Understanding Biogeochemical Cycles and Their Impact on Earth's Ecosystems
Biogeochemical cycles involve the cycling of essential nutrients like water, carbon, oxygen, nitrogen, phosphorus, and sulfur through abiotic components like water, air, soil, and rock to biotic components like plants, animals, fungi, and bacteria. Humans play a significant role in these cycles, impacting nutrient flow. Sustainable life on Earth is supported by solar energy, matter cycling, and gravity. The hydrologic cycle, with processes like evaporation, condensation, and precipitation, ensures the continuous movement of water globally.
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Chapter 4 Biogeochemical Cycles
What IS a biogeochemical cycle? BIO = life GEO = earth CHEMICAL = elements C, O, N, P, S a cycling of nutrients (water, carbon, oxygen, nitrogen, phosphorus, sulphur) from the abiotic components of the ecosystem (water, air, soil, rock) through the biotic components (plants, animals, fungi, bacteria)
Objectives: Identify and describe the flow of nutrients in each biogeochemical cycle. Explain the impact that humans have on the biogeochemical cycles.
Objectives: Identify and describe the flow of nutrients in each biogeochemical cycle. Explain the impact that humans have on the biogeochemical cycles.
What Sustains Life on Earth? Solar energy, the cycling of matter, and gravity sustain the earth s life. Figure 3-7
Two Secrets of Survival: Energy Flows and Matter Cycles An ecosystem survives by a combination of energy flow (from Sun to Earth) and matter cycling. Remember: the Earth is a CLOSED system Figure 3-14
MATTER CYCLING IN ECOSYSTEMS Nutrient Cycles: Global Recycling Global Cycles recycle nutrients through the earth s air, land, water, and living organisms. Nutrients are the elements and compounds that organisms need to live, grow, and reproduce. Biogeochemical cycles move these substances through air, water, soil, rock and living organisms.
Waters Unique Properties There are strong forces of attraction between molecules of water. (due to H bonds) Water exists as a liquid over a wide temperature range. Liquid water changes temperature slowly. It takes a large amount of energy for water to evaporate. Liquid water can dissolve a variety of compounds. (due to polar nature of water) Water expands when it freezes.
THE HYDROLOGIC (WATER) CYCLE Condensation Rain clouds Transpiration Evaporation Precipitation to land Transpiration from plants Precipitation Precipitation Evaporation from land Evaporation from ocean Surface runoff (rapid) Precipitation to ocean Runoff Surface runoff (rapid) Infiltration and Percolation Groundwater movement (slow) Ocean storage Fig. 3-26, p. 72
Effects of Human Activities on Water Cycle We alter the water cycle by: Withdrawing large amounts of freshwater. Clearing vegetation and eroding soils. Polluting surface and underground water. Contributing to climate change.
Effects of Human Activities on Carbon Cycle We alter the carbon cycle by adding excess CO2 to the atmosphere through: Burning fossil fuels. Clearing vegetation faster than it is replaced photosynthesis = CO2 Figure 3-28
Effects of Human Activities on the Nitrogen Cycle We alter the nitrogen cycle by: Adding nitrous oxide to the atmosphere from vehicles and factories which contributes to acid rain. Contaminating ground water from nitrate ions in inorganic fertilizers. Releasing nitrogen into the troposphere through deforestation (less N assimilated by trees).
Effects of Human Activities on the Nitrogen Cycle Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined. Figure 3-30
THE PHOSPHORUS CYCLE mining Fertilizer excretion Guano agriculture weathering uptake by autotrophs uptake by autotrophs leaching, runoff Dissolved in Soil Water, Lakes, Rivers Land Food Webs Marine Food Webs Dissolved in Ocean Water death, death, decomposition decomposition weathering sedimentation settling out uplifting over geologic time Rocks Marine Sediments Fig. 3-31, p. 77
Effects of Human Activities on the Phosphorous Cycle We remove large amounts of phosphate from the earth to make fertilizer. We reduce phosphorous in tropical soils by clearing forests. We add excess phosphates to aquatic systems from runoff of animal wastes and fertilizers excess phosphorus causes algal blooms
THE SULPHUR CYCLE Water Acidic fog and precipitation Sulfur trioxide Sulfuric acid Ammonia Ammonium sulfate Oxygen Hydrogen sulfide Sulfur dioxide Plants Volcano Dimethyl sulfide Industries Animals Ocean Sulfate salts Metallic sulfide deposits Decaying matter Sulfur Hydrogen sulfide Fig. 3-32, p. 78
Effects of Human Activities on the Sulfur Cycle We add sulfur dioxide to the atmosphere by: Burning coal and oil Refining sulfur containing petroleum Convert sulfur-containing metallic ores into free metals such as copper, lead, and zinc releasing sulfur dioxide into the environment
Assignment: Put the 6 cycles together on one poster! Draw the hydrologic, carbon, oxygen, nitrogen, phosporus and sulphur cycles onto one piece of poster paper. Include the required terminology Follow the criteria on the rubric provided Assessment will be done by performance (explanation of the cycles by the group)
The Gaia Hypothesis: Is the Earth Alive? Some have proposed that the earth s various forms of life control or at least influence its chemical cycles and other earth-sustaining processes. The strong Gaia hypothesis: life controls the earth s life-sustaining processes. The weak Gaia hypothesis: life influences the earth s life-sustaining processes.
