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 -- River inputs influenced by urbanization + agriculture -- Run-off / Septic systems -- Sewage Treatment Plants Natural eutrophication -- River inputs -- Run-off

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

Findings of NOAA’s National Estuarine Eutrophication Assessment:

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

(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.

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

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 )

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

Chesapeake Bay -- from Zhang et al., 2006 Oxygen (ml L -1 ) April July October

Extent of hypoxia in Chesapeake Bay is increasing: 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

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

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

Hood Canal oxygen profiles:

Hood Canal ORCA buoy oxygen profiles:

CO 2 + CaCO 3 + H 2 O  2HCO 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.

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

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