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04 - ECOSYSTEMS III

04 - ECOSYSTEMS III - ECOSYSTEMS III HUMAN IMPACTS I...

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ECOSYSTEMS III: HUMAN IMPACTS I. Nutrient enrichment a. What is it? i. Critical load – the amount of nutrient that can be absorbed by plants ii. Excess fertilizer iii. Excess nutrients leach into aquatic ecosystems – lakes, near-shore oceans b. Where does it come from? i. Nutrient additions: 1. Agricultural fertilizer 2. Runoff from animal feedlots, pastures, range 3. Storm drains (lawn fertilizers, pet waste) 4. Sewage spills c. What are the effects? i. Eutrophication 1. Increase productivity as a result of an increase in nutrients 2. What happens? Phytoplankton (algae & cyanobacteria) grow and die a. Reduces dissolved oxygen in water due to decomposition by bacteria b. Anoxic conditions kill fish and other aquatic life c. Reduces biodiversity ii. Dead zones 1. Areas of low oxygen in the world’s oceans 2. Largest ‘dead zone’ in the world – where Mississippi into Gulf of Mexico iii. Other effects 1. San Diego Union Tribune – Sept 24, 2007; nutrient runoff contributing to large number of deformed frogs (AP) 2. Amphibian abnormalities increasing in US, Canada, last decade (20-30% frogs have malformed limbs) 3. Why? Parasites (trematode) 4. Hypothesis: eutrophication a. Trematodes use snails as intermediate host b.
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