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

Transcription

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 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 Cd contaminated soils in Flanders (OVAM, 2007)

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): ET Phytoremediation is a technique that involves the use of plants for the removal of pollutants from the environment or to render them harmless input via litterfall extraction versus stabilization accumulation litter decomposition 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)

7 203 ha Study site

8 Study site

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

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11 Methods Leaf litter litterfall traps Cd, Zn, base cations, C, N Forest floor leachates zero tension lysimeters Cd, Zn, base cations, DOC, ph

12 Methods

13 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)

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

15 Results Leaf litter: base cations and C/N ratio b b a a a b a a a a a a litter quality: low versus rich

16 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

17 Results Forest floor leachates: fluxes of DOC, H +, base cations

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

19 Results Forest floor leachates: Cd & Zn fluxes

20 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

21 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

22 Thank you for your attention! Questions?