The Inorganic Carbon Cycle

2. The Inorganic Carbon Cycle GyörgyVÁRALLYAY 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

3. Sphere interrelationships atmosphere biosphere hydrosphere soil lithosphere Várallyay nyomán

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

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

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

7. A simplified representation of the global carbon cycle. (in Pg=1015g) Balance: 218.5 Pg/year enter the atmosphere 215 Pg/year is removed from the atmosphere. increasing CO2 concentration

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

9. 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 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 sequestration

10. Soil Inorganic Carbon – SIC • primary 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 carbonates CaCO3 - accumulation horizon MgCO3 - limecoatings (pseudomycelium) Na2CO3 - concretions - lime pans

11. CO2 + H2O H2CO3 + Ca2+ CaCO3 ? Acid volatiles + igneous rocks  sedimentary rocks + salty oceans/seas ( > 0.018 + 0.13 · 1015 g C/year emission from volcanic activities) • climatic • hydrologic • vegetation • soil zones

12. Idealized soil C cycle for humid conditions (ppt. > Evtr) Atm CO2 Soil CO2 HCO3- SIC Plant C groundwater HCO3- SOC (loss) (Drees et al., 2001)

13. Idealized soil C cycle for subhumidtosemi-aridconditions (ppt.  Evtr) Atm CO2 Soil CO2 HCO3- SIC Plant C ? (Steady state) Groundwater (Drees et al., 2001)

14. Idealized soil C cycle for semi-arid to arid conditions (ppt. < Evtr) eolian Atm CO2 Soil CO2 HCO3- SIC Plant C (Long-term storage) SOC (Drees et al., 2001)

15. Pathways, reasons and consequences of the inorganic carbon cycle 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.

16. 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 weatheredrocks on the surface, sometimes with characteristic „karst” symptoms, and peculiar carbonate regimes.

17. In the Carpathian Basin the main carbonate resources are the • calcareous Quaternary (Pleistocene) loessdeposited to drylands or into water andwaterlogged territories; • calcareous Holocene aeolian sand; • calcareous alluvial deposits of rivers comingfrom limestone watersheds; • calcareous colluvial materials transported bylateral 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 cycle and carbon sequestration.

18. H2O (rainfall) H2O with CO2 content (soil solution) SOC CO2-loss  CaCO3 precipitation SIC CaCO3 accumulation layer level of groundwater effect concentration  weakly soluble CaCO3 (and MgCO3 precipitation) SIC groundwater level Development of calcium carbonate accumulation layers in the Danube Plain leaching evaporation

19. In Hungary – due to various reasons (acid rain, improper fertilizer application etc.) – a quite serious CaCO3-loss was measured: • part of the dissolved carbonates was „destroyed”completely CaCO3 + 2H+ H2CO3 H2O + CO2 and contributed to the increase in CO2 concentrationof the surrounding atmosphere • another part was leached by downward filtration.Leaching has world-wide significance in the SICcycle. According to comprehensive C balance studies the ice-free land area of the Earth surface for potential leaching is 45×1012m², consequently, if we assume a 8 g C/m²/year flux, then the sequestration rate is estimated as 0.36×1015 g C/year.

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

21. A Gaunt view

22. Thank you very much for your attention !