Transcript soilppt
Soil What is soil? Mixture of inorganic material (rocks) and organic material (SOM) as well as organisms (microbes). Soil formation involves: Parent Material (glacial deposits? Sediment? Lava?) Biotic Factors Plant roots break up soil, add nutrients and organic material Climate influences Temp, precipitation, wind: leaching: movement solute thru soil Topography More water flow? Steep slopes? Time Characteristics of Soil Color Dark: humus, other colors: minerals present Texture Gravel, sand, silt, clay Structure moisture, air capacity and ion exchange ability Moisture Wet soils vs dry soils support different forms of life Depth What role does soil serve in the ecosystem? Part of both food webs Provides nutrients for plants Plants are a sink for toxic metals, organic toxins, carbon Plants are a food source Plants prevent erosion Detritovores: recycle nutrients so they can be used by other organisms Turn Nitrogen into nitrates Recycle the nitrogen and carbon out of dead things (mineralization) Eat up pollutants Holds moisture/ filters water Structure of Soil: Inorganic Silicon is to geologists what carbon is to biologists... Rocks and soils basic structure: Silica: SiO2 Aluminosilicate: Al3+ can be substituted for Si4+ 1 in 4 will give a -1 charge 2 in 4 gives a -2 charge AlSi3O8- or AlSi3O8Negative charge allows soil to hold on to important mineral cations: Ca2+, K+, Na+, Mg2+, NH4+, Soil Organic Matter Non-living organic components present in soil resulting from decomposition of once living creatures Holds onto nutrients to exchange with plants Improves soil structure Increase air More oxygen, Easier for roots to grow Increased moisture Heat capacity / smaller temperature deviations Reduces soil erosion Soil Organic Matter The organic material from bacterial breakdown of plants and other organisms Nature's way of recycling important nutrients: Sugars, amino acids, proteins, polysaccharides Humic acids (Hummus) Still don't really know what it is Stable organic material that isn't broken down any more by organisms. Organisms will only “eat” what will give them a net energy gain. Soil Ecosystem: Detrital Food Chain Soil Organic Matter: Possible Structure Polar parts Hold water Hold inorganic nutrients (ions: nitrate, phosphate) Importance of Soil Organic Matter SOM gives the soil better “Structure” More moisture, more oxygen can diffuse, more pockets for microorganisms to live Better soil structure supports more microorganisms Microorganisms mineralize nutrients Amino acids → Nitrates → Natural fertilizer for plants Using compost is a way to increase soil organic matter into bad soil Pollutants Pesticides Excess Fertilizer Organic Pollutants VOCs, Semi-VOCs, PCBs, PAHs, petroleum, solvents, organotin compounds Sources: Agrichemicals Household cleaners Gasoline, oil Dry cleaning Paints Partition in SOM (humic substances) Sludge Adsorb to surface of inorganic soil Etc (see pg 458 in IB bk) Heavy metals Landfills Soil Degradation Salinization Water used for irrigation leaves behind salts Too much salt and plant life cannot survive Water tables rise (due to deforestation), more evaporation occurs since surface is warmer so salinization occurs Acid Rain and Storm water runoff Leaching of important nutrients for plants Sources Green J., Damji S. Chemistry 3rd Ed. IBID Press, 2007. http://www.science.org.au/nova/032/032box01.htm Smith, T. M., and R. L. Smith. 2009. Elements of Ecology, 7th edition. Benjamin Cummings.