Hypoxia in the Northern Gulf of Mexico (eBook)

Acknowledgments 8
Contents 12
List of Figures 16
List of Tables 22
Contributors 26
Glossary 30
List of Acronyms and Symbols 36
Conversion Factors and Abbreviations 42
Executive Summary 44
Findings 45
Recommendations for Monitoring and Research 47
Recommendations for Adaptive Management 49
Management Options 50
Protecting and Enhancing Social Welfare in the Basin 51
Conclusion 52
1 Introduction 53
1.1 Hypoxia and the Northern Gulf of Mexico A Brief Overview 53
1.2 Science and Management Goals for Reducing Hypoxia 55
1.3 Hypoxia Study Group 56
1.4 The Study Groups Approach 59
2 Characterization of Hypoxia 61
2.1 Historical Patterns and Evidence for Hypoxia on the Shelf 61
2.2 The Physical Context 64
2.2.1 Oxygen Budget: General Considerations 64
2.2.2 Vertical Mixing as a Function of Stratification and Vertical Shear 65
2.2.3 Changes in Mississippi River Hydrology and Their Effects on Vertical Mixing 67
2.2.4 Zones of Hypoxia Controls 70
2.2.5 Shelf Circulation: Local Versus Regional 72
2.3 Role of N and P in Controlling Primary Production 75
2.3.1 Nitrogen and Phosphorus Fluxes to the NGOM Background 75
2.3.2 N and P Limitation in Different Shelf Zones and Linkages Between High Primary Production Inshore and the Hypoxic Regions Farther Offshore 76
2.4 Other Limiting Factors and the Role of Si 81
2.5 Sources of Organic Matter to the Hypoxic Zone 83
2.5.1 Sources of Organic Matter to NGOM: Post 2000 Integrated Assessment 85
2.5.2 Advances in Organic Matter Understanding: Characterization and Processes 86
2.5.3 Synthesis Efforts Regarding Organic Matter Sources 89
2.6 Denitrification, P Burial, and Nutrient Recycling 90
2.7 Possible Regime Shift in the Gulf of Mexico 93
2.8 Single Versus Dual Nutrient Removal Strategies 96
2.9 Current State of Forecasting 98
3 Nutrient Fate, Transport, and Sources 103
3.1 Temporal Characteristics of Streamflow and Nutrient Flux 103
3.1.1 MARB Annual and Seasonal Fluxes 108
3.1.1.1 Annual Patterns 108
3.1.1.2 Seasonal Patterns 113
3.1.2 Subbasin Annual and Seasonal Flux 117
3.1.2.1 Annual Patterns 117
3.1.2.2 Annual Flux Estimates 118
3.1.2.3 Annual Yield Estimates 119
3.1.2.4 Seasonal Patterns 124
3.2 Mass Balance of Nutrients 128
3.2.1 Cropping Patterns 128
3.2.2 Nonpoint Sources 129
3.2.3 Point Sources 136
3.3 Nutrient Transport Processes 139
3.3.1 Aquatic Processes 139
3.3.2 Freshwater Wetlands 145
3.3.3 Nutrient Sources and Sinks in Coastal Wetlands 146
3.4 Ability to Route and Predict Nutrient Delivery to the Gulf 148
3.4.1 SPARROW Model 149
3.4.2 SWAT Model 155
3.4.3 IBIS/THMB Model 156
3.4.4 Discussion and Comparison of Models 158
3.4.5 Targeting 158
3.4.6 Model Uncertainty 159
4 Scientific Basis for Goals and Management Options 162
4.1 Adaptive Management 162
4.2 Setting Targets for Nitrogen and Phosphorus Reduction 166
4.3 Protecting Water Quality and Social Welfare in the Basin 171
4.3.1 Assessment and Review of the Cost Estimates from the CENR Integrated Assessment 172
4.3.2 Other Large-Scale Integrated Economic and Biophysical Models for Agricultural Nonpoint Sources 176
4.3.3 Research Assessing the Basin-Wide Co-benefits 179
4.3.4 Principles of Landscape Design 180
4.4 Cost-Effective Approaches for Nonpoint Source Control 184
4.4.1 Voluntary Programs -- Without Economic Incentives 185
4.4.2 Existing Agricultural Conservation Programs 186
4.4.3 Emissions and Water Quality Trading Programs 188
4.4.4 Agricultural Subsidies and Conservation Compliance Provisions 189
4.4.5 Taxes 191
4.4.6 Eco-labeling and Consumer Driven Demand 192
4.5 Options for Managing Nutrients, Co-benefits, and Consequences 194
4.5.1 Agricultural Drainage 194
4.5.1.1 Alternative Drainage System Design and Management 194
4.5.1.2 Bioreactors 196
4.5.2 Freshwater Wetlands 197
4.5.2.1 Nitrogen 197
4.5.2.2 Phosphorus 200
4.5.3 Conservation Buffers 202
4.5.4 Cropping Systems 206
4.5.5 Animal Production Systems 209
4.5.5.1 System Development and Nutrient Flows 209
4.5.5.2 Manure as a Component of N and P Mass Balances 211
4.5.5.3 Remedial Strategies 212
4.5.5.4 Alternative Manure Management Technologies 213
4.5.6 In-Field Nutrient Management 215
4.5.6.1 Fertilizer Sources 215
4.5.6.2 Fertilizer Use and Application Technology 216
4.5.6.3 Watershed-Scale Fertilizer Management 223
4.5.6.4 Controlled-Release Fertilizers 223
4.5.6.5 Effects of N Management on Soil Resource Sustainability 224
4.5.6.6 Precision Agriculture Management Tools for Nitrogen 227
4.5.6.7 Precision Agriculture Management Tools for Phosphorus 229
4.5.6.8 Nutrient Management Planning Strategies 232
4.5.7 Effective Actions for Other Nonpoint Sources 234
4.5.7.1 Atmospheric Deposition 234
4.5.7.2 Residential and Urban Sources 236
4.5.8 Most Effective Actions for Industrial and Municipal Sources 237
4.5.9 Ethanol and Water Quality in the MARB 241
4.5.9.1 Water Quality Implications of Projected Grain-Based Ethanol Production Levels 242
4.5.9.2 Impacts on Nutrient Application to Corn 243
4.5.9.3 Grain Versus Cellulosic Ethanol and Water Quality 244
4.5.10 Integrating Conservation Options 246
5 Summary of Findings and Recommendations 256
5.1 Characterization of Hypoxia 256
5.2 Nutrient Fate, Transport, and Sources 258
5.3 Goals and Management Options 260
5.4 Conclusion 262
Appendices 265
Appendix A: Studies on the Effects of Hypoxia on Living Resources 265
Appendix B: Flow Diagrams and Mass Balance of Nutrients 272
Global Material Cycles 272
Atmospheric Deposition 272
Appendix C: Animal Production Systems 277
Intensification of Animal Feeding Operations 277
Nutrient Budgets 277
Nutrient Surpluses 278
Targeting Remedial Strategies Within the MARB 279
Managing Manures 279
Crop Selected to Receive Manure Application 280
Rate and Frequency of Application 280
Intensity and Duration of Grazing 280
Stream-Bank Fencing 281
Appendix D: Calculation of Point Source Inputs of N and P 281
Appendix E: USUSEPAs Guidance on Nutrient Criteria 283
Comparison of SAB Nitrogen and Phosphorus Recommendations with USEPA Nitrogen and Phosphorus Criteria Recommended Reference Conditions ' Submitted by USEPA's Office of Water, 8-24-07. 284
A More Comprehensive Approach 286
References 289
Subject Index 327

"Chapter 3 Nutrient Fate, Transport, and Sources (p. 51-52)

The Study Group was asked to review the available literature and information, especially that developed since 2000, that would allow them to assess any changes and improvements in the understanding of nutrient sources and flux estimates within the Mississippi and Atchafalaya River basins (MARB) (see Fig. 1.2) and the current ability to use watershed models to route and predict nutrient delivery to the Gulf of Mexico. The following sections discuss the current levels of understanding and provide brief summaries of the Study Group’s key findings and recommendations.

3.1 Temporal Characteristics of Streamflow and Nutrient Flux

The research needs identified in the Integrated Assessment to understand and document the temporal characteristics of MARB riverine nutrient loads included (1) studies on small watersheds to better document nutrient export on the short timescales needed; (2) detailed information on tile drainage intensity; (3) increased monitoring of stream sites; and (4) measurements of point source discharges rather than estimates from permits. Only a limited number of these needs have been met. However, more recent estimates of agricultural drainage appear to be more representative than those used in the original assessment (e.g., see Sands et al., 2008), and new procedures for load calculations have resulted in changes in estimates of nutrient fluxes. A brief discussion of each of the improvements follows. Current extent and patterns of agricultural drainage.

The Integrated Assessment relied largely on the 1987 USDA-ERS report (Pavelis, 1987), which based estimates of agricultural drainage on land capability class and crop information from the 1982 Natural Resources Inventory (NRI). NRI estimates were dropped after 1992, and NRI is statistically valid only at a watershed or county level. Based on the USDA surveys, some degree of subsurface drainage is present on 13 million hectares (over 32million acres) in the Midwest states. However, there is considerable uncertainty with respect to the actual extent and distribution of drainage of cultivated cropland.

In the absence of additional survey data, more recent estimates of the extent of drained agricultural land have been developed based on land use and soil class/characteristics (Jaynes and James, 2007; Sugg, 2007). This general approach needs further development and validation but seems to provide the best current estimate of the extent of agricultural drainage. The approach takes advantage of the now extensive and detailed GIS coverages and provides a considerably finer level of spatial resolution than previously available.

In the following example, USDA STATSGO soil data were used to estimate the extent of agricultural drainage based on the distribution of row crops (primarily corn and soybean) on soils with a drainage class of poorly drained soils and slopes 2% or less (Fig. 3.1, per D. Jaynes, National Soil Tilth Lab, Ames, IA). These patterns of agricultural drainage predicted using this approach are generally similar to patterns in land use (Fig. 3.2) and in-stream nitrate concentration estimated from STORET data selected to exclude point source influences (Fig. 3.3). Drainage estimates could be further refined by using improved land-use data and by using SSURGO rather than STATSGO data."