Geological Perspectives on Upstate Soils William A. Ranson Department of Earth & Environmental Sciences Furman University
In Reality a Closed System 4.6 Ga After Formation! [From Press et al., 2004, Understanding Earth, 4th Edition]
Implications of a Closed System Earth Finite resources No “away” to throw things - all waste remains on Earth A change in one part of the Earth System eventually affects all parts of the Earth system
Atmosphere Hydrosphere Geosphere Biosphere
Global Commons = Natural Capital
Global Commons Clean Air Clean Water Energy Resources Mineral Resources Fertile Soil Biological Diversity
Soil A complex medium of: Clay minerals Al-Fe-hydroxides Bedrock fragments Humus Microorganisms Air Water
Pangaea at 290 Ma
Appalachian cross section
Rocks and Minerals of the Upstate: The Raw Materials for Soil Felsic Gneiss - feldspar, quartz, mica (biotite & muscovite), hornblende Schist - muscovite, biotite with minor feldspar and quartz Mafic Amphibolite - hornblende, feldspar Diabase - feldspar and pyroxene
Weathering of Rock Mechanical Ice wedging/frost action Exfoliation Vegetation Chemical Dissolution Hydrolysis Oxidation
Hydrolysis Feldspar+water+carbonic acid=>Clay+dissolved ions Oxidation Iron silicates+Oxygen=>Iron oxides/hydroxides Lack of glaciation means a thick accumulation of clay minerals and saprolite.
Climate - temperature, rainfall Bedrock Mineralogy Bedrock Structure/Faults/Fractures Topography Influences on Weathering & Soil Production
Products of Weathering Saprolite - in situ, chemically weathered bedrock; retains the structural features of the rock Soil - a complex medium of clay minerals+ Al-Fe-hydroxides+bedrock fragments+humus+ microorganisms+air+water
Photo of saprolite
Saprolite!
Rock and Mineral Chemistry Gneiss - K, Na, Al, Si minor Fe, Mg Schist - K, Al, Si, minor Na, Fe, Mg Amphibolite - Ca, Fe, Mg, Al, Si, minor Na, K Diabase - Ca, Na, Fe, Mg, Si
Soil Horizons
Soil pH and Plant Diversity Felsic Rocks with Rich A-Horizon Acidic Soils with pH~ Lower Plant Diversity Mafic Rocks with Rich A-Horizon Circum Neutral Soils with pH~ Greater Plant Diversity Mafic Rocks with Depleted A-Horizon Acidic Soils with pH~ Lower Plant Diversity
Threats to Soil Erosion - physical removal by: Running water Wind Ice Bulldozer Degradation - physical or chemical changes to the soil that render it unviable Increased salinity Heavy application of fertilizers/pesticides/herbicides Removal of vegetation and exposure to sun
Influences on Erosion in the Upstate Naturally steep slopes and hillsides Hard, relatively impermeable silicate bedrock Temperate, humid climate=>abundant water & clay ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Urbanization=reduced permeable surface area Considerable agriculture Lack of riparian buffers Improper logging practices Road construction Less than optimal land-clearing practices
About 5.6 tons/acre/year or ~4 cm/100 years Average Rate of Soil Production in the US ~0.6 cm/100 years Average Loss of Soil in the US [US Soil and Water Conservation Service, 2002]
Along the Blue Ridge Escarpment steep slopes combined with hard, relatively impermeable gneisses result in a thin soil profile that is susceptible to mass movement. Mass movement is the slow to rapid down slope movement of soil and/or rock debris under the influence of gravity.
Glassy Mountain Development 1984
Mature Piedmont landscape
Average Annual Transport of Rock & Soil Wind erosion1.0 Glaciers4.3 Mountain building14 Oceanic volcanism30 Humankind42 Water53 Billion Tons [Source: Hooke, 1994]
a physical contaminant a chemical contaminant if laden with pesticide, herbicide, or fertilizer residue Eroded Soil
Careful land-use planning Better construction practices Better logging practices Riparian buffers for agriculture/grazing Terracing Strip cropping Alley cropping or agroforestry Windbreaks or shelterbelts Gully reclamation Conservation-tillage farming More soil/water conservation education and enforcement Some Obvious Solutions