The Inorganic Carbon Cycle GyörgyVÁRALLYAY György VÁRALLYAY 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

atmosphere biosphere soil hydrosphere lithosphere Várallyay nyomán Sphere interrelationships

soil carbon pools and fluxes organic inorganic The assessment of soil carbon pools and fluxes includes both soil organic carbon (SOC) and soil inorganic carbon (SIC) pools their dynamics their interactions with aquatic and biotic (primarily vegetational) regimes their C-sequestration „activities”

Major C reservoirs in the Earth System (Drees et al., 2001)

Soil C pool of world soils (adapted from Eswaran et al., 2000)

A simplified representation of the global carbon cycle. Balance: Pg/year enter the atmosphere 215 Pg/year is removed from the atmosphere. increasing CO 2 concentration (in Pg=10 15 g)

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 pool The SIC pool is considerably higher, but more stable and less reactive than the SOC pool. CaCO 3 MgCO 3 Na 2 CO 3 The importance of SIC in the global C balance is often ignored, in spite of the fact that pedogenic processes, as carbon sequestration carbonate leaching are important factors silicate-mineral weathering of carbon sequestration

Soil Inorganic Carbon – SIC primary or lithogenic carbonatesprimary or lithogenic carbonates (originating from the parent rock material) dissolutionwater translocationby(organic) acids transportCO 2 (soil atmosphere)  + soil Ca 2+, Mg 2+, Na + secondary or pedogenic carbonatessecondary or pedogenic carbonates CaCO 3 - accumulation horizon MgCO 3 - lime coatings (pseudomycelium) Na 2 CO 3 - concretions - lime pans

CO 2 + H 2 O H 2 CO 3 + Ca 2+ CaCO 3 ? sedimentary rocks Acid volatiles + igneous rocks  sedimentary rocks + salty oceans/seas ( > · g C/year emission from volcanic activities) - climatic - hydrologic - vegetation - soil zones

Idealized soil C cycle for humid conditions (ppt. > Evtr) Atm CO 2 Soil CO 2 HCO 3 - SIC Plant C groundwater HCO 3 - SOC(loss) (Drees et al., 2001)

Idealized soil C cycle for subhumid to semi-arid conditions (ppt.  Evtr) Atm CO 2 Soil CO 2 HCO 3 - SIC Plant C ? (Steady state) Groundwater (Drees et al., 2001) (Drees et al., 2001)

Idealized soil C cycle for semi-arid to arid conditions (ppt. < Evtr) eolian Atm CO 2 Soil CO 2 HCO 3 - SIC Plant C (Long-term storage) SOC (Drees et al., 2001)

Pathways, reasons and consequences of the inorganic carbon cycle weatheringsoil genesis During weathering and soil 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 CaCO 3, was formed during the various geological periods. „karst” symptoms, 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, and peculiar carbonate regimes.

Carpathian Basin In the Carpathian 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. carbon cyclecarbon sequestration. Surface and subsurface waters play an important, often decisive role in their state, horizontal and vertical distribution and have significance in the carbon cycle and carbon sequestration.

Development of calcium carbonate accumulation layers in the Danube Plain H 2 O (rainfall) H 2 O with CO 2 content (soil solution) SOC CO 2 -loss  CaCO 3 precipitation SIC CaCO 3 accumulation layer level of groundwater effect concentration  weakly soluble CaCO 3 (and MgCO 3 precipitation) SIC groundwater level evaporation leaching

In Hungary In Hungary – due to various reasons (acid rain, improper fertilizer application etc.) – a quite serious CaCO 3 -loss was measured: destroyed  part of the dissolved carbonates was „destroyed” completely CaCO 3 + 2H +  H 2 CO 3  H 2 O + CO 2 and contributed to the increase in CO 2 concentration of the surrounding atmosphere Leaching  another part was leached by downward filtration. Leaching has world-wide significance in the SIC cycle. sequestration rate According to comprehensive C balance studies the ice- free land area of the Earth surface for potential leaching is 45×10 12 m², consequently, if we assume a 8 g C/m²/year flux, then the sequestration rate is estimated as 0.36×10 15 g C/year.

This inorganic carbon sequestration „potential” inorganic carbon sequestration „potential” (capacity”) is a new soil function; consequently it should be evaluated in a modern, function-specific „soil quality” assessment system.

A Gaunt view

Thank you very much for your attention !