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The Inorganic Carbon CycleThe Inorganic Carbon Cycle
GyörgyGyörgy VÁRALLYAYVÁRALLYAY
Research Institute for Soil Science and Agricultural Chemistry of the Hungarian Academy of Sciences
Budapest, Hungary
IV. Alps-Adria Scientific Workshop 28 February–5 March, 2005, Portorož, Slovenia
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atmosphereatmosphere
biospherebiosphere
soilsoilhydrospherehydrosphere
lithospherelithosphere
Várallyay nyománVárallyay nyomán
Sphere interrelationshipsSphere interrelationships
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The assessment of soil carbon pools and soil carbon pools and fluxesfluxes includes both soil organicorganic carbon (SOC) and soil inorganicinorganic carbon (SIC) pools
• their dynamics
• their interactions with aquatic and biotic (primarily vegetational) regimes
• their C-sequestration „activities”
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Major C reservoirs in the Earth SystemMajor C reservoirs in the Earth System
SSIICC SSOOCC TToottaall CC SSpphheerree 11001155 gg
AAttmmoosspphheerree 776600 –– 776600
BBiioosspphheerree –– 556600 556600
PPeeddoosspphheerree 11 770000 11 550000 33 220000
HHyyddrroosspphheerree 3388 000000 11 000000 3399 000000
LLiitthhoosspphheerree 4488 000000 000000 1177 000000 000000 6655 000000 000000
(Drees et al., 2001)(Drees et al., 2001)
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Soil C pool of world soilsSoil C pool of world soils
SOC SIC Soil order Density Pool Density Pool
Area (Mha)
(tons/ha) (bill. tons) (tons/ha) (bill. tons)
Alfisols 1262 125 158 34 43 Andisols 91 220 20 0 0 Aridisols 1570 38 59 290 456 Entisols 2114 42 90 124 263 Gelisols 1126 281 316 6 7 Histosols 153 1170 179 0 0 Inceptisols 1286 148 4190 26 34 Mollisols 901 134 121 96 116 Oxisols 981 128 126 0 0 Rocky land 1308 17 22 0 0 Shifting sand 532 4 2 9 5 Spodosols 335 191 64 0 0 Ultisols 1105 124 137 0 0 Vertisols 316 133 42 50 21 Total 13,083 1526 945
(adapted from Eswaran et al., 2000)
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A simplified representation of the global carbon cycle.
Balance: 218.5 Pg/year enter the atmosphere 215 Pg/year is removed from the atmosphere.
increasing CO2 concentration
(in Pg=1015g)
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The long-term geochemical cycle of carbon at the surface of the Earth
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Soils and near-surface geological formations – as a biogeochemical interface between the spheres of the Earth system – play a strategic role in the global C balance.
The SIC poolThe SIC pool is considerably higher, but more stable and less reactive than the SOC pool.
CaCO3
MgCO3
Na2CO3
The importance of SIC in the global C balance is often ignored, in spite of the fact that pedogenic processes, as
carbonate leaching are important factors silicate-mineral weathering of carbon sequestrationcarbon sequestration
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Soil Inorganic Carbon Soil Inorganic Carbon –– SIC SIC
• primary or lithogenic carbonatesprimary or lithogenic carbonates
(originating from the parent rock material)
dissolution water
translocation by (organic) acids
transport CO2 (soil atmosphere)
+ soil Ca2+ , Mg2+, Na+
• secondary or pedogenic carbonatessecondary or pedogenic carbonatesCaCO3 - accumulation horizon
MgCO3 - lime coatings (pseudomycelium)
Na2CO3 - concretions
- lime pans
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CO2 + H2O H2CO3 + Ca2+ CaCO3
?Acid volatiles + igneous rocks sedimentary sedimentary
rocksrocks + salty oceans/seas( > 0.018 + 0.13 · 1015 g C/year emission from volcanic
activities)
- climatic- hydrologic- vegetation- soil
zones
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Idealized soil C cycle for Idealized soil C cycle for humidhumid conditions conditions (ppt. > Evtr) (ppt. > Evtr)
Atm CO2
Soil CO2 HCO3- SIC
Plant C
groundwater HCO3-
SOC (loss)
(Drees (Drees et al.,et al., 2001) 2001)
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Idealized soil C cycle for Idealized soil C cycle for subhumidsubhumid toto semi-aridsemi-arid conditions (ppt. conditions (ppt. Evtr) Evtr)
Atm CO2
Soil CO2 HCO3- SIC
Plant C ? (Steady
state) Groundwater
(Drees (Drees et al.,et al., 2001) 2001)
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Idealized soil C cycle for Idealized soil C cycle for semi-aridsemi-arid to to aridarid conditions (ppt. < Evtr)conditions (ppt. < Evtr)
eolian
Atm CO2
Soil CO2 HCO3- SIC
Plant C (Long-term storage)
SOC
(Drees (Drees et al.,et al., 2001) 2001)
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Pathways, reasons and consequences Pathways, reasons and consequences of the inorganic carbonof the inorganic carbon cycle cycle
During weatheringweathering and soil genesissoil genesis considerable changes take place in the SOC and SIC cycles:- physical, chemical and biological weathering;- dissolution – precipitation;- leaching – accumulation
depending on soil reaction, carbonate status, texture, structure, moisture regime, biological activities, etc.
The processes are strongly influenced by climate (and climate changes), surface and subsurface hydrology, vegetation and land use pattern and various human activities.
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In the Alpok-Adria region In the Alpok-Adria region a huge amount of sedimentary rocks, mainly CaCO3, was formed during the various geological periods.
In some places these sediments are the „parent material” of the soil formation processes, but in extended areas there are only non- or slightly weathered rocks on the surface, sometimes with characteristic „karst” symptoms,„karst” symptoms, and peculiar carbonate regimes.
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In the Carpathian BasinCarpathian Basin the main carbonate resources are the calcareous Quaternary (Pleistocene) loess deposited to drylands or into water and waterlogged territories; calcareous Holocene aeolian sand; calcareous alluvial deposits of rivers coming from limestone watersheds; calcareous colluvial materials transported by lateral erosion from carbonatic surroundings.
Surface and subsurface waters play an important, often decisive role in their state, horizontal and vertical distribution and have significance in the carbon cyclecarbon cycle and carbon sequestration. carbon sequestration.
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Development of calcium carbonate accumulation layers in the Danube Plain
H2O (rainfall)
H2O with CO2 content (soil solution)SOC
CO2-loss CaCO3 precipitationSIC
CaCO3 accumulation layer
level of groundwater effect
concentration weakly soluble CaCO3 (and MgCO3 precipitation)SICgroundwater level
evaporation
leaching
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In HungaryIn Hungary – due to various reasons (acid rain, improper fertilizer application etc.) – a quite serious CaCO3-loss was measured: part of the dissolved carbonates was „destroyeddestroyed” completely
CaCO3 + 2H+ H2CO3 H2O + CO2
and contributed to the increase in CO2 concentration of the surrounding atmosphere
another part was leached by downward filtration. LeachingLeaching has world-wide significance in the SIC cycle.
According to comprehensive C balance studies the ice-free land area of the Earth surface for potential leaching is 45×1012 m², consequently, if we assume a 8 g C/m²/year flux, then the sequestration ratesequestration rate is estimated as 0.36×1015 g C/year.
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This
inorganic carbon sequestration inorganic carbon sequestration „potential” „potential” (capacity”)
is ais a new soil functionnew soil function;;
consequently
it should be evaluated in a modern, function-specific
„„soil quality” assessment system. soil quality” assessment system.
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A Gaunt view
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Thank you very much Thank you very much
for your attentionfor your attention ! !