1. Global Nitrogen Cycle, Eutrophication, and Coastal Hypoxia: State of Knowledge and Management
Robert J Díaz

2. Bringing the problem into focus

3. How Eutrophication/Hypoxia Became a Global Problem
Economic growth from expanding population caused increasing input of nutrients to coastal areas over last 60 years resulted in system overload.
Strong correlation through time between:
population growth and agriculture expansion
increased nutrient discharges and disruption of global cycles
increased primary production
increased occurrence of hypoxia and anoxia.
7,000,000,000 by end of 2011.
9,000,000,000 by 2050.

4. Bringing the problem into focus
From the start of the ‘Industrial Revolution’ in 1700s it has taken >100 years to alter global Carbon Cycle.
With the start of the ‘Green Revolution’ in 1940s it took <50 years to alter global Nitrogen Cycle.

5. Fate of Haber-Bosch Nitrogen
14% of N produced in Haber-Bosch process enters the human mouth if you are a vegetarian.
4% of N used for animal production enters human mouth.
82% of N is lost to the environment.

6. Reactive Nitrogen
Galloway et al. 2008

7. Global Nitrogen Cycle
Gruber & Galloway 2008

8. What are Consequences?
Caddy 2000

9. What is at stake for our future
What is at stake for our future? Coastal and Continental Shelf Habitats Fisheries Production

10. Eutrophication Driven Dead Zones Oxygen Minimum Zones
550 Hypoxic Areas
60 Hypoxic Areas in recovery
250 Eutrophic Areas in Danger of Hypoxia
OMZ Touching 1,150,000 km2 of Seabed
Helly & Levin 2004
Diaz et al. 2010

11. Area of Ecosystem Affected
Hypoxic Habitat:
Total Area
(Km2)
Hypoxic Area (Km2)
Habitat Hypoxic
Global Flow Lost to Hypoxia
Shelf from
OMZ
26,600,000
1,150,000
4.3%
0.4%
Nutrients
170,000
0.6%
0.1%
Estuaries
1,800,000
70,000
6.9%
Costanza et al. 1997, Helly and Levin 2004, Diaz and Rosenberg 2008

12. What are the direct causes?
Coastal dissolved oxygen trends
are driven by:
Runoff from land
Point discharges
Global climate change

13. Two Part Key to Future Hypoxia
Diaz & Breitburg 2010

14. Management of Hypoxia
Prevention and long-term remediation can be achieved by reducing excess nutrients (N & P) entering from the land, atmosphere, and groundwater.
Nutrient reduction will require:
Knowledge of local environmental conditions.
Diagnosis of main nutrient sources.
Integrated, cross-sector land & sea management.

15. Management of Hypoxia Science supporting hypoxia reduction is complex.
But
Current scientific understanding is sufficient to support managing in an ecosystem context.

16. Recovered with Nutrient Management
There is encouraging news. Small and large systems such as the Black Sea and Boston Harbor have responded positively to decreased anthropogenic stressors.
In all cases where hypoxia has be significantly reduced, it has been achieved through intense nutrient management or reduction.
60 systems have responded positively.

17. Mangement of Hypoxia
Not all hypoxia can be readily controlled but
case-specific knowledge can clarify solutions.
Causes and effects are embedded in economic and societal values:
Land-use and development policies can constrain nutrient reduction actions.
Changing relationship of ecosystem response to nutrients and hypoxia.
Coastal regime changes or threshold shifts will require managers to work with new conditions

18. Policy Issues to Overcome to Solve Hypoxia
Management Side:
Cross-sector mission conflicts.
Inadequate pollution management.
Low environmental awareness among policymakers and public as to the ecological and economic costs.
Lack of a master plan for the coastal area as a whole (Coastal Zone Planning).

19. Knowledge Gaps to Overcome to Solve Hypoxia
Science Side:
Habitat loss/alteration impacts on populations and economies.
Nutrient sources, loadings, and transformations.
Natural factors and climate change.
Provide holistic ecosystem view.