DOES AN 'IRON-GATE' REGULATE DROUGHT EFFECTS ON … Wang.pdfSchematic diagram of the iron trap at...
Transcript of DOES AN 'IRON-GATE' REGULATE DROUGHT EFFECTS ON … Wang.pdfSchematic diagram of the iron trap at...
DOES AN 'IRON-GATE' REGULATE DROUGHT EFFECTS ON PEAT
DECOMPOSITION?
Hongjun Wang, Mark River, Curtis J. Richardson
Duke University Wetland Center, Nicholas School of the Environment, Box 90333, Duke University, Durham, NC 27708.
Email: [email protected]
K Lalonde et al. Nature 483, 198-200, doi:10.1038/nature10855, 2012
Control-corrected percentage of the total sedimentorganic carbon bound to reactive iron phases.
“Rusty Sink” in mineral soil
21.5% of OC bound to Fe
OC: 0.3-7%
0
1
2
3
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7
OC
%
∗ Barber et al., Scientific Report, 7:366, DOI:10.1038/s41598-017-00494-0, 2017
Co-localized C and Fe
Scan Maps for carbon(a) and iron (b)
∗ Van Bodegom et al.,
Biogeochemistry 76, 69-83, 2005
Fe2+ stimulates phenol oxidase activity and C decomposition
∗ Emsens et al., Plos One 11, DOI:10.1371/journal.pone.0153166, 2016
Fe stimulates C mobilization in rewetted fens
∗ Wang et al. Nat. Commun. 8, DOI: 10.1038/ncomms15972 (2017)
“Iron gate”— carbon preservation in organic-rich wetlands
OC > 20%
“More important in mineral-rich and/or vascular plant-dominated wetlands”
Schematic diagram of the iron trap at redox interfaces depicting the export of anoxic peat pore water, oxidation of iron at the oxic surface, and
coprecipitation of terrestrial DOM with Fe(III).
Thomas Riedel et al. PNAS 2013;110:25:10101-10105
©2013 by National Academy of Sciences
∗ Can iron protect carbon in organic-rich wetlands, peatlands in particular?∗ Does Fe oxidation promoted lignin derivatives sorption
and decrease in phenol oxidase activity preserve carbon? A black-box experiment needed
∗ Does iron oxidation reduce phenolics and increase decomposition? (~100 times higher in phenolics)
Scientific questions
∗ (1) A ‘black-box’ experiment by adding FeSO4or K2SO4as control (0, 2.5, and 5 mmol L-1 FeSO4 or K2SO4) to a high-lignin peatland soil to test how carbon decomposition responds to iron and iron oxidation,
∗ (2) A physical evidence test by running scanning electron microscopy (SEM) to check whether, similar to mineral sediment, iron film forms outside of carbon to protect carbon in peatlands.
Experimental test
∗ No Fe2+ detected after drainage
An “iron key”
0 1 2 3 4 5
0
50
100
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200
250
0 1 2 3 4 5
5
10
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Ph
enol
ics
(µg
C g
-1 s
oil)
Added iron (m mol L-1)
Phenolics
0.0
0.5
1.0
1.5 Ferrus iron
Ferru
s iro
n (m
g g-1
soi
l)
Soil
resp
iratio
n (µ
g C
O2 h
r-1 g
-1 s
oil)
Added iron (m mol L-1)
Flooded Drought
Scanning Electron Microscope (SEM) image of framboidal pyrite (FeS2) in a sawgrass-dominated peatland (bog) in the Florida Everglades.
∗ Percentage of USGS peat samples in USA, grouped by percentage of mineral content, containing enough element sulfur to form pyrite (S/Fe>2).
Fe-Sulfur-Carbon
0.0 0.5 1.0 1.5 2.0 2.50.00
0.25
0.50
0.75
1.00
1.25
S:Fe <2
Fe (m
mol
/g)
S (m mol/g)
S:Fe >2 56%
S:Fe=2
0 10 20 30 40 50 60 700
20
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60
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100
Sam
ples
with
S/F
e >
2 (%
)
Mineral content (%)
Data from USGS, n=696
Summary
1) Rusty Sink in Mineral soil
Low phenolics, SOC and sulfur, high iron
Iron coating, chelation, co-precipitation
2) An ‘iron key’ not ‘iron gate’ in organic-rich soil
High phenolics, SOC and sulfur, low iron
Iron-phenolics co-precipitation—loss of microbial inhibitor More carbon expose to microbes