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  Affects Structure  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: SiO 2  Aluminosilicate: AlSi 3 O 8 - or AlSi 3 O 8 - Negative charge allows soil to hold on to important mineral cations: Ca 2+, K +, Na +, Mg 2+, NH 4 +, Al 3+ can be substituted for Si 4+ 1 in 4 will give a -1 charge 2 in 4 gives a -2 charge

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  Heavy metals  Sources:  Agrichemicals  Household cleaners  Gasoline, oil  Dry cleaning  Paints  Sludge  Landfills  Etc (see pg 458 in IB bk)

Soil Degradation  Salinization  Water used for irrigation leaves behind salts  Too much salt and plant life cannot survive  Water tables rise, more evaporation occurs since surface is warmer so salinization occurs  Water table rose because land was cleared of trees  When it rained the trees held a lot of the moisture  Without the trees, the water seeps into the groundwater and becomes part of it. The water table rises.  The salty water of the water table mixes with the rain water...  Acid Rain and Storm water runoff  Leaching of important nutrients for plants

Sources  Green J., Damji S. Chemistry 3 rd Ed. IBID Press,   Smith, T. M., and R. L. Smith Elements of Ecology, 7th edition. Benjamin Cummings.