LAB 12 Soil-Vegetation
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Jan 14, 2025
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LAB 12: Soils and Vegetation Section 1: SoilsSoilis the thin layer of unconsolidated material covering the Earth’s surface composed of both mineral and organic material. Dirtis soil without the organic material. Soil is an important part of many ecosystems and can influence the land uses that occur in specific areas. Various processes of weathering(physical, chemical, and biological) provide the raw materials (parent material) for soil formation and development. Physical weatheringis the breaking down or disintegration (fragmentation) of rocks with no chemical alteration. The resulting fragments have the same chemical composition as the large rock, they are simply smaller in size. Chemical weatheringis the decomposition of the minerals in rock through chemical alteration. The chemical bonds holding the rock minerals together are broken. This results in the smaller pieces having a different chemical composition than the larger rock. Water is often necessary, since the rock is essentially dissolved away. Rates of decay are dependent on temperature and precipitation. In most cases rocks will be broken down by a combination of both chemical and physical weathering processes. Regolithis the partially weathered rock below the surface which overlays the bedrock. This may in time become the parent materialfor soil. Parent materialis the unconsolidated material, from organic and mineral sources, that is the basis of soil development/formation.Soil formation, also known as pedogenesis, is the result of a combination of on-going processes. Soil is comprised of four components, minerals, organic matter, water, and air. Mineralsare the inorganic compounds of a soil with a definite chemical composition and crystalline structure. They are the weathered material of the parent rock. The organic matterrefers to the organic compounds of a soil originally from living (organic) matter. They result from the decay of plant and animal matter, or their waste products. Waterfills the pore spaces in the soil and forms a thin film around soil particles. Airfills the pore spaces of soil when water isn’t present. The formation of a soil involves five soil formation factors, parent material, climate, biological agents, topography, and time. Parent Materialrefers to the type of rock and minerals from which the soil was formed. The materials in the rock will be in the soil. A soil may be either a residual soil, one formed from the underlying rock, or a transported soilone formed from material not found in the underlying rock, but that was transported into the area by water, wind, a glacier, or some other agent. Climaterefers to how temperature and precipitation (moisture) differ from one area to another, thus yielding different soils, even from same parent material. Biological Agentsrefers to the quantity and type of decomposers (microorganisms, bacteria, fungi, etc.) which will affect the rate of organic matter decay and the amount of humus (organic matter) in the soil. Topographyrefers to elevation differences, slope angle differences, and slope aspect which can all influence soil formation. Timerefers to the idea that for a given place, the more time a soil has to develop, the more complete the development of individual soil horizonsand the soil profile. A soil horizonis a layer of soil within the soil profile, which is distinct from the layers above and below it in the sequence. The soil profileis the vertical array of soil layers (horizons) in the sequence from the top (surface) to the bottom (bedrock).In addition to the five soil forming factors there are four primary soil forming processes, addition, transformation, depletion, and translocation which also act to develop soils into distinct horizons (layers). Additionis the process of adding material to the top of the soil already present. This includes adding organic matter by decomposition to the top layer (the O or organic horizon), or material that has been transported into the area by a river, glacier, wind, landslide, etc. Transformationis the continued weathering of rock, minerals, and soil particles already present. This is soil components being physically and/or chemically broken down into their smallest size possible. This normally occurs in all soil horizons. Depletionis the process whereby particles are carried downward through the soil by water from one area to another. The percolating water reduces (depletes) the abundance of the substance in the upper area. This process forms the E horizon. Translocationis the process whereby the material moved during the depletion process is deposited into a lower layer. When the water slows down or evaporates, the dissolved material comes out of solution (precipitates) thus has been
translocated or moved. Depletionand Translocationare basically the beginning and ending of an overall process.There can be as many as six main soil horizons in a soil profile (Figure 1), but not every soil will have all six horizons. Which horizons exist in a specific soil is determined by the soil forming factors and processes discussed above. These six horizons are the ‘O’ horizonor Organic horizon, which consists of a high percentage of organic material and is formed primarily by Addition. The ‘A’ horizonis the upper most layer developed from the parent material, and is often darker in color than it would be due to organic leaching from the O horizon above. The A horizon is formed by Transformationand Addition. The ‘E’ horizonis the lighter colored layer just below the A horizon, and is formed by Depletion. The ‘B’ horizonis formed by Translocationof particles from the ‘A’ and ‘E’ horizons above. This layer usually takes the most time to develop. The ‘C’ horizonis the lowest soil horizon in a soil profile and formed by Transformation. This layer is comprised of material exhibiting a wide variety of particle size from sand grains to boulders. The ‘R’ horizonin any soil profile is the solid rock (bedrock) and is the lowest horizon in the profile. Figure 1: A typical sequence of soil horizons (O, A, E, B, C, R) in a complete soil profile.Q 1. Describe the four soil components. (4 pt)Q 2. Describe the five soil formation factors. (5 pt)
Q 3. List the four soil forming processesin soil formation and which process is involved in forming each of the top five soil horizons (O, A, E, B, and C)? (5 pt)Every soil consists of soil particles of a variety of sizes which is the soil textureof the soil. This can be an indication of the soil’s compactness (how tightly the soil particles can fit together) thus the amount of pore space or porositywithin the soil. This has a direct bearing on the movement of water through the soil, the soil’s field capacity. Field Capacityis the ability of a soil to hold water against the downward pull of gravity. The texture of a soil horizon will greatly determine its field capacitybecause it affects the porosity of the soil. There are three basic texture categories based on particle size, Sand, Silt, and Clay. Sand consists of the largest sized soil particles and clay the smallest soil particles. Sandy soils have a greater amount of pore space since they cannot compact as tightly thus water can move through these soils much more easily, yielding a lower field capacity. Clay soils have a lower amount of pore space since they can compact more tightly thus water cannot move through these soils as easily, yielding a higher field capacity. Soils can be categorized by the percentage of sand, silt, and clay sized particles in the soil. An analysis of any soil will reveal these percentage and the specific category can be determine using a Soil Texture Triangle (Figure 2).Figure 2: The Soil Texture TriangleQ 4. Using Figure 2 (above) determine the specific type of soil based on the percentages of sand, silt, and clay for each of the following samples. (4 pt)10% silt, 40% clay, and 50% sand _________________________
30% clay, 10% sand, and 60% silt _________________________20% silt, 10% clay, and 70% sand _________________________20% sand, 70% silt, and 10% clay _________________________Soil taxonomyrefers to classifying soils based on their characteristics, similar to the classification of plants and animals. Several classification schemes are in use today often developed by different countries. The U.S. Soil Survey is comprised or 12 Orders, 53 Suborders, 230 Great Groups, ~1000 Subgroups, ~5000 Families, and ~16,000 Series. Figure 3 illustrates the distribution of these 12 Soil Orders across the planet.Figure 3: World soil map of the 12 Soil Orders as classified by the U.S. Soil Survey.Q 5. Use Google Earth to locate each site below. Then using Figure 3, and/or the same map in the PPt presentation for LAB 12, determine the soil order found at that location. Also give the country in which this location is found (be sure you have the Labels turned-on). You may need to zoom out to clearly see the country name. (6 pt)The soil order and country at 6° S, 67° W (eye alt 1000 miles) ______________________________________The soil order and country at 63° N, 17° E (eye alt 250 miles) ______________________________________The soil order and country at 24° S, 119° E (eye alt 500 miles) _____________________________________The soil order and country at 49° N, 29° E (eye alt 300 miles) ______________________________________The soil order and country at 64° N, 113° W (eye alt 300 miles) ____________________________________The soil order and country at 33° N, 83° W (eye alt 100 miles) ______________________________________
Section 2: Vegetation BiomesBiomeis the broadest justifiable division of plants and animals although in most usage of the term it refers only to the plant assemblages of the area. This assemblage or association of plants at forms a regional or geographical ecological unit. It is a biogeographical unit consisting of a biological community or assemblage that has formed in response to the physical environmentin which they are found and a shared regional climate. The idea of a biome is a broader term than habitat and can comprise a variety of habitats. It is similar to the idea of an ecosystem but without the inclusion of the interactions between the biotic (living) and abiotic (non-living) aspects of the environment. There are three basic or broad categories of biome, forests, grasslands, and deserts. Depending on the classification scheme used there can several sub-categories, i.e. tropical rainforest, and subtropical rainforest, and temperate broadleaf forest, and montane forests, etc. There are also sub-categories of deserts and grasslands. Areas of the same biome classification can be found on more than one continent, but every continent will have every biome. (See Figure 4 and 5)Figure 4: One classification scheme for the world’s biomes.Q 6. Use Google Earth to locate each site below. Then using Figure 5, and/or the same map in the PPt presentation for LAB 12, determine the biome found at that location. Also give the country in which this location is found. You may need to zoom out to clearly see the country name. (6 pt)The biome and country at 39° N, 3° W (eye alt 185 miles) __________________________________The biome and country at 0° S, 21° E (eye alt 450 miles) __________________________________The biome and country at 37° N, 85° W (eye alt 160 miles) __________________________________
The biome and country at 34° S, 62° W (eye alt 350 miles) __________________________________The biome and country at 21° N, 52° E (eye alt 365 miles) __________________________________The biome and country at 67° N, 168° E (eye alt 1000 miles) __________________________________Figure 5: Another classification scheme for the world’s biomes.