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Environment Midterm Exam- Cycles.docx

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University of Toronto Mississauga
Barbara Murck

Environment Midterm Exam Geological Cycles:  determine soil chemistry and replenish soil nutrients, which influences the distribution of vegetation and ecosystems  control the formation of mineral resources and fossil fuels  influence the development of landscapes and mountain ranges, distribution of climatic zones, oceanic and atmospheric circulation Rock cycle:  Heating, melting, cooling, breaking, reassembling of rocks and minerals  Dominated by surface processes Tectonic cycle:  Processes related to the movement of large fragments of lithosphere  Dominated by internal processes Hydrologic Cycle:  Water is essential for life and biochemical reactions  Water is involved in nearly every environmental system  Water is both a participant in and the main transport medium for environmental processes  We will return to the hydrologic cycle and human impacts later in the term. Biogeochemical Cycle: Supports Life  Nutrient (biogeochemical) cycle = the movement of nutrients through environmental systems  Elements that are crucial for life support  Transformation from organic to inorganic forms  Movement through biotic and abiotic reservoirs - Carbon - Oxygen - Nitrogen - Sulphur - Phosphorus Carbon Cycle:  Carbon is in carbohydrate, fat, protein, bone – all organic matter – as well as in inorganic forms  Photosynthesis moves carbon from the atmosphere to biosphere  Respiration returns carbon to atmosphere and hydrosphere  Decomposition returns carbon to the geosphere, the largest reservoir of carbon  Ocean is the second largest reservoir of carbon Some important points about the Carbon Cycle: - Complex, poorly understood - Fluxes vary in time and space  Many carbon species - oxidized, reduced - organic, inorganic  Many reservoirs - biotic, abiotic - Models depend on time scale: o Short-term (100s of yrs): controlled by rates of photosynthesis and respiration o Medium-term (1,000s to millions of yrs): controlled by rates of deposition and burial of organic matter o Long-term (millions to billions of yrs): controlled by rates of weathering, limestone formation, and plate tectonics How Humans Affect the Carbon Cycle:  Main impact is carbon mobilization  Burning fossil fuels moves carbon from the geosphere to the atmosphere  Cutting forests and burning fields moves carbon from the biosphere to the atmosphere  Cattle and rice production move carbon from the biosphere to the atmosphere  Today’s atmospheric carbon dioxide reservoir is the largest in the past 650,000 years - The driving force behind the climate change  The missing carbon sink: 1–2 billion metric tons of carbon are unaccounted for - It may be the plants or soils of northern temperate and boreal forests The Oxygen Cycle:  Short- to medium-term: controlled by photosynthesis, respiration, decay  Long-term: oxygen bound up in minerals in the geosphere  Rapid accumulation and burial of organic sediments and plant matter causes a build-up of atmospheric oxygen The Nitrogen Cycle:  Many forms of Nitrogen: - NH A3monia - NO nxtrous oxides (NO2 nitrite, NO3 nitrate) - N 2olecular nitrogen  Importance of atmospheric reservoir (N gas =278% of atmosphere) Important Points:  Nitrogen fixation = nitrogen gas is fixed in a useable form (ammonia, NH ) by 3 nitrogen-fixing bacteria  N 2as is inert (not in a usable form)  Nitrification = bacteria convert ammonium ions first into nitrite ions then into nitrate ions - Plants can take up these ions - Animals obtain nitrogen by eating plants or other animals  Denitrification = bacteria convert nitrates in soil or water to gaseous nitrogen, releasing it back into the atmosphere Human Effects on the Nitrogen Cycle:  Increased emissions of nitrogen-containing greenhouse gases and smog precursors from fossil-fuel burning - Climatic change - Acidified water and soils (HNO nit3ic acid)  Synthetic production of fertilizers - Humans are fixing as much nitrogen as nature does - Increased transfer from rivers to oceans - Changes to estuaries, coastal ecosystems, and fisheries – eutrophication, algal blooms, hypoxia The Phosphorus Cycle:  P is a key component of cell membranes, bones, teeth, nucleic acids, DNA, RNA  Most phosphorus is in minerals (phosphate PO ), released by weathering 4 - No significant vapour form - Oxidation, reduction not important  Plants take up phosphorus in dissolved form - A limiting factor for plant growth Human Effects of the Phosphorus Cycle:  Mining rocks for fertilizer moves phosphorus from the geosphere to the hydrosphere  Runoff containing phosphorus causes eutrophication of aquatic systems - Fertilizer runoff - Wastewater discharge - Household detergents The Sulphur Cycle:  Three main components: - Rocks, minerals & sediments - Pyrite, gypsum, anhydrite - Organic sediment  Aqueous (dissolved sulphate) – ocean  Atmospheric sulphur - Reduced sulphur - Sulphur dioxide SO 2 - Sulphate aerosols SO 4 Human Effects the Sulphur Cycle:  Anthropogenic sulphur in the global cycle now exceeds sulphur mobilized by natural processes  Impacts of human activities (fossil fuel burning): - Role of sulphur in acidity of water - acid precipitation  Role of sulphate aerosols in climate system (even though sulphates are not GHGs) - impacts on global energy balance The Earths Layers:  The core  Made of Fe-Ni metal - Inner core: Solid - Outer Core: Liquid  The Mantle - Made of rock - Asthenosphere (near the top part of the mantle = “weak zone”)  The Crust  Oceanic crust – made of basalt - dense, thin  Continental crust – made of granite - less dense, thick Several Types of Plate Environments:  Intraplate = plate “middle”  Plate boundaries = edges, where plates interact  Plate boundaries: 1. Divergent (rifting, spreading apart) - Oceanic (ex: mid-Atlantic ridge) - Continental (ex: East African Rift  Plate boundaries: 2. Divergent 3. Convergent (coming together) - Ocean-Ocean subduction zone (ex: Japan) - Ocean-Continent subduction zone (ex: Andes) - Continent-Continent collision zone (ex: Himalayas)  Plate boundaries 1. Divergent 2. Convergent 3. Strike-slip (sliding-past, transform, lateral) (ex: San Andreas Fault)  Earthquakes – plates grind and scrape past each other, causing earthquakes  Volcanic eruptions – magma rises to the surface along plate boundaries, creating
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