Soil Formation and Erosion PDF

Topic 4.2 Soil Formation and Erosion Soil: mix of geologic and organic components. Soil has many benefits: 1. A medium for plant growth 2. Filters water as it moves from the atmosphere into rivers, streams, and groundwater. 3. Contributes to biodiversity by serving as habi...

Topic 4.2 Soil Formation and Erosion Soil: mix of geologic and organic components. Soil has many benefits: 1. A medium for plant growth 2. Filters water as it moves from the atmosphere into rivers, streams, and groundwater. 3. Contributes to biodiversity by serving as habitat 4. Filter chemicals deposited by air  Formation of Soil Takes hundreds to thousands of years!! Involves physical and chemical weathering. 5 Determinants of Soil Properties 1. Parent Material: rock material underneath. 2. Climate 3. Topography: surface slope and arrangement of a landscape. 4. Organisms: plants, animals and human activity. 4.2 As soils form, they develop characteristic horizons, which are horizontal layers with distinct physical features. - O Horizon: at the surface; layers of organic detritus like leaves, needles, twigs 4.2 - A Horizon: Mixed organic and mineral materials; known as topsoil because it is frequently the top layer, especially in soil used for agriculture 4.2 - E Horizon: eluviation zone, AKA zone of leaching. Not always present but when it is it is above the B horizon - B Horizon: known as the subsoil, mostly mineral material with very little organic material. - C Horizon: Least weathered, similar to the parental material. Topic 4.3 Soil Composition and Properties Physical properties Particle Size – the units that make up the inorganic portion of soil can have varying size; Gravel > Sand > Silt > Clay Texture is a measurement of the percentages of sand, silt, and clay a soil contains Soil texture charts can be used to identify and compare soil types.  Physical Properties continued Porosity – describes how much space is found in a soil The larger the particle size, the more porous the soil will be.  Physical Properties continued Permeability – the ability of water and nutrients to move down the soil horizons Larger particles increase permeability  Physical Properties continued Water-holding capacity – the amount of water that soil can hold against the pull of gravity Smaller particles retain water better; the amount of organic material in a soil also contributes to WHC CHECK FOR UNDERSTANDING Dwight claims that Scranton is a soil high in clay considering lining is best for beet its landfill with a farm. Do you 1-foot layer of agree or disagree? clay. Should they Why? do this? Explain. 4.3 Chemical Properties of Soil Cation Exchange Capacity (CEC): The ability of a particular soil to absorb and release cations. Based on the amount of clay in a soil because clay has a negative charge. Thus, it can attract positive ions. Too much clay can mean high water retention and waterlogging roots.  Base Saturation: measure of soil bases to soil acids, expressed as a percentage Essentially a measure of pH Acids are detrimental to plant growth whereas bases promote growth. A high CEC and a high base saturation are likely to support high productivity. 4.3 Biological Properties of Soil Determined by the organisms and plants that live in the soil Microscopic and macroscopic Soil degradation: the loss of some or all of the ability of soils to support plant growth. 4.4 Earth’s Atmosphere The Earth’s atmosphere is made up of a number of gases, the most abundant of which is nitrogen gas (78%) and oxygen gas (21%). 5 layers of gases Lower layers have a greater mass that the higher layers 1. Troposphere: closest to Earth, extends 16 km (10 miles) above Earth; densest layer, where weather occurs. 2. Stratosphere: 16 – 50 km (10-30 miles), less dense; ozone forms here. Ozone: absorbs most of the sun’s ultraviolet-B (UV-B) 4.4 Mesosphere 4._______________, 3. ______________, Thermosphe and Exosphere 5. _______________ re Pressure, density and gravity lessens. Thermosphere blocks X-rays and UV radiation. Thermosphere contains charged gas molecules that when hit by solar energy begin to glow: Northern Lights or Aurora Borealis 4.4 As the Sun’s energy passes through the atmosphere and strikes land and water, it warms the planet’s surface. However, this warming does not occur evenly across the planet. This uneven warming pattern has 3 causes: 4.4 1. The amount of time the solar radiation spends in the atmosphere varies.  Surface area over which the Sun’s rays are distributed is smaller at the Equator. 3. Some areas reflect more solar energy than others. Albedo: the percentage of incoming sunlight that is reflected from a surface. The higher the albedo of a surface, the more solar energy it reflects and the less it absorbs.  The uneven heating of the Earth has a direct effect on global wind patterns, the Earth’s seasons, and the Earth’s climates. 4.5 Global Wind Patterns 4 properties that determine how air circulates in the atmosphere: 1) air density – mass of air per volume 2) Saturation point 3) air’s response to changes in pressure Adiabatic cooling vs adiabatic heating 4) Production of heat when water condenses These four properties, along with unequal heating of the Earth, result in global patterns of air movement called convection currents. - Hadley Cells - Intertropical Convergence Zone(ITCZ): most intense sunlight! Polar Cells Convection currents formed by air that rises at 60 N and S and sinks at the poles.  Convection currents cause air to move directly north or south. However, actual air currents are deflected to the east or west. This is known as the Coriolis effect. Rain Shadows: Windward side has a lot of precipitation whereas the leeward side has arid condition. 4.6 Watersheds A watershed is all the land in a given landscape that drains into a particular stream, river, lake or wetland. Watersheds are also known as drainage basins. Understanding the physical makeup of a watershed is significant when tracking the potential sources of pollution. 4.7 Solar Radiation and Earth’s Seasons Cities on 97° W Longitude  The Earth’s tilt (23.5°) causes the amount of solar radiation reaching various latitudes to shift over the course of a year. For example, when the Northern Hemisphere is tilted toward the Sun, the Southern Hemisphere is tilted away from the Sun.  Spring and Fall equinox – the Sun’s rays strike the Earth’s equator directly so all places will receive 12 hours of daylight and 12 hours of darkness.  Summer solstice – day where the Northern Hemisphere experiences more daylight hours than any other day of the year. Winter solstice – day where the N.H. experiences less daylight hours than any other day of the year. 4.8 and 4.9 Ocean Currents Ocean circulation affects the transport of heat around the globe and affects the climate of continents  Ocean currents are driven by a combination of temperature, gravity, trade winds, the Coriolis effect, salinity and the location of continents. Tropical waters receive the most direct sunlight. This causes tropical water surface to be about 3 inches higher than mid-latitude waters. This slight slope causes water to flow away from the Equator and circulate.  The Coriolis effect causes ocean currents between the Equator and the mid-latitutes to rotate in a clockwise direction in the Northern Hemisphere and in a counterclockwise direction in the Southern Hemisphere. These large-scale water movements are called gyres.  Ocean currents also help some areas of the ocean support highly productive ecosystems. In areas called upwellings, surface currents diverge, causing deeper waters to rise and replace water that have moved away. Thermohaline Circulation: sinking of dense, salty water in the North Atlantic drives a deep, cold current that moves slowly around the world. The effect of global warming El Nino Southern Oscillation (ENSO)  El Nino- Southern Oscillation: Trade winds weaken or reverse. This causes warm surface water builds up along the coast of South America and prevents upwelling of deep cold water. Happens every 3 to 7 years Can last from a few weeks to a few years ENSO has several consequences: 1) Rainier and stormier off the west coast of SA 2) Cooler and wetter conditions in the Southeast US 3) Unusually dry weather in Southern Africa and Southeast Asia 4) Reduces the fish population