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ABSTRACT: Extractability of Cd, Cr, Cu, Ni, Pb, and Zn in a dredged sediment disposal site was assessed using single extraction procedures (H2O; 0.01 M CaCl2; 1 M NH4OAc; NH4OAc-EDTA; CaCl2-TEA-DTPA). Only Cd and Zn were found to exceed statutory threshold values for total content. The field was planted with Salix viminalis "Orm" and accumulation of heavy metals in bark, leaves, roots, and wood was evaluated at seven sampling locations along an observed gradient in texture and pollution. Biomass production was high, ranging from 13.2 to 17.8 t ha(-1) y(-1) dry weight. Metal accumulation in aboveground plant parts was low, amounting to the following annually extracted mass of metals per ha: 5034 g Zn, 83 g Cd, 145 g Cu, 83 g Pb, 12 g Ni and 6 g Cr. The use of accumulating clones and the use of soil amendments might enhance extraction efficiency in future research.
Environmental Pollution 10/2005; 137(2):354-64. · 3.75 Impact Factor
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ABSTRACT: Establishing fast growing willow stands on land disposed contaminated dredged sediment can result in the revaluation of this material and opens possibilities for phytoremediation. A field trial was designed to assess the impact of planting a willow stand (Salix viminalis L. 'Orm') on the dissipation of organic contaminants (mineral oil and PAHs) in dredged sediment. In addition, the accumulation of heavy metals (Cd, Cu, Pb and Zn) in the biomass was determined. After 1.5 years, a significant decrease of 57% in the mineral oil concentration in the sediment planted with willow was observed. Degradation of mineral oil in sediment which was left fallow, was only 15%. The mineral oil degradation under willow was most pronounced (79%) in the root zone of the stand. In the sediment which was left fallow there was a significant reduction of the total PAH content by 32% compared with a 23% reduction in the planted sediment. The moderate and selective metal uptake, measured in this study, limits the prospects for phytoextraction of metals from dredged sediment.
Environmental Pollution 02/2003; 126(2):275-82. · 3.75 Impact Factor
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ABSTRACT: 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.
Journal of Environmental Monitoring 07/2002; 4(3):408-12. · 1.99 Impact Factor
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Mededelingen (Rijksuniversiteit te Gent. Fakulteit van de Landbouwkundige en Toegepaste Biologische Wetenschappen) 02/2001; 66(4):129-33.
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Mededelingen (Rijksuniversiteit te Gent. Fakulteit van de Landbouwkundige en Toegepaste Biologische Wetenschappen) 02/2001; 66(4):135-9.
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Mededelingen (Rijksuniversiteit te Gent. Fakulteit van de Landbouwkundige en Toegepaste Biologische Wetenschappen) 02/2001; 66(4):141-6.
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ABSTRACT: Disposal sites for dredged material are often polluted with heavy metals. The uptake of Cd and Zn by small mammals and willow trees was assessed on three sites with a different pollution degree. Detailed soil sampling showed a huge variation in soil characteristics within the sites, typical for disposal sites for dredged material. This variation made risk assessment and interpretation of soil chemical analyses complicated. Small mammals were thought to give a more integral description of the contaminant level because they cover a large area. Cd concentrations in small mammals were elevated compared with background levels whereas Zn concentrations were rather low. There were no significant differences between sites in Cd or Zn levels in animals. Leaf analysis showed a clear response to the pollution degree of the sites. The calculations using the BIOMAG model indicated that the Cd of the soil caused low risk for predators. However, the elevated Cd and Zn concentrations in the willow leaves on the polluted sites and the high Cd concentrations in the small mammals on all sites indicated that ecosystem development should be carefully considered.
Environmental Pollution 02/2001; 115(1):17-22. · 3.75 Impact Factor
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ABSTRACT: Willow (Salix spp.) stands are often proposed as vegetation covers for the restoration and stabilization of contaminated and derelict land. Planting willows on dredged sediment disposal sites for biomass production can be an alternative to traditional capping techniques. However, with the introduction of willow stands on dredged sediment disposal sites, the possibility of increased contaminant availability in the root zone must be acknowledged as it can increase the risk of leaching. Two trials investigated the availability of Cd, Zn, Cu, and Pb in the root zones of willows grown on contaminated sediment. To assess the effects of willow root growth on metal extractability and mobility, bulk and rhizosphere sediment samples were extracted with deionized water, ammonium acetate at pH 7, and ammonium acetate-EDTA at pH 4.65. A rhizobox experiment was used to investigate the short-term effect of willow roots on metal availability in oxic and anoxic sediment. Longer-term effects were assessed in a field trial. The rhizobox trial showed that Cd, Zn, and Cu extractability in the rhizosphere increased while the opposite was observed for Pb. This was attributed to the increased willow-induced oxidation rate in the root zone as a result of aeration and evapotranspiration, which masked the direct chemical and biological influences of the willow roots. The field trial showed that Cu and Pb, but not Cd, were more available in the root zone after water and ammonium acetate (pH 7) extraction compared with the bulk sediment. Sediment in the root zone was better structured and aggregated and thus more permeable for downward water flows, causing leaching of a fraction of the metals and significantly lower total contents of Cd, Cu, and Pb. These findings indicate that a vegetation cover strategy to stabilize sediments can increase metal availability in the root zone and that potential metal losses to the environment should be considered.
Journal of Environmental Quality 33(3):976-83. · 2.32 Impact Factor
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ABSTRACT: Extractability of Cd, Cr, Cu, Ni, Pb, and Zn in a dredged sediment disposal site was assessed using single extraction procedures (H2O; 0.01 M CaCl2; 1 M NH4OAc; NH4OAc-EDTA; CaCl2-TEA-DTPA). Only Cd and Zn were found to exceed statutory threshold values for total content. The field was planted with Salix viminalis “Orm” and accumulation of heavy metals in bark, leaves, roots, and wood was evaluated at seven sampling locations along an observed gradient in texture and pollution. Biomass production was high, ranging from 13.2 to 17.8 t ha−1 y−1 dry weight. Metal accumulation in aboveground plant parts was low, amounting to the following annually extracted mass of metals per ha: 5034 g Zn, 83 g Cd, 145 g Cu, 83 g Pb, 12 g Ni and 6 g Cr. The use of accumulating clones and the use of soil amendments might enhance extraction efficiency in future research.
Environmental Pollution.
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ABSTRACT: The combination of energy production from biomass with phytoremediation opens perspectives for bringing land with moderate metal contamination into safe and beneficial use. Small scale fixed bed downdraft gasifier installations (150 kWe–1 MWe) can be employed for on-site conversion of biomass to electricity and heat. To assess the fate of heavy metals, batch gasification operations were run in a small scale fixed bed downdraft gasifier (100 kW thermal power). The gasification of 1 kg of wood resulted in the production of 40 g of ashes, 1.2 kWh of electricity and 9 MJ of heat. Per kg dry mass of willow wood, 31 g bottom ashes, 7 g cyclone ashes, 2 g filter ashes, and 18 g DM of gasifier bed ashes were produced. Cd, Zn and Pb were enriched by a factor 7–100 in the fly ashes compared to the bottom ashes. Low mass recoveries (30–40%) were found for Cd, Cr, Ni and Pb. This was mainly attributed to measurement uncertainties. 60% and more of recovered Cd, Pb and Zn were present in the finer filter and cyclone ashes, while Cr, Cu and Ni were mainly found in the bottom ashes and to a lesser extent the bed ashes. The scrubber placed after the hot cyclone has an essential role in intercepting the more volatile heavy metals before combustion of the gas. The bottom ashes constituted the largest fraction and ideally should be recycled if limits for metal contents are met. Only Cd and Zn exceeded Flemish threshold values for use of this fraction as a fertilizer, albeit by a small margin. This leaves perspectives for future research to optimise process parameters towards the production of bottom ashes that can be recycled.
Biomass and Bioenergy.
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ABSTRACT: The periodic dredging of inland waterways and the subsequent disposal of the dredged sediment result in the continuous establishment of contaminated sites. As this dredged sediment is rich in nutrients, occupies extended areas and is often unsuitable for agriculture and public works due to the presence of contaminants, planting energy crops is one option for the remediation of this waste material. To evaluate dredged sediment as a substrate for growing willows, a disposal depot was successfully planted using rolls of connected willow rods (SALIMAT). Rods of a Salix fragilis clone and a Salix triandra clone were equally mixed in each mat. This SALIMAT proved to be an economic and effective planting technique for large areas of wet substrate. Leaf nutrient contents were determined to identify potential limiting growth factors Biomass production and tree survival over 4 years of stand development were assessed for three different planting spacings (10, 20 and ). Results of the foliar analyses indicated that both species were supplied with sufficient N, P, K and Ca to ensure optimal growth. The introduction of SALIMAT resulted in the rapid development of a high-density fast growing stand characterised by shoot densities of up to . An average annual production of DM/ha was measured. The mixture of the two clones did not result in a polyclonal stand as Salix triandra was suppressed by Salix fragilis. The development of a willow stand was unsuccessful on parts of the depot with a sand fraction of 60%.
Biomass and Bioenergy.
