1. Chapter 4 – The Lithosphere Lithosphere (soils) affected by… composition of atm. gases (e.g. 4Fe 3+ + 30 2  2Fe 2 O 3 ) atmospheric circulation climate biological processes (exudation, respiration) Weathering Mechanical: fragmentation w/out chemical Rx wind, plant roots, freezing/thawing, erosion Sediment flux in southern France (Rhone River) December 7, 2003

2. Chemical: minerals react w/acids or oxidizing substances; includes H 2 O and constituents are released as ions Key process for biotic uptake of non-gas phase elements (Ca, K, Mg, P) Rate of Chemical Weathering I. Mineral Composition Igneous & [rock formed by the solidification of molten magma] Metamorphic [rock changing from one form to another @ high temp (T) and pressure (P) without passing through a liquid phase e.g., limestone  marble & shale  slate silicate rocks contain 1 o minerals formed at high T & P deep in Earth rate of chemical weathering follows reverse order of mineral formation viz. minerals rapid, early crystallization.. - few bonds among crystal units - substitutions of various cations [Ca,Mg,K,Fe] -distorted shape c c Isolated crystal units Linkage of crystal units & Lower O:Si ratio

3. II.Physical Environment wet areas > dry areas warm areas > cold areas Si yield among earth’s major rivers [Turner et al. 2003, Biogeochemistry]

4. Copyright © 2013 Elsevier Inc. All rights reserved. FIGURE 4.2 Loss of silicon (SiO 2 ) in runoff as a function of mean annual temperature and precipitation in various areas of the world. Source: Modified from White and Blum (1995). 4

5. III.Biotic Processes A. Respiration “carbonation” weathering H 2 O + CO 2  H + + HCO 3 -  H 2 CO 3 Atm = 0.040% pCO2 Soil = 2 – 7% pCO2 B. Organic acids  weathering (acetic, citric, oxalic acids) biotite mica ([K,Mg]Si 4 O 10 )  K, Mg

6. Bluth & Kump (1994) dominance of Al and Fe oxides in old Hawaiian soils [Kauai] resulting from carbonation weathering

7. C.Chelation: processes that combine (a metal ion) with a chemical compound to form a ring (e.g., humic and fulvic acids) EDTA [(HO 2 CCH 2 ) 2 NCH 2 CH 2 N(CH 2 CO 2 H) 2 ] - amino acid, commonly exuded by plants/fungi CaAl 2 Si 2 O 8 Ca-Feldspar Weathering Ca 2+ 2Al 3+ Si 2 O 8 Leaching Plant Uptake Accumulation of Al 3+ & 2 o mineral formation Chelating Agent + Al 3+ …allows weathering to resume plant root

8. Stability of common minerals under current weathering conditions Most stableFe 3+ oxides2 o mineral Al 3+ oxides2 o mineral Quartz (SiO 2 )1 o mineral Clay2 o mineral K + feldspar1 o mineral Na + feldspar1 o mineral Ca 2+ feldspar1 o mineral Least stableOlivine (Mg bearing)1 o mineral From Press and Siever (1986) …these accumulate and control nutrient availability nutrient bearing minerals are lost through time Secondary Minerals

9. Abundant: Clay (layered aluminum-silicate minerals,<2  M particles) Clays  Si Layers : Al (Fe, Mg) layers Temperate Forest Soils: 2:1 ratio (unweathered) Illite: (K,H 3 O)(Al,Mg,Fe) 2 (Si) 4 O 10 (OH) 2 Tropical Soils: 1:1 ratio (highly weathered) Kaolinite: Al 2 Si 2 O 5 (OH) 4 Tetrahedral sheets (4 sided) Octahedral sheets

10. Tetrahedral sheets (4 sided) Octahedral sheets Iron Implications: 1.Substitution of divalent cations (e.g. Mg 2+ ) for iron or aluminum results in a permanent net negative charge on clay crystal. 2.This enables “free” cations in solution to “exchange” onto clay surfaces Cation Exchange Capacity (CEC) -- Temperate Zone -- clays have net negative charge  bind cations -- Al 3+ > H + > Ca 2+ > Mg 2+ > K + > NH 4 + > Na +

11. What factors contribute to Cation Exchange Capacity (“CEC”) of Soils? I.Ionic substitution in clays, irreversible -- Mg 2+ for Al 3+  crystal - II.Clay particles (pH dependent) -- hydroxide groups (-OH)  H + dissociates  net negative charge on O - III.Soil Organic Matter (pH dependent) -- H+ dissociates from phenolic (-OH) and organic acid (-COOH) components of organic matter

12. Chapter 4 – The Lithosphere Acid rain depletes CEC of “base” cations (e.g. Ca 2+ and Mg 2+ ) Al 3+ > H + > Sr 2+ > Ca 2+ > Mg 2+ > Rb+ > K + > NH 4 + > Na + > Li + SO 4 3-, NO 3 - are dominant components that draw H + from organic material H + competitively displaces Ca 2+ and Mg 2+ from CEC Anions “carry” cations in soil solution “Clean Air Act” has reduced acid inputs

13. Chapter 4 – The Lithosphere Secondary Minerals Abundant:Clay (layered aluminum-silicate minerals, <2  M particles) <2  M particles) Al 3+ & Fe 3+ oxides Copyright © 2013 Elsevier Inc. All rights reserved. FIGURE 4.9 The specific absorption of phosphate by iron sesquioxides may release OH or H 2 O to the soil solution. Source: From Binkley (1986).

14. Chapter 4 – The Lithosphere In a highly weathered soil…(e.g. subtropical and tropical soils) A. Dominated by Al and Fe oxides B. Highly acidic C. Base cations are sequestered in biomass or lost to leaching AlO - Soil Mineral H + (aq) High pH AlOH Soil Mineral + H Low pH Tropical soils often have net positive charge and AEC not CEC PO 4 3- > SO 4 2- > Cl - > N O 3 - Anion Exchange Capacity > CEC

15. Chapter 4 – The Lithosphere Effects of Vegetation, Climate and Time on Soil Development Generalized Soil Profile Largest mass of SOM Active plant and microbial processes Largest pool plant-available nutrients Fe 3+ Fulvic Acids chelation & precipitation (includes clays) Microbial degradation of lipids, proteins, carbohydrates, lignin

16. In addition to reading the text for more information on soil development, check out this YouTube video! https://www.youtube.com/watch?v=mZUjbFNOdxQ

17. Spodosol Northern Michigan

19. Ultisols North Carolina

23. Gelisols Alaska

24. Congruent Dissolution: all primary minerals are released to solution CaCO 3 + H 2 CO 3  Ca 2+ + 2HCO 3- Incongruent Dissolution: fraction of primary minerals released (Na-feldspar, albite) 2NaAlSi 3 O 8 + 2H 2 CO 3 + 9H 2 O  2Na + + 2HCO 3 - + 4H 4 SiO 4 + Al 2 Si 2 O 5 (OH) 4 (Kaolinite)