic matrix models it has been shown that long-term results may be misleading as populations are rarely in their stable structure. We therefore develop methods to analyze transient dynamics of periodic matrix models. In particular, we show how to calculate the effects of perturbations on population size within and at the end of environmental cycles. Using a model of a weed population subject to a crop rotation, we show that different cyclic permutations produce different patterns of sensitivity of population size and different population sizes. By examining how the starting environment interacts with the initial conditions, we explain how different patterns arise. Such understanding is critical to developing effective management and monitoring strategies for populations subject to periodically recurring environments.     

Assessment of natural coagulants to remediate Tunisian textile wastewater by combining physicochemical,analytical, and toxicological data

Environmental Science and Pollution Research - Due to the complexity and variability of textile wastewater composition, a constant search for new treatment strategies that are efficient,...