Understanding the Global Linkage Between Eutrophication and Hypoxia

1. A GLOBAL PERSPECTIVE ON THE LINKAGE BETWEEN EUTROPHICATION AND HYPOXIA Robert Diaz College of William and Mary Virginia Institute of Marine Science diaz@vims.edu

2. Outline • Global picture on development of anthroprogenic low dissolved oxygen. • Consequences low dissolved oxygen to ecosystems.

3. 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. Human Health Costs (1) Filter Climate Change Production Energy Flow FishingHarvest Social and Economic Costs Impetus to Build Science-Based (5) Tools Toxic Contaminants Predator/ Prey Benthic/ Pelagic Climate System Exotic Species Nutrient Cycling Yield Other Impacts Aquaculture Hydrologic Manipulations Rehabilitation/Restoration Actions Cloern 2001, Marine Ecology Progress Series

4. Bottom Line: Seriousness of low Dissolved Oxygen best expressed by old motto of American Lung Association: “When You Can’t Breathe, Nothing Else Matters.”

5. 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

6. 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

7. 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

8. Eutrophication/Hypoxia is now a Global Problem: Tokyo Bay (Kodama et al. 2002) Time Fisheries & WQ <1930  Mid 30s  Late 40s  Early 70s 

9. 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.

10. The Size of the Problem

11. 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

12. 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.

13. Interaction of Eutrophication/Hypoxia and Energy Daily production was related to DO.

14. Interaction of Eutrophication/Hypoxia and Energy On an annual, Bay wide basis hypoxia reduces secondary production by: 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?

15. Interaction of Eutrophication/Hypoxia and Energy

16. Interaction of Eutrophication/Hypoxia and Energy Interaction between Benthic Production, Dissolved Oxygen, and degree of Eutrophication:

17. 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?

18. Global Summary • Low dissolved oxygen has potential to be driver for regime shift. • 1990s some improvement in hypoxia was observed in large systems: • Black Sea, Gulf of Finland • Improvement seen in some systems from nutrient regulation: • 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

19. 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