O'Connor Lecture 5 - Biology 171 Friday Lecture 5 Cycling...

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Lecture 5: Cycling of Matter & Climate Change Biology 171 Friday, September 14, 2012 Today’s Topics: Announcements Next Week in Discussion: Energy flows but matter cycles! Exam I: Wed. Sep. 26 ! Text Reading: Lecture 5: 4 th : Chapter 54 (1098-1102) Lecture 6: 4 th : Chapter 53 (1058-1062) The Water Cycle Nitrogen Cycle Carbon Cycle Fossil Fuels & Industrialization Greenhouse Gases Dif±cult Choices 1
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NPP also varies among ecosystems by biome ( Figure 54.9 ).
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Global Biogeochemical Cycles When nutrients leave one ecosystem, they enter another. The movement of ions and molecules among ecosystems links local biogeochemical cycles into one massive global system.
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Global water cycle Estimates of the amount of water that moves between major components of the cycle over 1 year. Solar energy absorbed by liquid water to create water vapor is the energy source driving the water cycle. Over oceans, evaporation exceeds precipitation. On land, precipitation exceeds evaporation and transpiration (from plants). Water returns to oceans from land via runoff and groundwater. On a global scale, total evaporation = total precipitation; The water cycle is in global balance. Humans have little effect. Fig. 54.14
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Nitrogen The vast majority of molecular nitrogen (N 2 ) in the atmosphere is unavailable to producers because they can use nitrogen only in the form of ammonium (NH 4 + ) or nitrate (NO 3 ) ions. Nitrogen is added to ecosystems in a usable form only when it is reduced (or fixed) – that is, converted from N 2 to NH 4 . Nitrogen fixation results natually from lightning-driven reactions in the atmosphere and from enzyme-catalyzed reactions in bacteria that live in soils and the water column.
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The Global Nitrogen Cycle Producers can use nitrogen only in the form of ammonium (NH 4 + ) or nitrate (NO 3 ) ions. Producers require N to make proteins and nucleic acids. N moves up the food chain when herbivores eat producers and when carnivores eat the herbivores. N in organic molecules in detritus is converted to inorganic forms that producers require by decomposers: bacteria, archaea & fungi. Other bacteria break down organic molecules and release molecular N 2 back to the atmosphere. Fig. 54.16
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Human-fixed nitrogen in the form of fertilizers, nitric oxide from burning fossil fuels, and cultivation of certain crops is having a major impact on the global nitrogen cycle. Because mineral nitrogen can be transported in the air, “nitrogen deposition” is occurring all over the surface of the Earth Fig. 54.17
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Negative effects of increased nutrient input include anaerobic "dead zones," harmful algal blooms, and eutrophication the conversion of a water body to a (short-term) highly productive ecosystem with rapid decomposition, low oxygen levels, and rapid filling with decomposing organic matter .
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O'Connor Lecture 5 - Biology 171 Friday Lecture 5 Cycling...

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