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Biology notes- Chapter 54.docx

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Richard B Day

Chapter 54 Global Biogeochemical Cycles  When nutrients leave on ecosystem and enter another  The movement of ions and molecules among ecosystems links local biogeochemical cycles into one massive global system. The Global Water Cycle  Figure 54.13  Water evaporates out of the ocean and precipitates back into it; evaporation exceeds precipitation.  When this water vapor moves over the continents, it is augmented by water transpired by plants. Precipitation falls on the continents.  The cycle is completed both by water that moves from the land to the oceans via streams and by groundwater; water that is found in soild.  Humans are affecting the water cycle in many ways. One of the most direct ways is in groundwater storage. The water table, the upper limit of saturated soil, is dropping on every continent. The Global Carbon Cycle  The global carbon cycle involves the movement of carbon among terrestrial ecosystems, the oceans, and the atmosphere.  The oceans is by far the largest of these three reservoirs. Carbon moves into and out of the atmospheric reservoir rapidly via the photosynthesis and respiration of organisms.  Local Carbon Cycle- purple arrows show movement of carbon. Oxygen moves in the opposite direction as carbon. Photosynthesis releases oxygen into the atmosphere. Respiration, decomposition and burning take oxygen from the atmosphere.  Carbon Storage- storage of carbon in detritus and then fossil fuels maintains higher atmospheric O . Carbon storage in soils now varies globally. Carbon storage has varied over 2 geological time.  There are high levels of carbon storage in boreal forests and tundras, particularly in wetlands. Acidity and anoxia slow decomposition.  Carbon dioxide is a greenhouse gas; a gas that traps heat radiated from Earth and keeps it from being lost to space.  Increases in the amounts of greenhouse gases have the potential to warm Earth’s climate by increasing the atmosphere’s heat trapping potential.  Human activities such as intensive agriculture, deforestation and burning of fossil fuels have changed the carbon cycle by adding large amounts of carbon dioxide to the atmosphere. Mangroves  A kind of tropical forest on seacoasts, have very high carbon storage  Continent of Pangea was forming. Climate was tropical, many shallow wetland swamp forests with periodic flooding. This led to high levels of carbon storage Carbonife
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