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Eutrophication, Hypoxia, and Ocean Acidification Puget Sound Oceanography 2011.

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Presentation on theme: "Eutrophication, Hypoxia, and Ocean Acidification Puget Sound Oceanography 2011."— Presentation transcript:

1 Eutrophication, Hypoxia, and Ocean Acidification Puget Sound Oceanography 2011

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 Kemp et al., 2005 System of feedbacks in eutrophication: Nutrient Feedback Water clarity feedback Large-scale / long-term stresses 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

6 (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). Alternate Stable States Changes in sea floor communities in shallow coastal waters following eutrophication.

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 Bacteria Zooplankton Benthic macrofauna Sinking Thermocline Upper mixed layer: Generation of organic matter (Release of O 2, use of CO 2 ) Lower layer: Breakdown of organic matter (use of O 2, release of CO 2 )

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 Oxygen (ml L -1 ) 1996 199719992000 April July October

11 Extent of hypoxia in Chesapeake Bay is increasing: 1950 2000 DO<0.2 mg/l DO<1.0 mg/l DO<2.0 mg/l 10 9 m 3 Observed Modeled (Observed flow) Modeled (Avg Flow) Modeled (Low Flow) Modeled (High flow) 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:

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18 CO 2 + CaCO 3 + H 2 O  2HCO 3 - + Ca 2+ CO 2 + H 2 O ⇌ H 2 CO 3 (carbonic acid) equilibrium H + + HCO 3 − (bicarbonate ion) ⇌ H + + CO 3 2− (carbonate ion) Ocean Acidification – lowered pH of the ocean due to increased CO 2 concentrations.

19 Feely et al., 2010 ‘Anthropogenic’ acidification Increased atmospheric CO 2 concentrations ‘Natural’ acidification Respiration  increased CO 2 Atmosphere

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

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