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Forest floor leachate fluxes under six tree species on a metal contaminated site

EUROSOIL 2012, Bari 3 July. Forest floor leachate fluxes under six tree species on a metal contaminated site. Lotte Van Nevel, Jan Mertens & Kris Verheyen. Ghent University Forest & Nature Lab. Cd contaminated soils in Flanders (OVAM , 2007). Metal pollution problem.

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Forest floor leachate fluxes under six tree species on a metal contaminated site

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  1. EUROSOIL 2012, Bari 3 July Forest floor leachate fluxes under six tree species on a metal contaminated site Lotte Van Nevel, Jan Mertens & Kris Verheyen Ghent University Forest & Nature Lab

  2. Cd contaminated soils in Flanders (OVAM, 2007) Metal pollution problem • Campine region, NE Belgium • Zn and Pb refineries during ± 100 years 1950: emission 340 kg Cd / day !! 1992: emission 0,04 kg Cd / day

  3. Metal pollution problem • Campine region, NE Belgium • Zn and Pb refineries during ± 100 years 1950: emission 340 kg Cd / day !! 1992: emission 0,04 kg Cd / day • severe historical pollution problem, despite reductions of metal emissions in the last decades => diffuse pollution over 700 km² (Be + Nl); mainly Cd, Zn, Pb • poor sandy soils: low buffering capacity => risks of metal leaching and spreading • Phytoremediation

  4. Phytoremediation • Definition (Garbisu & Alkorta, 2001): Phytoremediation is a technique that involves the use of plants for the removal of pollutants from the environment or to render them harmless • extraction versus stabilization

  5. Phytoremediation • Definition (Garbisu & Alkorta, 2001): Phytoremediation is a technique that involves the use of plants for the removal of pollutants from the environment or to render them harmless • extraction versus stabilization ET input via litterfall litter decomposition accumulation uptake leaching

  6. Research objectives • Tree species effects on mobilization of Cd and Zn • possibilities and limitations for phytostabilization • how to minimize the risk of metal dispersion in the ecosystem? • above- and belowground metal dispersion • In situ research • 6 tree species: oak (Quercus spp.), aspen (Populus tremula), silver birch (Betula pendula), black locust (Robinia pseudoacacia), Scots pine (Pinus sylvestris), Douglas fir (Pseudotsuga menziesii)

  7. Study site 203 ha

  8. Study site

  9. Methods • Leaf litter • litterfall traps • Cd, Zn, base cations, C, N

  10. Methods • Leaf litter • litterfall traps • Cd, Zn, base cations, C, N • Forest floor leachates • zero-tension lysimeters • Cd, Zn, base cations, DOC, pH

  11. Methods

  12. Results • Leaf litter: Cd & Zn normal Cd range in leaves = up to 2.4 ppm (Alloway, 1995) toxic Cd range in leaves = 5 - 30 ppm (Kabata-Pendias & Pendias, 1992)

  13. Results • Leaf litter: Cd & Zn normal – toxic Zn range in leaves: ± 400 ppm (Alloway, 1995)

  14. Results • Leaf litter: base cations and C/N ratio  litter quality: low versus rich b b b a a a a a a a a a

  15. Results • Forest floor leachates • Metal accumulating species => higher metal fluxes in leachate? • Low litter quality => DOC and H+ leachate fluxes ? => base cation leachate fluxes ? soil acidification metal mobility risk for groundwater pollution

  16. Results • Forest floor leachates: fluxes of DOC, H+, base cations

  17. Results • Forest floor leachates: fluxes of DOC, H+, base cations • Scots pine & oak: • high DOC & H+ fluxes • low base cation fluxes • aspen: • extremely low H+fluxes (130 x less than oak) • low DOC fluxes • high base cation fluxes metal mobilization metal mobilization

  18. Results • Forest floor leachates: Cd & Zn fluxes

  19. Results • Forest floor leachates: Cd & Zn fluxes • Total Cd fluxes slightly higher under aspen • No tree species effect on Zn fluxes • differences between aspen and other species forest floor leachate << leaf litterfall • high abundance of earthworms under aspen ? • Dissolved Cd fluxes • differences between aspen and other species almost disappeared • extremely low H+ fluxes (high pH) in aspen leachate

  20. Conclusions • Aspen accumulates Cd & Zn in leaves • aboveground dispersion risks • Cd & Zn fluxes in aspen leachate lower than expected • belowground dispersion risks lower than expected? • DOC, H+, base cation fluxes in leachates: significant tree species effects • Scots pine & oak: metal mobilizing • aspen: metal immobilizing • other species: intermediate • Implications for phytostabilization? • Further research is essential

  21. Thankyou for your attention! Questions? Lotte.VanNevel@UGent.be

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