Transcript ECOLOGICAL CONSEQUENCES OF HYPOXIA IN THE …

A GLOBAL PERSPECTIVE ON THE
LINKAGE BETWEEN
EUTROPHICATION AND HYPOXIA
Robert Diaz
College of William and Mary
Virginia Institute of Marine Science
[email protected]
Outline
•
Global picture on development of
anthroprogenic low dissolved oxygen.
•
Consequences low dissolved oxygen to
ecosystems.
How Nutrient Enrichment and Other Stressors are Connected:
(2) Multiple Stressors
(3) Coastal Ecosystem Responses
(4) Impacts on the
Earth System
Nutrient
Enrichment
Hypoxia
Geochem.
Climate Change
Production
Fishing Harvest
Toxic
Contaminants
(1)
Filter
Energy
Flow
Human Health
Costs
Social and
Economic Costs
Impetus to Build
Science-Based
Benthic/
Pelagic
Predator/
Prey
(5) Tools
Climate System
Exotic Species
Aquaculture
Nutrient
Cycling
Yield
Hydrologic
Manipulations
Rehabilitation/Restoration Actions
Cloern 2001, Marine Ecology Progress Series
Other Impacts
Bottom Line:
Seriousness of low Dissolved Oxygen
best expressed by old motto of
American Lung Association:
“When You Can’t Breathe,
Nothing Else Matters.”
How Eutrophication/Hypoxia
Became A Global Problem
The increasing input of nutrients to coastal
areas over the last 50 years resulted in
system overload.
Strong correlation through time between:
–
–
–
–
population growth.
increased nutrient discharges
increased primary production
increased occurrence of
hypoxia and anoxia.
N
N


People  Standard of Living

Agriculture & Industry
Boesch 2002, Estuaries
Eutrophication/Hypoxia Now a Global Problem:
• Reviewed literature for eutrophication related hypoxia (+700 articles)
• About 200 sites found.
• Listed contributing factors:
• Rising level of nutrients
• Blooms
• Discharge of organic matter
• Hydrological changes
Eutrophication/Hypoxia Now a Global Problem:
Doubling of sites first reporting hypoxia started in 1960s.
OMZ and Upwelling areas not included.
Decade for First Report of Hypoxia
Dacade New Sites
<1910
6
1920
3
1930
5
1940
1
1950
6
1960
12
1970
26
1980
38
1990
87
00-06
13
Hypoxia Type
Episodic
Annual
Periodic
Persistent
%
19
55
10
13
Eutrophication/Hypoxia is now a Global Problem:
Tokyo Bay (Kodama et al. 2002)
Time
Fisheries & WQ
<1930

Mid 30s

Late 40s

Early 70s

Nutrients are one of
many human related
factor in development of
oxygen depletion.
14,000 km2
Annual Hypoxia
Li and Daler 2004
For marine systems
Nitrogen is primary problem.
Current knowledge
restricted by lack of
scientific investigation.
The Size of the Problem
Hypoxic Area
<1000 km2
1000-10000
>10000
%
67
25
8
N
40
15
5
Eutrophication/Hypoxia Consequences to Benthos
 Eutrophication increases organic Carbon:

Increases secondary production

Favors opportunistic species
 Hypoxia becomes a key factor in regulating energy flow:

Forcing ecosystem to pulse through Mortality

Favors opportunistic species
Diaz&Rosenberg 1995
Interaction of Eutrophication/Hypoxia and Energy
Example from Chesapeake Bay
Benthic Monitoring Program
Random Sampling in MD and VA
Summer Sampling from 1996 to 2004
Assumptions:
DO measured at time of sampling
is representative of station’s
annual condition.
Daily production estimated from
individual species AFDW and Edgar
(1990).
Productivity provides an index of
community processes proportional to
total community respiration and
consumption.
Interaction of Eutrophication/Hypoxia and Energy
Daily production was related to DO.
Difference
mg C/m2/day % Reduction
Normoxia-Mild Hypoxia
13
49
Normoxia-Hypoxia
22
85
Interaction of Eutrophication/Hypoxia and Energy
On an annual, Bay wide basis hypoxia reduces secondary production by:
Average Hypoxic Year
Max Hypoxia 1993
Km2
900
3900
P lost mt C/day
11
85
120 average Hypoxic days
1400
10200
Annual, Bay wide secondary production (Diaz and Schaffner 1990):
17 g C/m2/year or 194000 mt C for entire Bay (11,427 km2)
Hypoxia interferes with 1 to 5 % of total production.
Hypoxia creates a separation between pelagic and benthic systems.
Questions:
Is the Bay really 1 to 5 % less productive of benthos?
Is this level of production shifted to normoxic period?
Is this energy required for this production shifted to microbes?
Interaction of Eutrophication/Hypoxia and Energy
Location
Transf er %
Citation
Swedis h Wes t C oas t
66
P ihl 1 9 8 5
51-75
M oller et al. 1 9 8 5
24-34
E vans 1 9 8 4
C hes apeake Bay
39-67
20-60
60
H olland et al. 1 9 8 9
M ars h & T enore 1 9 9 0
D iaz & S c haffner 1 9 9 0
G eorges Bank
30-50
Sis s enwine 1 9 8 4
G alves ton Bay
11-47
Wilber & C larke 1 9 9 8
Interaction of Eutrophication/Hypoxia and Energy
Interaction between Benthic Production, Dissolved Oxygen, and degree of
Eutrophication:
Global Summary






Up to the 1950s, reports of mass mortality of marine
animals caused by lack of oxygen were limited to small
systems that had histories of oxygen stress.
1960s the number of systems with reports of hypoxia
related problems increased. Start of decadal doubling
for first reports.
1970s many large systems report hypoxia.
1980s with increased awareness more reports of
hypoxia.
1990s most estuarine and marine systems in close
proximity to population centers report oxygen depletion.
First report of coastal upwelling hypoxia being
worsened by additional nutrients.
2000s will doubling continue?
Global Summary


Low dissolved oxygen has potential to be
driver for regime shift.
1990s some improvement in hypoxia was
observed in large systems:


Improvement seen in some systems from
nutrient regulation:



Black Sea, Gulf of Finland
Hudson River, Delaware River, East River
Mersey Estuary, Elbe Estuary, Idefjord
No improvement in some systems with
nutrient regulation:

Chesapeake Bay, Lake Erie, Tokyo Bay
Ecosystem response to Eutrophication/Hypoxia



Increased organic matter leads to increase
biomass, but Hypoxia/Anoxia tend to reduce
biomass.
Opportunistic species favored, lower species
diversity, and increased importance of
microbes.
Response to hypoxia related to:
 Concentration of dissolved oxygen
 Duration
Nestlerode&Diaz 1998