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Lecture+10-20-08+Soils+Amundson - Soil: The Skin of the...

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Unformatted text preview: Soil: The Skin of the Earth ES 100 Ronald Amundson Gracia por su atencin Terrestrial Planets Wikipedia Solar System Habitability Zone Wikipedia "The Earth is not just an ordinary planet!" Antoine de Saint Exupery, The LiCle Prince The Earth's Biosphere greater than 4 By of feedback between life and earth materials Life/nonlife interacMons have made, and sustained, planetary habitability biological "waste gases" (O2, CH4, CO2, N2) keep planet about 30 0C warmer than abioMc planet life/earth interacMons buffer global perturbaMons Soil is the interface between life and rock, where many processes maintaining earth habitability occur "We might say that the earth has a spirit of growth, that its flesh is the soil" Leonardo da Vinci Soil and Earth Sustainability The Basics What is soil and how does it form? The Issues Soils and climate change Soils and erosion Soils and biodiversity The Basics Soils = f (climate, biota, topography, parent material, and Mme) Hans Jenny. 1941. Factors of Soil Forma7on parent material: largely silicate rocks on Earth (O,Si,Al, Fe, Ca, Mg, Na, K) climate: provides water that dissolves rock via chemical weathering, controls temperature which drives rates of biological and chemical reacMons biota: a source of energy, chemicals etc to modify soil topography: controls phyiscal processes of erosion and deposiMon Mme: soils commonly have geological ages (103 to 106 y) The Basics Rocks + water + CO2 = soil + HCO3 + dissolved compounds Soil: chemically altered rock contains array of organic compounds + life varies verMcally with depth 125W 115W 105W 95W 85W 75W 65W 50N 45N E Soil and Climate Change Earth Global Soil Carbon (~ 10 kg C/m2 global average) Humans Soils and Global C Cycle about 20% of all anthropogenic CO2 from land use unknown amount from global warming and release from soils The Soil C Cycle Atmospheric CO2 CO2 erosion respiration leaching DOC The Soil C Cycle and Humans Atmospheric CO2 CO2 Cultivation, global warming erosion respiration Accelerated erosion leaching DOC ? What will soil response be to global warming? ~1.4 Gt C loss in year 1 aeer 0.5 oC temperature increase ~ 13 Gt in 50 years Soils are a large and acMve posiMve feedback to global warming not well integrated into climate models Trumbore et al. 1996. Science 272:393. Current Consensus (?): Soil C Feedbacks to Warming May be Larger than Previously Expected "over a Jmescale of decades to centuries, the dominant slow pools will be more sensiJve to temperature than the faster pools, causing a larger feedback in response to global warming than previously thought" Powlson. 2005. Nature. 433:204 Field Evidence SuggesMng Soil C Loss Due to Warming Soil C loss offset all other efforts to sequester/ reduce CO2 emissions Summary of Soils and Climate Change Soils have more C than the atmosphere + global plants Soil C decomposiMon is strongly temperature dependent Growing evidence is suggesMng soils will, and maybe already are, a posiMve feedback to global warming Soils and Erosion and Biodiversity We live in the geological epoch of humans. Crutzen. 2002. Nature 415:23 Began ~ 250 years ago Population expansion Mass extinction Atmosphere/hydrosphere changes land conversion/soil movement Natural vs. Accelerated Soil Erosion Hillslopes are natural "conveyor belts" of soil soil moved downhill (proporMonal to slope) by biologically mediated processes soil produced/ replaced by conversion of rock to soil a "steady state" in many locaMons Global Cropland = ~ 15 x 1012 m2 Land scoured by glaciers = 25 x 1012 m2 Wikipedia: Geology of Minnesota Physical Impacts of Humans on Soil Movement "The net impact of humans as geological agents has been to lower the Earth's landscape by ~ 6 cm" Wilkinson and McElroy, GSA Bull. 2007. 119:140 "The total earth moved in the past 5000 yr would be sufficient to build a 4000mhigh mountain range, 40 km wide and 100 km long" Hooke. 2000. Geology. 28:843 Much lost "soil information" Consequences of Erosion Loss of soil in face of a growing global populaMon soils on slopes are no longer at steady state soil loss > soil producMon Loss of soil nutrients Increased fresh and marine water polluMon (ex: dead zones) Unknown impact on global C cycle Soils and Biodiversity the microbial biodiversity of soil is largely unknown, but is argued to be the most biodiverse ecoystem on Earth important for "ecosystem services" important for major advances in anMobioMcs and enzymes Early Benefits of Soil Bioprospecting Selman Waksman: 1952 Nobel Prize Hans Jenny Nature. 2006. 439 "Exploring (soil) microbial diversity is more like exploring outer space. The are more than 1016 prokaryotes in a ton of soil compared to a mere 1011 stars in our galaxy" 107 distinct prokaryote taxa in 10 g of pristine soil Most taxa are rare Rare taxa subject to pollution/disturbance (are they important to us?) TP Curtis and WT Sloan. 2005. Science. 306:1331 Soils and the Future Soils are living features on earth surface that take thousand to millions of years to form Humans have physically mixed, eroded, or altered > 25% of Earth's surface Are certain soils "endangered" or "exMnct", and does it maCer? 125W 115W 105W 95W 85W 75W 65W 50N 45N 1 endangered soil series 1 Endangered 29 endangered soils Urban land N 2-9 Endangered series Agricultural land 30N Urban land 300 Agricultural land 0 300 Km 25N Endangered soil series in USA Reasons for Preserving Bio(geo)diversity Ehrlich and Wilson, 1991 Earth/human sustainability climate/water modificaMon food and fiber producMon aestheMc ethical economical food medicines and industrial products ...
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This document was uploaded on 07/22/2009.

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