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: hjwang78@gmail.com

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

4

5

6

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

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0 1 2 3 4 5

5

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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

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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