Since 1985, scientists have been documenting a hypoxic zone in the Gulf of Mexico each year. The hypoxic zone, an area of low dissolved oxygen that cannot s- port marine life, generally manifests itself in the spring. Since marine species either die or ee the hypoxic zone, the spread of hypoxia reduces the available habitat for marine species, which are important for the ecosystem as well as commercial and recreational shing in the Gulf. Since 2001, the hypoxic zone has averaged 2 1 16,500 km during its peak summer months , an area slightly larger than the state 2 2 of Connecticut, and ranged from a low of 8,500 km to a high of 22,000 km . To address the hypoxia problem, the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force (or Task Force) was formed to bring together represen- tives from federal agencies, states, and tribes to consider options for responding to hypoxia. The Task Force asked the White House Of ce of Science and Technology Policy to conduct a scienti c assessment of the causes and consequences of Gulf hypoxia through its Committee on Environment and Natural Resources (CENR).

Based upon a lengthy review conducted by the Hypoxia Advisory Panel (HAP) of the Science Advisory Board for the Environmental Protection Agency (EPA) chaired by Virginia Dale

Table of Figures *List of Tables *Glossary of Terms *List of Acronyms *Conversion Factors and Abbreviations *Executive Summary *1. Introduction *1.1. Hypoxia and the Northern Gulf of Mexico ¿ A Brief Overview *1.2. Science and Management Goals for Reducing Hypoxia *1.3. Hypoxia Study Group *1.4. The Study Group¿s Approach *2. Characterization of Hypoxia *2.1. Processes in the Formation of Hypoxia in the Gulf of Mexico. *2.1.1. Historical Patterns and Evidence for Hypoxia on the Shelf *2.1.2. The Physical Context *2.1.3. Role of N and P in Controlling Primary Production *2.1.4. Other Limiting Factors and the Role of Si *2.1.5. Sources of Organic Matter to the Hypoxic Zone *2.1.6. Denitrification, P Burial, and Nutrient Recycling *2.1.7. Possible Regime Shift in the Gulf of Mexico *2.1.8. Single Versus Dual Nutrient Removal Strategies *2.1.9. Current State of Forecasting *3. Nutrient Fate, Transport, and Sources *3.1. Temporal Characteristics of Streamflow and Nutrient Flux *3.1.1. MARB Annual and Seasonal Fluxes *3.1.2. Subbasin Annual and Seasonal Flux *3.2. Mass Balance of Nutrients *3.3. Nutrient Transport Processes *3.4. Ability to Route and Predict Nutrient Delivery to the Gulf *4. Scientific Basis for Goals and Management Options *4.1. Adaptive Management *4.2. Setting Targets for Nitrogen and Phosphorus Reduction *4.3. Protecting Water Quality and Social Welfare in the Basin *4.4. Cost-Effective Approaches for Nonpoint Source Control *4.4.1. Voluntary programs ¿ without economic incentives *4.4.2. Existing Agricultural Conservation Programs *4.4.3. Emissions and Water Quality Trading Programs *4.4.4. Agricultural Subsidies and Conservation Compliance Provisions *4.4.5. Taxes *4.4.6. Eco-labeling and Consumer Driven Demand *4.5. Options for Managing Nutrients, Co-benefits, and Consequences *4.5.1. Agricultural drainage *4.5.2. Freshwater Wetlands *4.5.3. Conservation Buffers *4.5.4. Cropping systems *4.5.5. Animal Production Systems *4.5.6. In-field Nutrient Management *4.5.7. Effective Actions for Other Nonpoint Sources *4.5.8. Most Effective Actions for Industrial and Municipal Sources *4.5.9. Ethanol and Water Quality in the MARB *4.5.10. Integrating Conservation Options *5. Summary of Findings and Recommendations *5.1. Charge Questions on Characterization of Hypoxia *5.2. Charge Questions on Nutrient Fate, Transport and Sources *5.3. Charge Questions on Goals and Management Options *5.4. Conclusion *References *Appendices *A. Appendix A: Studies on the Effects of Hypoxia on Living Resources *B. Appendix B: Flow diagrams and Mass Balance of Nutrients *C. Appendix C: USEPA¿s Guidance on Nutrient Criteria *D. Appendix D: Calculation of Point Source Inputs of N and P *E. Appendix E: Animal Production Systems *