EESB05 - Chapter 1.docx

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Environmental Science
Marney Isaac

EESB05 Chapter 1: The Soils Around Us - Soils play 6 key roles SOILS AS MEDIA FOR PLANT GROWTH - Provide a medium for plant roots and supply nutrient elements - Properties of soil determines the nature of the vegetation present - Properties of soil indirectly determines the number and types of animals and people that can be supported - Shoots are plant leaves, flowers, stems, and limbs - Roots are underground and have many functions in which the plant obtains from the soil 1) Physical Support - Soil mass anchors the root system so that the plant does not fall over or blow away 2) Air - Process of respiration to obtain energy - Roots produce CO a2d uses O in 2ts ventilation process through soil pores 3) Water - Soil pores absorb rainwater and hold it where it can be used by plant roots - Plants require a continuous stream of water to use in cooling, nutrient transport, turgor maintenance, and photosynthesis - Rainfall varies from place to place, and deep soils may store enough water for plants to survive long periods without rain 4) Temperature moderation - Insulating properties of soil protect root system from extremes of hot and cold that occur at the soil surface 5) Protection from toxins - Phytotoxic substances are chemicals that are toxic to plants, produced by human activity, plant roots, microorganisms, or by natural chemical reactions - Soils protect plants from these toxic substances by ventilating gases, decomposing or adsorbing organic toxins, or suppressing toxin-producing organisms 6) Nutrient Elements - Soil supply plants with mineral nutrients - Fertile soil provide continuing supply of dissolved mineral nutrients for optimal plant growth Ex. Metallic elements such as potassium, calcium, iron, copper, etc. and non-metallic elements such as nitrogen, sulphur, phosphorus, and boron Essential elements – chemical elements required for normal plant growth - There are 92 naturally occurring chemical elements, but only 17 are essential elements Geophagy – the practice of eating soil deliberately, a widespread practice in some societies Ex. Thailand, Uganda, Turkey, rural Alabama - Benefits vary such as gaining iron, calcium, etc. - Drawbacks include parasitic worm infection, lead poisoning, mineral nutrient imbalances, etc. SOIL AS REGULATOR OF WATER SUPPLIES - The nature and management of soils has a major influence on the purity and the amount of water that end up in aquatic systems - Rainwater travels through soil or flow over its surface at some point before reaching aquatic systems - Water can be soaked by soil and stored, while some will seep through to the groundwater - Water is purified through the upper layers of soil, which removes impurities or kills disease organisms - If soil is shallow or impermeable, then surface flowing water will pick up debris and can cause a flash flood of muddy water SOIL AS RECYCLER OF RAW MATERIALS - Recycling a vital process in ecosystems (forests, farms, cities, etc.) - Soil plays an important role in geochemical cycles, by assimilating great quantities of organic waste and turning it into beneficial humus - Humus is stable organic matter that cannot be broken down any further - Minerals have been converted into forms that can be utilized by plants and animals, and carbon returned to the atmosphere as carbon dioxide SOIL AS MODIFIER OF THE ATMOSPHERE - Soil interacts in many ways with the air and atmosphere - Dry, poorly structured, and unvegetated soils contribute dust particles to the atmosphere - Evaporation of soil moisture contributes water vapour in the atmosphere, which alters temperature, composition, and weather patterns - Soils can absorb gases (such as oxygen and methane) and release gases (such as carbon dioxide and nitrous oxide), which can influence atmosphere composition and global warming SOIL AS HABITAT FOR SOIL ORGANISMS - The most complex and diverse ecosystems on Earth are underground - Soil is home to a diversity of organisms where they interact SOIL AS ENGINEERING MEDIUM - Soil is one of the earliest and most widely used building materials Ex. African mud huts, cement-stabilized buildings, etc. - Some soils are a good base on which to build roads and structures, while others are not as stable PEDOSPHERE AS ENVIRONMENTAL INTERFACE - The soil acts as an interface between rock (lithosphere), air (atmosphere), water (hydrosphere), and living things (biosphere) Pedosphere – a conceptual zone within the ecosystem consisting of soil bodies - There are different functions and interfacing at different levels and scales Ex. Soils channel water from bedrock to the oceans (scale of kilometres) SOIL AS A NATURAL BODY - Soil is referred to as “material” or as “natural bodies” - It is a material composed of minerals, gases, water, organic substances, and microorganisms - Soil is a three-dimensional natural body that covers the Earth, but is highly variable from place to place - Soils are natural bodies composed of soil, roots, animals, rocks, artifacts, etc. Regolith – an unconsolidated layer of weathered rock and soil material above solid rock - Regolith material has been transported from other areas, therefore all or part of the regolith may not be related to the rock now found below it Saprolite – soft weathered bedrock that retains the fabric and structure of the parent rock, but is porous and loose enough to be dug with a spade - Soil is the product of destructive and creative (synthetic) processes that form contrasting layers called soil horizons Pedology – the study of soils as natural bodies, the properties of soil horizons, and relationships among soils within a landscape] Edaphologists – soil scientists that focus on the soil as habitat for living things especially plants THE SOIL PROFILE AND ITS LAYERS (HORIZONS) - Scientists dig a large hole called a soil pit, usually several metres deep and about a metre wide, to expose soil horizons for study Soil profile – the exposed vertical section of soil horizons - They can warn you about potential problems in using land or contain information on the environment or history of a region Ex. Differences between soils from dry regions and humid regions Soil Horizons - Layers vary in thickness, with irregular boundaries, but are generally parallel to the land surface - Uppermost layers tend to have changed the most because weathering of regolith occurs first at the surface and work its way down - Deeper regolith is most similar to the original regolith, known as the soil’s parent material O Horizon - Organic horizon of mineral soils - Plant and animal remains accumulate on the surface of older decomposed debris, and they undergo physical and biochemical breakdown A Horizon - The layers nearest the surface that are mostly mineral particles, but have been darkened by the accumulation of organic matter - Also known as topsoil - The plow layer is the layer of plowed and cultivated soil (12-25 cm), and is often removed by contractors and the topsoil is used later or sold E Horizon - The layer just below the A Horizon - Intensely weathered and leached horizons that have not accumulated organic matter B Horizon - Underlying layers, known as subsoil that have accumulated materials washed down from horizons above or formed through weathering - Varying amounts of accumulated silicate clays, iron, aluminum oxides, etc. C Horizon - The least weathered part of the soil profile SOIL: THE INTERFACE OF AIR, MINERALS, WATER, AND LIFE - The 4 major components of soil are air, water, mineral matter, and organic matter - Air, rock, water, and living things intermingle at where regolith meets the atmosphere - Soil appear to be solid, but typically soil in good condition for plant growth is 50% solid and 50% pore spaces - About 5% of the soil solids consist of organic matter - Plant roots need both air and water, and optimum soil condition will consist of 25% water and 25% air in pore spaces - If there is more water than air then soil will be waterlogged, and if there is more air than water then soil will suffer from drought MINERAL (INORGANIC) CONSTITUENTS OF SOILS - Soil’s solid framework consists of mainly mineral particles - Larger soil particles (stones, gravel, and coarse sands) are generally rock
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