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Eutrophication, Hypoxia, and Ocean Acidification Puget Sound Oceanography 2011

Eutrophication, Hypoxia, and Ocean Acidification Puget Sound Oceanography 2011. Eutrophication : The enrichment of a body of water with dissolved nutrients to the point that phytoplankton are released from nutrient-limited growth. Cultural / anthropogenic eutrophication

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Eutrophication, Hypoxia, and Ocean Acidification Puget Sound Oceanography 2011

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  1. Eutrophication, Hypoxia, and Ocean AcidificationPuget Sound Oceanography2011

  2. Eutrophication: The enrichment of a body of water with dissolved nutrients to the point that phytoplankton are released from nutrient-limited growth. Cultural / anthropogenic eutrophication -- River inputs influenced by urbanization + agriculture -- Run-off / Septic systems -- Sewage Treatment Plants Natural eutrophication -- River inputs -- Run-off

  3. Findings of NOAA’s 2004 National Estuarine Eutrophication Assessment: Extent of eutrophication (measured as number and severity of symptoms)

  4. Findings of NOAA’s National Estuarine Eutrophication Assessment:

  5. System of feedbacks in eutrophication: Short-term / regional-scale stresses Large phytoplankton standing stock Shading of benthos (loss of sea grasses) increased turbidity impacts on benthic community lower filtering ….biological feedbacks Water clarity feedback Nutrient Feedback Large-scale / long-term stresses Kemp et al., 2005

  6. Alternate Stable States Changes in sea floor communities in shallow coastal waters following eutrophication. . (a) The structural diversity afforded by the plants and the availability of oxygen in the sediment promote a diverse community of animals. (b) The loss of structural diversity and oxygen from the sea-bed causes the animal community to be replaced by one of bacterial decomposers. (Open University)

  7. Hypoxia and anoxia in natural and in eutrophied systems Hypoxia: Low dissolved oxygen. Various thresholds, often defined as <2 mg DO l-1 Anoxia: An absence, or near-absence (below detection limits), of dissolved oxygen

  8. The fundamental metabolic processes driving hypoxia Upper mixed layer: Generation of organic matter (Release of O2, use of CO2) Sinking Thermocline Lower layer: Breakdown of organic matter (use of O2, release of CO2) Bacteria Zooplankton Benthic macrofauna

  9. Conditions for bottom hypoxia: • Sufficient nutrients • Excess phytoplankton production (exceeding grazing) • Stratification • Sinking material • Low flushing/long residence time

  10. Chesapeake Bay -- from Zhang et al., 2006 1997 1999 2000 1996 April July Oxygen (ml L-1) October

  11. Extent of hypoxia in Chesapeake Bay is increasing: DO<0.2 mg/l Observed Modeled (Observed flow) Modeled (Avg Flow) Modeled (Low Flow) Modeled (High flow) 109 m3 DO<1.0 mg/l 109 m3 DO<2.0 mg/l 109 m3 2000 1950 Hagy et al., 2004

  12. Rate of oxygen drawdown: Typical = 75 days from winter level to anoxia. Hagy et al., 2004

  13. Main Stem Hood Canal oxygen patterns: Ocean end Hoodsport Density Oxygen

  14. Hood Canal oxygen profiles:

  15. Hood Canal ORCA buoy oxygen profiles:

  16. Ocean Acidification – lowered pH of the ocean due to increased CO2 concentrations. CO2 + H2O ⇌ H2CO3 (carbonic acid) equilibrium H+ + HCO3− (bicarbonate ion) ⇌ H+ + CO32− (carbonate ion) CO2 + CaCO3 + H2O  2HCO3- + Ca2+

  17. ‘Anthropogenic’ acidification • Increased atmospheric CO2 concentrations • ‘Natural’ acidification • Respiration  increased CO2 Atmosphere Feely et al., 2010

  18. Calcium carbonate (as aragonite) saturation depths: from 1991-1996 cruises. Feely et al., 2002

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