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Presentation given at the Goldschmidt Conference in Florence
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© University of Reading 2013 www.reading.ac.uk
Geography and Environmental Science
August 28, 2013
The role of earthworm-produced CaCO3 in the terrestrial carbon cycle Mark E. Hodson, Emma A. A. Versteegh & Stuart Black
The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
Earthworm secreted CaCO3 granules
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Canti (2007) Versteegh et al. (2013)
The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
How are the granules produced?
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Darwin (1881) / Canti & Piearce (2003)
• Calciferous glands
• Milky fluid
• → CaCO3 concretions
• → granules
The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
Why do they produce them?
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• “It is probable that they primarily serve as organs of excretion, and secondarily as an aid to digestion” (Darwin, 1881)
• Egg formation?
• Triturate food in gizzard?
• Absorption of food products?
• Water regulation → evolutionary adaptation to terrestrial habitat?
• Excretion of toxic cations?
• pH regulation / eliminate excess CO2?
The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
What are they made of?
• Calcite
• Amorphous calcium carbonate (ACC)
• (some aragonite / vaterite)
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Backscattered SEM
Electron backscatter diffraction (EBSD) crystallographic orientation
The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
Questions
• What is the carbon sequestration potential of earthworms? – Influence of temperature – Influence of [CO2] on CaCO3 production rates
• What are the sources of carbon in earthworm CaCO3 granules? – Food / organic matter – CO2
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
Lumbricus terrestris – lob worm
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
Experiment 1
• 3 soils
• 3 types of water (England, Fiji, Norway)
• 5 temperatures (3, 10, 16, 18, 20 °C)
• 3 weeks acclimatisation
• 1 month
• 6 replicates
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
Experiment 2
• 1soil; 1 type of water, 1 temperature (16 °C)
• 4 [CO2] (low, medium, high, ambient)
• 3 weeks acclimatisation + 1 month experiment
• 6 replicates
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
Analyses • CaCO3 production
• [CO2] (ppm)
• δ13C values of: – Soil organic matter – Food (horse manure) – Soil CO2
– Earthworm body wall tissue
– Calciferous gland tissue – Milky fluid – Granules in pouches – Granules in soil
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
A δ18O-based palaeothermometer
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1000 ln α = 20.21 (103 T-1) - 38.58
The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
At what rate are granules produced?
• 0.8-2.9 mg/individual/day
• Larger worms produce more
• Well-fed worms produce more
• High-pH soils yield more
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Lambkin et al. (2011)
The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
CaCO3 production and temperature
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
CO2 concentrations
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
CaCO3 production and CO2
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
δ13C values
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
δ13C values of CO2
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
δ13C values of earthworm tissues
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
δ13C values of CaCO3
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
δ13C values of CO2 and CaCO3
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
Contribution to C sequestration • CaCO3 production: 0.49-3.64
mg/individual/day
• Typical population density: ~15 individuals/m2 (max 62)
• CaCO3 production: ~113 kg/ha/y
• C sequestration: ~45 kg C/y/ha (max. 329)
• ~ 1% of total soil carbon
• < 0.5 % of UK C emissions
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
Conclusions • CaCO3 production by L. terrestris increases with temperature;
• CaCO3 production is higher at higher [CO2];
• There is no relationship between δ13C values of earthworm tissues and the CaCO3 produced;
• A decrease in δ13C values of milky fluid → granules in pouches → granules in soil probably reflects transformation of ACC into calcite;
• δ13C values of soil CO2 and granule CaCO3 are correlated, indicating a direct contribution of CO2 to the granules;
• Earthworm-produced CaCO3 forms only a minor contribution to C sequestration in soils.
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The role of earthworm-produced CaCO3 in the terrestrial carbon cycle
Thank you!
Questions?
Versteegh EAA, Black S, Canti MG, Hodson ME (2013) Earthworm-produced calcite granules: a new terrestrial palaeothermometer? Geochimica et Cosmochimica Acta, 10.1016/j.gca.2013.06.020
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