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

atmosphereatmosphere

biospherebiosphere

soilsoilhydrospherehydrosphere

lithospherelithosphere

Várallyay nyománVárallyay nyomán

Sphere interrelationshipsSphere interrelationships

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”

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)

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)

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)

The long-term geochemical cycle of carbon at the surface of the Earth

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

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

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

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)

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)

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)

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.

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.

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.

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

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.

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.

A Gaunt view

Thank you very much Thank you very much

for your attentionfor your attention ! !