Lecture notes 321 part 2 2011

Lecture notes 321 part 2 2011 - ESR 321 Lecture Notes...

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Unformatted text preview: ESR 321 Lecture Notes Portland State University Dr. Alan Yeakley 1 Outline Part 2 of ESR 321 1. Introduction 2. Rock weathering 3. Soil chemical reactions 4. Soil Development 5. Biogeochemical cycling in plants 6. Nutrient allocations 7. Biogeochemical cycling in soil 8. Watershed scale nutrient cycling 9. Bibliography ESR 321 Lecture Notes Portland State University Dr. Alan Yeakley 2 1. Introduction Early development of earths chemistry- early atmosphere contained volcanic acids - these volatilized acids dissolved in water and reacted with surface minerals - over time, oxygen accumulated due to algal emergence and evolution - increasing levels of oxygen allowed oxidation of reduced minerals (e.g. FeS 2 ) - land plants evolved caus ed CO 2 concentrations in soil - soil CO 2 is a primary agent of chemical weathering and weathering accelerated - recently, humans have added NO X and SO X ; these constituents have further accelerated weathering ESR 321 Lecture Notes Portland State University Dr. Alan Yeakley 3 Primary link between atmosphere and land salts Ocean rocks mentary Sedi volatiles Acid rocks Igneous + +- 75% of exposed land is uplifted sedimentary rocks - rock weathering is important to the bioavailability of elements that have no gaseous forms 2. Rock weathering Weathering = any process that decomposes rock Two types of weathering 1. Mechanical weathering- climate controlled - freeze/thaw process - wind abrasion - plant roots ESR 321 Lecture Notes Portland State University Dr. Alan Yeakley 4- soil development related to transport 2. Chemical weathering- reactions with acidic and oxidizing substances - usually water based - mechanical weathering can expose surfaces - rate depends on chemical composition - igneous and metamorphic rock contain primary minerals - two classes 1. mafic (Fe, Mg) 2. felsic (Al) Weathering rates- weathering rate follows reverse rate of cooling < Fig 4.1 (S) > - this occurs for two primary reasons: 1. Minerals formed at high temperatures have fewer bonds linking units of crystalline structure ESR 321 Lecture Notes Portland State University Dr. Alan Yeakley 5 2. minerals formed at high temperatures have more frequent substitutions (Ca, K, Na, Mg) that distort shape - Saprolite (meaning, literally, rotten rock) occurs when ions are removed, but rock structure remains - density decreases in saprolite compared to bedrock - 40% porosity can be reached in saprolite - Quartz is most resistant to weathering and is the primary component of sand - Climate controls chemical weathering also - higher temperature increases weathering rates - higher precipitation increases weathering rates - weathering is more rapid in tropical forests than in temp erat e forest s - weathering is more rapid in forests than in grasslands Carbonation reaction ESR 321 Lecture Notes Portland State University Dr. Alan Yeakley 6- carbonation is the dominant weathering react ion: 3 2 2 ) ( 2 CO H O H CO aq +- note that + + + 3...
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This note was uploaded on 01/12/2012 for the course ESM 321 taught by Professor Environmentalsystem during the Winter '10 term at Portland State.

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Lecture notes 321 part 2 2011 - ESR 321 Lecture Notes...

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