Formation of Soil Resources

Formation of Soil Resources - ESM 203: Formation of Soil...

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1 ESM 203: Formation of Soil Resources Biogeochemical Role of the Lithosphere Fall 2007
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2 Summary of previous two lectures Global tectonic processes generate global patterns of rock types and landscape types (defined by their form and functioning) Lithosphere reacts with atmosphere, hydrosphere, and biosphere Incorporation of water into subducted sediments, tectonic and volcanic breakage and erosion of rocks, chemical reactions Intensity of interaction varies with the type of geologic environment Interactions most intense at plate margins
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3 These interactions … Sustain the nutrition of the biosphere, mainly through release of lithologic elements into solution in hydrosphere Generate a water-holding soil that sustains primary production Keep some ecosystems impoverished Create some toxic hydrochemical and soil environments Cause high rates of erosion and sedimentation Margins of mountain belts and sedimentary basins (downwarps in Earth’s crust) Major floodplains and deltas Sedimentation stores rock minerals, carbon, and incorporated solutions Modulates CO 2 content of the atmosphere and ocean over the long term (~10 4 yr) by incorporating CO 2 into weathered minerals
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4 The effects result from a set of biogeochemical processes called weathering , defined as Mechanical disintegration and chemical decomposition of rock minerals in situ near Earth’s surface (within ~1 km), and … Short-distance translocation of the dissolved substances within the near-surface environment
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5 General weathering“reaction” ‘Primary’ rock minerals + H 2 O, CO 2 , HNO 3 , O 2 , organic acids, ± changes in temperature and pressure Solutes (Na + , Ca 2+ , K + , Fe 2+ , Mg 2+ , Zn 2+ , etc.) Solid residuum ‘Secondary’ minerals separated into fragments (clay to gravel), coated with precipitates of amorphous oxides, storing cations and trace metals
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6 General weathering“reaction” ‘Primary’ rock minerals + H 2 O, CO 2 , HNO 3 , O 2 , organic acids, ± changes in temperature and pressure Solutes (Na + , Ca 2+ , K + , Fe 2+ , Mg 2+ , Zn 2+ , etc. temporary storage in soils Solid residuum ‘Secondary’ minerals separated into fragments (clay to gravel), coated with precipitates of amorphous oxides, storing cations and trace metals To groundwater and streams (water quality)
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7 Mechanical weathering Unloading or pressure release Crystal growth (salt or ice) Create microfractures and joints in rocks that allow penetration of water
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8 Solution of carbonates , e.g. CaCO
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Formation of Soil Resources - ESM 203: Formation of Soil...

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