eutrophication, hypoxia, and ocean acidification puget sound oceanography 2011
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
Eutrophication, Hypoxia, and Ocean Acidification
Puget Sound Oceanography2011
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:
Nu
trie
nt
Fe
ed
ba
ck
Wa
ter
cla
rity
fee
db
ack
Large-scale / long-term stresses
Short-term / regional-scale stresses
Large phytoplankton standing stockShading of benthos (loss of sea grasses)increased turbidityimpacts on benthic communitylower 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 StatesChanges 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
BacteriaZooplankton
Benthic macrofauna
Sin
king
Thermocline
Upper mixed layer:Generation of organic matter(Release of O2, use of CO2)
Lower layer:Breakdown of organic matter(use of O2, release of CO2)
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
Ox
yg
en
(m
l L
-1)
1996 1997 1999 2000
April
July
October
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
109
m3
109
m3
109
m3
ObservedModeled (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:
CO2 + CaCO3 + H2O 2HCO3- + Ca2+
CO2 + H2O ⇌ H2CO3 (carbonic acid) equilibrium
H+ + HCO3− (bicarbonate ion) ⇌ H+ + CO3
2− (carbonate ion)
Ocean Acidification – lowered pH of the ocean due to increased CO2 concentrations.
Feely et al., 2010
• ‘Anthropogenic’ acidification• Increased atmospheric CO2 concentrations
• ‘Natural’ acidification• Respiration increased CO2
Atmosphere
Feely et al., 2002
Calcium carbonate (as aragonite) saturation depths: from 1991-1996 cruises.