Soil Formation and Properties: An Overview of Spodosols, Aridisols, and Oxisols, Study notes of Environmental Science

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This Week’s Lecture (as much as we can cover ☺) • Origins (WILL FINISH) • Pedosphere: What is it? • Transported Soil/Sediment • In-Situ Soil Formation and Weathering • Soil Types and Global Distribution • Landscape Reduction • Soil Environmental Properties • Terrestrial Biosphere • Soil/Watershed Biogeochemistry • Hubbard Brook 15/09/2005 14:09:46 Intro > Origins > Solid Earth > Pedosphere > Biosphere > Atmosphere > Hydrosphere U Shori-wave radiation Long-wave yy elaine •NaAlSi3O8 + H+ + H2O = Al(OH)3 (gibbsite) + Na+ + 3SiO2,aq •NaAlSi3O8 + H+ + 2.5H2O = 0.5Al2Si2O5(OH)4 (kaolinite) + Na+ + SiO2,aq A little plug for Aqueous Geochemistry (ERTH 4690 – Spring 2006) More plug for Aqueous Geochemistry (ERTH 4690 – Spring 2006) Time (Reaction Progress) Too much plug for Aqueous Geochemistry (ERTH 4690 – Spring 2006) Gelisols - (permafrost) soils with permafrost within 2 m of the surface Histosols - (organic) organic soils Spodosols - (podzolic) acid soils with a subsurface accumulation of metal-humus complexes (podzol) Andisols - soils formed in volcanic ash Oxisols - (lateritic) intensely weathered soils of tropical and subtropical environments (laterites) Vertisols - clayey soils with high shrink/swell capacity Aridisols - (orthic) CaCO3-containing soils of arid env. with subsurface horizon development (caliche) Ultisols - soils with a subsurface zone of silicate clay accumulation and <35% base saturation Mollisols -(chernozemic) grassland soils with high base status Alfisols - (luvisolic) soils with a subsurface zone of silicate clay accumulation and >35% base saturation Inceptisols - (brunisolic) soils with weakly developed subsurface horizons Entisols - (regosolic) soils with little or no morphological development SOIL TAXONOMY: 12 Soil Orders Spodosol: Podzolic Soils SOIL STRUCTURE O-horizon: leaf litter, organic material A-horizon: plough zone, rich in organic matter B-horizon: zone of accumulation ¢-horizon: weathering soil; little organic material or life R-horizon: unweathered parent material  < 25 cmiyr < 25-50 omfyr bee a a Precipitati n : : M4 4 Oxisols High oO Vegetation o $ Moderate € 5 = < None L Figure 5.13 Schematic representation showing soil formation as a function of the relationship between climate and vegetation, which alters parent material over time. Soil-forming processes operate most vigorously where precipitation and temperatures are high o Temperature (°C)  Global Soil Regions Atmospheric circulation Prevailing winds drive surface ocean currents. Coriolis Force Tikku Lecture Soil and Water Balance eva poration exceeds 2x rainfall | Faintall exceeds 2x evaporation at oe es Controls over Soil Formation • Parent Material • Climate • Topography • Time • Potential Biota • Human Activities Landscape Reduction (Erosion): • As drainage basins evolve, the system approaches a "dynamic equilibrium" whereby the total mass of rock weathered (chemical + physical) is removed from the basin. This means no net accumulation of weathered material (soil profile may change composition but not thickness or mass. Example: Black Hills, South Dakota Springs draining limestone to Cheyenne River TDS = 150 to 2280 mg/l mainly Ca++, Mg++, HCO3- from 23 springs Cheyenne River carries 143 x 106 kg/yr TDS. If average rock density is 2.7 g/cc Total volume removed = 143 x 106 kg/yr / 2.7 kg/m3 = 53,000 m3/yr Total landscape reduction by chem. weathering: 53,000 m3/yr / 3.9 x 109 m2 (area) = 14 mm/kyr • Dominant controls: topography (slope), surface material, vegetation Uplift Rates Additional Aspects of Soil Chemistry: • pH is the negative log of the hydrogen ion (H+) activity (effective concentration) in solution and is a measure of the active acidity of the system. pH strongly affects nutrient availability through its effects on cation exchange. • Cation exchange capacity (CEC) reflects the capacity of a soil to hold exchangeable cations on negatively charged sites on the surfaces of soil minerals and organic matter. • Base saturation is the percentage of the total exchangeable cat ion pool that is accounted for by base cations (the non-hydrogen, non-aluminum cations). In general, cations occupy exchange sites and displace other ions in the sequence H(Al3+)>H+>Ca2+>Mg2+>K+ NH4+>Na+ • As with cations, anion absorption depends on the concentration of anions and their relative capacities to be held or to displace other anions. Anions generally occupy exchange sites and displace other ions in the sequence PO43->SO43->Cl->NO3- • The high CEC and base saturation provide buffering capacity that keeps the soils from becoming acid. When additional H+ is added to the system in solution (in acid rain, for example), it exchanges with cations that were held on cation exchange sites. IU Nita Ks The TERRESTRIAL Surface Environments: • Consider the surface of the earth. About 71 % Water, 29 % Land (14.9 billion hectares). • Of the 14.9 billion hectare of land surface on Earth, only 77% is vegetated land (23 % is desert plus ice-covered), plus semi-desert or simply rocky). • Of the 11.5 billion hectares that is vegetated, about 17 % (or 1.9 billion hectares) have been directly influenced by human activities (deforestation, grazing, agriculture, fuel wood, industrial and waste pollution). • The environmental and ecological diversity in terrestrial systems, like its marine counterpart, largely is reflective of this physical framework. Temperature/humidity/climatic variations. • Soil and terrestrial surface water are the "substrates" of terrestrial biota. Water transport from one reservoir to the next is the principal means by which biological nutrients and "waste" are transported within the terrestrial environment as well as in and out of it. Temperature/Humidity/Climatic Variations • Hadley cells and perturbations from the norms. • Koppen Climatic types (A-Tropical Humid; B-Dry; C-Temperate Humid; D - Cold Humid; E - Polar) • Soil Types (previous lecture) • Biomes • Biome - large ecosystem in which relatively uniform climatic conditions lead to uniformity of plant communities. − Tropical rainforest − Seasonal tropical forest − Mid-latitude forest − Boreal forest − Tropical grasslands − Mid-latitude grasslands − Desert − Tundra − Mediterranean forest and scrub. • Biomes can be associated with specific temperature and precipitation regimes. Another way of looking at it Major Terrestrial Biomes -15 ~ T T T T T 7 aes Zz T 50 100 150 200 250 300 350 400 450 Mean annual precipitation (cm) :  Dominant Forest Type Current Fla HREOC =z = 9 a a o c a a 7 a 3 a Spruce-Fir Longleaf-Slash Pine Loblally-Shertleat Pine Oa k-Pine Oa k-Hic kory Oa k-Gum-Cyvpress Elm-Ash-Cottenwood Maple-Beech-Birch Aspen-Birch Moa Data Based on average of 5 models Major changes in NY and NE USA