forest floor leachate fluxes under six tree species on a metal contaminated site
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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
EUROSOIL 2012, Bari3 July
• Campine region, NE Belgium
• Zn and Pb refineries during ± 100 years 1950: emission 340 kg Cd / day !! 1992: emission 0,04 kg Cd / day
Metal pollution problem
Cd contaminated soils in Flanders (OVAM, 2007)
• 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
Metal pollution problem
• Definition (Garbisu & Alkorta, 2001):
Phytoremediation is a technique that involves the use of plants for the removal of pollutants from the environment orto render them harmless
• extraction versus stabilization
Phytoremediation
• Definition (Garbisu & Alkorta, 2001):
Phytoremediation is a technique that involves the use of plants for the removal of pollutants from the environment orto render them harmless
• extraction versus stabilization
Phytoremediation
ET
uptake
input via litterfall
accumulationlitter decomposition
leaching
• 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)
Research objectives
Study site
203 ha
Study site
• Leaf litter litterfall traps Cd, Zn, base cations, C, N
Methods
• Leaf litter litterfall traps Cd, Zn, base cations, C, N
• Forest floor leachates zero-tension lysimeters Cd, Zn, base cations, DOC, pH
Methods
Methods
• 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)
Results
silv
er b
irch
oak
blac
k lo
cust
aspe
n
Scot
s pi
ne
Dou
glas
fir0
4
8
12
16
Cd
conc
(m
g kg
-1)
0
1000
2000
3000
Zn c
onc
(mg
kg-1
)
• Leaf litter: Cd & Zn
normal – toxic Zn range in leaves: ± 400 ppm (Alloway, 1995)
Results
silv
er b
irch
oak
blac
k lo
cust
aspe
n
Scot
s pi
ne
Dou
glas
fir0
4
8
12
16
Cd
conc
(m
g kg
-1)
0
1000
2000
3000
Zn c
onc
(mg
kg-1
)
• Leaf litter: base cations and C/N ratio
litter quality: low versus rich
Resultssi
lver
birc
h
oak
blac
k lo
cust
aspe
n
Sco
ts p
ine
Dou
glas
fir0
400
800
1200
1600
2000
Bas
e ca
tion
conc
(m
eq k
g-1)
silv
er b
irch
oak
blac
k lo
cust
aspe
n
Sco
ts p
ine
Dou
glas
fir0
10
20
30
40
50
C:N
ratio
a a
a
a a
b
a aa
a
bb
• 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
Results
• Forest floor leachates: fluxes of DOC, H+, base cations
Results
0
1
2
3
diss
Zn
flux
(kg
ha-1
yr-1
)
a a
aa a
a
silv
er b
irch
oak
blac
k lo
cust
aspe
n
Sco
ts p
ine
Dou
glas
fir
0
40
80
120
H+ f
lux
(mol
ha-1
yr-1
)
ab
b
ab
a
ab
ab
0
50
100
150
200
DO
C fl
ux (k
g ha
-1 y
r-1)
a
b
aba
b
a
silv
er b
irch
oak
blac
k lo
cust
aspe
n
Sco
ts p
ine
Dou
glas
fir
0
2000
4000
6000
8000
10000
Bas
e ca
tion
flux
(eq
ha-1
yr-1
)
a
ab
bcc
a
a
0
10
20
30
diss
Cd
flux
(g h
a-1 y
r-1)
a abab
bab
ab
0
1
2
3
tot Z
n flu
x (k
g ha
-1 y
r-1)
a a
a
a
a
a
0
10
20
30
tot C
d flu
x (g
ha-1
yr-1
)
a
ab
bc
c
aba
• 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
Results
metal mobilization
metal mobilization
• Forest floor leachates: Cd & Zn fluxes
Results
0
1
2
3di
ss Z
n flu
x (k
g ha
-1 y
r-1)
a a
aa a
a
silv
er b
irch
oak
blac
k lo
cust
aspe
n
Sco
ts p
ine
Dou
glas
fir
0
40
80
120
H+ f
lux
(mol
ha-1
yr-1
)
ab
b
ab
a
ab
ab
0
50
100
150
200
DO
C fl
ux (k
g ha
-1 y
r-1)
a
b
aba
b
a
silv
er b
irch
oak
blac
k lo
cust
aspe
n
Sco
ts p
ine
Dou
glas
fir
0
2000
4000
6000
8000
10000
Bas
e ca
tion
flux
(eq
ha-1
yr-1
)
a
ab
bcc
a
a
0
10
20
30
diss
Cd
flux
(g h
a-1 y
r-1)
a abab
bab
ab
0
1
2
3
tot Z
n flu
x (k
g ha
-1 y
r-1)
a a
a
a
a
a
0
10
20
30
tot C
d flu
x (g
ha-1
yr-1
)
a
ab
bc
c
aba
0
1
2
3
diss
Zn
flux
(kg
ha-1
yr-1
)
a a
aa a
a
silv
er b
irch
oak
blac
k lo
cust
aspe
n
Sco
ts p
ine
Dou
glas
fir
0
40
80
120
H+ f
lux
(mol
ha-1
yr-1
)
ab
b
ab
a
ab
ab
0
50
100
150
200
DO
C fl
ux (k
g ha
-1 y
r-1)
a
b
aba
b
a
silv
er b
irch
oak
blac
k lo
cust
aspe
n
Sco
ts p
ine
Dou
glas
fir
0
2000
4000
6000
8000
10000
Bas
e ca
tion
flux
(eq
ha-1
yr-1
)
a
ab
bcc
a
a
0
10
20
30
diss
Cd
flux
(g h
a-1 y
r-1)
a abab
bab
ab
0
1
2
3
tot Z
n flu
x (k
g ha
-1 y
r-1)
a a
a
a
a
a
0
10
20
30
tot C
d flu
x (g
ha-1
yr-1
)
a
ab
bc
c
aba
0
1
2
3
diss
Zn
flux
(kg
ha-1
yr-1
)
a a
aa a
a
silv
er b
irch
oak
blac
k lo
cust
aspe
n
Sco
ts p
ine
Dou
glas
fir
0
40
80
120
H+ f
lux
(mol
ha-1
yr-1
)
ab
b
ab
a
ab
ab
0
50
100
150
200
DO
C fl
ux (k
g ha
-1 y
r-1)
a
b
aba
b
a
silv
er b
irch
oak
blac
k lo
cust
aspe
n
Sco
ts p
ine
Dou
glas
fir
0
2000
4000
6000
8000
10000
Bas
e ca
tion
flux
(eq
ha-1
yr-1
)
a
ab
bcc
a
a
0
10
20
30
diss
Cd
flux
(g h
a-1 y
r-1)
a abab
bab
ab
0
1
2
3
tot Z
n flu
x (k
g ha
-1 y
r-1)
a a
a
a
a
a
0
10
20
30
tot C
d flu
x (g
ha-1
yr-1
)
a
ab
bc
c
aba
• 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 speciesforest 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
Results
• 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
Conclusions
