Science for Solutions -

NOAA COASTAL OCEAN PROGRAM 

Decision Analysis Series No. 

Reducing Nutrient Loads, Especially 

Nitrate-Nitrogen, to Surface Water, Ground Water, 

and the Gulf of Mexico 

Topic 5 Report for the Integrated Assessment 

on Hypoxia in the Gulf of Mexico 

William J. Mitsch, JohnW. Day, Jr., 

J. Wendell Gilliam, Peter M. Groffman, Donald L. Hey, 

Gyles W. Randall, and Naiming Wang 

May 1999 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Ocean Service 

Coastal Ocean Program 
GULF OF MEXICO HYPOXIA ASSESSMENT 

This report is the fifth in a series of six reports developed as the scientific basis for an integrated assessment 

of the causes and consequences of hypoxia in the Gulf 

of Mexico, as requested by the White House Office of 

Science and Technology Policy and as required by Section 604a of P.L. 105-383. For more information on the 

assessment and the assessment process, please contact 

the National Centers for Coastal Ocean Science at 

(30 1) 7 13-3060. 

DECISION ANALYSIS SERIES 

The Decision Analysis Series has been established by 

NOAA's Coastal Ocean Program (COP) to present 

documents for coastal decision makers which contain 

analytical treatments of major issues or topics. The issues, topics, and principal investigators have been selected through an extensive peer review process. To 

learn more about the COP or the Decision Analysis 

Series, please write to: 

NOAA 

National Centers for Coastal Ocean Science 

Coastal Ocean Program 

13 15 East-West Highway, Room 9700 

Silver Spring, Maryland 209 10 

phone: 301-713-3338 

fa: 30 1 -7 1 3-4044 

web: http://www.cop.noaa.gov 

e-mail: coastalocean@cop.noaa.gov 

Cover image: Nitrogen transformation in wetlands. 
Science for Solutions 

NOAA COASTAL OCEAN PROGRAM 

DecisionAnalysis Series No. 19 

Reducing Nutrient Loads, Especially 

Nitrate-Nitrogen, to Surface Water, Ground Water, 

and the Gulf of Mexico 

Topic 5 Report for the Integrated Assessment 

on Hypoxia in the Gulf of Mexico -

William J. Mitsch, The Ohio State University 

JohnW. Day, Jr.,LouisianaState University 

J. Wendell Gilliam, North Carolina State University 

Peter M. Groffman, Institute of Ecosystem Studies 

Donald L. Hey, The Wetlands Initiative 

Gyles W. Randall, University of Minnesota 

Naiming Wang, The Ohio State University 

May 1999 

U.S. DEPARTMENT OF COMMERCE 

William M. Daley, Secretary 

National Oceanic and Atmospheric Administration 

D. James Baker, Undersecretary for Oceans and Atmosphere 

National Ocean Service 

Nancy Foster, Assistant Administrator 

National Centers for Coastal Ocean Science 

Donald Scavia, Director 

Center for Sponsored Coastal Ocean Research-Coastal Ocean Program 

David Johnson. Director 
This publication should be cited as: 

Mitsch, William j., John W. Day, Jr., j. Wendell Gilliam, Peter M. ,Groffman, Donald L. Hey, 

Gyles W. Randall, and Naiming Wang. 1999. Reducing Nutrient Loads, Especially NitrateNitrogen, to Surface Water, Ground Water, and the Gulf of Mexico: Topic 5 Report for the 

Integrated Assessment on Hypoxia in the Gulf of Mexico. NOAA Coastal Ocean Program Decision Analysis Series No. 19. NOAA Coastal Ocean Program, Silver Spring, MD. I I I pp. 

Corresponding author information: 

William J. Mitsch 

Director, Olentangy River Wetland Research Park 

Professor, School of Natural Resources 

The Ohio State University 

2021 Coffey Road 

Columbus, Ohio 432 10 

This publication does not constitute an endorsement of any commercial productl 

or intend to be an opinion beyond scientific or other result; obtained by the National Oceanic and Atmospheric Administration (NOAA). No reference shall be 

made to NOAA, or to this publication furnished by NOAA, in any advertising or 

sales promotion that would indicate or imply that NOAA recommends or endorses any proprietary product mentioned herein, or that has as its purpose an interest to cause directly or indirectly the advertised product to be used or purchased 

1 because of this publi;ation. 
I 

Contents 

LIST OF FIGURESAND TABLES .................................................................................................vi 

LIST OF ABBREVIATIONS AND ACRONYMS ............................................................................x 

.. ACKNOWLEDGMENTS ..............................................................................................................XII 

... FOREWORD .............................................................................................................................XIII 

EXECUTIVE SUMMARY .............................................................................................................xv 

INTRODUCTION ..................................................................................................................I 

The Gulf of Mexico Hypoxia.................................................................................................. I 

Objectives ............................................................................................................................... 3 

Nutrient Sources to the Gulf of Mexico............................................................................... 3 

1.3.1 Crop production and soil drainage............................................................................ 5 

1.3.2 Feedlot discharges ...................................................................................................... 6 

1.3.3 Other nonpoint sources............................................................................................. 7 

1.3.4 Point-source discharges............................................................................................. 7 

1.3.5 Atmospheric sources................................................................................................. 7 

RESULTS-APPROACHES FOR CONTROLLINGNITROGEN .....................................10 

On-Site Control of Agricultural Drainage .............................................................; ..........I0 

The role of precipitation on agricultural drainage ..................................................II 

3.1 .1. I Precipitation and drainage ......................................................................... I I 

3.1.1.2 Precipitation and nitrate concentrations .................; ................................12 

3.1 .1 .3 Preci~itationand residual soil nitrate .......................................................13 

3.1 .1 .4 Precipitation and nitrate loads ..................................................................14 

3.1 . 1 .5 Long-term changes in precipitation .......................................................15 

Changing cropping systems .................................................................................... I5 

Controlling nitrogen fertilizer application rates ..................................................16 

Managing manure spreading ..................................................................................... 19 

Managing the time of nitrogen application ............................................................... 19 

Using nitrification Inhibitors .................................................................................... 20 

Changing tillage methods ......................................................................................... I 

Increasing drainage tile spacing ................................................................................. 22 

iii 
iv ReducingNutrient Loadsto Surface and Ground Waters and the Gulf 

Off-Site Agricultural Nonpoint-Source Control ................................................................ 22 

3.2.1 Nitrogen processes in wetlands and riparian systems ...........................................24 

3.2.2 Wetlands................................................................................................................... 26 

3.2.2.1 Natural freshwater marshes .........................., ..........................................27 

3.2.2.2 Created and restored marshes .................................................................27 

3.2.2.3 Peatlands .................................................................................................... 29 

3.2.2.4 Forested wetlands..................................................................................... 30 

3.2.2.5 Case studies-Nitrogen retention by wetlands in the Midwest .............30 

3.2.2.6 Design considerations ............................................................................... 37 

3.2.3 Riparian buffers......................................................................................................... 43 

3.2.3.1 Design considerations and limitations ...................................................... 44 

3.2.3.2 Comparison of wetlands and riparian buffers ..........................................47 

3.2.4 Controlled drainage .................................................:...............................................48 

3.2.4.1 Design considerations and limitations ......................................................48 

3.2.4.2 Controlled drainage in the Midwest.........................................................52 

Urban Nonpoint Source Control.......................................................... :.............................53 

3.3.1 Existing development ............................................................................................... 54 

3.3.1. I Stormwater runoff.................................................................................... 54 

3.3.1 .2 On-site sewage disposal systems .............................................................56 

3.3.2 New development.................................................................................................... 57 

Point-Source Control .......................................................................................................... 58 

3.4.1 Environmental technology ........................................................................................ 58 

3.4.1 .I Physical/chemical processes...................................................................... 60 

3.4.1.2 Biological processes.................................................................................. 60 

3.4.1.3 Feasibility................................................................................................... I 

3.4.2 Ecotechnology-treatment wetlands ...................................................................... 61 

3.4.2.1 Surface or subsurface flow........................................................................I 

3.4.2.2 Treatment wetland design ........................................................................ 63 

Control of Atmospheric N O, ............................................................................................. 64 

3.5.1 Stationary sources................................................................................................64 

3.5.1. I Modified combustion processes ............................................................... 65 

3.5.1.2 Post-combustion processes ...................................................................... 65 

3.5.2 -Mobile sources......................................................................................................... 66 

315.2.1 Base engine improvement ........................................................................66 

3.5.2.2 Improvements in air-fuel ratio control ....................................................67 

3.5.2.3 Improvements to exhaust after-treatment systems................................67 

3.5.2.4 Advanced technologies .............................................................................. 67 

3.5.3 Regulatory issues ...................................................................................................... 67 

3.5.3.1 Recent developments................................................................................ 67 

Mississippi Delta Diversions................................................................................................ 69 

3.6.1 The Mississippi Delta............................................................................................... 70 

3.6.2 Nitrogen dynamics in deltaic wetlands and shallow coastal waters.......................71 

3.6.3 Case studies-Mississippi River diversions ............................................................I 

3.6.3.1 The Caernarvon freshwater diversion .....................................................I 

3.6.3.2 The Bonnet Carre Spillway ....................................................................... 75 

3.6.3.3 The Atchafalaya Delta region.................................................................... 77 

3.6.4 Advantages and limitations of coastal restoration ..................................................80 

Upper Mississippi River Flood Control and Restoration..................................................80 
Contents 9' 

4. REDUCING NUTRIENT LOADINGS TO THE GULFOF MEXICO ...............................82 

4.1 Best Practices for Reducing Nitrogen Loadings ..................................................................82 

4.2 Changing Farm Practices ......................................................................................................82 

4.3 Intercepting Agricultural Drainage with Wetlands and ~i~arian' Buffers ............................84 

4.3.1 Wetlands...................................................................................................................84 

4.3.2 Riparian zones ..........................................................................................................85 

4.3.3 Local benefits ............................................................................................................86 

4.3.3.1 Local water quality improvement .............................................................86 

4.3.3.2 Wetland restoration .................................................................................86 

4.3.3.3 River ecology enhancement ......................................................................87 

4.3.3.4 Terrestrial wildlife enhancement .............................................................87 

4.3.3.5 Flood control .............................................................................................87 

4.4 Tertiary Treatment of Domestic Wastewater ................................................................. 88 

4.5 River Diversions in Louisiana..............................................................................................88 

4.6 Mitigating Issues .................................................................................................................... 89 

4.6.1 Scale effect ................................................................................................................89 

4.6.2 Comparing "apples and oranges" .............................................................................89 

4.6.3 System delay and buffering .......................................................................................89 

4.6.4 Agricultural production ............................................................................................89 

4.6.5 Other nutrients ........................................................................................................90 

4.6.6 Long-term prognosis................................................................................................90 

4.6.7 Catastrophic events ..................................................................................................90 

4.6.8 Uncertainty of ecotechnology ..................................................................................90 

4.6.9 Production of greenhouse gases..............................................................................I 

5 . RESEARCHNEEDS ............................................................................................................92 

6 . CONCLUSIONSAND RECOMMENDATIONS.................................................................94 

6.1 Conclusions....................................................................................i...................................94 

6.2 Recommendations...............................................................................................................94 
List of Figures and Tables 

FIGURES 

FIGURE 1.1. 

FIGURE 1.2. 

FIGURE 3.1. 

FIGURE 3.3. 

FIGURE 3.4. 

FIGURE 3.5. 

FIGURE 3.6. 

FIGURE 3.7. 

FIGURE 3.8. 

FIGURE 3.9. 

The Mississippi River Basin and location of the Gulf of Mexico hypoxia..............2 

Estimated trends in the 20th century of the hypoxia area, nitrogen 

concentrations and fluxes, nitrogen fertilizer use, and land drainage 

in the Mississippi River Basin ..................................................................................4 

Relationship between subsurface drainage volume and: (a) annual flowweighted nitrate-nitrogen concentration; (b) annual nitrate-nitrogen loss 

in tile-drainage water from a corn-soybean rotation that received 150 kg 

N/ha as anhydrous ammonia in late October each year following soybeans 

at Waseca, MN; (c) annual flow-weighted nitrate-nitrogen concentration; 

and (d) annual nitrate-nitrogen loss in tile-drainage water from continuous 

corn that received 200 kg N/ha each spring at Waseca, MN ...............................13 

Nitrate-nitrogen concentration in tile-drainage water as affected by rate 

of nitrogen fertilizer application for continuous corn at (a) Lamberton 

and (b) Waseca, MN ............................................................................................. 18 

Extent and location of artificially drained agricultural land in the 

United States......................................................................................................... 23 

Nitrogen transformation in wetlands....................................................................25 

Three types of wetlands that could be used to control nonpoint-source 

pollution: (a) freshwater marsh, (b) peatland, and (c) riparian forest....................28 * 

Four original experimental wetlands at the Des Plaines River Wetland 

Demonstration Project in northeastern Illinois....................................................31 

A strong seasonal pattern of nitrate-nitrogen and total nitrogen typical of 

midwestern U.S. streams was seen with high concentrations in the spring 

and fall (inlet data) from the Des Plaines River in northeastern Illinois..............32 

Olentangy River Wetland Research Park, Columbus, OH, showing 

two l-ha experimental deep-water marshes used in a multi-year study 

of nitrate-nitrogen retention.. ............................................................................. ..35 

Seasonal patterns of nitrate retention by mass and concentration during 

summer, autumn, winter, and spring for (a) wastewater treatment 

wetland in Licking County, OH, and (b) and (c) l-ha river-fed created 

wetlands in Franklin County, O H........................................................................ 36 
List of Figures and Tables vii-' 

FIGURE 3.10. 

FIGURE 3.11. 

FIGURE 3.14. 

FIGURE 3.15. 

FIGURE 3.16. 

FIGURE 3.17. 

FIGURE 3.18. 

FIGURE 3.19. 

FIGURE 3.20. 

FIGURE 3.21. 

FIGURE 3.22. 

FIGURE 3.23. 

FIGURE 3.24. 

FIGURE 3.25. 

Summary of 17 wetland-years of nitrate-nitrogen retention data from the 

Des Plaines River (IL) and Olentangy River (OH) experimental wetlands ........38 

Examples of wetland nitrogen retention versus loading rate: (a) nitrogen 

retention from several constructed and natural wetlands, and (b) 

cumulative nitrogen mass retained versus mass loading of a marsh 

receiving low-level nutrients for eight years ..........................................................39 

Nitrogen retention in an Australian wetland in an agricultural area 

during storm events showing (a) seasonal pattern of retention and release, 

and (b) effect of storm flow on retention or release..............................................40 

Examples of locations of createdhestored wetlands in the landscape: (a) 

riparian bifurcation of river; (b) riparian wetland with seasonal flooding; 

(c) created marshes in small streams and intercepting tile drainage; (d) 

details of lateral wetland interceptingground water carried by drainage tiles; 

(e) landscape location choices for wetlands; and (f) terraced in hilly terrain.........42 

Hypothetical locations of riparian buffers, farm ponds, constructed 

wetlands, and grassed waterways in region of livestock facilitie. ...........................43 

Schematics of riparian buffer zones: (a) three-zone riparian buffer system, and 

(b) multi-species riparian buffer strip model, which includes tree rows closest 

to the stream, shrubs, and a strip of switchgrass adjacent to the cropland ............45 

Controlled drainage system showing (a) flashboard riser and (b) water 

profile in drainage ditch upstream of flashboard riser............................................50 

Results of controlled drainage study represent approximately 125 site-years 

of data from 14 sites in eastern North Carolina showing: (a) average annual 

outflows, and (b) average annual nitrogen transport (TKN + NO,-N) in 

drainage outflow as measured at the field edge for 14 soils and sites.....................51 

Decision tree for determining which nitrate control practice to use ....................52 

Schematic showing differences between (a) surface-flow and 

(b) . subsurface-flow treatment wetlands ...............................................................-62 

Hypothetical nitrogen fluxes in wastewater treatment wetlands based 

on hydrologic loading of 5.5 crdday and first-order decay rates 

determined from multiple sites .............................................................................. 63 

Combustion and post-combustion NO, control options for stationary sources...65 

Stationary and mobile NO, control cost range by source category .......................68 

Caernarvon diversion and Breton Sound Estuary in coastal Louisiana ................72 

Pre- and post-diversion data with standard error bars for Louisiana's 

Breton Sound Estuary for (a) nitrite + nitrate; (b) ammonium-nitrogen, 

(c) total Kjeldahl nitrogen, and (d) total nitrogen ................................................73 

Post-diversion salinity mixing curve and overall averages at each water 

quality station for (a) nitrite + nitrate-nitrogen, (b) ammonium-nitrogen, 

(c) total Kjeldahl nitrogen, and (d) total nitrogen ................................................74 
viii ReducingNutrient Loads to Surface and Ground Waters and the Gulf 

FIGURE 3.26. 

FIGURE 3.27. 

FIGURE 3.28. 

TABLES 

TABLE 1.1. 

TABLE 1.2. 

TABLE3.1. 

TABLE 3.2. 

TABLE 3.3. 

TABLE 3.4. 

TABLE 3.5. 

TABLE 3.7. 

TABLE 3.8. 

TABLE 3.9. -

TABLE 3.10. 

TABLE 3.11. 

TABLE 3.12. 

TABLE 3.14. 

Map of Lake Pontchartrain near New Orleans, Louisiana, showing 

the locations of the Bonnet CarrC Spillway and sampling stations ......................76 

Atchafalaya Bay and Fourleague Bay in coastal Louisiana ....................................78 

Nitrate concentrations in various transects from Atchafalaya River to 

coastal waters 'for spring, summer, fall, and winter ...............................................79 

Sources of nitrogen and phosphorus in the Mississippi River Basin 

and export from the basin via the river ....................................................................3 

Contrast of nutrient concentrations in secondary effluent from a 

municipal wastewater treatment plant, wastewater from a confined 

animal feeding operation, runoff from croplands of the midwestern 

U.S., and urban (residential) runoff ........................................................................6 -

Possible approaches for controlling nitrogen in the Mississippi River Basin........10 

Influence of precipitation on drainage volume and annual nitrateN losses........11 

Annual water loss via subsurface tile drainage for cropping systems in Iowa.. ......12 

Effect of crop system on amount of subsurface drainage water ............................12 

Effect of crop system on flow-weighted annual nitrate-N concentrations 

and four-year total nitrate-N loss .......................................................................... 15 

Average nitrate concentration and annual nitrate loss in subsurface, 

tile-drainage water in Iowa as a function of crop and tillage technique ...............16 

Effect of nitrogen application rate and time of application on 

nitrate-N losses and corn yield ..............................................................................20 

Effect of time of N application and nitrapyrin on nitrate-N losses 

and corn yield in a corn-soybean rotation during 1990-93 ..................................20 

~ffictof tillage on nitrate losses in subsurface drainage .......................................21 

Drainage statistics of selected states in the upper reaches of the ..... Mississippi ILver Basin........................................................................................... 23 

Nitrogen loss rates as reported in the literature for wetland and . . nparlan zone studies............................................................................................... 26 

Selected studies that have investigated nitrogen retention of natural 

and created freshwater marshes, peatlands, and forested wetlands 

and riparian zones .................................................................................................. 29 

Nitrate reduction in the experimental wetlands at the Des Plaines 

River Demonstration Project, Lake County, IL ...................................................33 

Annual nitrate-nitrogen, organic nitrogen, and total nitrogen budgets 

for the Des Plaines River experimental wetlands, April-November 1991 ............33 
List of Figures and Tables ix. 

TABLE 3.15. 

TABLE 3.16. 

TABLE 3.17. 

TABLE 3.18. 

TABLE 3.20. 

TABLE 3.21. 

TABLE 3.22. 

TABLE 3.23. 

TABLE 3.24. 

TABLE 3.25. 

TABLE 3.26. 

Average + standard error (# samples) of weekly nutrient concentrations 

at Olentangy River experimental wetlands, 1994-96 ............................................34 

Above-ground woody . . vegetation uptake of nitrogen and phosphorus 

in coastal plain rlpanan forests ......................................!........................................47 

Estimated mean runoff concentrations for land uses, based on the 

nationwide urban runoff program .........................................................................53 

Comparison of percolation of nitrate-nitrogen from fertilized 

and unfertilized urban lawn with fertilized corn cropland ....................................53 

Summary of existing development management practices for 

controlling sediments, phosphorus, and nitrogen in urban runoff .......................55 

On-site sewage disposal system effectiveness and cost summary...........................56 

Step-by-step guide to watershed management for new urban sources 

of pollution................................................................................1..........................59 

Nitrate and total nitrogen removal rates and efficiency of natural 

and constructed wastewater wetlands, as averaged from a number 

of systems in North America.................................................................................64 

Feasible technologies for NO, emission reductions (from Tier 1 levels) 

for mobile sources.. ................................................................................................ -66 

Coal-fired boiler types and the best continuous control systems used 

by EPA to establish NO, emission limits under Title IV of the 

Clean Air Act Amendments ................................................................................. 68 

List of potential Tier 2 technologies and associated emission reductions 

of NO, for mobile sources...................................................................................... 69 

Nutrient loading rates and removal efficiency of wetlands north of the 

first two water quality monitoring stations at the Caernarvon freshwater 

diversion of the Mississippi River, Louisiana .........................................................75 

TABLE4.1. - Recommended approaches for reducing significant amounts of 

nitrogen loading to streams and rivers in the Mississippi River Basin 

and the Gulf of Mexico .........................................................................................83 

TABLE4.2. Estimated area of riparian forests needed to control nitrogen in the 

Mississippi River Basin and selected sub-basins, assuming a reduction 

of 15 g-N/m2-yr ..................................................................................................... 85 

TABLE4.3. Estimated area of riparian forests needed to control nitrogen in the 

Mississippi River Basin and selected sub-basins, assuming a reduction 

2 of 4 g-N/m -yr....................................................................................................... 86 
I 

List of Abbreviations and Acronyms 

BACI 

BOD 

CAAA 

CNG 

CP 

CRP 

CT 

CZARA 

DIN 

Eff ' 

EGR 

ET 

EW 

HDE 

HEGO 

HLR 

IHNC 

LDT 

LDV 

LEV 

LNB 

LR 

MP 

MRB 

N 

NI 

NO, 

NO, + NO3 

NO3 

NPS 

NRC 

NT 

OSDS 

RR 

RSN 

RT 

SCR 

SNCR 

TKN 

Before-After, Control-Impact Analysis 

Biochemical Oxygen Demand 

Clean Air Act Amendments 

Compressed natural gas 

Chiselplow 

Conservation Reserve Program 

Conventional tillage 

Coastal Zone Act Reauthorization Amendments 

Dissolved inorganic nitrogen 

Efficiency 

Exhaust gas recirculation 

Evapotranspiration 

Experimental wetland 

~eky-dut~ engine 

Heated exhaust gas oxygen sensors 

Hydraulic loading rate 

Inner Harbor Navigation Canal 

Light-duty truck 

Light-duty vehicle 

Low-emission vehicle 

Low-NO, burner 

Loading rate 

Moldboard plow 

Mississippi River Basin 

Nitrogen 

Nitrapyrin 

NO and NO, (gas) 

Nitrite plus nitrate (dissolved in water) 

Nitrate 

Nonpoint source 

National Research Council 

No tillage 

On-site sewage disposal 

Removal rate 

Residual soil nitrate 

Ridge tillage 

Selective catalytic reduction 

Selective noncatalytic reduction 

Total Kjeldahl nitrogen 
List of Abbreviations and Acronyms xiTN 

TP 

TSS 

UEGO 

ULEV 

USDA 

USEPA 

ZEV 

Total nitrogen 

Total phosphorus 

Total suspended solids 

Universal exhaust gas oxygen sensors 

Ultra-low-emission vehicle I 

United States Department of Agriculture 

United States Environmental Protection Agency 

Zero-emission vehicle 
1 

Acknowledgments 

We would like to thank Terry LeMaster for her cheerful assistance in arranging all of the committee meetings, both in St. Louis and over the phone. Eric Domyan provided a valuable literature review on point-source technology. Sarah Harter and Virginie Bouchard assisted with many 

aspects of this study. Raghavan Srinivasan of Texas A&IM participated in our first meeting's discussion. Ruthmarie H. Mitsch assisted with manuscript proofing. 

We appreciate the efforts of Don Scavia, Mike Dowgiallo, and others at NOAA's Coastal 

Ocean Program in Silver Spring, MD, for their leadership and assistance in the project. We also 

appreciate the support provided by the Gulf of Mexico Program of the U.S. Environmental 

Protection Agency, Stennis Space Center, Mississippi, on Grant #MX984357-98-0. 

Jerry Hatfield coordinated a comprehensive and useful peer-review process. We would also like to 

thank the six anonymous reviewers for the time that they took to do provide very useful comments to the authors. 

Riparian information on habitat was largely taken from USDA's Riparian Forest Bufler Handbookfor the Chesapeake Bay Watershed, 1997. Thanks to A1 Todd for letting us use the draft version of this document. Don Goolsby was very accommodating in providing much-needed data 

on nitrogen sources. 

Thanks go to our home institutions for allowing us the time to complete this project: The Ohio 

State University, Louisiana State University, University of Minnesota, North Carolina State 

University, Institute of Ecosystem Studies, and The Wetlands Initiative. 

xii 
Foreword I 

Nutrient overenrichment from anthropogenic sources is one of the major stresses on coastal 

ecosystems. Generally, excess nutrients increase algal production and the availability of organic 

carbon within an ecosystem-a process known as eutrophication. Scientific investigations in the 

northern Gulf of Mexico have documented a large area of the Louisiana continental shelf with 

seasonally depleted oxygen levels (< 2 mg/l). Most aquatic species cannot survive at such low oxygen levels. The oxygen depletion, referred to as hypoxia, forms in the middle of the most important commercial and recreational fisheries in the conterminous United States and could threaten 

the economy of this region of the Gulf. 

As part of a process of considering options for responding to hypoxia, the U.S. Environmental 

Protection Agency (EPA) formed the Mississippi River/Gulf of Mexico Watershed Nutrient 

Task Force during the fall of 1997, and asked the White House Office of Science and Technology Policy to coiduct a scientific assessment of the causes and consequences of Gulf hypoxia 

through its Committee on Environment and Natural Resources (CENR). A Hypoxia Working 

Group was assembled from federal agency representatives, and the group developed a plan to 

conduct the scientific assessment. 

The National Oceanic and Atmospheric Administration (NOAA) has led the CENR assessment, although oversight is spread among several federal agencies. The objectives are to provide 

scientific information that can be used to evaluate management strategies, and to identify gaps in 

our understanding of this complex problem. While the assessment focuses on hypoxia in the 

Gulf of Mexico, it also addresses the effects of changes in nutrient concentrations and loads and 

nutrient ratios on water quality conditions within the Mississippi-Atchafalaya River system. 

As a foundation for the assessment, six interrelated reports were developed by six teams with expem from within and outside of government. Each of the reports underwent extensive peer review by independent experts. To facilitate this comprehensive review, an editorial board was 

selected based on nominations from the task force and other organizations. Board members were 

Dr. Donald Boesch, University of Maryland; Dr. Jerry Hatfield, U.S. Department of Agriculture; Dr. George Hallberg, Cadmus Group; Dr. Fred Bryan, Louisiana State University; Dr. 

Sandra Batie, Michigan State University; and Dr. Rodney Foil, Mississippi State University. The 

six reports are entitled: 

Topic I: Characterization ofHypoxia. Describes the seasonal, interannual, and long-term 

variations of hypoxia in the northern Gulf of Mexico and its relationship to nutrient loadings. Lead: Nancy N. Rabalais, Louisiana Universities Marine Consortium. 

Topic 2: EcoZogical and Economic Conseyuences of Hypoxia. Evaluates the ecological and 

economic consequences of nutrient loading, including impacts on the regional economy. Coleads: Robert J. Diaz, Virginia Institute of Marine Science, and Andrew Solow, Woods Hole 

Oceanographic Institution, Centerfor Marine Policy. 

xiii 
xiv ReducingNutrient Loadsto Surface and Ground Waters and the Gulf 

Topic3: Flux and Sources of Nutrients in the Mississippi-Atchafalaya River Basin. Identifies the sources of nutrients within the Mississippi-Atchafalaya system and Gulf of Mexico. 

Lead: Donald A. Goolsdy, US. Geological Survey. 

Topic 4: Eflects of Reducing Nutrient Loads to Suface Waters Within the Mississippi River 

Basin and Gulfof Mexico. Estimates the effects of nutrient-source reductions on water quality. Co-leads: Patrick L. Brezonik, Universityof Minnesota, and VictorJ. Bierman, Jr., LimnoTech, Inc. 

Topic5: Reducing Nutrient Loads, Especially Nitrate-Nitrogen, to Suface Water, Ground 

Water,and the Guyof Mexico. Identifies and evaluates methods for reducing nutrient loads. 

Lead: WilliamJ. Mitsc8, Ohio State University. 

Topic 6: Evaluation of the Economic Costs and BeneJits of Methods for Reducing Nutrient 

Loads to the Gulfof Mexico. Evaluates the social and economic costs and benefits of the 

methods identified in Topic 5 for reducing nutrient loads. Lead Otto C. Doering, Purdue 

University. -

These six individual reports provide a foundation for the final integrated assessment, which the 

task force will use to evaluate alternative solutions and management strategies called for in Public 

Law 105-383. 

As a contribution to the Decision Analysis Series, this report provides a critical synthesis of the 

best available scientific information regarding the ecological and economic consequences of hypoxia in the Gulf of Mexico. As with all of its products, the Coastal Ocean Program is very interested in ascertaining the utility of the Decision Analysis Series, particularly with regard to its 

application to the management decision process. Therefore, we encourage you to write, fax, call, 

or e-mail us with your comments. Our address and telephone and fax numbers are on the inside 

front cover of this report. 

David Johnson, Director 

Coastal Ocean Program 

Donald Scavia, Chief Scientist 

National Ocean Service 
Executive Summary 1 

The goal of this report to identify and evaluate approaches for solving the problem of the hypoxia in the Gulf of Mexico. This zone of low dissolved ovgen, which covers an area from 

13,000 to 20,000 krn2 off the shore of Louisiana, has been shown to be due to excess nutrients, 

particularly nitrate-nitrogen, being transported to the Gulf from the Mississippi River Basin. To 

accomplish our goal, we (1)reviewed appropriate literature on methods for controlling nutrients, 

particularly nitrate-nitrogen, from entering waterways; (2) evaluated these methods to reduce 

the amount of nitrogen released to streams and rivers; (3) put the methods in the context of the 

entire Mississippi River Basin and the significance of the sources; and (4) presented recommendations for the most reasonable combination of approaches that would be necessary to solve the 

problem. 

Techniques reviewed included on-farm practices, created and restored wetlands and riparian 

zones, controlled drainage systems, stormwater runoff control, atmospheric controls on mobile 

and stationary sources, point-source control on wastewater treatment plants, Mississippi River 

diversion, and flood control in the Upper Mississippi River Basin. We concluded that a suite of 

practices is needed to effectively deal with hypoxia in the following general categories: (1) modification of farm practices to make the use of nitrogen from fertilizer and manure more effective 

and efficient; (2) the creation and restoration of wetlands and riparian ecosystems between 

farmland and streams and rivers, but particularly in those areas where concentrations of nitratenitrogen in subsurface drainage is highest; (3) the implementation of nitrogen controls on domestic wastewater treatment plants; and (4) diversion of floodwaters to backwaters of the Mississippi River Delta and coastal wetlands. If policies are devised to implement only one or two of 

these policies, then improvement in the Gulf of Mexico is not as likely. 

We make be following specific recommendations: 

1. Several on-farm practices for reducing discharges of nitrogen to streams and rivers should 

be implemented. These practices, which could lead to 15-20% reductions of nitrogen 

sources to the Gulf, include a 20% reduction in fertilizer nitrogen application through 

proper nitrogen crediting for legumes and manure and realistic yield goals. Other recommended management practices include optimum timing of fertilizer application, use 

of alternative crops, such as perennials, wider spacing of subsurface drains, and better 

management of livestock manures whether stored or applied to the land. 

2. A major effort to restore or create 24 million acres (10 million hectares, or 3.4% of the 

Mississippi River Basin) of riparian zones and wetlands to reduce nitrogen in the Mississippi River and its tributaries by an average of 40% should be undertaken in the Mississippi River Basin. 
xvi ReducingNutrient Loadsto Surface and Ground Waters and the Gulf 

3. Wetlands and riparian zones should be strategically placed in watersheds to optimize nitrogen removal as, for example, in tile-drained farmlands that are prone to export high 

concentrations and amounts of nitrate-nitrogen. 

4. Although point sources of nitrate-nitrogen appear to be of little consequence (c 5%)in 

the overall Mississippi River Basin nitrogen load, an effort to control these sources 

through tertiary treatment should become a formal policy for new wastewater treatment 

plants in the basin. 

5. The restoration of flood-prone lands in the Upper Mississippi River Basin to wetlands 

needs to be revisited and more seriously considered in light of the 1993 flood and the 

need to control nitrate-nitrogen to protect the Gulf. 

6. Nitrate reduction should be an important consideration in the design and operation of 

diversions of the Mississippi River for flood events in the Mississippi Delta in Louisiana. 

Approximately 400,000 to 1 million hectares (1-2.5 million acres) or more of inshore 

coastal areas (forested wetlands, marshes, and water bodies) should be used for nitrate reduction in diverted waters. An important additional benefit of such diversions would be 

to address the land-loss problem in Louisiana. 

7. Further reductions beyond those now being implemented through the authority of the 

Clean Air Act are probably not warranted for controlling stationary and mobile atmospheric emissions of nitrogen, at least insofar as protecting the Gulf of Mexico is concerned. 

8. There is a strong need for any nitrogen mitigation effort to be coupled to a comprehensive program of monitoring, research, and modeling to evaluate which practices are effective and why, and to allow for "adaptive management" of the hypoxia problem. 
CHAPTERI I 

Introduction 

1.1 THE GULF OF MEXICOHYPOXIA 

The main focus of this report is the identification and evaluation of methods to reduce nutrient 

loads from the continental United States-particularly from the Mississippi, Missouri, and Ohio 

River basins-to surface and ground waters and, ultimately, the Gulf of Mexico. For at least the 

past 10years, seasonally severe and persistent hypoxia (low dissolved oxygen conditions) has been 

measured on the continental shelf of the northern Gulf of Mexico to the west of the Mississippi 

and Atchafalaya River deltas. The hypoxia zone has ranged from 13,000 to 20,000 km2 from 

1993 through 1999 (Rabalais et al. 1996, 1997, 1999; Rabalais personal communication). The 

hypoxia appears to be most widespread, persistent, and severe in June, July, and August (Rabalais 

et al. 1996). There also appears to be spatial and temporal variability in the distribution of the 

hypoxia on the shelf, which is, in part, related to the amplitude and timing of the Mississippi 

and Atchafalaya stream flows. 

The waters that discharge to the Gulf originate in the combined Mississippi/OhioiMissouri 

watersheds (referred to as the Mississippi River Basin in this report). In total, these watersheds 

encompass about 3,000,000 km2 (1,200,000 mi2), or about 40% of the area of the lower 48 states 

(Figure 1.1). Two-thirds of the flow from this system enters the Gulf through the Mississippi 

River, while the remaining one-third enters through the Atchafalaya River. The Mississippi 

River Basin accounts for 90% of the freshwater inflow to the Gulf (Rabalais et al. 1996). 

Linkages between the freshwater inflow from the Mississippi/Atchafalaya River systems (and 

subsequent nutrient flux) and net surface productivity and bottom-water oxygen deficiency have 

been generally established (Atwood et al. 1994; JustiC et al. 1995; Rabalais et al. 1996) and are 

discussed in detail in other reports in this series (Rabalais et al. 1999; Diaz and Solow 1999; 

Brezonik et al. 1999). Freshwater discharge and nutrient fluxes from the Mississippi and Atchafalaya Rivers appear to influence the distribution and intensity of the hypoxia, along with water 

column stratification and mixing (Rabalais et al. 1991). 

The hypoxia zone in the Gulf of Mexico is characterized by increased primary production in the 

upper water column. Oxygen-demanding organic carbon derived from this primary production 

sinks, decomposes, and leads to the seasonally severe oxygen depletion in the lower waters and 

sediments (Turner and Allen 1982; Rabalais et al. 1991, 1992; Bierman et al. 1994; JustiC et al. 

1996, 1997). The low oxygen causes the benthic community to be characterized by limited species; reduced abundance, species richness, and biomass; and domination by pollution-tolerant 

organisms. Effects of hypoxia on fishery resources, covered in a companion report (Diaz and 

Solow 1999) could include direct mortality of fish and their food base, as well as indirect effects, 

such as altered migration, reduction in suitable habitats, increased susceptibilityto predation, and 

disruption of spawning, recruitment, and migration. 
2 ReducingNutrient Loadsto Surface and Ground Waters and the Gulf - -

FIGURE I.I. The MississippiRiver Basin and location of the Gulf of Mexico hypoxia. 

(Adapted from Goolsby et a/. 1999.) 
Chapter I: Introduction 3. 

It is the goal of this report to identify and evaluate approaches for solving the problem of the hypoxia in the Gulf of Mexico. To accomplish this goal, we have the following objectives: 

review appropriate literature on methods for controlling nuirients, particularly nitratenitrogen, from entering waterways; 

evaluate the efficacy of these methods; 

put the methods in the context of the entire Mississippi River Basin and the significance 

of the sources; and 

give recommendations as to the most reasonable combination of approaches that would 

be necessary to solve the problem. 

1.3 NUTRIENT SOURCESTO THE GULFOF MEXICO 

Nutrient loadings, particularly nitrogen loadings associated with eutrophication of coastal marine 

systems, are transported via atmospheric, surface flow, and ground-water -pathways. Nitratenitrogen concentrations in the Mississippi River have increased dramatically in this century, and 

have accelerated since 1950, coinciding with increasing fertilizer use in the Mississippi Basin 

(Turner and Rabalais 1991; Figure 1.2). Other factors-such as artificial drainage and other 

changes to the hydrology of the Midwest, atmospheric deposition of nitrates within the Mississippi River Basin, nonpoint discharges from urban and suburban areas, and point discharges, 

particularly from domestic wastewater treatment systems and feedlots-all contribute to the nutrients that reach the Gulf of Mexico. Table 1.1presents estimates of the relative inputs of these 

sources. Controlling these sources through agricultural management, environmental technology, 

and ecotechnology is the focus of this report. The sources are briefly discussed in the following 

subsections. 

TABLE I.I. Sources of nitrogen (N) and phosphorus (P) in the Mississippi River Basin (MRB) and export from the basin via the river. 

-Sources to MRB 

Fertilizer Use 

Mineralized Soil Nitrogen 

Legume N-fixation 

FeedlotsIManure 

Atmospheric Deposition 

Point Sources-Municipal 

Point Sources-Industrial 

Urban Nonpoint Sources 

Output to Gulf of Mexico 

From Mississippi River 

From Atmosphere 

'Sources should not be added, as that would lead to double accounting of some 

nutrients. 

Source: Goolsby et al. 1999. 
4 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf . 

Estimatednitrogen fertilizer use in the 

Mississippi River basin, 

-

-

0 

-

-

-

-

-

1900 1920 1 940 1960 1980 2000 

Year 

FIGURE 1.2. Estimated trends in the 20th century of the hypoxia area, nitrogen concentrations and fluxes, nitrogen fertilizer use, and land drainage in the Mississippi River Basin. 

(Data from Rabalais et al. 1999, Goolsby et al. 1999, and USDA 1987.) 
Chapter I:-Introduction 5-

1.3.1 Crop Production and Soil Drainage 

Nitrogen (N) is a naturally occurring element that is essential to plant growth and crop production. Agriculture has been identified frequently as a major contributor of nitrate-nitrogen to 

surface water throughout the developed world. Omernik (1977) reported that total nitrogen 

concentrations were nearly nine times greater downstream from agricultural lands than downstream from forested areas, with the highest concentrations being found in the Corn Belt states 

of the Upper Mississippi Basin. As stated by Power et al. (1998), "the global nitrate problem is 

most apparent in the North Central region of the United States where 83 percent of the nation's corn is produced and 53 percent of the commercial nitrogen fertilizer is used." Nitratenitrogen is continually supplied to streams and rivers through mineralization of soil organic 

matter, particularlywhere tile drainage has exposed formerly wet soils to oxidation and through 

the application of fertilizer and animal manures to cropland. Goolsby et al. (1999) estimate these 

two sources (fertilizer and mineralization) contribute about 13 million metric tons per year of 

nitrogen to the Mississippi River Basin (MRB) (Table 1.1). Ago-industrial wastes, atmospheric 

deposition of volatilized ammonia from manure and fertilizer, and dinitrogen furation, all of 

which either occur as nitrate-nitrogen or can be converted to nitrate-nitrogen through mineralization and nitrification, are other important sources. Nitrogen furation by legumes contributes 

4 milhon metric tons per year of nitrogen to the basin (Table 1.1). 

Nitrate-nitrogen is mobile and, therefore, can be lost from the soil profile by leaching. Subsequent transport of nitrate-nitrogen to surface waters occurs primarily through subsurface drainage (tile lines) or base flow. Subsurface drainage is a common water management practice in 

highly productive agricultural areas of the MRB, where poorly drained soils have seasonally 

perched water tables or shallow ground water. Very little nitrate-nitrogen is lost from the agricultural landscape via surface runoff (Jackson et al. 1973; Logan et al. 1994). 

Several long-term studies on rivers of different stream order draining widely different scales of 

watershed basins all point to the fact that agricultural practices do affect the nitrate-nitrogen 

concentrations in river water. Nitrate-nitrogen concentrations in stream water collected from 

water years 1984-93 for a portion of the Upper MRB were significantly greater (2-6 mg-N/L) 

from rivers that drain a large percentage of agricultural land compared to rivers that drain a larger 

percentage of forested land (0.1-0.5 mg-N/L) (Kroening 1996). For perspective, the national 

drinking water standard of nitrates is 10 mg-N/L. In the Mississippi River, mean concentrations 

were significantly greater (1.8-2.5 mg-N/L) downstream of the confluence with the Minnesota 

River (an agricultural watershed) than upstream (0.2-0.9 mg-N/L). Keeney and DeLuca (1993) 

examined nitrate concentrations in the Des Moines River in 1945, 1955, 1976, and 1980-90 

and found the average nitrate-nitrogen concentrations to have changed little in the last 45 years 

(5.0 mg-N/L in 1945 and 5.6 mg-N/L in 1980-90). They concluded that intensive agricultural 

practices that enhance mineralization of soil nitrogen, coupled with subsurface artificial drainage, 

are the major contributors of nitrate-nitrogen to streams and rivers of the Midwest. 

Somewhat similar conclusions were drawn by David et al. (1997), who surmised that agricultural 

disturbance leading to high mineralization rates and nitrogen fertilization combined with subsurface tile drainage contributed significantly to nitrate export in the Embarras River in Illinois. 

In their six-year study, an average of 49% (with a range of 25-85%) of the large pool of nitratenitrogen remaining after harvest was leached through drainage tiles and exported by the river. 

Precipitation exerted a large influence on drainage losses, with a few days of high-flow events 

leading to most of the annual loss in some years. Rivers with higher concentrations of nitratenitrogen seem to be surrounded by landscapes with similar general characteristics: (1) humid/high rainfall conditions;(2) soils high in organic matter; (3) poorly drained, fine-textured 
6 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf 

soils needing artificial subsurface drainage for optimum crop production; and (4) domination by 

corn- and soybean-intensive agriculture. 

Soils high in organic matter can mineralize a substantial amount of nitrate-N that is susceptible 

to loss in subsurface tile drainage, especially when wet years follow'very dry years. Tile drainage 

from continuous corn plots that received only 20 kg N ha-' yf' at Lamberton, Minnesota, contained annual flow-weighted nitrate-nitrogen concentrations of 13 to 19 mg-N/L (Gast et al., 

1978). After an extremely dry year followed by a year with slightly above-normal rainfall, nitrate-nitrogen concentrations averaged 28 mg-N/L from these plots. 

In a study at Waseca, Minnesota, four plots were fallowed (no crop grown and no fertilizer applied), with periodic tillage each year from 1987 through 1993. Nitrate-nitrogen concentrations 

in the tile drainage water averaged 57 mg-N/L in 1990 following three dry years. Concentrations dropped to 38,25, and 23 mg-N/L in 1991, 1992, and 1993, respectively (Randall, unpublished data). Hatfield (1996) found that nitrate-nitrogen concentrations in the Walnut Creek 

watershed in Iowa ranged from 15 to 20 mg-N/L throughout most of the year and stated that 

this loss was due primarily to the high organic matter content of the soils and their ability to 

mineralme nitrogen. Elevated levels of nitrate-nitrogen will be lost to drainage water in these 

tile-drained soils, regardless of fertilizer management practices, especially in wet years following 

dry years when crop production was limited. 

1.3.2 Feedlot Discharges 

Dairy, cattle, swine, poultry, and aquaculture systems can cause significant discharges of oxygendemanding substances and nutrients to local streams and rivers. Untreated wastewater from 

these systems generally has very high concentrations of phosphorus and nitrogen (Table 1.2), 

the latter most often as ammonia-nitrogen, although high concentrations of nitrate-nitrogen 

are also possible. Estimates range widely as to the importance of this source in the total nutrient 

loading to the MRB. Goolsby et al. (1999) found 2.7 million metric tons per year of nitrogen 

being discharged into the basin, or about 40% of the total fertilizer use in the basin (Table 1.1). 

Care needs to be taken not to double count nutrients, as some amount of the fertilizer in crop 

production ends up as effluent in feedlots. 

TABLE 1.2. Contrast of nutrient concentrations in secondary effluent from a municipal 

wastewater--treatmentplant, wastewater from a confined animal feeding operation, runoff 

from croplands of the midwestern U.S., and urban (residential) runoff. 

Nutrients Secondarily Confined Corn Belt Urban 

Treated Animal Feeding Cropland (Residential) 

Effluent Operations Runoff - - -- -----

Suspended Solids 5-20 585 50- 1,000 228 

(mg/L) 

Total P (mglL) 6.8 24 0.14 0.5 

Total N (mglL) 15.8 254 4.4 2.0 

Soluble inorganic 8.4 - 3.4 1.8 

N (mg-NIL) 

Ammonia (mg-NIL) - 122 - -

I N:P ratio 2.4 10.6 31.4 4 I 

Sources: Baker 1992; USEPA 1993; and CH2M-Hill 1997. 
Chapter I: Introduction 7-

1.3.3 Other Nonpoint Sources 

Urban and suburban areas have significant runoff from lawns, parking lots, rooftops, roads, 

highways, and other impervious and semi-impervious sources. Goolsby et al. (1999) were unable 

to provide accurate estimates of nitrogen and phosphorus in urbah nonpoint runoff in the 

MRB, as such accounting or monitoring systems do not exist. Concentrations and fluxes of nutrients, particularly nitrogen and phosphorus, are generally low compared to nonpoint agricultural sources. Concentrations of total nitrogen are generally half or less in urban runoff 

compared to agricultural land runoff (Table 1.2), and fertilized agricultural land covers a much 

greater area in the MRB than do urban and suburban land (Figure 1.1). 

1.3.4 Point-Source Discharges 

Point-source discharges of nitrogen (N) are estimated to add 0.27 million metric tons per year of 

nitrogen to the streams and rivers of the MRB, or about 1.5% of the total loading generally 

coming from agricultural lands (fertilizer use, mineralizing soil, and legume N-fixation) (Goolsby 

et al. 1999; Table 1.1). The major point sources of direct discharges of nutrients, particularly ni- - - - trate-nitrogen, appear to be domestic wastewater treatment plants. Conventional wastewater 

treatment, through secondary treatment, involves removal of suspended materials, pathogens, 

and oxygen-demanding organics. Organic matter is converted into inorganic forms, including 

ammonia-nitrogen, nitrate-nitrogen, and ortho-phosphates. Baker (1992) reported that a conventional wastewater treatment $ant effluent Las a-total N concentration *of 16 mg-N/L, a 

soluble inorganic N concentration of about 8 mg-N/L, and a total phosphorus (P) concentration of about 7 mg-N/L. Domestic wastewater is generally phosphorus-rich, with a much lower 

N:P ratio than agricultural runoff (Table 1.2). 

1.3.5 Atmospheric Sources 

The importance of atmospheric sources of nitrogen to the Gulf of Mexico has been difficult to 

quantify. Nitrogen enters the atmosphere from human and natural sources. In high-temperature 

combustion, characteristic of the internal combustion engine and fossil-fuel burning electric 

generating stations, N, and 0, gases are combined to form NO, (NO and NO,). NO, and airborne nitrates return to the earth's surface with rain, snow, and fog (wet deposition) or as gases 

and particulate (dry deposition). This nitrogen then enters streams and rivers and/or is retained 

in terrestrial systems in the same pathways as nitrate-nitrogen fertilizer. Intensive agricultural 

practices, particularly feedlots where ammonia-nitrogen concentrations are high, also result in 

ammonia volatilization, which increases local ammonia-N concentrations in the atmosphere. 

These emissions also return to earth through precipitation and dry fallout. For the Gulf of Mexico, direct deposition of nitrogen from upwind sources-e.g., refineries of Texas, New Orleans, 

and other urban areas-may contribute some nitrogen to the overall loading of the hypoxic zone. 

In 1992, NO, emissions in the United States were about 23 million metric tons/year (USEPA 

1995a). An estimated 1.2 million metric tons/year (or 5% of the total US. emission) are deposited in the Mississippi watershed (Goolsby 1999; Table 1.1),or about 18% of the fertilizer input 

, and about 6% of the total nitrogen input to the MRB. 

About one-third of the total NO, emissions in the United States comes from electric utilities. 

Coal-fired combustion contributed about 90% of estimated electric utilities' NO, emissions 

(USEPA 1995a), most in the eastern half of the country. Mobile sources are estimated to contribute more than half of the NO, emission nationwide. Highway vehicles contribute about 
8 ReducingNutrient Loads to Surface and Ground Waters and the ~ulf 

one-third of the total NO, emission, mostly from light-duty vehicles and trucks (including all 

passenger cars)-the most common types of vehicles. In fact, these vehicles alone comprised almost 22% of national NO, emissions in 1996 (USEPA 1998a). 

NO, emissions contribute to ozone formation, smog, and add deposition. In 1996, in a rule 

promulgated by the U.S. Environmental Protection Agency, NO, emissions were also recognized for the first time as being a significant source of coastal eutrophication (USEPA 1996a). 

For example, it was estimated that approximately 27% of the total nitrogen loading to Chesapeake Bay comes from atmospheric sources in the form of NO, emissions (Linker et al. 1993; 

Valigura et al. 1994). 
CHAPTER 2 

Methods 

The charge to the committee that authored this report was the following: 

The main focus of this report will be to identify and evaluate methods to reduce 

nutrient loads to surface water, ground water, and the Gulf of Mexico. The 

analysis will not be restricted to reduction of sources. It will also include means to 

reduce loads by allowing the system to better accommodate those sources 

through, for example, modified hydraulic transport and internal cycling routes. 

This report was developed through a series of meetings and subsequent writing assignments by 

the authors, followed by a compilation, review, and rewriting of the report's sections. Meetings 

were arranged for the committee in St. Louis, Missouri, on March 26, 1998, and May 21, 1998. 

The first meeting was held to have a general discussion on the subject, decide on an outline for 

the report, and assign writing tasks. Most committee members prepared their sections for discussion at the second meeting, which involved initial presentations of the sections by the 

authors, which was followed by discussion and feedback. 

Final versions of manuscripts were submitted by most authors by mid-June. Sections were integrated into this final report through significant editing and review. A preliminary draft was distributed to the committee on September 21, 1998, and a phone conference of the committee 

was held on October 6, 1998. A second draft of the final three chapters, including the recommendations, was circulated to the committee on October 12, 1998, for final comments. A third 

draft was prepared based on these comments and was submitted to the National Oceanic and 

Atmospheric Administration (NOAA) for review on October 15, 1998. The manuscript was 

reviewed by six extramural reviewers and returned to the committee by mid-February 1999. The 

reviewers' comments were taken into account in a fourth draft, which was returned to the review team on March 10,1999. 

In this analysis, a full suite of possible methods for reducing nitrogen loading to the Gulf of 

Mexico was initially considered. Then a shorter list of "more feasible" approaches-both onfarm, between the farm and the streams and rivers, and in and along the Mississippi River basin 

itself-was compiled based on the following criteria: (1) the significance of the source that was 

being controlled, (2) the proven effectiveness of the methodology; and (3) the positive ancillary 

benefits that the methods would have both locally and in the Gulf of Mexico. Methods were 

chosen that would be effective and generally realistic, within broad social and economic constraints. This shorter list of methodologies was then quantified where possible to give overall 

quantifiable goals in the series of recommendations. Recommendations were then rechecked to 

make sure that adequate scientificjustification was present in the report. 
CHAPTER 3 I 

Results-Approaches for Controlling Nitrogen 

Preventing nutrients, particularly nitrate-nitrogen, from reaching the Gulf of Mexico can be 

accomplished through a number of general approaches and specific techniques (Table 3.1), 

ranging from modification of agricultural practices to the construction and restoration of riparian zones and wetlands as buffer systems between agricultural lands and waterways. This section 

provides an overview of each major category of nutrient reduction listed in Table 3.1. This report 

emphasizes reducing nitrogen, particularly nitrate-nitrogen, in the streams and rivers of the 

Mississi~~i Rver Basin. The focus on nitrogen reduction is based on the strong: evidence of L I U 0 

cause and effect between nitrate-nitrogen increases and subsequent increases in the hypoxia in 

the Gulf of Mexico, and on the long-time understanding that coastal waters are generally nitrogen-limited (see Rabalais et al. 1999). 

TABLE 3.1. Possible approaches for controlling nitrogen in the Mississippi River Basin. 

On-Site Control of Agricultural Drainage Urban Nonpoint-SourceControl 

Changing Cropping Systems Stormwater Runoff 

Reducing Nitrogen Fertilizer Application Rates On-Site Sewage Disposal 

Managing Manure Spreading 

Managing Time of Nitrogen Application 

Point-Source Control -Municipal Wastewater and Feedlot Wastewater 

Using Nitrification Inhibitors 

Change Tillage Methods 

Increasing Drainage Tile Spacing 

Off-Site Control of Agricultural Drainage 

Wetlands -

Environmental Technology 

Ecotechnology -

Control of Atmospheric NO, 

Stationary-Source Control 

Mobile-Source Control 

Riparian Zorres 

Controlled Drainage Mississippi Delta Diversions 

Upper Mississippi River Flood Control and 

Restoration 

3.1 ON-SITE CONTROL OF AGRICULTURAL DRAINAGE 

The primary factors that influence the nitrate content of surface and subsurface waters draining 

agricultural landscapes can be divided into two categories-uncontrollable and controllable. Uncontrollable factors include precipitation and other climatic factors. controllable factors, which 

include agricultural management practices that can be used by crop producers to best fit the 

needs of their enterprise, such as: (1) cropping system used, (2) rate of nitrogen applied, (3) time 

of nitrogen application, (4) placement method, (5) use of a nitrification inhibitor, (6) tillage systems, and (7) tile spacing in subsurface drainage. 
Chapter 3: ResultoApproaches for Controlling Nitrogen I I 

Drainage studies can be very useful for assessing the impact of agricultural management practices 

on surface- and ground-water quality (Hallberg et al. 1986; Kanwar et al. 1987). Subsurface 

drains integrate the effects of spatial variabihty and may be a better tool for studying chemical 

leaching than such methods as porous suction cups and soil cores (Richard and Steenhuis 1988). 

However, solute concentrations in subsurface drain flow have been shown not to respond immediately to changes in chemical application rates or residual levels in the soil (Jury 1975a, 

1975b; Gast et al. 1978; Baker and Johnson 1981). Some time lag is exhibited due to travel time, 

depending on drain spacing, soil hydraulic properties, and precipitation. 

3.1.1 The Role of Precipitation on Agricultural Drainage 

Loading of nitrates into surface water is a function of flow and nitrate concentration in the 

transported water. The amount of subsurface drainage water leaving the landscape is largely a 

function of climate and soil properties-e.g., precipitation, soil texture, infiltration rate. Drainage 

is further influenced by the temporal distribution of precipitation within a year and by the 

amount of annual or growing-season precipitation that occurs. For instance, -an 8-cm rainfall in 

the spring, when evapotranspiration (ET) losses are low and soil moisture in the profile is likely 

near field capacity, will have a much greater effect on drainage volume than the same rainfall 

during the middle of the summer, when daily ET losses are high and soil moisture content is far 

short of field capacity. In the former scenario, storage capacity is minimal and drainage water 

carrying nitrates is plentiful. A significant soil-water storage reservoir can exist in the soil in the 

latter scenario, and subsurface drainage may or may not even occur. 

3.1.1.1 PRECIPITATIONAND DRAINAGE 

The effect of climate on subsurface drainage volume is clear in the following subsurface drainage 

studies. Annual subsurface drainage in an 11-year Minnesota study (Randall and Iragavarapu 

1995) with continuous corn ranged 26-618 mm/yr, with an average of 297 mm/yr (Table 3.2). 

Drainage was least in 1989, when growing-season precipitation was 35% below normal, and 

greatest in 1991, when growing-season precipitation was 51% above normal. In addition, drainage in a three-year dry period (1987-89) averaged only 43 mm/yr, compared to the following 

three-year wet period (1990-92), when drainage averaged 549 mm/yr. Similar findings were reported by Weed and Kanwar (1996), who measured tile drainage under both continuous-corn 

TABLE 3.2. lnfluence of precipitation on drainage volume and annual nitrate-N losses. 

Year April-October Precipitation Nitrate 

~ain'fall'(mm) Drainage (mm) Conc.'(mg-NIL) Lost (kg-Nlha) 

' 196 1-90 normal = 639 mm. 

'Annual flow-weighted concentration. 

Source: Randall and lrogavarapu 1995. 
I2 Reducinn Nutrient Loadsto Surface and Ground Waters and the Gulf 

and a corn-soybean rotation on Kenyon-Clyde-Floyd soils in Iowa. Averaged across four tillage 

systems, drainage in 1991totaled 244 mm, or 44% above the 1990-92 average (Table 3.3). A sixyear study conducted on a Normania clay loam at Lamberton, Minnesota, showed no tile drainage in the first two years, when annual precipitation was 69% and 76% of normal, respectively 

(Randall et al. 1997). Annual precipitation in those four subsequent years was 95%, 125%, 117%, 

and 160% of normal, respectively (Table 3.4). These three studies indicate the strong relationship between precipitation and volume of subsurface drainage. 

TABLE 3.3. Annual water loss via subsurface tile drainage for cropping systems in Iowa. 

Continuous Corn 18.5 28.0 12.2 19.5 

Rotation Corn 14.3 16.7 7.2 12.7 

Rotation Soybean 16.0 28.8 11.3 - 18.7 

Source: Weed and Kanwar 1996. 

TABLE 3.4. Effect of crop system on amount of subsurface drainage water. 

Crop System Subsurface DrainageWater (cm) 

1990 1991 1992 1993 

r 

Continuous Corn 

Corn-Soybean 

Soybean-Corn 

Alfalfa 

CRP' 

Average of Row Crop Systems 

Average of Perennial Crop Systems 

I % of Normal Annual Precipitation 

22 

0 

95 

223 

42 

125 

143 

71 

117 

469 15 

160 

1 

1 

'CRP = Conscryation Reserve Program (mixture of grass and alfalfa). 

Source: Randall et al. 1997. 

3.1.1.2 PRECIPITATIONAND NITRATE CONCENTRATIONS 

Nitrate concentrations in subsurface drainage water do not appear to vary consistently with daily 

drain flow but do show seasonal and yearly variability (Kladivko et al. 1991). Factors affecting 

this variability include crop uptake of N, residual nitrate in the soil from the previous year, and 

amount and distribution of rainfall. Goolsby et al. (1997) noted that the concentration and flux 

of nitrate in rivers of the MRB tend to be highest in the spring, when stream flow is highest. 

These patterns have been noted in several other studies in the Midwest (Keeney and DeLuca 

1993; Phipps and Crumpton 1994; Mitsch and Carmichael1997). 

The general effects of precipitation on nitrate concentrations can be illustrated using basin-wide 

water quality monitoring data collected in the Minnesota River Basin, a 4 million-ha agricultural 

basin draining to the Upper MRB (Mulla 1997). Mean annual precipitation in the Minnesota 

River Basin varies from 56 cm on the western side of the basin to 81 cm on the eastern side. The 
Chapter 3: Result-Approaches for ControllingNitrogen I 3 

basin is dominated by intensive row-crop agriculture, has soils that generally have organic matter 

levels greater than 3%, and has subsurface tile drainage on over half of the farmed acreage. Water 

quality monitoring data from 1977-94 show that nitrate concentrations range from 0.36 mgN/L in the head waters on the western side to 4.6 mg-N/L at the !mouth of the river on the 

eastern end where it enters the Mississippi kver. Mean annual precipitation increases by about 

25 cm across this distance, which produces a corresponding and dramatic increase in the discharge from subsurface tile drains into ditches and streams that eventually flow into the Minnesota River. Fewer than 1% of the water quality samples collected since 1977 from the western 

portion of the basin have a nitrate concentration that exceeds the drinlung-water standard of 10 

mg-N/L. About 10% of the water quality samples collected over the same period exceed 10 mgN/L on the eastern side of the basin. 

3.1.1.3 PRECIPITATIONAND RESIDUAL SOIL NITRATE 

Nitrate concentrations and losses are also greatly affected by dry and wet climatic cycles (Randall 

1998). Thirty-two tile drainage plots were planted to a corn (16 plots)-soybean (16 plots) rotation from 1987 through 1993 at Waseca, Minnesota. Late each fall after soybean harvest, anhydrous ammonia was applied to four plots at a rate of 150 kg N/ha for corn the following year. 

Average annual flow-weighted nitrate concentrations and losses from the corn plots are shown 

in Figure 3.1. 

a) , '1 30 

Nitrate-Nconcentration, mg/L Nitrate-Nconcentration, rng/L 

1990 1991 

20 1988 

10 

1987 

100 200 300 400 100 200 300 400 500 600 7W 

Drainage, mm Drainage, mm 

Drainage, rnrn Drainage, mm 

FIGURE 3.1. Relationshipbetween subsurface drainage volume and: (a) annual flow-weighted 

nitratenitrogen concentration; (b) annual nitratenitrogen loss in tile-drainage water from a 

corn-soybean rotation that received 150 kg Nlha as anhydrous ammonia in late October 

each year following soybeans at Waseca, MN; (c) annual flow-weighted nitratenitrogen concentration; and (d) annual nitrat-nitrogen loss in tile-drainage water from continuous corn 

that received 200 kg Nlha each spring at Waseca, MN. 
I4 ReducingNutrient Loads to Surface and Ground Waters and the Gulf 

In 1987 and 1988, when April-October rainfall was 8% and 33% below normal, respectively, 

subsurfacedrainage was < 50 mm/yr, and nitrate concentrations ranged between 7 and 18 mgN/L. Less than 2 mm of drainage occurred in 1989 when April-October rainfall was 35% below 

normal, and no samples were collected for nitrate-N analyses. Under these dry conditions during 

the three-year period, corn yields and nitrogen uptake were low. However, residual soil nitrate 

(RSN) continued to increase in the soil profile to levels as high as 259 kg-N/ha in the top 1.5-m 

profile following corn. April-October precipitation in 1990 was 23% above normal, causing 

drainage volume to total > 350 mm. Moreover, annual flow-weighted nitrate concentrations in 

the corn plots averaged 35 mg-N/L-two times as high as during the dry years (Figure 3.la). 

Nitrate-nitrogen concentrations in the soil and drainage water returned to background levels in 

1991and 1992 when rainfall was 50% and 14% above normal, respectively. Nitrate losses from 

the corn plots showed the combined effect of drainage volume and nitrate-N concentration 

(Figure 3.lb). These data suggest that RSN can accumulate in the soil profile during dry climatic 

cycles because of soil mineralization, reduced crop uptake, and every-other-year nitrogen fertilization, even in a corn-soybean rotation. These elevated RSN levels are then poised for delivery 

to subsurface tile drainage when growing season precipitation returns to above normal. 

3.1.1.4 PRECIPITATION AND NITRATE LOADS 

In another set of drainage plots at Waseca, nitrogen fertilizer was applied at a rate of 200 kg/ha 

each spring to corn grown for eight years. Annual flow-weighted nitrate concentrations in 1985 

and 1986 averaged 13 and 14 mg-NIL, respectively, although the drainage volume ranged from 

143 mm in 1985 to 402 mm in 1986 (Figure 3.1~).Dry conditions during 1987-89, when 

April-October rainfall was 25% below normal, resulted in < 50 mm drainage/yr and annual average nitrate concentrations ranging from 9 to 15 mg-N/L. RSN totaled 225 kg-N/ha in the 0-

1.5 m profile in October 1989. In 1990 and 1991, April-October rainfall averaged 36% above 

normal and generated annual drainage volumes > 480 mm/yr. In addition, nitrate concentrations 

in the drainage water doubled from the previous three dry years to 24 mg-N/L in these two wet 

years. RSN at the end of 1991 was 50% lower than at the end of the dry years. In the third 

consecutive wet year (1992), more than 400 mm of water drained from the plots, nitrate concentrations in the drainage water returned to 14 mg-N/L, and RSN totaled only 50 kg-N/ha. 

Nitrate loading in the subsurface drainage water each year was greatly affected by both nitrate 

concentrations and drainage flow (Figure 3.1d). These data clearly indicate a buildup of RSN in 

the soil profile during dry years when drainage was limited. Much of the RSN build-up could be 

attributed to mineralization of soil organic matter, annual additions of N fertilizer, and limited 

uptake of N by the poor-yielding corn. In the subsequent wet years, substantial losses of nitrate 

occurred in subsurface drainage due to high concentrations of nitrate and high drainage volumes. 

Differences in nitrate contributions across the Minnesota River Basin discussed above in response to gradients in precipitation are even larger when nitrate loads, rather than nitrate concentrations, are compared. Four watersheds located in the wetter eastern portion of the 

Minnesota River Basin account for 75% of the total nitrate load in the entire basin, yet they 

drain only 31% of the total basin area. Six watersheds on the drier western side of the basin collectively generate only 7% of the nitrate load. Nitrate yields for watersheds in the Minnesota 

River Basin average 2.1 kg-N krf2 day1 but vary from 0.5 to over 6 kg-N km-2day1, with the 

larger yields occurring in the watersheds on the wetter eastern side of the basin. 

In summary, precipitation has a great effect on the export of nitrate-nitrogen from crop fields in 

the MRB, particularly on the nitrate-nitrogen discharged through subsurface drains. Dry years 

can result in very low discharges of nitrate-nitrogen. Wet years, particularly if they follow one or 

two dry years, can result in very high discharges of nitrate-nitrogen through subsurface drains. 
Chapter 3: Results-Approaches for Controlling Nitrogen 1 5 

However, nitrate-nitrogen concentrations do not vary consistently with daily flow, but rather do 

vary seasonally. Highest concentrations are generally in the spring after spring rains. Between 

rain events, residual soil nitrate can accumulate in the soil due to fertilization, reduced crop uptake, and soil mineralization, only to be released during high rainfall euents. 

3. I.1.5 LONG-TERM CHANGES IN PRECIPITATION 

Long-term changes in annual precipitation due to climate shifts could have a major effect on 

nitrate loading to the Gulf of Mexico from the MRB. Increased amounts of annual precipitation would most likely lead to greater surface runoff and subsurface drainage of water containing 

nitrates. Since 1910, precipitation has increased by about 10% across the contiguous United 

States, largely due to heavy and extreme precipitation events (Karl and Knight 1998). For extremely heavy precipitation events (>50 cm), an increasing intensity is also significant. Kunkel et 

al. (1999) studied the trends of extreme precipitation events and found lengthy periods of belowaverage numbers of events in the 1930sand 1950s and an above-average number of events in the 

early 1940s, early 1980s, and 1990s. The overall trend covering the period 1931-96 has been upward at a highly statistically significant rate in a broad region from the central Great Plains 

across the middle Mississippi River and the southern Great Lakes. The national trend is upward 

at a rate of 3% per decade for this period. 

3.1.2 Changing Cropping Systems 

Nitrate concentrations in subsurface drainage water are related to cropping systems. Tiledrainage water from row-crop systems (continuouscorn and a corn-soybean rotation) that were 

fertilized with nitrogen based on a soil nitrate test averaged nitrate-nitrogen concentrations 

between 14 and 40 mg-N/L from 1990 to 1993 at Lamberton, Minnesota (Table 3.5). In comparison, perennial crops (alfalfa and a conservation reserve program (CRP) grass-alfalfa mix) resulted in nitrate concentrations ranging from 0.3 to 4 mg-N/L. Due to higher-flow volumes 

from the plots planted to row crops, nitrate losses from the row crops were 30-50 times higher 

than from the perennial crops (Randall et al. 1997). 

TABLE 3.5. Effect of crop system on flow-weighted annual nitrate-N concentrations and 

four-year total nitrate-N loss. 

Cropsystem - Annual Nitrate-Nitrogen Concentration (mg-NIL) Four-Year Total 

1990 1991 f 992 1993 Nitrate Loss 

(kg-Nlha) 

Continuous Corn 3 0 3 9 

Corn-Soybean 22 29 

Soybean-Corn 26 3 8 

Alfalfa - 4 

CRP ' - 4 

'CRP = Conservation Reserve Program (mixture of grass and alfalfa). 

Source: Randall et a/. 1997. 

Nitrate concentrations under alfalfa were also shown to be much lower compared to corn or 

soybeans in Iowa (Baker and Melvin 1994).These findings are similar to those reported by Logan et al. (1980), who found highest nitrate losses with corn, intermediate with soybean or sys-
I6 ReducingNutrient Loads to Surface and Ground Waters and the Gulf 

tems where other crops were in rotation, and lowest with alfalfa. Weed and Kanwar (1996) 

found higher nitrate losses from plots planted to continuous corn compared to a corn-soybean 

rotation in Iowa (Table 3.6). A four-year field study on a poorly drained, fine-textured soil in 

northwestern Ohio showed concentrations of nitrate with soybeans were as high as or higher 

than with corn in a corn-soybean rotation, especially in the spring (Logan et al. 1994). That 

study concluded that a significant portion of the nitrate in tile drainage is due to nitrogen carried 

over from the previous corn crop. 

TABLE 3.6. Average nitrate concentration and annual nitrate loss in subsurface, tile drainage water in Iowa as a function of crop and tillage technique 

Continuous Corn 

Moldboard plow 

Chisel plow 

Ridge tillage 

No tillage 

Corn-Soybean 

Moldboard plow 

Chisel plow 

Ridge tillage 

No tillage 

Source: Weed and Kanwar 1996. 

In summary, these studies show substantially higher nitrate concentrations in subsurface drainage from row crops, especially continuous corn, compared to perennial crops that have an extended period of greater root activity (water and nutrient uptake) and where cycling of nitrogen 

is optimized. Thus, some control of nitrogen losses is possible by changing cropping systems. 

3.1.3 CONTROLLING NITROGEN FERTlLlZERAPPLICATION RATES 

Applying the proper rate of nitrogen for a crop is a major management decision facing crop producers. Using too little nitrogen for a highly responsive crop such as corn or wheat results in 

lower yields, poorer grain quality, and reduced profits. When too much nitrogen is applied, crop 

yields and quality are not affected, but profit can be reduced somewhat and negative environmental consequences most likely will result. Thus, many farmers choose to err on the liberal side 

when making decisions on nitrogen rates. This "extra" nitrogen is often called "insurance" nitrogen. The application rate of this excess nitrogen, while difficult to find precisely in the peerreviewed literature, is stated by one publication to vary between 22 and 67 kg-N/ha (20-60 

lb/acre) of excess nitrogen in Minnesota (Legg et al. 1989). 

University long-term research provides guidance necessary to make decisions about nitrogen application rates. The recommended application rate provided via various extension bulletins and 

software venues are based on numerous field experiments conducted across a broad range of soils, 

cropping systems, and weather conditions. The recommendations also include credits for nitrogen from other sources, such as manure and nitrogen fxed by legumes. These nitrogen credits 

are then subtracted from the total amount of nitrogen required by the crop to provide a fertilizer 
Chapter 3: Results-Approaches for Controlling Nitrogen I T' 

nitrogen rate recommendation. Even though the examples used in the following discussion focus on nitrogen fertilizer, it should be remembered that these principles also relate to nitrogen 

supplied by manure and legume furation. 

The relationship between the annual fertilizer nitrogen application rite for continuous corn and 

annual flow-weighted nitrate concentrations in subsurface drainage water is shown for two 

studies in southern Minnesota in Figure 3.2. Climatic conditions during the six-year period 

(1974-79) at Lamberton, Minnesota, were marked by drier-than-normal conditions, especially 

during each growing season. Although corn yields were below normal in five of six years with no 

yield in 1976-a drought year--they were optimized at the 112 kg-N/ha rate in four of five 

years. Consequently, nitrate concentrations in subsurface drainage water were extremely high 

with the 224 and 448 kg-N/ha rates, especially in the last three years of the study (Figure 3.2a). 

Nitrate concentrations from the 20 kg-N/ha plots ranged between 16 and 28 mg-N/L, indicating the contributing role of soil mineralization in this highly organic soil. Average nitrate 

concentrations in the drainage water for the two-year pre-drought and the three-year postdrought periods were increased by 16 and 50 mg-N/L when the nitrogen application rate was 

increased from 112 to 224 kg-N/ha (100-200 lb/acre), respectively. Thus, if a grower decided to 

apply an extra 45 kg-N/ha (40 lb/acre) of "insurance N" to the recommended 135 kg-N/ha (120 

lb/acre) rate for a total of 180 kg-N/ha (160 lb/acre), these data indicate that nitrate concentrations in the tile water would be increased about 6 mg-N/L prior to the drought year and 20 mgN/L after the drought year. For a six-year period, nitrate concentrations in the drainage water 

would be expected to increase 14-15 mg-N/L with this extra annual 45-kg "insurance" rate. 

During this six-year period, if applications of manure yielding about 100 kg-N/ha of available 

nitrogen annually were not credited, resulting in a total application rate of 235 kg-N ha-' yr-l 

(135 from the fertilizer and 100 from the manure), the nitrate concentrations would be expected 

to increase by about 25 mg-N/L. On the other hand, if the annual N fertilizer rate were reduced 

by about 10% to 125 kg-N/ha and no other nitrogen were applied, one could expect a small yield 

decrease, and nitrate concentrations could be expected to decrease by about 3 mg-N/L. 

At Waseca, the annual nitrogen rates were begun in 1975, but no drainage occurred in 1975 and 

1976 due to very dry weather. Thus, at the beginning of 1977 increasingly high amounts of residual soil nitrate remained in the soil profile with each added amount of nitrogen. Consequently, high concentrations of nitrates were found in the 12 cm of drainage water in 1977 

(Figure 3.2b). -

Nitrate concentrations in the drainage water were lower in 1978 and were further reduced in 

1979 as drainage volume increased and yields improved. Annual flow-weighted nitrate concentrations from the control plots (no fertilizer) ranged from 13 to 16 mg-N/L, indicating the role 

that soil mineralization played during this dry-to-wet climatic cycle in this highly organic soil. 

Averaged across the three years when tile flow occurred, nitrate concentrations in the drainage 

water were increased by 16 mg-N/L when the fertilization rate was increased from 112 to 224 

kg-N/ha and by 20 mg-N/L when the rate was increased from 224 to 336 kg-N/ha. If 190 kgN/ha (170 lb/acre) were the recommended nitrogen application rate for a yield goal of 10 metric 

todha (160 bu/acre), but the grower decided to apply an additional 45 kg-N/ha (40 lb/acre) for 

"insurance" purposes, based on these data, nitrate concentrations in the drainage water would be 

projected to increase by about 7 mg-N/L. If an annual nitrogen credit of 100 kg-N/ha from 

manure were ignored and a total of 290 kg-N/ha were applied annually, nitrate concentrations 
18 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf 

..' 

73 (4cm)'74(9 an)75 (13 cm) '77(1 cm) '78 (5 cm)79 (21) -' 

_ ." 

112 224 

N rate applied, kg hi1yi' 

1977 -(12 cm) 1978 (14 cm) 1979 (43 cm) ..... -.. 

112 224 

N rate applied, kg hd'yi' 

FIGURE 3.2. Nitrate-nitrogen concentration in tile-drainagewater as affected by rate of N 

fertilizer application for continuous corn at (a) Lamberton and (b) Waseca, MN. 
Chapter 3: Results-Approaches for ControllingNitrogen 19 ' 

could be expected to increase by about 17 mg-N/L. On the other hand, if the nitrogen fertilization rate were reduced by 10% to 170 kg-N/ha (150 lb/acre), nitrate concentrations could be expected to decrease by about 3 mg-N/L with a relatively low yield reduction (0.3-0.4 metric 

todha, or 5-6 bdacre). I 

Although abnormally dry conditions prevailed for portions of the two above studies, the results 

clearly show the effect of increasing nitrogen application rates on the concentration of nitratenitrogen in tile drainage water. Nitrogen applied in excess of crop need leads to dramatic increases in nitrate concentrations. A simple excess application of 45 kg N/ha for "insurance" purposes can elevate nitrate concentrations by 6-20 mg-N/L, depending on the severity and length 

of the dry period and on crop yield. 

Residual soil nitrate (RSN) that accumulates in the soil profile during dry periods is the major 

source of the nitrate lost in tile drainage. Accounting for RSN following dry years by using 

spring soil N tests could be quite helpful to growers (Magdoff et al. 1984; Blackmer et al. 1989; 

Bundy et al. 1992; Schmitt and Randall 1994). Unless the nitrate has been leached below the 

top 30 cm, these tests should be able to provide information that would lead to reductions in the 

recommended rate of nitrogen fertilizer, resulting in lower nitrate-nitrogen losses in subsurface 

drainage water. 

3.1.4 Managing Manure Spreading 

Improved manure management, including uniform application of known nutrient amounts and 

immediate incorporation, is critical if the optimum nitrogen rates are to be achieved in livestock 

production systems. All too often manure is applied with a disposal objective in mind, rather 

than with a utilization objective. When this occurs, rates of nitrogen as manure tend to be high 

and are not distributed evenly across the field. Consequently, credit is not given for nitrogen in 

the manure, and the total rate of nitrogen application (fertilizer plus manure) becomes excessive. 

When the nutrient content of manure is known and best management practices are used in land 

application, manure does not lead to greater nitrate losses to subsurface tile drainage than does 

nitrogen from commercial fertilizer (Iragavarapu et al. 1997). If manure is applied at greater than 

agronomic rates, concentrations of nitrate in the drainage water will be elevated. 

3.1.5 Managing the Time of Nitrogen Application 

The time of nitrogen application is another management decision that crop producers make 

each year. Agronomically and environmentally speaking, spring is frequently superior to fall application because less nitrogen is lost in the two- to three-month period between application and 

nitrogen uptake by the crop. However, many corn growers, especially in the northern part of the 

Corn Belt, prefer applying nitrogen in the fall because they usually have more time in the fall, 

N-fertilizer prices are often lower, and field conditions are better. In the spring, early planting of 

corn as soon as the soils are fit is desirable for highest yields and profit. Thus, the window of opportunity for spring N application becomes very narrow (Randall and Schmitt 1998). 

N-fertilizer management, particularly managing the rate and time of application, plays a dominant role in the loss of nitrate to surface waters. In one series of experiments, nitrogen was applied in the fall and spring for continuous corn during a sic-year period at Waseca, Minnesota, to 

investigate the importance of the time of application (Buzicky et al. 1983). In general, nitrate 

losses from the crop lands were higher when fertilizers were applied in fall. Corn yields were 8% 

lower and annual losses of nitrates in the subsurface drainage water were 36% higher with a late-
20 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf 

fall (early November) application of fertilizer compared to spring application (Table 3.7). Averaged across time of application, yields and nitrate losses in the drainage water were 17 and 30% 

higher, respectively, for the 202 kg-N/ha fertilizer application rate compared to the 134 kg-N/ha 

rate. At the end of the study, 65% of the nitrogen being lost in lthe drainage from high fall 

treatment was derived from the fertilizer, whereas only 15% of the nitrogen in the drainage water lost from a low spring treatment was derived from the fertilizer (Buzicky et al. 1983). 

Based on these data, obtained during a climatic period without a very dry year or years, a 45 kgN/ha application of "insurance N" above the recommended 190 kg-N/ha rate would increase 

nitrate losses in tile drainage water by about 6 kg ha-' F'.Reducing the optimum nitrogen application rate by 10% and 20% to 170 and 150 kg-N/h, respectively, would most likely reduce 

nitrate losses by 2.5 and 5.0 kg-N ha-' yfl,respectively. Corn yields would also most likely be reduced slightly (by .0.3 and 0.7 metric ton/ha (5 and 12 bdacre) respectively) with the 10% and 

20% reductions in the fertilizer application rate. 

TABLE 3.7. Effect of nitrogen application rate and time of application on nitrate-N losses 

and corn yield. 

-

Fall 

Spring 

Fall 

Spring 

'Ammonium sulfate applied about INovember or IMay. 

Source: Buzicky et al. 1983. 

3.1.6 Using Nitrification Inhibitors 

In another set of experiments (Randall and Vetsch 1995))anhydrous ammonia fertilizer was applied in four-treatments with and without a nitrification inhibitor to drainage plots at Waseca, 

Minnesota (Table 3.8). 

TABLE 3.8. Effect of time of N application and nitrapyrin (NI) on nitrate-N losses and corn 

yield in a corn-soybean rotation during 1 990-93. 

Fall 

Fall + NI 

Spring 

S~lit 

Fallow 3 6 365 

'Anhydrous ammonia applied 25 October (fall) or IMay (spring). 

Source: Randall and Vetsch 1995. 
Chapter 3: ResultoApproachesfor Controlling Nitrogen 2 I-' 

Results obtained from this study and other similar studies suggest that application of anhydrous 

ammonia in the spring or in late fall along with a nitrification inhibitor (N-Serve) would reduce 

nitrate concentrations and fluxes in drainage water and increase corn yields, compared to a late 

fall application of anhydrous ammonia without a nitrification inhibitor. Early fall applications of 

anhydrous ammonia, when soil temperatures are warmer and conversion to nitrate (nitrification) 

is fister, would be expected to produce even greater losses of nitrate to drainage water and also 

poorer yields. 

3.1.7 Changing Tillage Methods 

Tillage methods appear to have little influence on nitrate losses from agricultural fields. Studies 

conducted in Iowa showed that tillage methods have less effect on nitrate loss to drainage water 

than do crop rotations (Bjorneberg et al. 1996; Weed and Kanwar 1996). Moldboard plowing 

gave the lowest flow volumes, while ridge tillage and no tillage had the lowest nitrate-nitrogen 

concentrations (Table 3.6). 

An 11-year study with continuous corn at Waseca, Minnesota, showed similar results (Randall 

and Iragavarapu 1995). Although slightly more water drained from the no-till plots, nitrate concentrations were slightly lower compared to moldboard plow plots (Table 3.9). Thus, nitrate flux 

in subsurface drainage was not significantly reduced by no-till farming practices. Drain flow 

from corn grown on a loam soil in Ontario was significantly greater for no tillage compared to 

conventional tillage (CT), while nitrate concentrations tended to be greater with CT (Patini et 

al. 1996). During a 40-month period, nitrate loss in tile effluent was not significantly different 

for the two tillage treatments. Thus, nitrate flux in subsurface drainage does not appear to be reduced by no-till practices. This conclusion may not apply to all regions of the Midwest, however, 

because of changing nutrient management practices. Increased fall tillage has increased nitrate 

fluxes in subsurface drainage in studies in Iowa U. Hatfield, personal communication). 

TABLE 3.9. Effect of tillage on nitrate losses in subsurface drainage. 

Drainage Volume (mm) 279 3 15 

Nitrate-N Conc. (mgIL) 15 13 

Nitrate-N Lost (kglha) 43 4 1 

N Lost as % of Applied N 2 1 2 0 - -

' II-year (I982-92) average. 

Source: Randall and Iragavarapu 1995. 
22 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf 

3.1.8 Increasing Drainage Tile Spacing 

Many farmers install additional subsurface drain tile to narrow the spacing between tiles with 

the expectation that crop yields will be improved because of enhanced drainage. Studies have illustrated that this practice may also increase subsurface losses of nitrates to streams and rivers. 

A three-year study on a poorly drained Clermont silt loam soil in Indiana showed drain spacing 

to markedly affect nitrate losses in the subsurface drainage water (Kladivko et al. 1991). Annual 

nitrate losses averaged across the 'threeyears were 29,41, and 55 kg-N ha-' yfl for the 20-, lo-, 

and 5-m drain spacings, respectively. Crop yield measurements taken during a four-year period at 

this site showed lower corn yields on the 5-m spacings than on the 10-m or greater spacings 

(Larney et al. 1989). Averaged across a 10-year period, corn yields were not different among the 

three drain spacings. 

These data suggest the potential for greater residual soil nitrate in the profile due to less crop uptake in dry years, and thus greater leaching losses to subsurface drainage in the following wet year 

with narrower drain tile spacing. Although few data exist, inferences drawn-from this work suggest that narrowing tile drainage to spacings < 20 m could result in greater losses of nitrates 

compared to wider spacings. Additional research is needed to more clearly define the agronomic 

and environmental influences of tile spacing in subsurface drainage systems. 

3.2 OFF-SITEAGRICULTURALNONPOINT-SOURCECONTROL 

A second general approach, after on-site approaches, for preventing nitrogen from reaching 

streams and rivers of the Mississippi Ever Basin is to place ecosystems that are effective nitrogen 

sinks between the agricultural fields and the streams and rivers. This section discusses the general 

functioning of nitrogen in wetlands and riparian systems and then reviews some of the studies 

and design principles related to using three general ecological systems for controlling nitrogen: 

(1) natural and created wetlands, (2) riparian buffers, and (3) controlled drainage systems for the 

control of nonpoint-source pollution, particularly nitrogen, from agricultural fields. 

Many of the original freshwater wetlands and riparian zones that were once found throughout 

the MRB and that were once connected to streams and rivers of the basin are gone from the 

landscape. Without them, the landscape has lost part of its ability to maintain a biogeochemical 

balance, and-the streams and rivers are no longer buffered from upland regions (Mitsch 1994). 

The net result has been the loss of a valuable biological habitat and poorer water quality. 

For example, in the U.S. Midwest, states such as Ohio, Indiana, Illinois, and Iowa, where over 

80% of the wetlands have been drained (partly in response to the Swamp Lands Acts of 1849, 

1850, and 1860; Figure 3.3), water quality is particularly degraded as nutrients, pesticides, and 

sediments from farms and urban areas have nowhere to go except directly into waterways. Seven 

states in the Upper MRB (Indiana, Illinois, Iowa, Minnesota, Missouri, Ohio, and Wisconsin) 

collectively have had about 18.6 million ha (46 million acres) of land drained (Table 3.10). Statistics reveal that collectively, these seven states lost the equivalent of 14.1 million ha (35 million 

acres) over the past 200 years (Dahl1990). Had natural wetlands and riparian zones been left on 

the midwestern U.S. landscape, water pollution problems might not be as pervasive and nitrogen 

fluxes down the Mississippi to the Gulf of Mexico would not have been as extreme. 
Chapter 3: Results-Approaches for ControllingNitrogen 23' 

FIGURE 3.3. Extent and location of artificially drained agricultural land in the United States. 

(From Dahl 1990.) 

TABLE 3.10. Drainage statistics of selected states in the upper reachesof the MRB. 

Illinois 

Indiana 

Iowa 

Ohio 

Minnesota 

Missouri 

Wisconsin 

Total 

Source: USDA 1987, as cited in Zucker and Brown 1998. 
24 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf . 

3.2.1 Nitrogen Processes in Wetlands and Riparian Systems 

Nitrogen transformations in wetland and riparian soils, surface water, and ground water involve 

several microbiological processes, some of which make the nutrient less available for plant uptake 

(Mitsch and Gosselink, 1993; Figure 3.4). The ammonium ion is the primary form of mineralized nitrogen in most flooded wetland soils, although much of the nitrogen can be tied up in 

organic forms in highly organic soils. The presence of an oxidized zone over the anaerobic or reduced zone is critical for several of the pathways. Nitrogen mineralization refers to "the biological transformation of organically combined nitrogen to ammonium nitrogen during organic 

matter degradation" (Gambrell and Patrick 1978). This pathway occurs under both anaerobic 

and aerobic conditions and is often referred to as ammony5cation. Typical formulas for the mineralization of a simple organic nitrogen compound, urea, are given as: 

NH, CO NH, + H20--> 2NH3 + CO, 

NH, + H,O --> NH,' + OHOnce the ammonium ion (NH,') is formed, it can take several possible pathways. It can be absorbed by plants through their root systems or by anaerobic microorganisms and converted back 

to organic matter. It can also be immobilized through ion exchange onto negatively charged soil 

particles. Because of the anaerobic conditions in wetland soils, ammonium would normally be 

restricted from further oxidation and would build up to excessive levels were it not for the thin 

oxidized layer at the surface of many wetland soils. The gradient between high concentrations of 

ammonium in the reduced soils and low concentrations in the oxidized layer causes an upward 

diffusion of ammonium, albeit very slowly, to the oxidized layer. This ammonium nitrogen then 

is oxidized by a restricted number of chemoautotrophic bacteria through the process of nitrification in two steps: 

2NH4++ 30, --> 2NO; + 2H,O + 4H++ energy 

and, 

2NO; + 0, --> 2N03-+ energy 

Nitrification can also occur in the oxidized rhizosphere of plants, where adequate oxygen is often 

available to convert the ammonium-nitrogen to nitrate-nitrogen (Reddy and Graetz 1988). Nitrate (NO3-),as a negative ion rather than the positive ammonium ion, is not subject to immobilization bythe negatively charged soil particles and is thus much more mobile in solution. If it 

is not assimilated immediately by plants or microbes (assimilatory nitrate reduction), or lost 

through ground-water flow due to its rapid mobility, it has the potential of going through dissimilatory nitrogenous oxide reduction, a term that refers to several pathways of nitrate reduction, 

the most prevalent being reduction to ammonia and denitrzJication. Denitrification, carried out 

by microorganisms in anaerobic conditions with nitrate acting as a terminal electron acceptor, 

results in the loss of nitrogen as it is converted to gaseous nitrous oxide (N,O) and molecular nitrogen (N,): 

C6H,,06+ 4N03---> 6C0, + H,O + 2N2 

As illustrated in Figure 3.4, the entire process occurs after (1) ammonium-nitrogen diffuses to 

the aerobic soil layer, (2) nitrification occurs, (3) nitrate-nitrogen diffuses back to the anaerobic 

layer, and (4) denitrification occurs. Because nitrate diffusion rates in wetland soils is seven times 

faster than ammonium diffusion rates, ammonium diffusion and subsequent nitrification are 

thought to limit the entire process of nitrogen loss. 
Chapter 3: Results--Approaches for Controlling Nitrogen- 25 

FIGURE 3.4. Nitrogentransformation in wetlands. SON indicates soluble organic nitrogen. (From Mitsch and Gosselink 1993.) 
26 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf 

3.2.2 Wetlands 

Some rates of denitrification and nitrogen retention measured for wetlands or wetland soils in 

laboratories appear in Table 3.11. If sufficient nitrate and organic carbon are available, high rates 

of denitrification (> 100 g rn" yil)are physically possible. It also aipears that on a per unit-area 

basis, wetlands (swamps, marshes, and possibly peatlands) have a greater potential for nitratenitrogen reduction by denitrification than do riparian forests. 

TABLE 3.1 1. Nitrogen loss rates as reported in the literature for wetland and riparian zone 

studies. 

Rates Conditions References 

g-N m" day-' g-N ni2yr-' 

Laboratory Studies 

0.06-0.92 10 mg N-NOJL added Gale et al. 1993 

Wetlands 

0.03-5.5 Natural swamps (LA) Smith and DeLaune 1983 

28 Nutrient-enriched swamp (FL) Dieberg and Brezonik 198! 

Range for natural wetlands Nixon and Lee 1986 

6 Discharge fen, The Netherlands Koerselman et al. 1989 

20 Recharge fen, The Netherlands 

0.002-0.34 Low-nutrient wetlands Johnston 1991 

avg. = 0.19 

16- 134 N-enriched wetland 

avg. = 60 

20-92 Danish wetlands J~lrgensen 1994 

17' River-fed constructed wetlands (IL) Phipps and Crumpton 199 

280 Treatment wetland-theoretical rate Kadlec and Knight 1996 

80' Treatment wetland-based on I10 water 

quality analyses 

Agricult. runoff-Phragmites marshes &min et al. 1997 

10 1 ' 

Marshes in Spain 

Wastewater constructed wetland (OH) Spieles and Mitsch 2000 

- -62-66' River-fed constructed wetlands (OH) 

Riparian Systems 

4.5--6. 0 Riparian forest, Chesapeake Bay (MD) Peterjohn and Correll 1984 

0.22 NO, + glucose; buffer zones Groffman et al. 1991 

1.58 NO, + glucose; grass strips 

0.5- 1.6 Riparian maple swamp (unenriched) Hanson et al. 1994 

2.0-3.6 Riparian maple swamp (enriched) 

6.9 Restored riparian wetland Lowrance et al. 1995 

' 

4.3 Young hardwood riparian forest 

0.87-1.3 

' Moderately well-drained soil Groffman and Hanson 1997 2.6-24.4 Very poorly drained soil 

1.5- 15.5* Alluvial soil Groffman and Hanson 1997 

1 .o-2.02 Light till 

'Net reduction of NO, + NO, through wetlands. Range of annual means (14- 16 sarnpleslyr). 

Partial source: Groffman 1994. 
Chapter 3: Results-Approaches for Controlling Nitrogen 27 

Wetlands and riparian zones can be nutrient sources, sinks, or transformers. A wetland is considered a sink if it has a net retention of an element or a specific form of that element (e.g., organic 

or inorganic)-that is, if the inputs are greater than the outputs. If a wetland exports more of an 

element or material to a downstream or adjacent ecosystem than would occur without that wetland, it is considered a source. If a wetland transforms a chemical from, say, dissolved to particulate form, but does not change the amount going into or out of the wetland, it is considered to 

be a transformer. There is not consensus on this question for wetlands in general; in fact, there 

is little agreement in the literature even for particular nutrients in specific wetland types 

(kchardson 1985). All that can be said with certainty is that many wetlands act as sinks for particular inorganic nutrients, and many wetlands are sources of organic material to downstream or 

adjacent ecosystems. 

The three types of wetlands (Figure 33, whether natural, restored, or created, that could be 

utilized for the control of nonpoint source pollution in the Mississippi River Basin are: (1) 

freshwater marshes; (2) peatlands, e.g. bogslfens; and (3) forested wetlands, including riparian 

forests. 

Table 3.12 lists some of the studies where nitrogen retention has been examined in these types 

of systems for relatively low concentrations of nitrogen that would be typical of nonpoint-source 

pollution. There is a dramatic difference in nitrogen concentrations and N:P ratios for treated 

wastewater and rural nonpoint-source pollution (Table 1.2). Therefore this section will emphasize wetlands that are receiving concentrations typical of nonpoint-source pollution. Discussion 

of constructed wetlands for wastewater treatment is in Section 3.4. 

3.2.2.1 NATURAL FRESHWATER MARSHES 

Freshwater marshes are among the most studied types of wetlands for their role in water quality 

improvement. Early studies by Klopatek (1978) in a Wisconsin riverine marsh and by Simpson 

et al. (1978) in a tidal freshwater marsh showed the capacity for marsh wetlands to be at least a 

seasonal sink for inorganic forms of nitrogen and phosphork. A two-year study of the potential 

of managed marsh wetland in upper New York State to remove nutrients from agricultural 

drainage gave inconsistent results, with the wetland acting as a source of nitrogen and phosphorus in the first year and as a net sink in the second year (Peverly 1982). Studies of a freshwater marsh along Lake Erie's shoreline have shown that the wetland is effective in ameliorating 

nutrient loading from an agricultural watershed to the lake and that the effectiveness is dependent on the amount of annual runoff and the level of the lake (Klarer and Millie 1989; Mitsch 

and Reeder 1991,1992). 

3.2.2.2 CREATED AND RESTORED MARSHES 

Despite the apparent success of natural wetlands to retain some nonpoint-source pollution, it has 

become more common in the United States to discuss the construction or restoration of new 

wetlands, rather than the use of natural wetlands when purposeful use of a wetland for nonpoint-source pollution control is discussed (Olson 1992). The construction of new wetlands for 

controlling nonpoint-source pollution is a more recently proposed approach for wetlands and 

water quality, although studies have investigated the idea in detail (Livingston 1989; Hey et al. 

1989; Mitsch and Cronk 1992; Baker 1992; Mitsch 1990, 1992, 1995), compared to the more 

abundant literature on natural wetlands and wastewater wetlands. Wetlands built for controlling 

nonpoint-source pollution (e.g., sediments and nutrients) need to be considered part of a watershed or river floodplain restoration project. 
28 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf -. 

a) Freshwater Marsh 

c) Riparian forest 

FIGURE 3.5. Three types of wetlands that could be used to control nonpoint-source pollution: (a) freshwater marsh, @) peatland,.and(c) riparianforest. 
Chapter 3: Results-Approaches for ControllingNitrogen 29 

TABLE 3.12. Selected studies that have investigated nitrogen retention of natural and created freshwater marshes, peatlands, and forested wetlands and riparian zones. 

Types and Locationsof Wetlands NitrogenSink? References 

Natural Freshwater Marshes 

Four marshes, WI Yes Lee et al. 1975 

Water hyacinth marsh, FL Yes Mitsch 1977 

Theresa Marsh, WI Seasonal Klopatek 1978 

Managed marsh, NY Inconsistent Peverly 1982 

Natural marshes, Albury, Australia Seasonal Raisin and Mitchell 1995 

Phragmites marshes, Ebro River, Spain Yes Comin et al. 1997 

Constructed Freshwater Marshes 

Lake Jackson, FL Yes Johengen and LaRock 1993 

Des Plaines River wetlands, IL Yes Kadlec and Hey 1994 

Phipps and -Crumpton 1994 

Olentangy River wetlands, OH Yes Mitsch and Carmichael 1997 

Mitsch and Montgomery 1998 

Spieles and Mitsch 2000 

Boney Marsh, FL Yes Moustafa et al. 1996 

Constructed marsh, Albury, Australia Inconsistent Raisin and Mitchell 1995 

Raisin et al. 1997 

Peatlands 

Forested peatland, MI No Richardson et al. 1978 

Thoreau's Bog, MA Yes Hemond 1980 

Black spruce bog, M N Yes Verry and Timmons 1982 

Urban and Eisenreich 1988 

Thuja peatland, MI Yes Kadlec 1983 

Forested Swamps and Riparian Zones 

Riverine cypress swamp, SC Yes Kitchens et al. 1975 

Riparian forest, GA Yes Lowrance et al. 1984 

Fraxinus lakeside- wetland, WI Yes Johnston et al. 1984 

Swamp forest, LA Yes Kemp and Day 1984 

Riparian forest, M D Yes Peterjohn and Correll 1984 

Nyssa swamp, NC Yes Brinson et al. 1984 

Riparian forest, NC Yes Jacobs and Gilliam 1985 

Reedy Creek Swamp, FL Yes Knight et al. 1987 

Riparian buffer, IA Yes Schultz et al. 1995 

NOTE: Table does not generally include constructed wastewater wetlands, which are generally subjected to much 

greater concentration of nitrogen and are discussed in later parts of this report. 

3.2.2.3 PEATLANDS 

There have been few studies of the nitrogen retention capacity of natural bogs and fens, as they 

generally have no or simple outflows and rely to a great extent on inputs from precipitation 

(Johnston 1991).While peatlands are generally anaerobic, denitrification has not generally been 

considered a major pathway for nitrogen loss in these systems, at least in studies in Alaska, Mas-
30 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf 

sachusetts, and Minnesota (respectively, Barsdate and Alexander 1975; Hemond 1983; Urban 

and Eisenreich 1988). Studies by Kadlec and Tilton (1979) and Richardson and Marshall (1986) 

investigated the role of fens in Michigan in retaining nutrients, with the former study involving 

the addition of wastewater. A multiple-year study by Kadlec (1983),demonstrated that a peatland 

in Michigan that received wastewater was consistently a sink for nitrogen (75-81% removal) but 

began to export phosphorus after several years of phosphorus retention. 

3.2.2.4 FORESTED WETLANDS 

The functioning of forested wetlands, especially riparian zones, as nutrient sinks has been investigated mostly in the southeastern United States and less-so in the Midwest. Kitchens et al. 

(1975) found significant reduction in nutrients as the waters passed over the swamp. Kemp and 

Day (1984) and Peterjohn and Correll (1984) described the fate of nutrients as they are carried 

into riparian forests by agricultural runoff. The former study found that a Louisiana swamp forest acted primarily as a transformer system, removing inorganic forms of nitrogen and serving as 

a net source of organic nitrogen, phosphate, and organic phosphorus. The latter study in a riparian Maryland forest described the removal of nitrogen and phosphorus from runoff and 

ground water as the runoff passed through approximately 50 m of riparian vegetation. Significant reductions of both nutrients from runoff were noted in the study. A similar study of a 

floodplain forest in Georgia found 14% retention and 61% denitrificatiod of nitrogen (for total 

loss of 75% of the incoming nitrogen) and 30% retention of phosphorus (Lowrance et al. 1984). 

The Maryland and Georgia studies did not consider any river flooding in the calculations of their 

nutrient budgets. These are among the many studies (e.g., Johnston et al. 1984; Lowrance et al. 

1984, 1985, 1995, 1997;Jacobs and Gilliam 1985; Cooper et al. 1987; Cooper and Gilliam 1987) 

that illustrate the potential for riparian forests for reducing nutrient and sediment loads to 

streams and rivers. 

More recently, research on riparian buffers has been conducted in Iowa and Ihnois. Schultz et. 

al. (1997) have noted nitrate removals in Iowa to be very similar to those measured elsewhere (12 

mg-N/L of nitrate in field ground water was reduced to 3 mg-N/L in the buffer). Osborne and 

Kovacic (1993) installed a wetland grass buffer, rather than a forested buffer, between corn fields 

and a stream channel in an agricultural watershed in Illinois. They found that their buffers reduced nitrate entry into the stream by 35-45%. 

3.2.2.5 CASE STUDIES-NITROGEN RETENTION BY WETLANDS 

IN THE MIDWEST 

Two carefully designed multi-year studies of created wetlands have recently provided an extensive 

data base on nitrogen retention by newly created wetland basins in the Midwest: the Des 

Plaines River Wetland Demonstration Project in northeastern Illinois, and the Olentangy River 

Wetland Research Park in central Ohio. These are two major research wetland sites where extensive multi-year data have been collected to evaluate the retention of low concentrations of 

nutrients more typical of nonpoint-source pollution than wastewater wetlands. 

Des Plaines River Wetlands,IZZinois 

A number of studies of wetland function were carried out with four full-scale constructed wetlands at the Des Plaines River Wetland Demonstration Project in northeastern Illinois (Figure 

3.6; Sanville and Mitsch 1994; Kadlec and Hey 1994; Mitsch et al. 1995). In whole-ecosystem 

experiments in the early 1990s, hydrologic conditions were varied for high and low flow conditions for entire wetlands (average size = 2.4 ha); the studies were carried out over three years. 
Chapter 3: Result-Approaches for ControllingNitrogen 3 1 

feet 

0 100 200 

meters 

Site Location 

FIGURE 3.6. Four original experimental wetlands at the Des Plaines River Wetland Dernonstration Project in northeastern Illinois. NOTE: During the 1989-93 ' experimental period, experimental wetlands (EW) 3 and 5 were high-flow and 4 and 6 were low-flow. 
3 2 ReducingNutrient Loads to Surface and Ground Waters and the Gulf -. 

Researchers had important findings in estimating detention and mixing (Kadlec 1994), water 

quality function (Hey et al. 1994; Phipps and Crumpton 1994), sedimentation (Fennessy et al. 

1994a; Brueske and Barrett 1994), vegetation development (Fennessy et al. 1994b), aquatic metabolism (Cronk and Mitsch 1994a, 1994b), and avian success (Hicban 1994) in created wetlands, most as a function of hydrology. 

8 -

Outlets high-flow basins 

------ Outlets low-flow basins 

6 -

-

4 -

-

_--. I I I 

Qep M Mv Ded 

FIGURE 3.7. A strong seasonal pattern of nitrate-nitrogen and total nitrogen typical of mdwestern U.S. streams was seen with high concentrations in the spring and fall (inlet data) 

from the Des Plaines River. NOTE: Outflows are from one low-flow (EW 4) and two high-flow 

(EW 3 and 5) wetland basins at the Des Plaines Wetland Demonstration Project, shown in 

Figure 3.6. (From Phipps and Crumpton 1994.) 

8 -

-

6 -

--- Outlets high-flow basins 

------ Outlets low-flow basins 

-

4 -

2 -

0 I 1 I I 

Lp W'Jm Jut Aug'thpIoctI~~I~r 

34 Reducing Nutrient Loadsto Surface and Ground Waters and the Gulf . 

Olentangy River Wetlands, Ohio 

The Olentangy River Wetland Research Park at Ohio State University (Figure 3.8) includes 

two constructed wetland marshes that have been, and continue to be, compared since 1994. One 

was planted with typical freshwater marsh plants, while the other was left as an unplanted control (Mitsch 1995; Mitsch and Wilson 1996; Mitsch et al. 1998). Inflow nitrate-nitrogen concentrations vary seasonally, as at the Des Plaines River site, and average about 2-4 mg-N/L. 

This study area reveals several patterns regarding nitrate-N retention by constructed wetlands 

(Table 3.15). First, planting vegetation had little effect on nitrate-nitrogen reduction, and differences between the two wetlands were only significant in one year out of three. Second, there 

is a general decrease in nitrogen retention from the constructed wetlands over the first three 

years; some is due to the annual differences in hydrology. Third, there is a significant seasonal 

pattern of higher nitrate-N retention in the growing season, with lower rates of retention in 

the winter and spring (Figure 3.9). Nevertheless, the annual average nitrate-nitrogen reduction 

for these wetlands is in a relatively narrow range of 25-28 g-N m-2yflover four years, again suggesting this range to be a reasonable starting point for estimating the area- required for a given 

retention of nitrogen in created and restored wetlands in the Midwest. 

TABLE 3.15. Average f standard error (# samples) of weekly nutrient concentrations at - -

Olentangy River experimental wetlands, 1994-96. 

1994-No significant macrophytic vegetation cover in either wetland; heavy algal growth. 

Total Phosphorus 155f 12 (25) 52&8 (25) 427 (25) -66% -73 % 0.030 

(Pg-PIL) 

Soluble Reactive P 19f7 (23) 4f 1 (23) 3 f0 (23) -8 1 % -84% ND 

(Pg-W 

NO3+ NO, 1.7 1 f0.54 (23) 0.87kO.36 (24) 0.920.37 (23) -49% 46% ND 

(mg-NIL) . 

1995-Macrophytic vegetation cover is greater in planted than in unplanted wetland. 

Total Phosphorus 199f21 (34) 8x13 (33) 97f13 (35) -59% -5 1% ND 

k-PIL) 

Soluble Reactive P 15f3 (34) Sf1 (35) 9 f2 (35) -65% 45% 0.037 

(Pg-PIL) 

NO3 + NO2 I.86f0.25 (35) I.1 9 f0.22 (35) 1 .08&0.2 1 (35) -36% -42% ND 

(mg-NIL) - . 

1996-Both wetlands have approximately the same vegetative cover. 

Total Phosphorus 191f18 (30) 6&8 (34) 64f9 (35) -64% -66% ND 

049'4 

Soluble Reactive P 7W1 1 (29) Sf l (33) 9f2 (33) -89% -87% ND 

@g-PI4 

NO3+ NO2 4.420.42 (29) 2.97k0.40 (34) 3.30f0.38 (34) -33% -25% 0.032 

(mg-NIL) 

Note: + = increase; - = decrease; ND = no signifkant difference at a = 0.05. Source: Mitsch et 01. 1998. 
Chapter 3: Result-Approaches for Controlling Nitrogen 3 5-

FIGURE 3.8. Olentangy RiverWetland Research Park, showing two I-ha experimental deepwater marshes used in a multi-year study of nitrat-nitrogen retention. 
& 

36 Reducinn Nutrient Loads to Surface and Ground Waters and the Gulf 

a) Wastewater wetland 

80 a a 

u 100-mm b) River-fed riparian wetland (planted) 

80.-

a a a 

T 

a a 

I 

e 100 - a, 80 mm 

.. c) River-fed riparian wetland (unplanted) 

a a a 

a 

a T 

b 

.. -20-1 

-40-

Summer Autumn Winter Spring 

FIGURE3.9. Seasonal patterns of nitrate retention by mass and concentrationduring 

summer, autumn, winter, and spring for (a) wastewater treatment wetland in 

Licking County, OH, and (b) and (c) I-ha river-fed created wetlands in Franklin 

County, OH. NOTE: Date are average f standard error; same letters indicate no significant 

differences among all treatments (a = 0.05). (From Spieles and Mitsch 2000.) 
Chapter 3: ResultoApproachesfor Controlling Nitrogen 3 2. 

In both of these case studies, investigations of nitrogen retention by constructed midwestern 

marshes has been one of the aspects investigated over several years. The studies themselves represent a total of 17wetland-years of study, so general trends should be quite evident for midwestern U.S. regions. The retention of nitrate-nitrogen by concentration for the experimental 

marshes in Illinois varied between 40% and 95%, while the retentioh of the Ohio marshes was 

generally 17-49%. When the wetlands are normalized for flow conditions, there is a generally 

strong correlation (Y?= 0.50) between percent reduction and flow (Figure 3.10). The' multiple 

wetland years for this study, coupled with the detailed flow and concentration measurements, 

suggest an achievable ecological engineering desi n arameter for constructed wetlands for re- B !' moving nitrate-nitrogen of about 16-24 g-N m- yr ' (95% confidence interval). This range of 

retention would thus involve an inflow of about 50 g-N m-2y~"and would result in a 36-60% 

retention by mass and about 4042% retention by concentration (Figure 3.10). 

3.2.2.6 DESIGN CONSIDERATIONS AND LIMITATIONS 

Both kinds of wetlands, natural and constructed, have been shown to be effective sinks for nutrients, especially when the nutrient loads are not excessive. But each type has its benefits and 

shortcomings. With fewer and fewer natural wetlands due to drainage and land conversion, 

many natural resource managers and policymakers believe that we should not be adding any type 

of strong pollution to our remaining natural wetlands (Olson 1992). Constructing wetlands for 

controlling nonpoint-source pollution is a good alternative, even though there were some early 

indications that we have not been building wetlands correctly (Erwin 1991; Mitsch and Wilson 

1996), especially when they have been built to replace the function of a wetland lost for some 

type of human development project. Wetlands need to be designed, constructed, and restored in 

an ecologically sound and predictable manner (Mitsch and Cronk 1992; Mitsch 1992; Mitsch 

and Wilson 1996). Some of the many important variables to consider when creating and restoring wetlands for controlling nonpoint-source pollution are discussed here. 

Loading Rates 

Loading rates (flow times concentration of inflowing water) dictate the effectiveness of wetlands in reducing nitrogen (Figures 3.10 and 3.11). Empirical models, such as these graphs, can 

be used as first estimates of the potential nutrient retention in freshwater wetlands. Extensive 

experience with flow-through wetlands (see case studies above) suggested a narrow range that 

centers around 16-24 g-N m-2yfl as a reasonable target for wetland retention of nitratenitrogen. The. loading rate, assuming 50% retention, therefore, would be about 32-48 g-N m-2 

yr-'. This is the equivalent of 10 rdyr of inflow to a wetland with a concentration of 3-5 mgNIL. This flow is approximately 10 times normal rainfall for at least the eastern half of the 

MRB. If flows are less, concentrations would have to be greater to effectively load the wetland. 

Inflows to wetlands in rural areas are often due to pulses of runoff, stream flow, andlor river 

flooding. Storm events, if significant enough, can cause nitrogen to shoot through the system, 

bypassing effective retention (Figure 3.12). The optimum detention time has been suggested to 

be 5-14 days for treating municipal wastewater. Brown (1987) suggested a retention time of a 

riparian wetland system in Florida of 21 days in the dry season and more than 7 days in the wet 

season. 
3 8 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf 

FIGURE 3.10. 

0 20 40 60 80 100 120 140 160 180 200 

N03-N loading (g-N m-2 ~rl) 

measureddata -regression line ............. 95% CI 

Summary of 1 7 wetland-years of nitrate-nitrogen retention data from the Des 

Plaines River and Olentangy River experimental wetlands. NOTE: Wetland removal, percent 

removal by mass, and percent removal by concentration are plotted versus nitrate-nitrogen 

loading; 95th confidence intervals (CI) are also shown. Each data point represents one wetland-year. 
Chapter 3: Result+Approaches for Controlling-Nitrogen 3 9-

20 - A Constructed RootZone 

0 Natural 

0 

0 200 400 600 

Cumulative total N loading, tons 

FIGURE 3.1 1. Examples of wetland nitrogen retention versus loading rate: (a) nitrogen retention from several constructed and natural wetlands (from Mitsch and Gosselink 1993), and 

@) cumulative nitrogen mass retained versus mass loading of a marsh receiving low-level nutrients for eight years. (From Moustafa et al. / 996). 
40 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf ' 

RELEASE 

-4 A RETENTION I 

4- RELEASE 

A 

2 -

M 

0 * 

A~ -

I I 

A 

RETENTION 

-

FIGURE 3.12. Nitrogen retention in an Australian wetland in an agricultural area during 

storm events showing (a) seasonal pattern of retention and release, and @) effect of storm 

flow on retention or release. (From Raisin et a/. I99 7.) 

1131193 8119/93 3/7/94 912A194 411 1195 

Date 

Soil Carbon 

The organic carbon content of soils has great significance for many processes in a wetland, particularly denitrification. Microbes that carry out the process of denitrification require an organic 

carbon source for energy (Mitsch and Gosselink 1993). Furthermore the organic carbon also creates the sufficiently low redox conditions necessary for denitrification to occur. Wetland soils 

generally vary between 5% and 75% organic matter, with higher concentrations in peat-building 

systems, such as bogs and fens, and lower concentrations in mineral soil marshes subject to mineral sedimentation or erosion or in newly constructed wetlands. Riparian forests must have low 

concentrations of organic matter, about 5%, relative to wetlands. When wetlands are created or 
Chapter 3: ResultoApproaches for Controlling Nitrogen 4 1 

restored on mineral soils, one of the factors that most limits their being equivalent to natural 

wetlands is the accumulation of soil organic carbon (Mitsch and Flanagan 1997). Th' is accumulation takes many years on drained or upland soils that have been converted to wetlands. 

There is a definite effect of temperature and, hence, length of growing season, on biological 

processes such as denitrification. Studies of wastewater wetlands and nonpoint-source wetlands 

in central Ohio (Spieles and Mitsch 2000) show that percent removal of nitrate-nitrogen is related to season, with considerably less nitrate-nitrogen retention in nongrowing season months 

compared to growing season months (Figure 3.9). 

Landscape Position 

Wetlands should not be expected to control all of the influx of nutrients from a watershed, nor 

should one small wetland be expected to result in significant improvements in downstream water 

quality. If wetlands are to be constructed in the watershed for controlling nonpoint-source pollution, there are many possible positions in the landscape (Figures 3.13 and 3.14), including instream wetlands, riparian wetlands, and terraced wetlands. 

Wetlands can be designed as instream systems by adding control structures to the streams themselves, or by impounding a distributary of the stream (Figure 3.13a). Blocking an entire stream is 

a reasonable alternative only in low-order streams (see also Section 3.2.4, Controlled Drainage). 

This design is particularly vulnerable during flooding and may be very unpredictable in its ultimate stability. It has the advantage of potentially treating a significant portion of the water that 

passes that point in the stream. Maintenance of the control structure and the distributary may 

require significant management commitments to this design. The natural design for a riparian 

wetland fed primarily by a flooding stream (Figure 3.13b) allows for river floods to seasonally deposit sediments and chemicals in the wetland (see Section 3.2.3, Riparian Buffers). Because both 

man-made and natural levees are along major sections of streams, it is often possible to create 

such a wetland with minimal construction work. The wetland' could be designed to capture 

flooding water and sediments and slowly release the water back to the river after the flood passes. 

This is the design of natural riparian wetlands in bottomland hardwood forest areas. The wetland could also be designed to receive water from flooding and retain it by using flap-gates. 

Multiple wetlands can be constructed in the landscape to intercept small streams and drainage 

tiles (Figure 311-3c, d). The main stream itself is not diverted, but the wetlands receive their water, sediments, and nutrients from small tributaries, swales, and overland flow. More significant, 

if tile drains can be located and broken upstream of their discharge into tributaries, they can be 

very effective conduits for supplying adequate water to the wetlands. Because these tile drains are 

often the sources of the highest concentrations of chemicals, such as nitrates, the wetlands could 

be very effective in controlling nonpoint-source pollution when located downstream of them. 

The advantages of locating several small wetlands in the upper reaches of a watershed (but not in 

the streams themselves), rather than fewer larger wetlands in the lower reaches, should be considered (Figure 3.13e). Loucks (1990) argues that a better strategy for wetlands to survive extreme 

events is to locate a greater number of low-cost wetlands in the upper reaches of a watershed, 

rather than building fewer high-cost wetlands in the lower reaches. A modeling effort on flood 

control by Ogawa and Male (1983) suggested the opposite: the usehlness of wetlands in decreasing flooding increases with the distance the wetland is downstream. 
. . 

42 ReducingNutrient Loads to Surface and GroundWaters andthe ~"lf 

Berm . _--

st ream 

FIGURE 3.13. Examples of locations of createdlrestored wetlands in the landscape: (a) riparian bifurcation of riveu;(b) riparian wetland with seasonal flooding; (c) created marshes in 

small streams and interceptingtile drainage; (d) details of lateral wetland intercepting ground 

water carried by drainage tiles; (e) landscape location choices for wetlands; and (f) terraced 

in hilly terrain. (Illustrations from Mitsch 1992, Mitsch and Cronk 1992, Mitsch and 

Gosselink 1993, and Kovacic et al. 1995.) 

Wetlands are a phenomenon of naturally flat terrain. However, steeper terrain is often most susceptible to high erosion and, hence, high contributions of suspended sediments and organic nitrogen. One approach is to attempt to integrate terraced wetlands into the landscape (Figure 

3.130. In this case, wetland basins are constructed as smaller basins that stair-step down steep 

terrain. While there are some examples of these types of wetlands, particularly in the building of 

acid mine drainage wetlands in the Appalachians, few wetlands have been constructed of this 

type for controlling nonpoint-source pollution. 
Chapter 3: Result-Approaches for Controlling Nitrogen 4 3 

Figure 3.14 illustrates a hypothetical small watershed with a combination of livestock runoff 

treatment wetlands. nutriendsediment wetlands. " grassed watenvavs. , and ri~arian I buffers. All

would be effective in reducing nonpoint-source pollution in the agricultural landscape. 

I 

1 permanent

I st ream 

! #!-3 .Riparian - -

I"1.v;).nu. ! -buffer 

I .mmuuu Grassed 

I waterway 

Nutrient1 Im. sediment 

i system 

h I Constructed 

wet land 

treatment 

system 

facilities 

and lagoon 

3 ......,Natural 

FIGURE 3.14. Hypothetical locations of riparian buffers, farm ponds, constructed wetlands, 

and grassed waterways in region of livestock facilities. (From Hammer 1 9 92 .) 

3.2.3 Riparian Buffers 

Riparian buffers (Figure 3.15) are vegetated areas next to water resources that provide protection 

from nonpoint-source pollution and provide bank stabilization and aquatic and wildlife habitat. 

The formal definition of riparian buffer is diverse and depends on the individual or group defining the term. The USDA Forest Service (Welsch 1991) defines a riparian buffer as: 

"the aquatic ecosystem and the portions of the adjacent terrestrial ecosystem that 

directly affect or are affected by the aquatic environment." 

This includes streams, rivers, lakes, and bays and their adjacent side channels, flood plain, and 

wetlands. In specific cases, the riparian buffer may also include a portion of the hill slope that 

directly serves as streamside habitats for wildlife. Leading experts .(Lowrance et al. 1985) on riparian buffers define them as follows: 

"a complex assemblage of plants and other organisms in an environment adjacent 

to water." 

Without definitive boundaries, riparian buffers may include stream banks, floodplain, and wetlands, as well as sub-irrigated sites forming a transitional zone between upland and aquatic habitat. Mainly linear in shape and extent, they are characterized by laterally flowing water that rises 
44 Reducing Nutrient Loadsto Surface and Ground Waters and the Gulf 

and falls at least once within a growing season. Natural riparian buffers are composed of grasses, 

trees, or both types of vegetation. If riparian buffers are maintained or reestablished, they can exist under most land uses: natural, agricultural, forested, suburban, and urban. 1 

Since most existing or planned riparian buffers are forested, this discussion focuses on riparian 

forest systems. The ideal forested riparian buffer system (Figure 3.15a) was originally described by 

Welsch (1991) and has generally been accepted as a model for riparian buffers (Lowrance et. al. 

1997). Certainly, variations of the ideal buffer can be used to satisfy local conditions, as described 

later, but the mechanisms of pollutant removal must be understood before any system can be designed and used to its maximum capability. Integrated streamside riparian buffers (forest and 

grass or shrub) that are designed to intercept surface runoff and subsurface flow can be effective 

in controlling nonpoint-source pollution by removing nutrients, especially nitrogen and sediment (USDA 1997). 

Many factors determine the effectiveness of riparian buffers for any given pollutant. Hydrology is 

the most important of these factors (Hill 1996). For example, removal of contaminants from 

surface runoff requires that runoff water be sufficiently slowed to allow sediment to settle out. If 

the runoff water does not spread over the buffer, it will move through the buffer in channels. 

Channelized water moves almost as quickly through a buffer as it does from the field, thereby 

making the buffer ineffective at pollutant removal (Dillaha et al. 1989). This is the primary 

hnction of zone 3, shown in Figure 3.15a. Most nitrogen from agricultural fields reaches surface 

water as nitrate in the ground water below the soil surface. For nitrate to be removed from 

ground water before it reaches surface water, the ground water must enter a zone where plant 

roots are or have been active. These plant roots may absorb the nitrate for use in plant growth or, 

more important, may provide an energy source for bacteria that converts nitrogen in nitrate to a 

gas, which then escapes to the atmosphere. This process, denitrification, occurs almost exclusively in water-saturated zones, where abundant organic matter is present. Zones 2 and 3 in Figure 3.15a are primarily for removal of nitrate from subsurface flows, although they may serve 

other very important purposes that enhance overall stream health. 

The large majority of riparian buffer sites that have been investigated for nitrate removals have 

shown that nitrate concentrations in shallow ground water were significantly reduced as the 

water flowed through the riparian buffer (Gilliam et al. 1997a, 1997b). However, it is possible 

for nitrate to pass below the riparian buffer at depths far enough below the root zone where very 

little nitrate removal occurs (Correll et al. 1994). It is also possible for ground water to move 

through the riparian buffer so quickly that removal is limited (Haycock and Pinay 1993). This 

latter case would occur when subsurface drainage tiles are present. 

3.2.3.1 DESIGN CONSIDERATIONS AND LIMITATIONS 

Scientists agree that a corridor of vegetation can be effective at buffering valuable aquatic resources from the potential negative impacts of human use of the adjacent land. The streamside 

vegetated buffer filters nonpoint-source pollutants from incoming runoff (see Table 3.12) and 

provides habitat for a balanced, integrated, and adaptive community of riparian and aquatic organisms (Welsch 1991). These filtering and habitat functions are often best provided by natural 

vegetation ,such as trees and associated woodland or forest plants in the zone directly adjacent to 

the waterway. While there is general agreement about the benefits of buffers, the specific design 

criteria, such as buffer width, types of vegetation, and management, are the subject of considerable debate. 
Chapter 3: Results-Approaches for Controlling Nitrogen 45 -‘ 

Zone 3 Zone 2 Zone 1 Stream bottom -

Runoff Control Managed Forest UndisturbedForest 

ti-Species Riparian Buffer Strip Model 

A Fast growing tree species 

FIGURE 3.1 5. Schematics of riparian buffer zones: (a) three-zone riparian buffer system 

(from Welsch 1 99 1 ), and (b) multi-species riparian buffer strip modelwhich includestree rows 

closest to the stream, shrubs, and a strip of switchgrass adjacent to the cropland. (From R. 

Schultz.) 
46 ReducingNutrient Loads to Surface and Ground Waters and the Gulf 

Bufler Width 

Width is considered the most important controllable variable in determining the effectiveness of 

buffers in reducing pollutants and protecting stream health. Buffers that are too narrow may not 

be sustainable or effective in protecting stream banks. Conversely,'buffers that are wider than 

needed limit the use of adjacent land and are unpopular with landowners. Complicating the determination of design buffer widths are the effects of varying site characteristics associated with 

topography, hydrology, geology, and land use. Additionally, other factors, such as the value of 

the water resource and adjacent land, must be considered when determining widths. 

The width of most existing riparian forest buffers was established by leaving the area adjacent to 

the stream as forest. This area was generally too wet or too steep to be used conveniently for agricultural or urban purposes. Welsch (1991) recommended a widely acclaimed riparian buffer 

system that was 29-m wide on both sides of the stream. There is little debate among riparian 

buffer experts that the system he described is very good as an idealized multipurpose buffer to 

protect all aspects of stream quality. However, requiring this width along every stream is probably 

not necessary to protect the streams from nonpoint-source pollution and will result in widespread opposition from landowners. The width necessarily depends upon what functions are expected of the riparian buffer and the site characteristics. 

Most decisions about buffer widths will be a compromise between ideal widths based on environmental goals (wildlife corridors, bank stabilization, water quality protection) and sociological 

or economic constraints. Science-based criteria, for which research data may be available to support an informed decision, include the functional value of the water resource; watershed, site, 

and buffer characteristics; adjacent land use; and buffer function. The functional value of the 

water resource is important for determining buffer width in that a highly valued resource may 

merit a wider buffer for increased protection. 

Bufler Zonation 

Watershed, site, and buffer characteristics are most important when evaluating pollutantfiltering effectiveness.The size and topography of the watershed determine the amount and rate 

of surface and ground water passing through the buffer. Site characteristics, such as soil type, 

slope steepness, microbial populations, and vegetation, determine the amount of pollutants that 

are filtered out of the water before it enters the waterway. Buffer characteristics, such as the types 

of vegetatio-n and their location in the buffer, can also influence pollutant removal effectiveness. -. 

The most widely recognized buffer planning model is the three-zone buffer developed by the 

USDA Forest Service (Welsch 1991). Zone 1of the model begins at the normal water level or 

at the edge of the active channel and extends a minimum of 4.5 m along a line perpendicular to 

the water course. Dominant vegetation consists of existing or planted woody vegetation suitable 

for the site and intended purpose. This zone should remain undisturbed; therefore, tree removal 

is generally not permitted. Zone 2 begins at the edge of zone 1and extends a minimum of 18 m 

perpendicular to the water course. While vegetation in zone 2 should be similar to that of zone 

1,removal of trees and shrubs is permitted, provided they are replaced. The zone 3 begins at the 

outer edge of zone 2 and has a minimum width of 6 m. Vegetation in this zone can be grazed or 

ungrazed grass or other plant communities, as long as it facilitates sediment filtering, nutrient 

uptake, and the conversion of concentrated flow to uniform, shallow, sheet flow through the 

use of structural practices, such as level spreaders (Lowrance et al. 1995). 

Most nitrogen from nonpoint sources enters surface waters as nitrate-nitrogen in ground water. 

As the shallow ground water moves through the riparian buffer, microorganisms change the nitrate-nitrogen to gaseous nitrogen via a process known as denitrification. When the soil is 
Chapter 3: Results-Approaches for ControllingNitrogen 47 -' 

poorly aerated (anaerobic conditions), some microorganisms reduce nitrates to the gaseous components of nitrous oxide, nitric oxide, or free nitrogen gas. 

Denitrification is most effective in root-zone soil layers, where carbon sources are available for 

the denitrifjmg bacteria. Numerous researchers have reported that it is the complex interaction 

between vegetation and below-ground environment that provides the appropriate conditions for 

denitrification to occur (Lowrance et al. 1995). The area of interaction within the riparian 

buffer is generally quite narrow-3-15 m-from the field through the riparian buffer. The majority of denitrification that has been observed in riparian buffers occurred within the first 3 m of 

the forested riparian buffer. Denitrification as measured in coastal plain forested riparian buffer 

areas has removed as much as 29 g N m-2yfl.Typically, though, denitrification rates are generally 2-6 g N m-2yfl(Table 3.11). 

Most studies indicate that denitrification takes place throughout the year (Lowrance et al., 

1995). Climate would certainly have an influence on the amount of denitrification taking place 

during the winter months but it must be remembered that the primary processes are occurring in 

subsoils where temperatures are much higher than average winter air temperamres. 

Vegetation 

Vegetation in riparian buffers also removes nutrients through uptake. Some of these nutrients 

are sequestered in woody vegetation, whereas the nutrients absorbed into herbaceous materials 

generally are recycled as the vegetative matter dies. Several studies have indicated that uptake by 

above-ground, woody vegetation removes various amounts of nitrogen and phosphorus, depending on the riparian conditions (Table 3.16). Although nitrogen uptake by the vegetative 

portion of the riparian buffer contributes to nitrogen reductions, denitrification is the primary 

process that removes nitrate from the shallow ground water that flows through riparian buffers. 

TABLE 3.16. Above-ground woody vegetation uptake of nitrogen and phosphorus in coastal 

plain riparian forests. 

Correll & ~elier1989 Rhode R., M D ND' 1.2-2.0 ND' 0.3-0.5 

Peterjohn & Correll 1984 Rhode R., M D 7.7 1.2 I 0.17 

Fail et al. 1986, 1987 (mean) Little R., GA 11.4 5.2 0.75 0.38 

Fail et al. 1986 (max.) Little R., GA 19.44 9.76 1.26 0.69 

Fail et al. 1986 (min.) Little R., GA 8.0 3.46 0.19 

'ND = not determined. 

Source: Lowrance et al. 1995. 

3.2.3.2 COMPARISON OF WETLANDS AND RIPARIAN BUFFERS 

Scientific data thus far obtained show that wetlands and riparian buffers are not equally effective 

in all situations for nitrate reduction. This was clearly recognized by Lowrance et al. (1997) for 

the various physiographic provinces present in the Chesapeake Bay watershed. The scientists assembled by Lowrance spent a large amount of time applying available riparian buffer information 

to the landscape conditions present in the watershed in an attempt to estimate how effective 
48 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf 

buffers would be for nitrate removal. They concluded that in areas where the excess precipitation 

moves across, in, or near the root zone, riparian buffers should retain 50-90% of the nitrogen 

entering the buffer. Lower removals by buffers would be expected where these conditions do 

not exist. For example, where ground-water flow moves so far below the root zone of riparian 

buffers that little nitrate uptake can occur or little organic matter from the roots gets into the 

groundwater, little or no loss would be expected. 

Drainage water that enters a drainage line and is piped to a collector ditch or stream may be 

more suitable for a wetland basin than a riparian zone. This situation is very common in many 

agricultural areas of the Mississippi River Basin. Another common situation is the shallow 

ground water is intercepted by a shallow field ditch and transported through the drainage system. In either of these conditions, riparian buffers are not an attractive alternative. At sites in 

Great Britain, buffers were planted beside streams that had drainage tubes from agricultural fields 

entering into them. Just as one would predict, the buffers had little or no effect on nitrate entering the stream. 

The limitations with removing nitrate from tile drainage water with only riparian buffers was 

recognized by the scientists in both Illinois (Kovacic et al. 1995) and Iowa (Schultz et al. 1995) 

in their experimental system (Figure 3.15b). Both groups used constructed wetlands in addition 

to streamside buffers to treat tile drainage waters. Kovacic (personal communication) estimates 

that they are currently removing 46% of the nitrate from tile drainage water entering the wetland. He also estimates that 1-3% of the land currently under cultivation would be required for 

wetlands in areas similar to those in their study to achieve this level of nitrate reduction. There is 

little question that small wetlands can be used to make a significant reduction in the nitrate entering streams from agricultural lands, but construction and placement of these treatment areas 

will be extremely critical to both their effectiveness and their acceptance by landowners. 

A very similar situation to interception of ground water is interception by an open field ditch. 

This ditch may be an old stream that has been channelized or an original drainage way. In either 

situation, much less nitrate is removed from the drainage water as it moves into the surface water, compared to natural streams with riparian buffers. In many places where this situation exists, 

it may not be practical to have buffers along the ditch and still be able--tofarm the land. The only 

apparent option in these situations for nitrate removal is either wetlands or controlled drainage. 

3.2.4 Controlled Drainage 

Improved drainage has increased crop production in much of the Mississippi kver Basin. However, there is a potential for managing drainage systems in ditches and small streams to satisfy 

agricultural production needs and at the same time minimize adverse environmental effects. This 

approach is called controlled drainage. Currently, there is very little controlled drainage in the 

Mississippi River Basin, although this is an accepted best management practice in several states 

along the Atlantic Coast. Controlled drainage is very popular in North Carolina with both 

farmers and environmental regulators because the practice is responsible for increased yields and 

reduced nutrient losses to surface water. 

3.2.4.1 DESIGN CONSIDERATIONS AND LIMITATIONS 

Suface versus Subsurface Drainage 

Drainage is accomplished by two methods: (1)open-ditch systems designed to provide primarily 

surface drainage (surface runoff) or (2) underground systems comprised of drain tile or tubing 

designed to lower the water table by subsurface flow. Subsurface drainage is obtained by buried 
Chapter 3: Results-Approaches for Controlling Nitrogen 4 9-. 

tile or tubing (10-15 cm diameter) that is placed 1-2 m deep and 7-70 m apart. A subsurface 

system provides drainage when the water table rises above the drain depth and water flows toward and into the drain. The drainage process whereby water infiltrates into the soil and moves 

within the soil profile is referred to as subsurface drainage, shallow-ground water flow, or sometimes interflow. 1 

In practice, it is often difficult to differentiate between surface and subsurface drainage, because 

the outflow in drainage ditches or canals is usually a combination of both surface and subsurface 

flow. The relative proportion of surface and subsurface flow in the total drainage volume depends on many factors, including rainfall intensity, land surface roughness and slope, vegetation, 

soil permeability, and ditch or drain tubing spacing and depth. Open ditches are normally spaced 

farther apart than buried tubing, which typically causes subsurface flow to be slow, resulting in 

collection of predominately surface drainage. But in highly permeable soils, open ditches may 

provide significant subsurface drainage. 

The difference in drainage method (surface versus subsurface flow) is important from a water 

quality standpoint because the characteristics of the two drainage waters differ. Surface drainage 

systems result in rapid removal of excess water over a relatively short time period. This water 

flowing over the land surface has relatively high energy sufficient to detach and transport soil 

particles and constituents attached to them, such as phosphorus, organic nitrogen, and many 

pesticides (Gilham et al. 1978; Skaggs and Gilliam 1981; Deal et al. 1986). Subsurface drainage 

typically contains very little sediment and high concentrations of soluble constituents, such as 

nitrate-nitrogen (Gilliam et al. 1978; Logan et al. 1980; Skaggs and Gilham 1981; Skaggs et al. 

1982; Evans et al. 1987; Deal et al. 1986; Randall and Vetch 1995; Randall et al. 1997). 

Water Control Structures 

Water-control structures, such as a flashboard riser, installed in the drainage outlet allow the 

water in the outlet to be raised or lowered as needed. This water management practice has become known as controlled drainage. When the flashboards are lowered or removed, subsurface 

drainage occurs more quickly (Figure 3.16). When flashboards are added to the riser, the subsurface drainage rate is decreased, and the height of the water level in the ditches and surrounding 

fields rises. Using controlled drainage to manage the field water allows-timely drainage, but also 

maximum storage of water within the field for crop use. 

The transport of nitrogen from drained fields can be minimized by managing the drainage system such that only the minimum drainage water necessary is allowed to exit the field. In numerous field studies in North Carolina (Gilliam et al. 1978, 1979; Skaggs et al. 1982; Deal et al. 

1986; Evans et al. 1989), drainage control reduced the annual transport of total nitrogen at the 

field edge by 45% on average. Working in Ontario, Canada, Drury et al. (1996) obtained results 

almost identical to those in North Carolina. The crop, soil and climatic conditions in Canada 

should be very similar to those in parts of the northern section of the Mississippi watersheds. 

Nitrogen reductions from controlled drainage result from two processes. First, controlled drainage reduces the volume of drainage water leaving a field by 20-30% on average; however, outflow 

varies widely, depending on soil type, rainfall, type of drainage system, and management intensity. During dry years, controlled drainage may totally eliminate outflow. In wet years, control 

may have little or no effect on total outflow. Second, controlled drainage provides a higher field 

water table level, which promotes denitrification within the soil profile. In some cases, nitratenitrogen concentrations have been 10-20% lower in outflow from controlled systems, compared 

to uncontrolled, free-draining systems (Evans et al. 1989). The combined effect of reduced flow 

and reduced nitrate concentration results in the overall 45% reduction in nitrogen mass transport 
at the field edge (Figure 3.17). Controlled drainage has also been documented to reduce phosphorus transport by roughly 35%. 

50 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf . 

FIGURE 3.16. Controlled drainage system showing (a) flashboard riser and @) water profile 

in drainage ditch upstream of flashboard riser. 

ToPograPh~ 

Successful management of controlled drainage systems rests on two important objectives: (1) 

achieving optimum production efficiency and maximum nutrient utilization by the crop; and (2) 

attaining maximum water quality benefits. Controlled drainage structures require that the topography be relatively flat. The costs of installing and maintaining them will usually exceed their 

benefits when the land slope exceeds 0.2%. As a consequence, controlled drainage has for the 

most part been limited to very flat land. This is a result of equal emphasis being placed on crop 

production and water quality goals. 

However, water quality benefits can be obtained without being able to control the water table 

near the soil surface throughout the entire agricultural field. Slowing the water movement from 
Chapter 3: Results-Approaches for ControllingNitrogen 5 1 .-. 

a) NO Controlled Drainage I]Controlled Drainage 

Undeveloped Surface 

Drainage 

Subsurface 

Drainage 

Managed 

Forest 

Surface Subsurface 

Drainage Drainage 

FIGURE 3.17. Results of controlled drainage study represent approximately 1 25 site-years of 

data from 14 sites in eastern North Carolina showing: (a) average annual outflows, and @) 

average annual nitrogen transport (TKN + NO,-N) in drainage outflow as measured at the 

field edge for 14 soils and sites. (From Evans et al. 1991.) 

the field and maintaining it within 1m of surface will promote denitrification and reduce nitrate 

losses to surface water. If management emphasis shifts so that reduction of nitrogen losses to 

surface water is sufficiently important that adopted practices need not provide a positive financial 

return to the landowner, then controlled drainage may become more attractive to the landowner 

than some other control measures. 

This is happening in the Neuse hver watershed in North Carolina, where farmers are preferring to use controlled drainage wherever possible, as opposed to putting riparian buffers on their 

ditches. A scientific group in North Carolina (Gilliam et al. 1997a) recommended that average 

water table elevation throughout the length of the ditch be no lower than 90 cm (36 inches) 

below the land surface to get credit for using controlled drainage to reduce nitrate losses. However, it is recognized that during some seasons, particularly during planting and harvesting, control may have to be lowered to facilitate agricultural activities. 
5 2 ReducingNutrient Loads to Surface and Ground Waters and the Gulf . . 

3.2.4.2 CONTROLLED DRAINAGE IN THE MIDWEST 

Controlled drainage is not practiced frequently in the Corn Belt of the Midwest, and research 

on this practice has been limited. There appear to be three reasons why: the undulating, pothole 

topography, the cool temperatures that limit denitrification when subsurface drainage is greatest, 

and no sense of urgency to try the technique. The variable relief limits the area where controlled 

drainage can practically be used because installation of controlled drainage facilities in rolling 

land is expensive and unnecessary in the view of farmers. Raising the water table in cooler climates to increase denitrification in the late fall and spring when soils are cold and wet would not 

lead to as much denitrification as has been measured in the southern United States, where most 

controlled drainage research has been conducted. However the method has been applied with 

success in Canada, where temperatures are cool, and there has been political pressure to reduce 

nitrates below 10 mg-N/L (Drury et al. 1996). It seems likely that controlled drainage is a practical alternative in some areas of the Midwest to reduce nitrate discharges to surface waters. 

There has been some research on this practice in both Iowa and Ohio. Personal communication 

with scientists in both of these locations (James Baker in Iowa; Norman Fausey in Ohio) confirms that there is potential to use this practice in the Midwest. The results in very flat land 

should be very similar to those obtained in Canada and North Carolina. Even in some rolling 

land with subsurface drainage systems in place, controls can most likely be used to reduce nitrate 

losses to surface water. The selection of nitrogen control practice(s) should generally be made on 

a site-by-site basis. The decision tree presented in Figure 3.18 can assist best professional judgment in determining whether controlled drainage or riparian buffers should be considered. 

Slope 4% Slope >I% 

/ Yes 

Controlled Drainage 

No 

Riparian Buffer f 

- * 

Sdil Erosion? 

/ \

4 

Yes 

I

+ 

Forested Riparian 

Buffer: Trees or Forested Riparian 

Herbaceous Buffer: Trees or 

Vegetation & Herbaceous 

Grasses Vegetation 

(without Grass) 

If controlled drainage is 

used, can the water table be 

kept within 36 inches of the 

surface soil for 50% of the 

field are-a? 

FIGURE 3.18. Decision tree for determiningwhich nitrate control practice to use. 
Chapter 3: Results-Approaches for ControllingNitrogen 5 3-

3.3 URBANNONPOINT-SOURCE CONTROL 

Urban areas are well-known nonpoint sources of coastal pollution. Urbanization results in hydrologic changes that increase surface runoff and erosion, and urban areas contain numerous 

sources of nutrients produced by human activities. A large body of information is available on 

approaches for reducing nutrients from urban areas. This section provides information on the 

nature and extent of urban nonpoint-source pollutant control that is possible with current technology, along with scenarios for implementing these controls in the Gulf of Mexico watershed. 

The prospects for significantly reducing urban nonpoint-source pollutants, especially N, are not 

high. However, urban areas do not appear to be major contributors of nonpoint sources of nitrogen to the Gulf. Nitrate concentrations in urban nonpoint sources are generally not high, compared to concentrations in urban point sources or Corn Belt cropland (Tables 1.2 and 3.17). 

Furthermore, the land area of urban centers compared to rural land in the Mississippi River Basin is small. Several studies have documented that urban areas and lawns have low nitrate concentrations and fluxes relative to agricultural land (Table 3.18), but the comparison depends on 

the degree of fertilizer use and whether septic systems or central sewer systems are used in the 

urban setting (Morton et al. 1988; Gold et al. 1990; Petrovic 1990; Miller et al. 1997). 

TABLE 3.17. Estimatedmean runoff concentrations for land uses, based on the nationwide 

urban runoff program. 

Parameters Residential Commercial Industrial 

TKN (mg-NII) 

NO, + NO, (mg-NII) 

Total P (mgll) 

Copper (I@) 

Zinc (pgll) 

Lead (mgll) 

COD (mgll) 

TSS (mgll) 

BOD (mgll) 

Source: USEPA 1993. 

TABLE 3.18. Comparison of percolation of nitratenitrogen from fertilized and unfertilized 

urban lawn with fertilized corn cropland. 

Treatment Methods Flow-WeightedNitrate-N Nitrate-N Flux 

(mg

1997 

-NIL) 

1998 

(kg-N 

1997 

ha-' yr') 

1998 

Agriculture 

Urea-fertilized corn wl cover crop 

Urea-fertilized corn wlo cover crop 

Manure-fertilized corn 

15.3 

14.9 

4.2 

8.1 

15.6 

17.5 

79.3 

73.1 

20.2 

41.8 

79.8 

100.0 

Home Lawn 

Fertilized 1.6 0.3 9.3 1.9 

Unfertilized 0.2 0.2 1.3 1.4 

Oak-Pine Forest 0.2 0.2 1.2 1.5 

Source: Gold et al. 1990. 
54 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf . 

The U.S. Environmental Protection Agency (USEPA) has compiled a large amount of information on urban nonpoint sources and on control technologies and their effectiveness. The 

Nationwide Urban Runoff Program documented the nature and extent of nonpoint-source 

pollutant problems in urban areas (Table 3.19; USEPA 1977, 1983). The 1990 Coastal Zone 

Act Reauthorization Amendments (CZARA) required the states 'to implement management 

measures to protect coastal waters from urban nonpoint sources of pollution. Management 

measures are defined as economically achievable measures to control the addition of pollutants to 

coastal waters, that reflect the greatest degree of pollutant reduction achievable through the application of the best available nonpoint-source pollution control practices, technologies, processes, siting criteria, operating methods, or other alternatives. The USEPA (1993) has specified 

and evaluated a wide range of management measures for urban nonpoint sources of pollution. 

Controlling nonpoint-source pollution from urban areas requires the use of two primav strategies: prevention of pollutant loadings and treatment of unavoidable loadings. The USEPA 

management measures attempt to address the prevention and treatment of nonpoint-source 

pollutants from all phases of urbanization and are strongly watershed based. There are approaches for reducing pollutants from existing as well as from new development. 

3.3.1 Existing Development 

3.3. I.1 STORMWATER RUNOFF 

Reducing nonpoint-source pollutants from existing urban areas requires identifying opportunities for local and/or regional pollutant reduction via installation and/or improvements in existing 

urban runoff control structures. Table 3.19 presents specific management practices for treating 

runoff from exiting urban developments. Total nitrogen removal for these practices ranges from 

5% to 60%. The primary limitations to their effectiveness stem from their inability to remove N 

from surface runoff. Surface runoff is difficult to treat because it moves rapidly through the 

landscape, often as channelized flow, reducing the potential for biological attenuation of N. 

The total possible reduction of the nonpoint-source load from existing development is limited by 

the effectiveness of the site-specific practices listed in Table 3.19, multiplied by the percent of 

total urban runoff that is treated by the practices. For example, an effort in the Anacostia River 

watershed in Washington D.C., identified 125 sites that would benefit from improvement in 

storm-water runoff control structures; however, practicai considerations limited application of 

improvemen&to only 20 of these sites (Schueler et al. 1991). Similarly, in the Loch Raven Reservoir watershed in Baltimore, 24 sites were identified, but it was possible to implement improvements at only 7 of them (Stack and Belt 1989). 

A minimal-reduction scenario assumes that runoff is treated at 15% of all possible sites, with a 

removal efficiency of 30%, resulting in a 4.5% reduction of N loading from urban runoff. A 

middle-of-the-road scenario assumes that 30% of all possible sites are treated, resulting in a 9% 

reduction. And a high-reduction scenario assumes that 60% of all possible sites are treated, resulting in an 18% reduction of N loading from urban runoff. 
Chapter 3: Results-Approaches for Controlling-Nitrogen 5 5-

TABLE 3.19. Summary of existing development management practices for controlling sediments (TSS), phosphorus UP), and nitrogen (TN) in urban runoff. 

Management Practices % Removal Main Removal Efficiency 

TSS TP TN I Factors 

Water Quality InlebCatch Basin 

Average 15 5 5 Maintenance 

Reported Range 1 0-95 5-10 5- 10 Sedimentation storage volume 

Probable Range 10-25 5- 10 5-10 

Number of Values Considered 2 I I 

Water Quality Inlet-Catch Basins with Sand Filter 

~vera~e- 80 35 Sedimentation storage volume 

Reported Range 75-85 30-45 Depth of filter media 

Probable Range 70-90 30-40 

Number of Values Considered I I 

Water Quality Inlet- OillGrid Separator 

Average 15 5 Sedimentation storage volume 

Reported Range 10-25 5- 10 Outlet configurations 

Probable Range 10-25 5-10 

Number of References I I 

Dry Pond Modified into Ed Dry Pond 

Average 4 5 35 Storage volume 

Reported Range 5-90 20-60 Detention time 

Probable Range 70-90 20-60 Pond shape 

Number of Values Considered 6 4 

Dry Pond Modified into Wet Pond 

Average 60 35 Pool volume 

Reported Range (-30)-9 1 5-85 Pond shape 

Probable Range 50-90 10-90 

Number of Values Considered I I 7 

Dry Pond or Wet Pond Modified into Ed Wet Pond 

Average 80 65 55 Pool volume 

Reported Range . 50- 100 50-80 55 Pond .shape 

Probable Range 50-95 50-80 - Detention time 

Number of Values Considered I I I 

Streambank Stabilization 

Average - - NA NA 

Reported Range NA NA 

Probable Range - -

Number of Values Considered 0 0 

Riparian Forest (assumed same as Vegetated Filter Strip) 

Average 70 50 60 Runoff volume 

Reported Range 20-80 30-95 40-70 Slope 

Probable Range 40-90 30-80 20-60 Soil infiltration rates 

Number of Values Considered 6 3 2 Vegetative cover 

Buffer length 

Wetland (assumed same as Storm Water Wetlands) 

Average 65 25 20 Storage volume 

Reported Range (-20)- 100 (- 1 20)- 1 00 (- 1 5)- 1 Detention time 

Probable Range 50-90 (-5)-80 0-40 Pool shape 

Number of Values Considered 14 14 6 Wetland's biota 

Seasonal Variation 

Source: USEPA 1993. 
56 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf - -

3.3. I.2 ON-SITE SEWAGE DISPOSAL SYSTEMS 

The USEPA includes on-site sewage disposal (OSD) systems (or septic systems) under urban 

nonpoint sources. OSD systems have been identified as major sources of nitrogen in several 

coastal areas (Tyson 1997; Valiela et al. 1997). Although there are several technologies that can 

reduce nitrogen loads from OSD systems significantly (e.g., by 50%; see Table 3.20), they are 

considerably-more expensive than conventional OSD- systems; which inhibits their use in-new 

and existing developments. However, OSD systems have a turnover time of about 30 years, so 

there is potential to improve technology and nutrient removal performance systematically. 

TABLE 3.20. On-site sewage disposal (OSD) system effectiveness and cost summary. 

Conventional Septic System 

Average 

Reported Range 

Probable Range 

# Values Considered 

Mound Systems 

Average 

Reported Range 

Probable Range 

# Values Considered 

Low-Pressure Systems 

Average 

Reported Range 

Probable Range 

# Values Considered 

Anaerobic 4Jpflow Filter 

Average 

Reported Range 

Probable Range 

# Values Considered -

intermittent--sandFilter 

Average 

Reported Range 

Probable Range 

# Values Considered 

Recirculating Sand Filter 

Average 

Reported Range 

Probable Range 

# Values Considered 

Water-Separation System 

Average 

Reported Range 

Probable Range 

# Values Considered 4 J 6 6 I 
Chapter 3: Result-Approaches for Controllirig Nitrogen 5 7-

TABLE 3.20, continued. 

Constructed Wetlands 

Average 80 $710 $25 

Reported Range 60-90 $1,000-3,000 $25- 1 00 

Probable Range 50-983 $50-350 $25-25 

# Values Considered 19 I 

Eliminating Garbage Disposals 

Average 37 NA NA 

Reported Range 3540 Negligible Negligible 

Probable Range 37-37 NA NA 

# Values Considered 3 NA NA 

Low-Phosphate Detergents 

Average NA NA NA 

Reported Range NA Negligible Negligible 

Probable Range NA NA NA 

# Values Considered 0 0 0 

Holding Tanks 

Average NA $3,900 $1,300 

Reported Range 95- 100 $4,000-6,000 $1,000-200 

Probable Range NA $1,220-6,570 $100-2,400 

# Values Considered 0 8 12 

Note: NA = not available. 

'Efectiveness values reflect total system reduction, including soil absorption fields. 

'Costs are in 1988 equivalent dollars. 

3An average household with four occupants was assumed. 

Source: USEPA 1993. 

A minimal-reduction scenario assumes that no nitrogen-reducing OSD systems are installed because of their high cost. A middle-of-the-road scenario assumes that 10% of the existing OSD 

systems are--replacedwith systems that reduce nitrogen loads by 50%. These systems would be 

installed in ~articularlvsensitive coastal areas. as s~ecifiedin the USEPA manag-ement measures 

for OSD &stems recommended to achieve coApliance under the CZARA USEP PA 1993). 

This scenario would result in a total nitrogen reduction from OSD systems of 5%, but this reduction needs to be highly weighted because it would occur in the immediate coastal zone. A 

high-reduction scenario assumes that 50% of all OSD systems have nitrogen-reducing technology, for a total reduction of 25%. It is important to note that any OSD system reductions would 

require a 30-year implementation time, assuming that all systems are replaced on a 30-year cycle. 

3.3.2 New Development 

Analysis of nonpoint-source pollutant loads from urban areas is greatly complicated by the fact 

that new development is inevitable. In many coastal areas, urban and suburban development is 

rapidly replacing agricultural and natural areas. These land-use andlor land-cover changes must 

be considered in evaluations of nitrogen delivery to the Gulf of Mexico. 
58 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf . 

The USEPA management measures suggested to achieve compliance with the CZARA are designed to reduce the impacts of new development. They focus strongly on sediments, specifying, 

for example, either an 80% reduction in sediment loads or a limit of sediment loads to predevelopment levels (USEPA 1993). Given that practices that redu~esediment loadings also reduce nitrogen, but much less effectively (Tables 3.19 and 3.20), new development will result in 

increased nitrogen loadings to the Gulf over time. Though our scenarios will vary in the extent 

of the increase, some increase is inevitable and must be accounted for. 

The impacts of new development can be greatly reduced with watershed- and site-scale planning. Watershed planning efforts need to identify both areas most likely to cause problems if developed and areas that play an important role in absorbing nutrients (Table 3.21). Site planning 

efforts are used to avoid high pollutant outputs during construction activities. 

No data are available on the effectiveness-i.e., percent reductions-of planning efforts on nutrient outputs from new development. Moreover, predicting nutrient loads associated with new 

development requires detailed scenarios of land-use change, which can be difficult to evaluate. 

For example, conversion of agricultural land to urban and suburban uses, which is common in 

the Gulf of Mexico watershed, can result in decreases in nitrogen outputs, especially if state-ofthe-art nonpoint-source pollutant controls are used in the new development. Alternatively, conversion of forest and native grassland to urban and suburban uses will increase nitrogen outputs. 

Calculating reduction scenarios requires: (1)obtaining land-use/land-cover change scenarios for 

the watershed; (2) computing the change in nitrogen delivery that the scenarios would cause; 

and (3) computing the effect of instituting state-of-the-art nonpoint-source pollutant control 

technologies on this change. 

Municipal wastewater is the primary point-source discharge of nitrogen to waterways in the 

United States. In the Mississippi River Basin, it accounts for an estimated 200,000 metric 

tons/year of nitrogen discharged to streams and rivers in the basin (Goolsby et al. 1999). There 

are two basic methodologies for controlling nitrogen and phosphorus from wastewater treatment plants, generally referred to as tertiary treatment: (1) environmental technology and (2) 

ecotechnology involving wetland treatment systems. 

3.4.1 Environmental Technology 

Nitrogen, more specifically nitrate-nitrogen, can be removed from the water column by a number of engineered, treatment plant technologies that involve chemical, physical, and biological 

processes. These technologies rely on the controlled use of chemicals and of mechanical energy 

within structured environments, such as concrete or earthen containers. Generally, the engineered technologies are labor intensive, requiring continuous monitoring and management of 

the treatment factors; but on the positive side, they require little land. 

Because of the need for fxed containers, engineered technologies are limited to small fluctuations in flow. For example, during storm events when flow rates often double or triple within 

urban collection systems, the capacity of the receiving treatment plant is often exceeded and 

wastewater flow is bypassed to avoid damage to the physical plant or disruption of the treatment 

process. Consequently, engineered technologies are most efficiently applied in situations where 

flow variations are limited, such as in industrial or domestic sewerage applications. Applying 

these technologies to urban or agricultural runoff, which is subject to large variations in flow, 
Chapter 3: Results-Approaches for Controlling Nitrogen 54 

TABLE 3.21. Step-by-step guide to watershed management for new urban sources of pollution. 

I. Delineate and map watershed boundary and sub-basinswithin the watershed. 

1 2. lnventory and map natural storm-water conveyance and storage systems. 

3. lnventory and map man-madestorm-water conveyanceand storage systems. 

This includes all ditches, swales, storm sewers, detention ponds, and retention areas and such 

information as their size, storage capacity, and age.

1 4. lnventory and map land use by sub-basin. 1 5. lnventory and map detailed soils by sub-basin. 

6. Establisha clear understandingof water resources in the watershed. 

Analyze water quality, sediment, and biological data. Analyze subjective information on 

problems (such as citizen complaints). Evaluate waterbed use impairment-frequency, timing. 

seasonality of problem. Conduct water quality assessment-low flow, seasonality. 

-

7. lnventory point and nonpoint sources of pollution in the watershed. 

This includes pollutant identification, location, loadings, flow, capacity, and: 

land-uselloading-rate analysis for storm water; 

sanitary survey for septic tanks; and 

dry-flow monitoring to locate illicit discharges. 

8. ldentify and mag future land use by sub-basin. 

Conduct land-use loading-rate analyses to assess the potential effects of various land-use scenarios. 

9. ldentify planned infrastructure improvements-5 years, 20 years. 

Coordinate and schedule storm-water management deficiencies with other infrastructure or 

development projects. 

10. Analysis. 

Determine the infrastructure and natural resource management needs within each watershed. 

II.Set resource managementgoals and objectives 

Before corrective actions can be taken, a resource management target must be set. The target may be defined in terms of water quality standards (e.g., attainment and preservation of 

beneficial uses) or other local resource management objectives. --. 

12. Determine pollutant reduction (for existingand future land uses) needed to achieve water 

quality goals. 

13. Select appropriate management practices for point and nonpoint-sourcesthat can be used to 

achieve the goal. 

Evaluate the effectiveness of pollutant removal, landowner acceptance, financial incentives 

and costs, availability of land, operation and maintenance needs, feasibility, and availability 

of technical assistance. 

14. Develop a watershed managementplan. 

Since each watershed's problems are unique, each management plan will be different. However, all watershed plans should include such common elements as: 

an existing and future land-use plan; 

a master storm-water management plan that addresses existing and future needs; 

a wastewater management plan, including septic tank maintenance programs; and 

an infrastructure and capital improvements plan. 

Source: Livingston and hlccarron 1992, as cited in USEPA 1993. 
60 ReducingNutrient Loads to Surface and Ground Waters and the Gulf 

dramatically increases the capital cost because of the need for large containers, which are infrequently used. Further, treating storm-water runoff with engineered technologies is complicated 

by the means of capture. For example, agricultural tiles are widely spaced, and the distance between tile systems is extensive. Collecting and treating the effluent from these systems would be 

feasible, but would require expensive intercepting sewers or numerous small treatment plants. 

Engineered technologies have proved to be successfulin treating wastewater, with the exception 

of sewer systems that combine both wastewater and storm water. In the latter case, large, expensive reservoirs have had to be constructed to modulate the flow sufficiently to accommodate 

the technology. For industrial wastewater, the engineered application is most suitable, assuming 

the process is well defined and the waste nitrogen load is uniformly distributed. Engineered 

technologies also could work in agricultural fields, particularly with regard to contained feedlot 

operations, for example, for cattle, swine, or chickens. Less appropriate are those applications 

where nitrate concentrations are low, where storm-water runoff is mixed with wastewater, and 

where flow streams are dispersed over a wide area. 

3.4.1. l PHYSICAUCHEMICAL PROCESSES 

The three commonly used physical/chemical processes for controlling nitrogen in wastewater are 

air stripping, breakpoint chlorination, and ion exchange. These processes are relatively expensive 

and require careful monitoring and control (Metcalf and Eddy Inc. 1991). Air stripping requires 

the adjustment of pH through the addition of lime, causing ammonia gas to be formed, which 

is then released by mechanical stirring or aeration. In the breakpoint chlorination process, chlorine is added to the water, which strips the hydrogen atoms off the ammonia molecule, releasing 

nitrogen gas. A significant drawback to this process is that highly toxic residual chlorine often 

finds its way into the receiving stream. In the ion exchange process, ions of one species are displaced from an insoluble ion of a different species; a resin is stirred into the water, which attracts 

the ammonium cations; the resin then precipitates and can be removed and regenerated. 

3.4.1.2 BIOLOGICAL PROCESSES 

The activated sludge process is the principal biological mechanism for removing contaminants, 

including nitrogen from municipal and industrial sources. This process relies on using microbes 

to consume the unwanted substances, flocculate, settle, and form sludge, which is removed from 

the bottom of the container. Typically, the activated sludge process results in the conversion of 

ammonium-nitrogen to nitrate, through nitrification. Nitrate is then released to the receiving 

surface water. However, the process can be taken further to remove nitrate through denitrification. These processes are reasonably stable, require little land, and are generally cheaper than the 

physical/chemical methods. 

The activated sludge process may contain two stages-the first resulting in the conversion of 

ammonium to nitrate, and the second in the conversion of nitrate to nitrogen gas. The process 

can be carried out (1) in a suspended-growth medium, which requires the suspension of microbes in the wastewater by means of mechanical stirring or aeration; or (2) on an attachedgrowth medium, which involves hard substrates, such as gravels or synthetic substrates, on which 

the microbes attach and grow. The removal rate of nitrate is in the range of 80-90%. 

A variety of innovative variations to the basic activated sludge processes have been tested and explored in recent years. For instance: 

Simultaneous nitrification and denitrification can be accomplished in a single bioreactor 

by using both partly and completely submerged biofilms (Watanabe et al. 1994). 
Chapter 3: Results-Approaches for Controlling Nitrogen 6t 

In moving-bed biofilm reactors, the biofilm grows on small plastic elements shaped like 

short pipes with a cross inside (Rusten et al. 1995). 

A recently designed and tested biological nutrient-removal divides aeration basins into 

three functional zones-anaerobic, anoxic, and aerobic-fadilitating the removal of nitrogen from the flow stream process (DeBarbadillo et al. 1995). 

Integrated fixed-film media have been used to increase denitrification in anaerobic sections of anaerobic treatment plants (Randall and Sen 1996). 

A biofilm-sequencing batch reactor uses four phases to remove nitrogen: anaerobic, aerobic, anoxic, and aerobic. Denitrification accomplished in the anoxic phase has reduced 

nitrogen by 87% (Garz6n-Zuniga and Gonzilez 1996). 

Single-basin lagoon systems are achieving nitrification and denitrification by turning the 

aerators on and off at set intervals. This method yielded a nitrogen removal rate of 81% 

and a 95% ammonium-nitrogen conversion (Rothberg et al. 1993). 

3.4.1.3 FEASIBILITY 

Using engineered processes to remove nitrate-nitrogen from point sources is feasible where land 

is limited (such as in urban areas), when nitrate is concentrated in the flow stream, and when 

the flow stream is reasonably uniform with respect to time. Although these conditions are met 

for some municipal, industrial, and confined agricultural applications, the percentage of nitratenitrogen coming from treatment plants in the Mississippi River Basin is a small portion of the 

total load to the Gulf of Mexico. Consequently, implementing denitrification at existing plants 

would be ineffective and costly. 

Applying these technologies to urban and agricultural nonpoint-source runoff is equally infeasible because the flow paths are widely distributed, reasonably dilute, and highly variable. To meet 

peak demands, enormous capital investment would be required to provide for the necessary tankage or large reservoirs to moderate flow fluctuations. Further, production of the needed chemicals and electrical energy would degrade the environment by emitting greenhouse gases and solid 

waste by-products. Far more efficient and environmentally safe technologies can be found 

through ecotechnology. 

3.4.2 Ecotechnology-Treatment Wetlands 

Countless studies have demonstrated the capacity of created and natural marshes to be sinks for 

nitrogen and other contaminants in wastewater (e.g., Fetter et al. 1978 in Wisconsin; Kadlec 

and Tilton 1979 and Kadlec 1983 in Michigan; Dierberg and Brezonik 1984, 1985, and Dolan 

et al. 1981in Florida; Knight et al. 1987 in North Carolina; and Spieles and Mitsch (2000) in 

Ohio). There are now hundreds of documented wastewater wetlands in the United States and 

Europe. Results of many of these constructed wetlands for nutrient retention have been summarized in a data base maintained by the USEPA. Summaries of those data are given by Kadlec 

and Knight (1996). This section presents some design considerations for these treatment wetlands and contrasts them with natural and nonpoint-source wetlands described above. 

3.4.2.1 SURFACE OR SUBSURFACE FLOW 

Generally, constructed treatment wetlands are designed for either surface flow over the substrate 

or subsurface flow through a substrate (Figure 3.19). Surface-flow wetlands, though generally 

less effective in removing some pollutants at first, are closer in design to natural wetlands and are 

less prone to clogging and, therefore, require less maintenance. Subsurface flow through artificial 
wetlands can be through soil media (root-zone method) or through rocks or sand (rock-reedyters), with the flow in both cases 15-30 cm below the surface (Wieder et al. 1989). In a survey of 

several hundred wetlands built in Europe for sewage treatment in rural settings, Cooper and 

Hobson (1989) report that gravel is used in combination with soil, but that the substrate remains 

the greatest uncertainty in artificial-reed (Phragmites) wetlands used for water quality enhancement. Constructed wetlands with subsurface flow have the advantage of requiring a smaller area 

for the same retention of chemicals, but they are prone to clogging if overloaded. 

62 ReducingNutrient Loads to Surface and Grbund Waters and the ddf 

FIGURE 3.19. Schematic showing differences between (a) surface-flow and @) subsurfaceflow treatment wetlands. (From Knight / 9 90.) 
Chapter 3: ResultcApproaches for Controlling-Nitrogen , 63 

3.4.2.2 TREATMENT WETLAND DESIGN 

The nutrient retention capacity of wastewater wetlands has been well documented (reviewed by 

Kadlec and Knight 1996). A hypothetical nitrogen mass balance for a moderately loaded wastewater wetlands, as illustrated in Fi re 3.20, shows that wastewater wetlands are capable of routinely removing 100-300 g-N m-pF-l, a rate much higher than wetlands used for nonpointsource control. Kadlec and Knight (1996) point out that the role of vegetation uptake in the nitrogen budget is not trivial and can be 25% or more of the retention. However, only a fraction of 

that nitrogen is permanently buried in the sediments. In addition, the rates of nitrification and 

denitrification greatly exceed the rates that would be estimated from only a water quality inflowoutflow analysis. Kadlec and Knight (1996) estimated that the true rate of denitrification in 

wastewater wetlands, based on rate constants rather than water quality analyses, is on the order 

of 280 g-N m-2yr-I (Figure 3.20), a rate far in excess of those estimated for most natural wetlands and riparian forests. 

NO,-N = 5 mgll 

NH4-N= 10 mgA 80 0 

ORG-N = 10mgll 

20 

NO,-N = 1 mgll 

NH4-N= G mg/l 

ORG-N =2 mg/l 

FIGURE 3.20. Hypothetical nitrogen fluxes in wastewater treatment wetlands based on hydrologic loading of 5.5 cmlday and first-order decay rates determined fvom multiple sites. 

(From Kadlec and Knight 1 996.) 
64 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf -

Table 3.22 summarizes nitrogen removal efficiency of wastewater wetlands from the North 

American data base. Removal efficiencies range from 46% removal for constructed surface-flow 

treatment wetlands to 72% for natural surface-flow wetlands. Removal rates averaged from 69 to 

570 g-N m-2yfl,with the low number for natural wetlands receiving wastewater, and the high 

number for constructed subsurfacewastewater wetlands. These numbers are far in excess of what 

occurs in natural wetlands, where nitrogen retention rates are generally in the range of 0-40 gN m" yr". Because it is very unlikely that natural wetlands can continue to be used to treat 

wastewater because of wetland protection laws, it can be assumed that constructed wastewater 

wetlands are the primary wetland type for controlling nitrates from point sources. With loading 

on the order of 300-900 g-N m-2yfl,nitrogen flows could be expected to be reduced by about 

50% with some consistency. The high rates of nitrogen removal that are possible with constructed wetlands treating domestic wastewater suggest that these systems are efficient alternatives for controlling nitrogen from point sources. The generally lower costs of these wastewater 

treatment wetlands, as alternatives to the more costly environmental technology described above, 

add to their desirability as nitrogen control systems. 

TABLE 3.22. Nitrate and total nitro~enremoval rates and efficiency of natural and constructed wastewater wetlands as averaged from a number of systems in North America. 

Parameters Natural Wetlands ConstructedWetlands 

Surface Water Subsurface Water 

Nitrate + Nitrite N 

Inflow Concentrations (mglL) 

Outflow Concentrations(mg1L) 

Loading Rates (g m-2yr-I) 

Removal Rates (g m-2yr") 

Efficiency (%) 

Total N 

Inflow Concentrations (mglL) 

Outflow Concentrations (mglL) 

Loading Rates (g m-l yr-I) 

Removal Rates (g rn-2yr-I) 

Efficiency (%)-.. . 

Source: Kadlec and Knight 1996. 

3.5 CONTROL OF ATMOSPHERICNOx 

3.5.1 Stationary Sources 

Control technologies in stationary sources reduce NO, (NO + NO,) gaseous emissions during 

either combustion or post-combustion processes (Figure 3.21). The first type of technology 

modifies the combustion process, such as low-NO, burners and gas reburning. The second type 

involves post-combustion removal of NO, generated during the combustion process, including 

selective noncatalytic NO, reduction and selective catalytic reduction. Most of these technologies 

can be used on new boilers or retrofitted to existing boilers. 
Chapter 3: Results-Approaches for Controlling-Nitrogen 65 --

I- SNRC 

FIGURE 3.2 1. Combustion and post-combustionNO, control options for stationary sources. 

NOTE: SNCR = selective non-catalytic reduction; SCR = selective catalytic reduction; FGD = 

flue-gas desulfurization. (From Tavoulareas and Charpentier 1995.) 

3.5.1.1 MODIFIED COMBUSTION PROCESSES 

Low-NO, burners (LNBs) stage the combustion process to control the coal-air mixture at each 

stage (combustion zone). An oxygen-deficient region and delayed combustion of coal are created 

by introducing auxiliary air to the outside of the firing zone, thus limiting the availability of oxygen to react with the nitrogen in the coal. Approximately 30-55% of the NO, can be reduced by 

this method (Tavoulareas and Charpentier 1995). 

Gas reburning involves introduction of up to 20% of total fuel input from natural gas above the 

main combustion zone. When flue gas containing NO, drifts upward from the main combustion zone, NO, is reburned with gas in this upper level, &el-rich zone and converted into molecular nitrogen. LNBs plus reburning can reduce NO, by up to 72% of NO, (USEPA 1996b). 

3.5.1.2 POST-COMBUSTION PROCESSES 

Selective noncatalytic reduction (SNCR) is a post-combustion process that injects a nitrogenbased .reducingagent (such as urea and ammonia) into the flue gas to reduce NO, to molecular 

nitrogen and water. The general reaction is as follows: 

NO, + NH, + 0, + H,O + (H,) -> N, + H,O + Heat 

The reagent is usually injected at the top and backpass of the boiler, where internal temperature 

is between the optimal reaction range (87&1200"C). SNCR can reduce NO, by up to 3540% 

of NO,. 

Selective catalytic reduction (SCR) is similar to SNCR in that it injects ammonia in the flue gas, 

but at a lower temperature (340-380°C) with a catalyst (a vanadiumhitanium formulation and 

zeolite materials). The NO, in the flue gas reacts with NH, that is adsorbed onto the active sites 
66 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf . 

on the catalysts to form molecular nitrogen and water. The SCR technology was developed in 

the United States, but has been more aggressively implemented overseas (USEPA 1997a). It 

may provide the greatest opportunity for NO, reduction, as it is capable of decreasing NO, emissions by more than 90% (STAPPA &ALAPCO 1994). I 

3.5.2 Mobile Sources 

Automobile NO, emission control technology has made significant advances in the past several 

years. Many of the technologies discussed below can reduce NO, emissions beyond the level of 

control required by Tier 1standards, and have been already used on current Tier 1, national lowemission vehicles (LEVs) and California LEV technology vehicles (USEPA 1998a). These 

technologies include improvements in base engine-out emissions, air-fuel ratio control, fuel delivery and atomization, and exhaust after-treatment (Table 3.23). 

3.5.2.1 BASE ENGINE lMPROVEMENT 

Engine-out NO, emissions result from high combustion temperatures. Exhaust gas recirculation 

(EGR), multiple valves with variable valve timing and use of "fast burn" combustion chamber 

designs provide improved thermal efficiency and lower NO, emissions. A leak-free exhaust system can also be used to prevent outside ambient air from being drawn into the system that otherwise would increase emission level. These technologies provides 3-10% reductions of NO, 

from current Tier 1standards (Table 3.23). EGR can result 15-20% reduction in engine-out 

emissions. 

TABLE 3.23. Feasibletechnologiesfor NO, emission reductions (from Tier I levels) for mobile 

sources. 

Technology % NO, 

Reduction 

Modifications to combustion chamber 

Multiple valves with variable valve timing 

Increased EGR (including electronic control) 

Improved AIF control (i.e., improved HEGO, improved power-train control 

module microprocessor, faster fuel injectors, transient adaptive fuel control algorithms, dual HEGO, and improved calibration) 

Universal exhaust gas oxygen (UEGO) sensor 

Airlfuel control in individual cylinders 

Catalyst improvements (thermal stability, washcoat, cell densities) 

Increased catalyst loading and volume 

Advanced catalyst designs (tri-metal, multi-layered) 

Close-coupled catalysts 

Electrically-heated catalysts 

NOTE: In general, these percentages cannot be simply summed to achieve a total emission reduction when more 

than one emission control technology is being applied. 

Source: USEPA 1998a. 
Chapter 3: Results-Approaches for Controlling Nitrogen 67' 

3.5.2.2 IMPROVEMENTS IN AIR-FUEL RATIO CONTROL 

These technologies use dual-heated exhaust gas oxygen (HEGO) sensors, universal exhaust gas 

oxygen (UEGO) sensors, individual cylinder airlhel (A/F) control, adaptive fuel control systems, 

or electronic throttle control systems to aid in controlling air-fuel mixing for complete combustion (as close to stoichiometric operation as possible), thus maximizing the efficiency of the 

three-way catalyst to reduce NO,. These improvements can reduce NO, emissions by 35%. 

3.5.2.3 IMPROVEMENTSTO EXHAUST AFTER-TREATMENT SYSTEMS 

Many important advances have been made over the last five years in exhaust after-treatment systems. Improvements to the catalyst thermal stability, washcoat, cell density, and multi-layered 

designs can result in up to a 57% NO, reduction from the Tier 1level. 

3.5.2.4 ADVANCED TECHNOLOGIES 

In addition to the above improvements that have been already found in conventional vehicles, 

advanced technologies providing even better emission control are being developed on ultra-lowemission vehicles (ULEVs) and zero-emission vehicles (ZEVs). These developments include 

vehicles powered by compressed natural gas (CNG), battery, hybrid propulsion system (gasoline 

powered engine plus electric motor), and fuel cells promising a very low or zero emission. 

3.5.3 Regulatory Issues 

NO, emission is mainly regulated by the Clean Air Act Amendments (CAAA) of 1990. Title I 

of the CAAA requires states to regulate in ozone nonattainment areas and ozone transport regions: (1) existing major stationary sources of NOxto apply reasonably available control technology; and (2) new or modified major stationary sources of NO, to offset their new emissions and 

to install controls representing the lowest achievable rate. 

Title I1 of the CM calls for reductions in motor vehicle emissions. It sets specific emission 

standards, known as Tier 1,for light-duty vehicles (LDVs) and light-duty trucks (LDTs) made 

during and after 1994. Title I1 further requires the USEPA to study. whether more stringent 

emission standards, known as Tier 2, should be required beginning with the 2004 model year. 

Title IV of CAAA was designed to reduce harmful effects of acid deposition by limiting the allowable emissions of sulfur dioxide and nitrogen oxide. It requires NO, emission reduction from 

coal-fired utility sources through a two-phased program. Phase I reduces annual NO, emissions 

by more than 0.4 million tonslyear between 1996 and 1999, while Phase I1 sets further limitations for various boilers beginning in the year 2000. 

3.5.3.1 RECENT DEVELOPMENTS 

Over the past two years, the USEPA has released and proposed several rules and regulations 

aimed to reduce NO, and other atmospheric emissions under the CAAA. In December 1996, 

the USEPA released a new rule on Phase I1 of Title IV of the CAAA that sets lower emission 

limits for Group 1burners, and established limitations for Group 2 boilers based on NO, control 

technologies that are comparable in cost to LNBs applied in Phase I (Table 3.24). The new rule 

will reduce about 1.17 million tons of NO, emissions per year beginning in the year 2000 at a 

20% removal efficiency and an average cost-effectiveness of $229 per ton of NO, removed. This 

represents a 15% percent reduction of NO, emissions from utilities, or 5% of total NO, from all 

sources. The emission limitation set by this rule is very cost-effective compared to other source 

controls such as those for industrial and automobile sources (Figure 3.22). 
68 Reducing Nutrient Loadsto Surface and GroundWaters and the Gulf 

TABLE 3.24. Coal-fired boiler types and the best continuous control systems used by EPA to 

establish NO, emission limits under Title N of the CleanAir Act Amendments. 

Coal-FiredBoiler Types Characteristics , Control SystrEms 

Group I 

Dry-bottom wall-fired boilers Burners are located along the furnace Low NO, burners 

wall. 

Tangentially fired boilers Burners are located in the furnace corners. 

Group 2 

Cell burner-fired boilers Dry-bottom boilers with arrays of circular Plug-in and 

burners forming a cell mounted on the non-plug-in 

furnace wall. 

Wet-bottom boilers Ash is converted into molten slag at bot- Gas-reburning SCR 

tom of furnace by high internal temperature. 

Cyclones boilers Wet-bottom boilers that burn fuel in hori- Gas reburning SCR 

zontal water-cooled cylinders. 

Vertical-fired boilers Vertically oriented circular burners. Combustion controls 

Stoker boilers and fluidized- Low NO, emission by design. High cost 

bed combustion 

Source: USEPA 1 996a. 

NOx Control Cost Range 

(by source category) 

12,00@ 

Average Cost 

Average Cost 

$230 

Average Cost 

$2000 

Titile IV Phase II 

NOx Rule 

Industrial NOx 

Controls 

Automobile NOx 

Controls 

FIGURE 3.22. Stationary and mobile NO, control cost range by source category. (USEPA 

19960.) 
Chapter 3: Results-Approa~b,esfor ControllingNitrogen 69 \ 

On Sept. 24,1998, the USEPA announced a new anti-smog plan that calls for reducing NO, 

emissions by 1.1 million tons annually, or 28% percent overall, in 22 states and the District of 

Columbia by 2007 (USEPA 1998b). The controls must be in place by 2003. Ohio, the leading 

state in NOxemissions from utility power plants, will need to reducg: NO, emissions by 36% by 

2003, and 85% by 2007. 

According to the Tier 2 report sent to Congress (USEPA 1998a), the USEPA will most likely 

propose new emission standards at the end of 1999. However, the proposed Tier 2 standards will 

not be effective before the 2004 model year. Under current vehicle emission control technologies, including tighter air-fuel control and better catalyst designs, the USEPA estimates that 

NO, emissions can be reduced by 80% relative to current Tier 1 vehicles (Table 3.25). Meanwhile, under the national low-emission vehicle (LEV) program, a voluntary agreement among 

automakers and northeastern states will ensure vehicles meet cleaner LEV standards by model 

year 2001. A LEV-standard vehicle will reduce NO, by 50% relative to Tier 1vehicles. 

TABLE 3.25. List of potential Ti 2 technologies and associated 

emission reductions of NO, for mobilesources. -

Technology % Emission 

Reduction 

Improved AIF Control 20 

Increased Catalyst Volume and Loading 20 

Improved Catalyst WashcoatlSubstrate 10 

Close-Coupled Catalyst 10 

Advanced Catalyst Design 50 

Increased EGR 20 

Total' 80 

'Total NO, reduction = 100% - (100%-20%)*(100%-20%)*(1 OOOA1()%)*(I 00%-

I OX)*(/O&SO%)*(l 00°A20%) = 80%. 

Source: USEPA 1998~. 

New emission standards were also set for heavy-duty diesel engines (HDEs) used in trucks and 

buses that represent about one-quarter of the mobile source NO, emissions. The new rule requires all HDEs made after 2004 to have a 50% lower NO, level relative to 1998-2003 model 

year NO, standards (USEPA 1997b). This will result in a reduction of 1.1million tons/year by 

the year 2020. 

3.6 MISSISSIPPI DELTA DIVERSIONS 

The hypoxia in the offshore zone of the Gulf'of Mexico is likely to be at least partly due to the 

separation of the Mississippi River from its deltaic plain. Whereas the river once spread out over 

the delta during flood periods, it is now\mostly shunted directly to the sea. In historic times, a 

considerable amount of water flowed out of the main channel. As one calculation supporting 

this contention, Kesel et al. (1992) constructed a sediment budget for the lower Mississippi River 

for the period 1880-1911. They reported that below the Red River, about 26% of the sediment 

was retained by the delta. 
70 ReducingNutrient Loads to Surface and Ground Waters and the ~ulf 

There has been controversy as to the efficacy of diverting river water back into coastal wetlands 

for nutrient retention (Turner and Rabalais 1991; Rabalais et al. 1994; Day et al. 1997, 1999; 

Turner 1998). Yet wetlands and shallow-water bottoms with anaerobic sediments are natural 

sinks for nutrients (Hatton et al. 1982; Sharp et al. 1982; Reddy et al. 1993; see also previous 

sections), and represent a viable mechanism for decreasing the nutrient load of river water prior 

to reaching offshore. If river water could be reintroduced to the backwaters, coastal wetlands and 

shallow inshore bodies of water before its discharge to the Gulf of Mexico, a natural 

"downstream" pollution control system could be created, augmenting efforts to reduce nutrient 

inputs from the upstream Mississippi River Basin. 

Several case studies are presented in this section to demonstrate the nutrient and sediment dynamics that occur in Louisiana estuaries in response to the addition of Mississippi River water. 

Among the effects that might occur as .a result of this diversion, we hypothesize the following: 

1. suspended sediments, nitrate, and total inorganic nitrogen will rapidly assimilate in diverted water; 

2. ammonium and organic nitrogen will increase; -

3. there will be relatively lower uptake of phosphorus and silicon, resulting in a decrease in 

the N:P and N:Si ratios in waters going to the Gulf; and 

4. diversionswill lead to the creation of new wetlands and greater maintenance of existing 

wetlands. 

3.6.1 The Mississippi Delta 

The Mississippi River delta formed over the past 6,000-7,000 years as a series of overlapping delta 

lobes. The coast has often been described in terms of a series of hydrologic basins that are separated largely by current or abandoned distributary channels. The larger delta is made up of two 

physiographic units: the active deltaic plain to the east and the Chenier plain to the west. Active 

deltaic lobe formation took place in the deltaic plain. The Chenier plain is a series of old beach 

ridges formed by westward downdrift of sediments. 

The coast is characterized by a series of vegetation zones (sahne, brackish, intermediate, and fresh 

marshes and forested wetlands, from the coast inland) that run roughly parallel to the coast and 

are determined primarily by salinity. Changes in these zones over the past half century have been 

described in-aseries of four vegetation maps (O'Neil 1949; Chabreck 1972; Chabreck and Linscombe 1982; 1988). 

From the 1930s until the present, there has been a dramatic loss of wetlands in the Mississippi 

Delta, with estimates as high as 100 krn2 per year (Gagliano et al. 1981). Land loss rates were 

highest in the 1960s and the 1970s and have declined since, although rates remain high (Britsch 

and Dunbar 1993). An understanding of the causes of this land loss is important not only for 

developing effective management plans to deal with land loss but also for understanding the relationships among land loss, water quality, and offshore hypoxia. 

A number of factors have been linked to land loss, including elimination of riverine input to 

most of the coastal zone due to construction of flood-control levees along the Mississippi River, 

altered wetland hydrology mostly due to canal construction, saltwater intrusion, wave erosion 

along exposed shorelines, high subsidence rates, and sea level rise (see Boesch et al. 1994 for a review of these issues). Most studies have concluded that land loss is a complex interaction of these 

factors, acting at different spatial and temporal scales (e.g., Day and Templet 1989; Boesch et al. 

1994; Day et al. 1995, 1997). 
Chapter 3: ResultoApproaches for Controlling Nitrogen 7 1-

3.6.2 Nitrogen Dynamics in Deltaic Wetlands and 

Shallow Coastal Waters 

Various studies have reported rapid reduction of nitrite plus nitrate [NO, + NO,) in estuarine 

environments, with much of it due to denitrification and other processes (Koike and Hattori 

1978; Khalid and Patrick 1988; Lindau and DeLaune 1991; Nowicki et al. 1997). Jenkins and 

Kemp (1984) reported that up to 50% of NO, + NO, introduced into the Patuxent River estuary 

underwent denitrification. Vascular plants as well as algae incorporate NO, + NO, into cellular 

mass. Nitrate reduction to ammonium has also been found to occur (Smith et al. 1982). Sorenson (1978) found as much as 50% of nitrate applied to marine sediments can be reduced to ammonium. These processes are biologically driven and, therefore, are positively correlated with 

temperature. Denitrification takes place when anaerobic sediments are present. This is the case 

for coastal wetlands and practically all shallow inshore waters of the Louisiana coastal zone. 

Most estuaries are sources for ammonium due to its regeneration during the decomposition of 

organic matter (Kernp and Boynton 1984), as well as reduction of nitrite and nitrate to ammonium (Sorenson 1978). Numerous studies have shown the net mobilization of ammoniumnitrogen by benthic sediments (Koike and Hattori 1978; Blackburn 1979; Callender and Hammond 1982; Teague et al. 1988). The relatively shallow water depths and rapid settling rates and 

bacterial utilization result in fairly short residence times for organic material in estuarine waters 

(Moran and Hodson 1989). Even though ammonium increases, TIN (total inorganic nitrogen) 

decreases due to denitrification are much higher than regeneration. 

Another permanent loss of nitrogen is through burial. Relative sea level rise in coastal Louisiana 

is approximately 1cm F'(Penland and Ramsey 1990), which is partly compensated for by an 

accretion rate of 0.7-0.9 cm yr-' (Cahoon and Turner 1989; DeLaune et al. 1989). DeLaune et 

al. (1981) reported that nitrogen burial in wetlands accreting at a rate of 0.75 cm yr-' was 13.4 gN rn-, y-'. 

3.6.3 Case Studies-Mississippi River Diversions 

Three case studies in Louisiana where Mississippi River water has been diverted through shallow 

water bodies and over wetlands illustrate the effects of diversion of nutrients. 

3.6.3.1 THE-CAERNARVON FRESHWATER DIVERSION 

The Caernarvon diversion is the largest of six diversions currently in operation on the Lower 

Mississippi fiver below New Orleans. The structure is located on the east bank of the Mississippi, and water is diverted through several gates so that it can be passed at low river stages 

(Figure 3.23). The water-control structure has the capability of passing 226 m3 sec-I of water. 

Freshwater discharge began in August 1991and has ranged between 21 and 212 m3 sec-' (Lane 

and Day 1999).The diversion delivers water into Breton Sound estuary, which consists of 1,100 

km2 of fresh, brackish, and saline wetlands and many small, shallow water bodies. Breton Sound 

wetlands were initially formed several thousand years ago as part of the Plaquemines-St. Bernard 

Delta complex (Scruton 1960). Since then, approximately half of the original wetlands have 

submerged due to subsidence, as described by Penland et al. (1988). 

Several natural crevasses have been documented in the region surrounding Caernarvon, which 

delivered large amounts of river water into Breton Sound estuary, before the Mississippi fiver 

levee system was constructed (Russell 1936; Davis 1993). During the great flood of 1927, the 

Mississippi Rwer levee at Caernarvon was blown up to relieve New Orleans from possible flood-
72 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf 

ing (Barry 1997). The resulting crevasse was 979 m wide and diverted up to 9,200 m3 sec-l of 

water, equal to half of the mean flow of the Mississippi Rwer for four months (Davis 1993; 

Barry 1997). During the 1927 flood, a layer of river sediments up to 40 cm thick was deposited 

over an area of approximately 10 krn by 15 km.The historical record, therefore, indicates that 

the Breton Sound estuary has experienced massive periodic inputs of Mississippi River water as 

part of its evolution to its current ecological state. Villarrubia (1998) reported 164 ha of new 

marsh has formed in Breton Sound estuary since 1991, and existing wetlands have high rates of 

accretion on the marsh surface. 

10 kilometers 

FIGURE 3.23. Caernawon diversion and Breton Sound Estuary in coastal Louisiana. NOTE: 

Numbers refer to water quality monitoring stations. The Caernarvon, White's Ditch Siphon, 

and Bohemia structures are controlled freshwater diversions, and the Pointe a la Hache relief 

outlet and Bohemia spillway are areas of seasonal flooding of the Mississippi River. 
Lane and Day (1999) analyzed nutrient data taken before and after the diversion was opened in 

1991. A Before-After, Control-Impact (BACI) analysis, along with station-by-station (station 

numbers in Figure 3.23) contrasts, indicated that the diversion created no significant difference 

in nitrates or ammonium in the wetland and coastal waters but that total Kjeldahl nitrogen 

(TKN) and total nitrogen (TN) levels at stations 2, 5, and 6 decreased significantly as a result 

(Figure 3.24). Station 7 had high nitrate and total nitrogen concentrations compared to the 

other marsh stations due to the addition of river water in the region by the Bohemia structure 

and spillway. Mean pre- and post-diversion Mississippi River water nitrate concentrations 

ranged from 1.2 to 1.6 mg-N/L, while the marsh water quality ranged from 0.1 to 0.5 mg-N/L, 

suggesting rapid reduction in nitrate levels as river water entered the estuary. When the postdiversion data was broken down by season, nitrite + nitrate concentrations during summer and 

Chapter 3: Result+Approaches for ControllingNitrogen 73 

FIGURE 3.24. PB and post-diversion data with standard error bars for Louisiana's Breton 

Sound Estuary for (a) nitrite + nitrate, @) ammoniur+nitrogen, (c) total Kjeldahl nitrogen, 

and (d) total nitrogen. NOTE: Solid black data points are pre-diversion; open data points are 

post-diversion. 
74 ReducinnNutrient Loads to Surface and Ground Waters and the GUM . 

autumn were somewhat lower compared to winter and spring, but were not significantly different. Winter had the highest ammonium-nitrogen concentrations compared to the other seasons. Most important, salinity mixing diagrams (Figure 3.25; see Liss 1976 and Day et al. 1989 

for a discussion of mixing diagrams) indicated that the Breton Sound system was acting as a 

strong sink for nitrite + nitrate and total nitrogen and as a source for ammonium-nitrogen and 

organic nitrogen. Salinity was considerably reduced at stations 1through 4, indicating that the 

diversion significantly diluted estuarine water in the area. 

Salinity (ppt) 

Salinity (ppt) 

Salinity (ppt) 

Salinity (ppt) 

FIGURE 3.25. Fbst-diversion salinity mixing curve (with raw data points shown as circles) and 

overall averages at each water quality station (shown as diamonds) for (a) nitrite + ritratenitrogen, @) ammonium-nitrogen,(c) total Kjeldahl nitrogen, and (d) total nitrogen. 

Results of analysis of nutrient loading rates indicate 5.6-13.4 3-N mM2yr-I of nitrate-nitrogen,

8.9-23.4 g-N m-2yr-' of total nitrogen, and 0.9-2.0 g-P m-2yr of total phosphorus were delivered to the region north of the first two water quahty monitoring stations during 1992-94 

(Table 3.26). Removal efficiencies were 88-97% for nitrite + nitrate, 32-57% for total nitrogen, 

and 0-46% for total phosphorus. 
Chapter 3: Result+Approaches for Controlling Nitrogen 75.' 

TABLE 3.26. Nutrient loading rates and removal efCiciencyof wetlands north of the first two 

water quality monitoring stations at the Caernawon freshwater diversion of the Mississippi 

River, Louisiana. 

Parameters 1992 1993 1994 

NO, + NO2 

Loading (g-N m-' yil) 

Removal (g-N m-' yrl) 

% Removal 

Total Nitrogen 

Loading (g-N m-2yi') 

Removal (g- N m-' yil) 

% Removal 

Total Phosphorus 

Loading (g-P m-' yil) 

Removal (g-P m-' yi') 

% Removal 

3.6.3.2 THE BONNET CARRE SPILLWAY 

The Bonnet CarrC Spillway is a floodway designed to carry flood waters from the Mississippi to 

Lake Pontchartrain when New Orleans is threatened by high water levels (Figure 3.26). The 

spillway was constructed in 1931 after the devastating flood gf 1927 and has been opened eight 

times since during high-water events. It is located 25 km upstream of New Orleans in an area of 

natural crevasses that breached the Mississippi hver levee in the 1800s and introduced up to 

4,000 m3sec-I of water into Lake Pontchartrain (Davis 1993). The present spillway is designed 

to divert up to 7,000 m3 sec" from the river during floods. The forested wetlands in the Bonnet 

Carre Spillway have shown no land loss and are healthy compared to swamp and marsh areas 

just upriver and downriver where there has been land loss. 

Lake Pontchartrain is a large (1,630 km2) oligohaline lake located in southeastern Louisiana, 

with a mean depth of about 3.7 m. In its natural state, the lake was surrounded by extensive 

wetlands, but large areas have been reclaimed or impounded on the south shore due to growth in 

the New Orleans metropolitan area. The lake receives freshwater input from several rivers as well 

as periodic openings of the Bonnet CarrC Spillway, and is connected to the larger estuarine system through three large inlets (Figure 3.26). Two natural inlets-The Rigolettes and Chef 

Menteur Pass-communicate with Lake Borgne and Mississippi Sound; while a dredged canal, 

the Inner Harbor Navigation Canal (IHNC) is connected to Breton Sound. The Rigolettes, 

Chef Menteur, and the IHNC carry about 60%, 30%, and lo%, respectively, of the tidal exchange, and maximum combined flow is about 6,400 m3 sec-' (Swenson and Chuang 1983). 

The spillway was opened in 1997 during the fourth-largest flood of the century (Day et al. 

1999). Water flow through the structure increased to 6,800 m3sec" (240,000 cfs, or about 16.4% 

of the total flow of the river) on March 25-26, and then gradually declined due to both decreasing river discharge and closure of the structure. Concentrations of the different parameters 

in Mississippi River water varied during the diversion; TKN was 0.34-0.93 mg-N/1; total phosphorus, 0.17-0.33 mg-PA; ammonium-nitrogen, 0.08-1.26 mg-NA; nitrate-nitrogen, 1.08-

1.26 mg-NA; and total suspended solids, 34-110 mg/l. The introduction of river water reduced 
salinity and increased nutrient levels in the lake. This condition was most pronounced at stations 

2 and 3, where the system went completely fresh within two weeks of the opening and nutrient 

levels were the same as those in the river, indicating essentially unchanged river water. At these 

two stations, high concentrations of nitrate and total phosphorus )persisted for about a month 

after the closure of the structure but reached pre-opening levels by early to mid-June. By contrast 

to the rapid declines in nutrient concentration, salinity gradually increased, reaching pre-opening 

levels by late Augusdearly September. 

76 Reducing Nutrient Loadsto Surface and Ground Waters and the Gulf 

FIGURE 3.26. Map of Lake Pontchartrain near New Orleans, Louisiana, showing the Bonnet 

Car& Spillway and sampling stations. 

At Station 4 in the mid-lake, nitrate and total phosphorus concentrations reached the levels in 

the river, but a week or two later than at Station 2. Salinity declined more slowly and never 

reached completely fresh conditions. As with Stations 2 and 3, nutrient concentrations returned 

to pre-opening levels by mid June, while salinity did not return to pre-opening levels until September. The north shore (Station 5) was less effected by the river inflow, and nutrient concentrations were lower. There was less influence of river water at Station 6 in the northeastern 

portion of the lake than at Station 7. Nitrate and total phosphorus concentrations at Station 6 

were generally less than half of that in river water, while concentrations at Station 7 were close 

to river water for much of April and early May. Concentrations returned to pre-opening levels by 

mid June. Salinity was near fresh at Station 7 for about two weeks in mid April, while salinity 

was relatively higher at Station 6. 
Chapter 3: Result+Approaches for Controlling Nitrogen 77 

Following the closure of the spillway, there was an extensive blue-green algal bloom, predominantly Anabaena circinalis and Microcystis aeruginosa, in Lake Pontchartrain from late May 

that persisted through July (Dortch et al. 1998; Porrier and King 1998). Both of these species are 

capable of positive buoyancy, which allows them to avoid light limitption in turbid waters, and 

are known to be stimulated by excess nutrients (Dortch et al. 1998). Fish kills attributed to the 

bloom were reported during June and July, when algal cell counts were as high as 10'' cells per 

liter (Porrier and King 1998). Organic nitrogen levels in the central and northern portions of 

the lake increased during the period, the algal bloom was observed. 

The introduction of fresh water in estuaries has been found to have broad effects on phytoplankton productivity. High primary productivity in estuaries receiving fresh water has been related to the introduction of nutrients (Nixon 1981), but production is also limited by light 

availability, which is attenuated by high suspended sediment concentrations usually associated 

with freshwater inputs (Cole and Cloern 1984). In river-dominated estuaries-environments 

with suspended solid concentrations often exceeding 50 mg/L-light is attenuated rapidly in the 

water column and phytoplankton photosynthesis is confined to a shallow photic zone. For this 

reason, phytoplankton productivity in turbid estuaries is often higher in the coastal ocean, adjacent to estuaries, where suspended sediment has dropped out of the water column yet high nutrient concentrations are still available (Cloern 1996). High chlorophyll concentrations after the 

spillway was closed were probably due to this effect, with lower sediment concentrations in the 

lake due to settling, yet high residual nutrient availability. 

Clearly, the Bonnet CarrC diversion had both positive and negative effects. There was a significant reduction of nitrate as the water flowed through the lake. There was also a large algal 

bloom. Diversions should be carried out in a way that maximizes benefits, such as flood control 

and nutrient retention, while reducing detrimental impacts, such as algal blooms. 

3.6.3.3 THE ATCHAFALAYA DELTA REGION 

About one-third of the Lower Mississippi River is discharged via the Atchafalaya River (Figure 

3.27); the Atchafalaya Delta region, therefore, has a strong riverine influence. This area has the 

lowest land-loss rates in the Louisiana coastal zone (Britsch and Dunbar 1993), and two new 

deltas are forming in Atchafalaya Bay. In addition, the accretion and elevation gain offsets relative sea level rise in marshes surrounding Atchafalaya Bay (Baumann et al. 1984; Cahoon et al. 

1995). kverine input to the area has maintained high-elevation marshes that drain well and are 

characterized by strong elevation gains and high soil strength (Kemp et al. in press). This beneficial effect extends from fresh to saline marshes. 

A number of studies of the water chemistry in the area have been conducted, especially in Fourleague Bay, which is strongly affected by Atchafalaya River discharge. Fourleague Bay is a shallow (mean depth 1.5 m), highly turbid, vertically well-mixed estuary surrounded by extensive 

fresh, brackish, and saline wetlands. The Atchafalaya River's discharge strongly affects the bay. 

Salinity ranges from 0-8 ppt in the upper bay to 0-26 ppt in the lower bay (Caffrey and Day 

1986; Madden et al. 1988). During peak spring river discharge, the bay can be flushed in as little 

as seven days, while during low-discharge periods the residence time of the bay increases to about 

65 days (Madden et al. 1988). Fourleague Bay is connected to the Gulf of Mexico via Oyster 

Bayou, a 4-km-long tidal channel. The bayou is the only direct outlet of Fourleague Bay, and 

peak current velocities can exceed 2.0 m sec-l. Extensive intertidal and subtidal oyster reefs line 

the bayou, which is bordered by Spartina alternzJlora marshes. 
-

78 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf . 

FIGURE 3.27. Atchafalaya Bay and Fourleague Bay in coastal Louisiana. 

Nitrate concentrations are higher during the spring flood months between December and June, 

averaging 0,7-1.0 mg-N/L. From July to November, mean nitrate is 0.1-0.5 mg-N/L (Figure 

3.28). Concentrations are significantly lower in the lower bay. During most of the year there 

was a strong nonconservative uptake of nitrate. Ammonium is seasonally less than 0.1 mg-N/L 

and does not vary much. As a result of high nitrogen inputs in the winter and spring and relatively stable phosphorus concentrations, the N:P ratio in all of the bay was greater than 16:1, 

indicating potential phosphorus limitation. Ratios were especially high in the upper and middle 

parts of the bay, exceeding 60:l much of the time. In summer, as nitrogen inputs declined, the 

bay shifted from phosphorus to nitrogen limitation as ratios fell to below 10:l in the middle and 

lower sections. 

Mixing diagrams indicate that the river is always the primary source of nitrate to the bay and that 

the bay is nearly always a strong sink for nitrate. Evidence for dilution was found in March and 

April. Mixing diagrams for ammonium most often increased in the bay, indicating that the bay 

was a source for this compound. The reduction in nitrate concentrations, however, was almost 

ten times the increase in ammonia. Nitrate levels were also measured in water flowing from the 

Atchafalaya River to the Gulf of Mexico. Figure 3.28 illustrates significant reductions in nitrate 

concentrations from the Atchafalaya to the nearshore Gulf. 
Chapter 3: Result-Approaches for Controlling Nitrogen 79 -

Spkng Summer F& Winter 

Spring S&er Fall Winter 

c) 1.5 

Subner Fall Winter 

3.28. Nitrate concentrations in various transects from Atchafalaya River to coastal waters 

for spring, summer, fall, and winter. NOTE: Error bars indicate 95% confidence intervals of the 

mean. Regions with non-overlapping error bars are significantly different. An asterisk (*) indicates a significant difference for regions with questionable overlapping error bars (a < 

0.0 125). 
80 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf - -

3.6.4 Advantages and Limitations of Coastal Restoration 

The information presented above suggests that diversion of river water into the coastal zone can 

have two beneficial effects. First, diversions can help reduce the rate of land loss and create new 

land. Land loss is low in the Atchafalaya and Caernarvon outfall deas and in the Bonnet CarrC 

Spillway, and new land has been created in the Atchafalaya Delta and at Caernarvon. Second, 

some quantities of nitrate can be removed, thus reducing the input to the nearshore zone. The 

amount of potential nitrate reduction is probably limited to less than 10-15% of total flu); in the 

river. 

Flow of water through inshore areas should result in a strong reduction in the N:P and Si:N ratios. It is likely that similar changes will also occur in the ratios of N:Si, thus creating conditions 

more favorable for diatom growth, as described by Justidet al. (1995). Data from the different 

diversions indicate that the N:P and Si:N ratios are reduced. There seems to be a consensus 

among marine scientists that lowering the Si:P and Si:N ratios with respect to nutrient requirements of diatoms (-Si:P = 16:l and Si:N = 1:1, for nutrient replete diatoms) will most likely 

increase the incidence of nonsiliceous blooms in the coastal waters. These-blooms often include 

noxious and toxic forms. Turner et al. (1998) indicated that "diatom growth becomes Si-limited 

when the atomic ratio of silicate to dissolved inorganic nitrogen (Si:DIN) approaches 1:l." 

There is good evidence on this from a variety of coastal and estuarine waters that is summarized 

in Smayda (1989, 1990), Officer and Ryther (1980), Conley et al. (1993), and Justidet al. (1995). 

The effectiveness of these large-scale diversions on significant uptake of nitrate-nitrogen has 

been controversial and is not universally accepted (Turner 1998). Therefore, additional studies 

are needed to determine the actual discharge rates of diversions, the area of wetlands needed, 

potential and actual nitrogen reductions, and the linkages between riverine input and offshore 

response. Although a 10-15% reduction of NO, loading during the spring flood may have significant beneficial impacts on offshore production and hypoxia, several uncertainties remain. 

Without upstream controls, the deltaic system may become nitrogen-saturated or it may release 

nitrogen in a form and season different from when it entered the delta. 

3.7 UPPERMISSISSIPPIRIVERFLOOD 

CONTROL AND RESTORATION 

Controlling floods in the Mississippi River Basin by restoring and creating wetland areas was 

much discussed after the disastrous flood of 1993. A number of benefits are associated with wetland restoration along the Mississippi River and its many tributaries, such as enhanced wildlife 

habitat and recreational areas and, on a more practical note, enhanced flood control. In 1993, 

the flood waters that devastated significant parts of the 1.8 million km2 of the Upper Mississippi 

Basin could have been partly held within an estimated 5.3 million hectares (13 million acres) of 

wetlands (Hey and Philippi 1995). Most important, related to the subject of this report, if these 

wetlands had been able to capture and store the flood waters, the emanating discharge would 

have contained far less nitrate-nitrogen. Fewer wetlands would be needed to treat the mean annual flood or, even the smaller, mean annual flow. Flood control in the Upper Mississippi would 

also decrease the necessity or the possible overload (hydrologicallyand chemically) of downstream 

Mississippi River diversions. 

During the Upper Mississippi River flood of 1993 flood waters rushed southward through channels and over floodplains incapable of storing flood waters without economic loss or incapable of 

supporting the anaerobic environments necessary for the nitrate removal. Consequently, $16 bil-
Chapter 3: Result+Approaches for Controlling Nitrogen 8 Clion in losses resulted and large nitrate loads were swept downstream into the Gulf of Mexico. 

Applying the same criteria as used for the Upper Mississippi Basin to the larger basin at 

Vicksburg, Mississippi, of 2.95 million km2,approximately 10 million hectares (25 million acres) 

of wetlands would be necessary to effectively reduce the peak flow. On the other hand, only 6 

million hectares (15 million acres) would be required to reduce the nitrate load of the mean annual flow by about 80%. The larger area represents less than 3%of the basin, and the smaller less 

than 2%. 
CHAPTER 4 I 

Reducing Nutrient Loadings to the Gulf of Mexico 

4.1 BESTPRACTICESFOR REDUCING NITROGENLOADINGS 

Of the methods reviewed in Chapter 3, the most appropriate for reducing nitrogen that would 

otherwise reach the Gulf of Mexico appear to be the following: 

Change farming practices to minimize nitrate loss by reducing the use of nitrogen, principally by decreasing the use of excess nitrogen fertilizer, enhancing- the use of manure 

nitrogen, and applying an array of best management practices on farms. 

Intercept laterally moving ground water and surface water from farmland with riparian 

zones and created and restored wetlands, particularly targeting areas with artificial subsurface drainage and high concentrations of nitrates. 

Install tertiary treatment systems, particularly treatment wetlands, for the removal of nitrate on major sources of domestic wastewater in the Mississippi River Basin. 

Provide a system of river-diversion backwaters in the Mississippi River Delta, particularly 

for intercepting large flues of nitrogen associated with floods, and river flood backwaters 

in the Upper Mississippi for both flood control and nitrogen retention. 

Each of these management practices, presented in Table 4.1, has potential as well as limitations 

for use in selected areas. Although no single practice is applicable everywhere, the authors believe 

that one practice can reduce nitrogen entry into surface waters from the vast majority of the 

Mississippi River Basin. The challenge lies in selecting and adapting the most appropriate approach to fit local landscape conditions. 

This chapter presents the specifics of the four alternatives, along with rough estimates of the 

possible decreases from applying each of them. Estimated decreases in sources and in the outputs 

to the Gulf of Mexico are based on data in Table 1.1,which suggest that total nitrogen loadings 

from various sources to the Mississippi River Basin are on the order of 20 million metric 

tons/year, but only about 1.6 million metric tondyear of nitrogen are measured near the discharge of the Mississippi River to the Gulf of Mexico (Goolsby et al. 1999). 

Variable factors, such as climate, have a profound influence on nitrate-N concentrations and 

loadings in subsurface drainage water. The dynamics of nitrogen behavior in drained agricultural 

soils during periodic climatic events, particularly wet years, and the management of both crops 

and nutrient inputs (controllable factors) must be considered carefully by agriculturalists as they 

manage the land. These factors must be understood by scientists and policymakers as they edu-
Chapter 4: Reducing Nutrient Loadings to the Gulf of Mexico 83.. 

TABLE 4.1. Recommended approaches for reducing significant amounts of nitrogen (N) 

loadingto streams and riversin the Mississippi River Basin and the Gulf of Mexico. 

Approach Potential N 

I Reduction 

1 O3 metric tonslyr 

Change Farm Practices' 

N-management-Reduce "insurance" rates of N fertilizer application, 900- 1,400 

properly distribute manure, apply appropriate credits for previous crop 

legumes and manure, along with improved soil N testing methods. 

Alternative cropping systems-Substitute perennial crops for 10% of the 500 

present corn-soybean area. 

Create and Restore Wetlands and Riparian Buffers 

Create and restore 2 1,000-53,000 km2 (5-1 3 million acres) of wetlands in 300-800 

the Mississippi River Basin (0.7-1.8% of the basin). 

Improve management of animal manure in livestock-production areas. ' - 500 

Limit minimum spacing between farm drainage tiles to 15 meters. ? 

Restore 78,000-200,000 km2 (19-48 million acres) of riparian bottomland 300-800 

hardwood forest (2.7-7.0% of the basin). 

Reduce Point-Source Pollution 

Apply tertiary treatment to domestic wastewater. 20 

Control Flooding in the Mississippi 

Divert river flow in the Louisiana delta. 50- 100 

'Estimated on-site source reductions do not translate to equivalent reductions in Gulf of Mexico nitrogen loading, as 

only about 8% of nitrogen sources reach the lower Mississippi River (see Table I. I). 

cate the public and develop environmental guidelines regarding the loading of nitrates to surface 

waters. Several specific farm practices need to be undertaken: 

1. Nitrogen management, including both fertilizer and manure application, needs to be 

fine-tuned on the farm. This responsibility rests with the farmer, the supplier of the nutrients (fertilizer dealer or manure supplier), and the crop consultants. Applying the correct rate of nitrogen at the optimum time has been shown to substantially decrease 

nitrate losses over excessive nitrogen application during the wrong periods. Knowing the 

nutrient content and application rate of the manure, spreading it uniformly, and incorporating it in a timely manner will lead to better management and confidence in manure 

nitrogen as a nutrient source. If nitrogen were better managed on farms in the Mississippi River Basin by reducing "insurance" rates of nitrogen fertilizer application, properly 

distributing manure, and applying appropriate credits for previous legume crops and animal manure applications, nitrogen sources to streams and rivers via subsurface drainage 

could be reduced by about 10-IS%, or about 0.9-1.4 million metric tons/yr. 

2. Continued development and application of improved soil N-testing methods to determine the availability of mineralizable and carryover N from the previous crop would be 

helpful, especially following dry years, legumes, or past manure applications. Pre-planting 

and in-season soil nitrogen tests have been developed in the past 10-15 years to help 

farmers arrive at better rates of nitrogen application by assessing available nitrate in the 
84 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf . 

soil. Use of these tests should greatly help prevent overapplication of N fertilizer when 

residual nitrate remains from the previous crop, which will most likely happen following 

a dry year, when manure was applied to the previous crop and when corn is the crop. 

Alternative cropping systems that contain perennial crops ,would greatly reduce nitrate 

losses. Obtaining a market and a satisfactory economic return are obstacles farmers currently face. If alternative cropping systems involving perennial crops, such as alfalfa or 

grass-alfalfa mixes, were substituted for some of the present corn-soybean areas in the 

Mississippi kver Basin, nitrate losses would decrease by about 90% in these areas. Substituting perennial crops in 10% of the corn-soybean farms in the basin could decrease 

loadings to streams and rivers by an estimated 0.5 million metric tons/year 

Improved management of animal manure and subsequent runoff in livestock-producing 

areas would help lower nitrogen losses substantially. Decreasing feedlot runoff by 20% 

could reduce runoff to streams and rivers in the basin by 0.5 million metric tons/year. 

Although narrowing the spacing between tile lines may be desirable to many crop producers because of quicker drainage of excess water from the soil profile, keeping the 

spacing at > 15 m would likely be a good compromise that would allow adequate drainage 

without escalating nitrate losses in the subsurface drainage water. 

INTERCEPTING AGRICULTURAL DRAINAGEWITH 

wETLANDS AND RIPARIAN BUFFERS 

Wetlands, riparian zones, and controlled drainage projects share a common feature in that they 

are viable alternatives for serving as buffers between agricultural uplands and streams and rivers. 

Furthermore, all can be designed in the landscape to enhance nitrate-nitrogen reduction 

through two main ecological processes-denitrification and nitrogen uptake by plants (the latter 

is important only if nitrogen is stored in sod/biomass for a long time or is harvested and taken 

out of the basin). 

Studies cited above suggest ecological engineering design parameters of nitrogen reduction of 

about 4 g-N m-2F'with riparian forests and about 10-20 g-N m-2yr-' with restored/created 

wetlands. Thus, wetlands appear to be 2.5-5.0 times more "efficient" in reducing nitrogen loading per unit area. These design criteria were used to estimate the general extent of wetlands and 

riparian zones necessary to significantly reduce the nitrogen, particularly nitrate-nitrogen, 

reaching streams and rivers in the Mississippi River Basin. 

4.3.1 Wetlands 

Approximately 21,000-52,000 krn2 (5-13 million acres) of newly created and restored wetlands 

in the Mississippi River Basin (0.7-1.8% of the basin) would be needed to reduce nitrogen loading to the Gulf of Mexico by 20-50% (Tables 4.1 and 4.2). To put this in perspective, enforcement of Section 404 of the Clean Water Act through wetland mitigation has resulted in an 

estimated net gain of 336 km2 (83,000 acres) of wetlands in the entire United States (Mike 

Davis, communication), while conservation easement practices and partners-in-wildlife 

programs in the upper Midwest have increased wetland area by approximately 600 km2 (150,000 

acres). The national conservation set-aside programs in agriculture, ~articularlythe Conservation 

Reserve Program (CRP), were estimated to restore about 360 km in the United States from 

1987 to 1990 (Mitsch and Gosselink 1993), and the North-Central U.S. office of the U.S. Fish 

and Wildlife Service estimated it had restored approximately 280 km2 (70,000 acres) in the upper 

Midwest through 1997 (K. Kroonmeyer, personal communication). An effort estimated to be 
L 

Chapter 4: Reducing Nutrient Loadingsto the Gulf of Mexico 85. 

20-50 times current efforts of wetland restoration and creation would be needed in the Mississippi River Basin to achieve the goal of 2l,OOO-S2,OOO km2 of restored wetlands. 

The most effective use of wetland restoration and creation would be in watersheds that discharge high amounts of nitrogen (Table 4.2). For example, the Ihnois River Basin, with 7% of 

its watershed converted to wetland, could reduce about 50% of the 144,000 metric tons/yr of 

nutrients it generates, or about 5% of the entire nitrogen load to the Gulf of Mexico. In contrast, the James kver Basin in South Dakota contributes only 1,178 metric tons/yr of nitrogen 

to the basin; controlling all of this discharge would retain only 0.075% of the nitrogen load to 

the Gulf. So clearly, restoring and creating wetlands in the Mississippi River Basin would have 

to be strategic; that is, wetlands should be located where agricultural sources of nitrogen and 

subsurface drainage are the largest. A reasonable strategy for the Mississippi River Basin is to 

strategically point the conservation easement program toward conserving the Gulfs ecology by 

restoring flooding to lands that have been drained and are now exporting excessive amounts of 

nitrate-nitrogen to the Mississippi River Basin. 

TABLE 4.2. Estimated area of riparian forests needed to control nitrogen in the Mississippi 

River Basin (MRB) and selected sub-basins, assuming a reduction of 15 g-Nlm2-yr. 

River Basin Drainage Discharge Total WetlandArea (km2) % of Watershed 

Area (km2) (metric tons- Requiredfor Specific % Requiredfor Specific % 

N/Y~ Nitrogen Reductions Nitrogen Reductions 

70% 50% 20% 70% 50% 20% 

Entire MRB 2,953,895 1,568,000 73,173 52,267 20,907 2.5 1.8 0.71 

Raccoon R., IA 8,9 12 27,520 1,284 917 367 14.4 10.3 4.12 

Illinois R., IL 68,800 144,320 6,735 4,8 1 1 1,924 9.8 7.0 2.80 

Scioto R., OH 13,289 23,330 1,089 778 311 8.2 5.9 2.34 

Osage R., MI 37,555 15,4 10 719 514 205 1.9 1.4 0.55 

James R., SD 55,8 14 1,170 55 39 16 0.1 0.07 0.03 

Source: Nitrogen discharge from Goolsby et a/. 1999. 

4.3.2 Riparian Zones 

Decreasing the load of nitrogen to the Mississippi River Basin through riparian zones also appears to be a viable alternative, although the amount of denitrification and, hence, nitrogenuptake in these systems appears from the literature to be less effective per unit area than wetlands. Using an analysis similar to the one above, an estimated 3-7% of the Mississippi River Basin, or 78,000-200,000 km2 (19-48 million acres) would have to be restored to riparian 

bottomland hardwood forest (and/or controlled drainage) to control 2040% of the nitrogen 

reaching the Gulf (Tables 4.1 and 4.3). Because most of these riparian forests would export organic nitrogen to the streams and rivers as litterfall, the estimate is probably optimistic. Furthermore, to be effective, these restored botto'mland riparian systems would have to located near the 

major sources of subsurface nitrate drainage. 

To put these numbers in context, there are currently an estimated 120,000 km2 of forested wetlands (mostly as riparian forests) in the North Central and South Central regions of the United 

States. About 50,000 km2 are in the North Central part of the Mississippi River Basin, where 

most of the serious nitrogen sources to the MRB exist. A concerted effort to double or triple the 
86 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf 

amount of riparian forests and similar buffer systems in the basin would be necessary to have a 

significant impact on the nitrogen load of the basin to the Gulf of Mexico. 

TABLE 4.3. Estimated area of riparian forests needed to control nitrogen in the Mississippi 

River Basin (MRB) and selected sub-basins, assuming a reductiondf 4 g-Nlm2-yr. 

River Basin Drainage Discharge Total Wetland Area (km2) % of Watershed Required 

Area (km2) (metric Required for Specific % for Specific % Nitrogen 

tons-Nlyr) Nitrogen Reductions Reductions 

70% 50% 20% 70% 50% 20% % 

Entire MRB 2,953,895 1,568,000 274,400 196,000 78,400 9.3 6.6 2.7 

Raccoon R., IA 8,9 12 27,520 4,816 3,440 1,376 54.0 38.6 15.4 

Illinois R., IL 68,800 144,320 25,256 18,040 7,2 16 36.7 26.2 10.5 

Scioto R., OH 1 3,289 23,330 4,083 2,9 16 I,167 30.7 21.9 8.8 

Osage R., MI 37,555 15,4 10 2,697 1,926 77 1 7.2 5.1 2.1 

James R., SD 55,8 14 1,170 205 146 59 0.4 0.3 0. I 

Source: Nitrogen discharge from Goolsby et a/. 1999. 

4.3.3 Local Benefits 

Constructing and restoring wetlands and riparian zones in the Mississippi River Basin to control 

nonpoint-source pollution would contribute to several important national goals (in addition to 

reducing the hypoxia in the Gulf of Mexico), including cleaning up the waterways in the Midwest, particularly for drinking-water protection, adding to the nation's disappearing wetland 

habitat, improving river ecosystems, enhancing terrestrial wildlife in river corridors, and mitigating the effects of floods. These so-called "local benefits" would accrue to the local regions in 

which the wetlands and riparian zones are restored. 

4.3.3.1 LOCAL WATER QUALITY IMPROVEMENT 

Reducing nitrates would provide a much-needed improvement in stream and river water quality 

throughout the Midwest. The decrease in nitrate-nitrogen would result in safer drinking water 

for many communities in the Midwest and fewer nitrate alerts, the latter a common occurrence 

every spring in many parts of the Midwest. High concentrations of nitrates in drinking water 

cause a disease called methemoglominemia or "blue baby." As a result, water treatment plants in 

the Midwest watch nitrate concentrations in both ground water and surface water carefully, 

particularly in the spring. High levels of nitrates in streams can also contribute to eutrophication 

of inland waters when phosphorus is also abundant. 

4.3.3.2 WETLAND RESTORATION 

Restoring wetlands in the Mississippi River Basin is in keeping with an ambitious recommendation by the National Research Council's Committee on the Restoration of Aquatic Ecosystems 

(NRC 1992), which called for a national program of wetland restoration that would contribute 

to an overall gain of 10 million acres [4 million hectares] by the year 2010. Well-placed wetlands 

and riparian buffers generally support larger populations of wildlife because of the diverse habitats 

they provide. In wetlands with varying seasonal water depths and patterns of open water, emergent vegetation, and mud flats, a wide variety of birds, including herons, egrets, and rails, find 

their proper feeding niche. Amphibians, especially frogs, are often considered the "canary" of the 
Chapter 4: Reducing Nutrient Loadingsto the Gulf of Mexico 8F 

landscape because of their susceptibility to pollution, but they can thrive in a well-functioning 

wetland. 

Wetlands and riparian forests are among the most productive ecosystems in the landscape. This 

productivity is translated into the production of detritus and the support of food chains, both 

terrestrial and aquatic. The hydrologically open nature of these systems means that they are continually receiving propagules of plants, animals, and microbes from upstream systems. It also 

means that they are continually exporting organic carbon to downstream and/or adjacent aquatic 

systems. All of this biodiversity would occur wherever the wetland is built, not in a far-away 

coastal area; the habitat benefit would be local. 

4.3.3.3 RIVER ECOLOGY ENHANCEMENT 

Another recommendation by the Committee on the Restoration of Aquatic Ecosystems called 

for restoring 67,000 krn (40,000 miles) of streams, rivers, and floodplains. The riparian zone 

restoration recommended in this report would make a major contribution toward that goal. The 

restoration of riparian vegetation contributes several advantages to the ecology of streams and 

rivers (USEPA 1995b). Roots of riparian vegetation stabilize the stream bank and prevent 

stream bank erosion and sedimentation. Stabilized stream banks also help maintain the geometry 

of the stream, including such characteristics as the meander length and profile. Tree roots and 

woody debris are also important habitat features for macroinvertebrates and fish. Overhanging 

stream banks, stabilized by tree roots and large woody debris, can be important habitat for fish. 

Large woody debris provides critical macroinvertebrate habitat and can also create dams and trap 

sediment and detritus. Streamside vegetation also affects the amount of sunlight that reaches the 

stream and, in turn, the temperature of the water. 

4.3.3.4 TERRESTRIAL WILDLIFE ENHANCEMENT 

Wildlife habitat is greatly enhanced whenever riparian wetlands are restored. In a stratified riparian forest, different habitat zones exist vertically, including the soil-air interface, herbs and 

shrubs, intermediate-height trees, and the canopy. Included with the leaf litter and rotting logs 

at the soil-water interface are insects, isopods, spiders, and mites. These organisms are a food 

source for reptiles, mice, and birds. The herbs and shrubs provide habitat for insects, birds, and 

mammals. The intermediate zone and the canopy serve as habitat for birds, bats, squirrels, opossums, and raccoons. Bird habitat may be highly stratified, and birds generally show a preference 

for certain liyers that differ in habitat characteristics and food sources. Most important, wetlands 

and riparian forests serve as corridors linking dryer, less diverse uplands to more moist, more diverse bottomlands and are the natural highways for waterfowl and other birds, as well as numerous terrestrial animals. 

4.3.3.5 FLOOD CONTROL 

The role of floodplains and backwater wetlands in storing flood waters is an often overlooked 

value of these systems. The NRC (1992) reported that "their position in the landscape, whether 

as isolated wetlands or floodplains contiguous with rivers and streams, gives wetlands a major role 

in storage of floodwater and abatement of flooding." Hey and Philippi (1995) estimated that 

approximately 3% of the Upper Mississippi watershed, if restored back to backwaters and wetlands, would be sufficient to provide significant flood water retention even during the Upper 

Mississippi River flood of 19%. This is about 50,000 krn2 (13 million acres) of the Upper Mississippi River Basin. Interestingly, Hey and Philippi (1995) found that a similar area of restored 

wetland (53,660 km2 or 13.3 million acres) would be sufficient to provide improved water quality, even during the 100-year flood in the Upper Mississippi River Basin. 
88 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf - -

Thus, combining the flood-control capabilities of wetlands with their hnction to retain nitrate 

makes using wetlands in the Upper Mississippi River Basin even more attractive. This goal of 3% 

of the watershed is only slightly higher than our estimated 1.8-2.5% of wetlands in the watershed necessary to significantly reduce nitrate-nitrogen in the river pystem. Wetland restoration 

on a large scale could thus protect the Gulf of Mexico during excessive flooding in two ways: (1) 

denitrification has a chance to occur in the flood water that the wetlands retain, and (2) the retention of upstream flood water prevents downstream systems from becoming overloaded. 

4.4 TERTIARY TREATMENTOF DOMESTIC WASTEWATER 

Both environmental technologies and ecotechnologies are available for controlling nitrogen in 

the Mississippi River Basin, particularly nitrate-nitrogen from domestic wastewater. Goolsby et 

al. (1999) estimated that domestic wastewater sources contribute 0.2 million metric tons of nitrogen/yr to the basin. If tertiary treatment, such as constructed wetlands and nitrificationdenitrification basins, were used to control 50% of the nitrogen discharged from these point 

sources, the result would be a reduction of only a few percent of the load of nitrogen to the Gulf. 

Nevertheless, because nitrogen concentrations are relatively high and more easily controlled in 

point sources, requiring tertiary treatment for nitrogen in the basin should remain as a serious 

alternative. Wastewater wetlands offer the best alternative because of the lower costs and because 

of ancillary benefits, such as wildlife enhancement (Knight 1992) and others described above for 

nonpoint-source wetlands and riparian zones. 

4.5 RIVER DIVERSIONSIN LOUISIANA 

Some nitrate can be removed from the Mississippi's water if the river is diverted in large amounts 

over wetlands and shallow inshore waters in the Louisiana Delta, particularly during high flow. 

This assumes that the systems are not overloaded-i.e., the area is large enough, and the system 

does not become nitrogen-saturated with time. The issue is how much nitrate can be practically 

removed and whether it is enough to make any significant difference in offshore plankton production. 

To estimate the potential for NO, removal, various portions of the total nitrogen entering the 

coastal zone through the Mississippi River were theoretically diverted to backwaters and adjacent 

wetlands in Louisiana. Using a retention rate of 10 g-N m-2yr-l, based on nitrate removal rates 

of 10 g m'2 yi'l at Caernarvon, Louisiana, and on other studies documented in this report, a reduction of 50,000-100,000 metrics tons/yr of nitrogen could be achieved by diverting Mississippi 

River water in the delta region (Table 4.1). Removing 50,000 metric tons/yr would require about 

500,000 hectares and diversion of about 13% of the total river flow. Removing 100,000 metric 

tons would require about 1,000,000 hectares and diverting about 26% of river flow. Because nitrate removal can take place in marshes, swamps, or shallow open water, these areas can be compared to the areas of these habitats in the coastal zone. The deltaic plain of the Mississippi Delta 

has'at least 200,000 hectares of swamps, 1,200,000 hectares of marsh, and 1,400,000 hectares of 

inshore open water, or a total of 2,800,000 hectares of wetlands and shallow coastal areas. 
Chapter 4: Reducing Nutrient Loadingsto the Gulf of Mexico 89 

4.6.1 Scale Effect 

Caution is advised on applying any data derived in the small scale to e*tire watersheds. Of course, 

there have been no controlled studies at the scale of the Mississippi River Basin on the effects of 

management practices on actual retention of nutrients. There is some danger in extrapolating 

from small scale (e.g., 1-5 ha studies at the largest) to restoration that involves millions of hectares. Larger-scale studies appear to have less variability but are almost impossible to conduct in a 

controlled environment for a number of economic and institutional reasons. 

4.6.2 Comparing "Apples and Oranges" 

We have suggested a dual approach to on-site and off-site control of nitrogen as appropriate. But 

loss rates, such as those reported in Table 4.1, should be compared with caution. On-site source 

reduction due to such practices as reduction in fertilizer use do not translate to an equivalent reduction in load to the Gulf of Mexico. Table 1.1 illustrates that there are about 20 million metric 

tons of independent sources of nitrogen to the Mississippi River Basin (avoiding double counting) but only about 1.6 million metric tons of nitrogen reach the Gulf. Most of the difference is 

described by Goolsby et al. (1999) in food export and other losses. 

Reducing nitrogen application on the farms by 1million metric tons could cause a reduction as 

low as 0.08 million metric tons of nitrogen in the Gulf, using the ratio of 20:1.6. On the other 

hand wetlands and riparian zones intercept the drainage just before it reaches a stream or river. A 

reasonable assumption is that most of this nitrogen that leaves a farm field does reach the Gulf, 

as Goolsby et al. (1999) point out that there appears to be little in-stream loss of nitrogen once it 

reaches the streams and rivers. Reducing 1million metric tons of nitrogen in a wetland conceivably causes a reduction of 1million metric tons of nitrogen at the Gulf. 

4.6.3 System Delay and Buffering 

Two factors in the Mississippi River Basin confound the idea that a reduction of nutrients well 

up in the watershed will have an impact in the Gulf of Mexico. First there is a delay between the 

time that fertilizer and manure are applied and the time that nitrate appears in streams and rivers. 

Second, there is a considerable delay between the discharge of a kilogram of nitrogen in the upper part of the basin and its appearance in the Gulf. On its way, it has perhaps spiraled through 

the nitrogen cycle several times and is also subject to in-stream retention. On the other hand, if 

all sources of nitrogen were eliminated in the upper part of the basin, there would still be instream release of nitrogen chemicals from storages in the sediments of streams and rivers and 

from allochthonous sources along the streams-e.g. litterfall from riparian forests. It is almost 

impossible to estimate how important this buffering effect of in-stream processes would be. 

4.6.4 Agricultural Production 

Agricultural production would be minimally affected by some of these approaches, particularly 

on-farm practices, but there would be some loss of farmland with other practices, such as restored and created wetlands and riparian zones. If some of the nonagricultural alternatives given 

above, such as wetlands and riparian buffers, prove to be unacceptable or infeasible, major reductions in the use of nitrogen fertilizer may be the only way to significantly reduce concentrations 

of nitrates in streams and rivers in at least the northern half of the Mississippi River Basin. 
90 Reducing Nutrient Loads to Surface and Ground Waters and the Gulf ..-

There are major agricultural policy implications of a significant reduction in nitrogen fertilizer 

use, but if the public is willing to pay for cleaner streams and rivers in the Midwest and reduced 

severity of the Gulf of Mexico hypoxia, reducing fertilizer use far in excess of levels projected here 

would need to be discussed. I 

4.6.5 Other Nutrients 

The increase in nitrate-nitrogen observed in the Mississippi River near the Gulf over the past 50 

years has not been a one-variable experiment. Sediment, phosphorus, and silicate loads have also 

changed as a result of pollution, dam building, and land-use change in the basin. Although a 

significant literature implicates nitrogen as the limiting factor in coastal waters around the 

world, there are confounding factors involved in determining if the reduction of a known 

amount of nitrogen will reduce the area of hypoxia. There is the question as to whether other 

chemicals, particularly phosphorus and silicate, are now co-limiting factors in the Gulf. As the 

amount of nitrogen has continued to rise in the Mississippi River, the N:P and N:Si ratios have 

increased to the point that phosphorus and silicate could be seasonallylimiting. 

4.6.6 Long-Term Prognosis 

Even if we were able to reduce nitrogen loading to the Mississippi River by a substantial amount, 

there are no guarantees that this reduction would continue well into the future. Increases in 

populations in the basins, with their subsequent increased food requirements and domestic, 

commercial, and industrial waste production, would necessitate a continued increase in nitrogen 

control in the basin, or the system would slip back to loadings seen in earlier years. 

4.6.7 Catastrophic Events 

Catastrophic flooding, such as that seen in 1993 in the Upper Mississippi Basin, has a significant 

role in exporting a considerably greater amount of nitrogen to the Gulf and increasing the size of 

the hypoxia appreciably (Rabalais et al. 1998). Smaller scale studies of farmland have shown the 

same effect of wet years contributing considerably higher nitrogen concentrations to streams and 

rivers than do dry years (Randall, 1998). There is also the concern that catastrophic hydrologic 

events, such as floods, could overwhelm any engineered (ecological or otherwise) solution to nitrogen pollution. Therefore, ancillary benefits, such as flood control, that accompany approaches 

like wetland Creation are really part of the overall solution, as they would reduce the significance 

of these catastrophic events that would otherwise overwhelm the control systems. 

4.6.8 Uncertainty of Ecotechnology 

Because of its scale, the ecological problem of Gulf of Mexico hypoxia cannot be solved with 

conventional technology alone. In fact, the costs would be overwhelming. So ecotechnology, 

the use of natural ecosystems to solve environmental problems, should be a prominent part of the 

solution. Since ecotechnological systems, by their nature, are not rigidly engineered systems, 

their performance has a wider variance than that of conventional engineered systems. This uncertainty must be factored into any expectation of immediate results. Riparian zones will grow up 

into large forests that will export high amounts of organic matter to streams and rivers, sending 

some of the captured nitrogen downstream. Wetlands could become saturated with nitrogen if 

most of the nitrate is not lost through denitrification. Overall performance of these systems 
Chapter 4: ReducingNutrient Loadings to the Gulf of Mexico 9 1' 

could also be affected by wetland aging, excessive sedimentation, storms, and rivers changing 

courses over longer periods. 

4.6.9 Production of Greenhouse Gases J 

The extensive development of wetlands in the Mississippi River Basin should lead to increased 

denitrification, which produces both N, and N,O gases. In fact, denitrification is the primary 

process that needs to be accelerated in the Mississippi Rwer Basin to reduce nitrate-nitrogen 

before it reaches the Gulf of Mexico. N,O, a greenhouse gas, is considered 200 times more radiatively active than CO, on a molecular basis. It has also been increasing by 0.25% per year in 

the atmosphere (Rasmussen and Khalil 1986; Kang and Freeman 1998). Thus, consideration 

must be given to whether a massive increase in anaerobic zones (wetlands and riparian systems) 

in the Midwest would increase the emission of N,O. While this question needs further research, 

there is some evidence that the increase in wetlands would not lead to any serious problems: 

Most denitrified nitrogen is generally released as N, gas; the percentage that is emitted as 

N,O gas decreases with decreased redox potential, lower nitrate concentrations, higher 

soil moisture, and higher pH (Weller et al. 1994). Wetlands have lower redox potential 

and higher soil moisture than do uplands. Restored and created wetlands would thus be 

expected to release less N,O as a percentage of total N denitrified than more oxidized, 

drier soils. 

N,O is increasing annually in the atmosphere, despite a general decline in the extent of 

wetlands worldwide (Mitsch et: al. 1994). 

Agricultural fields are probably already significant sources of N,O and may be a greater 

source per unit area than wetlands. Goodroad and Keeney (1984) found higher concentrations of N,O in a drained marsh than in an undrained marsh, probably due to accelerated mineralization and decomposition in the former. Weller et al. (1994) found that 

while N,O emissions from corn fields and riparian forests were equal in the fall, corn 

field emissions were three times higher than those of riparian forests in the spring. 

It is likely that significant denitrification is currently occurring in the Gulf of Mexico hypoxic zone. Creation and restoration of anaerobic wetlands in the Mississippi River Basin 

would transfer some of this denitrification from the Gulf to the Mississippi River Basin. 

Production of nitrous oxide is ultimately related to the amount of nitrogen added to the 

basin by fertilizer use, soil mineralization, legumes, and other primary sources. 

Denitrification of nitrous oxide is ultimately related to the amount of nitrogen added to 

the basin by fertilizer use, soil mineralization, legumes, and other primary sources. 
CHAPTER5 

Research Needs 

The.Topic5 team has identified the following research needs for reducing nutrient loads to the 

Gulf of Mexico: 

More refined soil nitrogen testing procedures need to be developed and tested, including 

in-season testing of corn leaf tissue and the use of chlorophyll measurements, especially 

from remote-sensing platforms. -

The newly developing concept of'"precision farming" needs to be investigated thoroughly 

for its ability to reduce nitrate losses from an agricultural landscape. To date, little evidence exists to show that precision farming reduces nitrate losses to ground or surface 

water. 

Alternatives to the traditional corn-soybean rotation and their effects on nitrate loss to 

subsurface drainage water should be investigated. This study should also include economic analyses. 

The effects of variables, such as drainage tile spacing and depth, and the effectiveness of 

controlled drainage on nitrogen retention in poorly drained soils need to be determined 

through controlled experiments. 

There is a critical need for bettcr understanding of nitrogen behavior dwing floods and 

catastrophic events, particularly in ecotechnological methods for nitrate-nitrogen control, such as riparian zones and other wetlands. 

Controlled large-scale experiments on the fidte of nitrogefi are needed on the reflooding 

of formerly tile-drained lands as restored wetlands. 

Research is needed cn the long-term efficacy of wetlands for denitrification, including 

the time required for organic carbon a.ccumulation in created wetlands and the role that 

this accunlulation has on denitrification. 

There is a critical need for additional farm-scale studies on integration of crop land, riparian buffers, and wetlands to most effectively reduce nitrogen entry into streams. This 

information must be used by researchers in large-scale. watershed models designed to determine the most effective placement of these management options throughout much 

larger watersheds .toachieve multiple-objective gds. 

There should be a comprehensive effort to determine the mix of different nitrate reduction strategies that gives the best nitrate reduction for the least cost. This effort should 

involve pilot studies In different parts of the Mississippi River Basin. 

10.Additional study and modeling are needed to demonstrate the relationships among land 

subsidence, river diversion rates, and nitrogen uptake in the delta region of Louisiana. 
Chapter 5: Research-Needs 9J' 

11.A complete accounting of the production of the greenhouse gas N20,both from increased wetland development as well as from drained and fertilized agricultural land is 

needed in comparative studies. A basin-wide study is also needed to compare these fluxes 

to the current production of N20 in the rivers of the basin ,and in the hpoxic zone of 

the Gulf of Mexico. 

12. Studies are needed on projected increases in population and other development in the 

Mississippi River Basin and on how these changes might offset reductions in nitrogen 

loadings from the basin. 
CHAPTER 6 

Conclusions and Recommendations 

6.1 CONCLUSIONS 

We have reviewed the most likely methods for reducing nitrogen loading to the Gulf of Mexico 

from the Mississippi River Basin. The scale of the watershed (at 40% of the conterminous 

United States) and the climatological and geologic heterogeneity of the basin make recommendations of specific methods and sites to implement them particularly difficult. Nevertheless, we 

conclude that a significant (>50%) reduction of nitrogen loading to the Gulf is possible through 

the implementation of a number of proven techniques working in concert, including: 

modification of farm practices to make the use of nitrogen from fertilizer, soil, and manure more effective and efficient; 

the creation and restoration of wetlands and riparian ecosystems between farmland and 

streams and rivers, particularly in areas where concentrations of subsurface nitratenitrogen is highest; 

the reflooding of former wetlands that are now contributing excessive loadings of nitrate-nitrogen due to their drainage; 

the implementation of nitrogen controls on domestic wastewater treatment plants and 

on significant industrial sources; 

flood control in the Upper Mississippi that involves retention of flood waters, rather than 

preventing flood waters from leaving the major river channel; and 

the diversion of flood waters to backwaters of the Mississippi Delta and coastal wetlands. 

RECOMMENDATIONS 

Several of the following recommendations need to be implemented in concert if a major reduction in nitrogen loading to the Gulf of Mexico is expected. If policies are devised to implement 

only one or two of these recommended approaches, improvement in the hypoxia problem in the 

Gulf is not as likely. 

A suite of on-farm practices for reducing discharges of nitrogen to streams and rivers 

should be implemented. These practices could lead to reductions of 15-20% in nitrogen 

sources to the Gulf. This would require approximately a 20% reduction in fertilizer nitrogen application through proper nitrogen crediting for legumes and manure, elimination 

of "extra7' N to minimize risk, and use of realistic yield goals and proven yields when 

making nitrogen fertilizer recommendations. Other recommended management practices include optimum timing of fertilizer application; use of alternative crops, such as 

perennials; wider spacing of tile drains; and better management of livestock wastes, 

whether stored or applied to the land. 
L 

Chapter 6: Conclusions and Recommendations 9 5 

2. Reducing nonpoint sources of nitrogen from the Mississippi River Basin will also require 

extensive creation and restoration of riparian zones and/or wetlands. A major effort 

should be undertaken in the basin to restore or create 21,000 km2 (5 mihon acres, or 

0.7% of the basin) of wetlands and 78,000 km2 (19 million apes, or 2.7% of the basin) of 

riparian forest, or some other combination of these two approaches, to achieve a combined 40% reduction of nitrogen loading in the Gulf. 

3. The location and selection of type of riparian zone and wetland will be critical. Since 

much of the nonpoint-source nitrogen is currently entering surface waters through 

drainage tiles, wetlands should be strategically placed in watersheds to optimize nitrogen 

removal. For example, tile-drained farmlands that are prone to export high concentrations and fluxes of nitrate during high precipitation should be investigated for the possibility of drainage tile removal or interception to restore the natural hydrology to the land 

under various conservation easement and wildlife enhancement programs. The location 

of the wetlands should also try to optimize flood control and habitat provision. 

4. Although point sources of nitrogen appear to be of little consequence (< 5%) in the Mississippi aver Basin's overall nitrogen load, an effort to control these-sources through tertiary treatment should become a formal policy for new wastewater treatment plants in 

the basin because nitrate concentrations are relatively high in treated wastewater and because these plants represent more easily controlled point sources. Furthermore, there may 

be opportunities for nitrogen trading whereby agricultural interests can "buy" credit from 

municipalities for these reductions in nitrogen loading to the basin. 

5. The restoration of flood-prone lands in the Upper Mississippi River Basin to wetlands 

needs to be revisited and more seriously considered in light of the 1993 flood and the 

need to control nitrate-nitrogen to protect the Gulf. These wetlands would provide the 

triple advantages of retaining flood water, reducing nitrate-nitrogen loading to the Gulf, 

and providing needed wildlife habitat. 

6. Nitrate reduction should become an important consideration in the design and operation 

of diversions of the Mississippi River for flood events in the Mississippi Delta in Louisiana. The State of Louisiana should consider the implications of the use of 0.4-1.0 million hectares (1.0-2.5 million acres) of inshore coastal areas (forested wetlands, marshes, 

and water bodies) for reducing nitrate in diverted waters. The most important benefit of 

such diversions would be to address the land loss problem, while a secondary benefit 

would be reducing nutrient discharge to the nearshore Gulf of Mexico. 

7. Reductions of atmospheric nitrogen emissions beyond those now being implemented 

through the authority of the Clean Air Act Amendments are probably not warranted for 

controlling stationary and mobile sources of nitrogen, at least insofar as protection of the 

Gulf of Mexico is concerned. 

8. There is a strong need for any nitrogen mitigation effort to be coupled to a comprehensive program of monitoring, research, and modeling. We need to know what practices 

work, and why, so that "adaptive management" of the hypoxia problem can be carried 

out. 
I 

References 

Atwood, D.K., A Bratkovich, M. Gallagher, and G. Hitchcock, eds. 1994. Papers hm NOAA's Nutrient 

Enhanced Coastal Ocean Productivity Study -SpecialIssue. Estuaries 17(4):729-911. 

Baker, J.L., and H.P. Johnson. 1981. Nitrate-nitrogen in tile drainage as affected by fertilization. Journal of Environmental Quality 10:519-22. 

Baker, J.L., and S.W. Melvin. 1994. Chemical management: Status, and findings. In Agricultural drainage well research and demonstration projecf-Annual report and project summary, 27-60. Iowa Department of Agriculture and Land Stewardship and Iowa State University. 

Baker, L.A. 1992. Introduction to nonpoint sourcepollution in the United States and prospects for wetland 

use. Ecological Engineering 1:l-26. 

Barry, J.M. 1997. Rising tide: The great Mississippi Jlood of1927 and how it changed America. New 

York, NY: Simon and Schuster,Inc. 

Barsdate, R.J., and V. Alexander. 1975. The nitrogen balance of arctic tundra: Pathway, rates, and environmental implications. Journal of Environmental Quality 4:111-17. 

Baumann, R, J. Day, and C Miller. 1984. Mississippi deltaic wetland survival: Sedimentation versus 

coastal submergence. Science 224: 1093-95. 

Bierman, V.J., Jr., S.C. Him,W.J. Wiseman, Jr., N.N. Rabalais, and RE. Turner. 1994. A preliminary 

mass balance model of primary productivity and dissolved oxygen in the Mississippi River plumehnner 

gulfshelf region. Estuaries 17:886-99. 

Bjorneberg, D.L., R.S. Kanwar, and S.W. Melvin. 1996. Seasonal changes in flow and nitrate N loss fi-om 

subsurface drains. Transactions of the American Society of Agfultzrral Engineers 39:961-76. 

Blackburn, T.Hi 1979. Method for measuring rates ofNH, turnover in anoxic marine sediments, using a 

15N-NH4dilution technique. Applied and Environmental Microbiology 37:760-65. 

Blackrner, AM.,D. Pottker, M.E. Cerrato, and J. Webb. 1989. Correlations between soil nitrate conentrations in late spring and corn yields in Iowa. Journal of Production Agriculhsre. 2:103-9. 

Boesch, D.F., M.N. Josselyn, A.J. Mehta, J.T. Morris, W.K. Nuttle, CA Simenstad, and D.J.P. Swift. 

1994. Scientificassessment of coastal wetland loss, restoration and management in Louisiana. Journal of 

Coastal Research 20:l-84. 

Brezonik, P.L., V.J. Bierman, Jr., R Alexander, J. Anderson, J. Barko, M. Dortch, L.Hatch, G. Hitchcock, D. Keeney, D. Mulla, V. Smith, C Walker, T. Whitledge, and W. Wiseman, Jr. 1999. Efects ofreduring nutrient loads to surface waters within the Mississippi River Basin and the Gulf of Mexico. Topic 

4 reportfor the integrated assessment on hypoxia in the Gulf $Mexico. NOAA Coastal Ocean Program 

Decision Analysis Series No. 18. Silver Spring, MD: National Oceanic and Atmospheric Administration. 
.- References 97-

Brinson, M.M., M.D. Bradshaw, and E.S. Kane. 1984. Nutrient assimilative capacity of an alluvial 

floodplain forest. Journal ofApplied Ecolou 21:1041-57. 

Britsch, L.D., and J.B. Dunbar. 1993. Land loss rates: Louisiana coastal plain. Journal of Coastal Research 9:324-38. I 

Brown, M.T. 1987. Conceptual design for a constructed wetlands system for the renovation of treated efjluent. ReportJi-om the Centerfor Wetlands. Gainesville, FL: University of Florida 

Brueske, C.C., and G.W. Barrett. 1994. Effects of vegetation and hydrologic load on sedimentation patterns in experimental wetland ecosystems. Ecological Engineering 3:429-47. 

Bundy, L.G., MA. Schmitt, and G.W. Randall. 1992. Predicting N fertilizer needs for corn in humid regions: Advances in the Upper Midwest. In Predicting Nfertilizer needs for corn in humid regions, ed. 

B.R. Bock and K Kelley. Bulletin Y-226. Muscle Shoals, AL: National Fertilizer and Environmental 

Center, Tennessee Valley Authority. 

Buzicb, G.C., G.W. Randall, R.D. Hauck, and AC. Caldwell. 1983. Fertilizer N losses fiom a tiledrained mollisol as influenced by rate and time of 15-N depleted fertilizer application. In Agronomy abstracts, 213. Madison, WI: American Societyof Agronomy. -

Caffrey, J.M., and J.W. Day. 1986. Control of the variability of nutrients and suspended sediments in a 

Gulf Coast estuary by climatic forcing and spring discharge of the Atchafalaya River. Estuaries 9(4A):295-

300. 

Cahoon, D., and RE. Turner. 1989. Accretion and canal impacts in a rapidly subsiding wetland. 11. 

Feldsparmarker horizon technique. Estuaries 12:260-68. 

Cahoon, D., D.J. Reed, and J.W. Day. 1995. Estimating shallow subsidence in microtidal salt marshes of 

the southeastern United States: Kaye and Barghoorn revisited. Marine Geology 128:l-9. 

Callender, E., and D.E. Harnmond. 1982. Nutrient exchange across the sediment-water interface in the 

Potomac River Estuary. Estuarine, Coastal and Shelf Science 15:395-413. 

Chabreck, R.H. 1972. Vegetation, water, and soil characteristics of the Louisiana coastal region. Bulletin 

664. Baton Rouge, LA: Louisiana State University Agricultural Experiment Station. 

Chabreck, R.H., and RG. Linscombe. 1982. Changes in vegetative types in Louisiana coastal marshes 

over a ten-year period. Proceedings of the Louisiana Academy of Sciences 45:98-102. 

Chabreck, R.H., and G. Linscombe. 1988. Vegetative type map of the Louisiana coastal marshes. New Orleans, LA: Louisiana Department of Wddlife and Fisheries. 

CH2M-Hill. 1997. Constructed wetlands for livestock wastewater management. Prepared for Gulf of 

Mexico Program, under contract to the National Council of the Paper Industry for Air and Stream Im 

provement. 

Cloern, J. 1996. Phytoplankton bloom dynamics in coastal ecosystems: Areview with some general lessons 

fiom sustained investigations of San Francisco Bay, California. Review of Geophysics 34:127-68. 

Cole, B.E., and J.E. Cloern. 1984. Significance of biomass and light availability to phytoplankton productivity in San Francisco Bay. Marine Ecolou 17:15-24. 

Comin, F.A., J.A. Romero, V. Astorga, and C. Garcia. 1997. Nitrogen removal and cycling in restored 

wetlands used as filters of nutrients for agricultural runoff. Water Science &3 Technology 35:255-61. 

Conley, D.J., C.L. Schelske, and E.F. Stoermer. 1993. Marine Ecology Progress Series 101: 179-192. 
98 ReducineNutrient Loads to Surface and Ground Waters and the Gulf 

Cooper, J.R., andJ.W. Gilliam. 1987. Phosphorus redistribution from cultivated fields into riparian areas. 

Soil Science Society of America Journal 51:1600-1604. 

Cooper,J.R., J.W. Gilliam, R.B. Daniels, and W.P. Robarge. 1987. Riparian areas as filters for agricultural sediment. Soil Science Society of America Journal 51:416-20. I 

Cooper, P.F., andJ.A. Hobson. 1989. Sewage treatment by reed beds systems: The present situation in the 

United Kingdom. In Constructed wetlandsfor wastewater treatment, ed D.A. Hammer, 153-72. Chelsea, 

MI: Lewis Publishers, Inc. 

Correll, D.L., T.E. Jordan, and D.E. Weller. 1994. Failure of agricultural riparian buffers to protect surface waters &om groundwater contamination. In Groundwater surface water ecotones, ed. J. Gibert. 

UNESCO/R/LABAHP. London, England: Cambridge University Press. 

Cronk, J.K., and W.J. Mitsch. 1994a. Aquatic metabolism in four newly constructed freshwater wetlands 

with different hydrologic inputs. Ecological Engineering 3:449-68. 

Cronk, J.K., and W.J. Mitsch. 1994b. Periphyton productivity on artificial and natural surfaces in four 

constructed freshwater wetlands under different hydrologic regimes. Aquatic Botany- 48:325-41. 

Dahl, T.E. 1990. Wetlands losses in the United States: 1780's to 1980's. Washington, DC: U.S. Department 

ofthe Interior, U.S. Fish and Wildlife Service. 

David, M.B., L.E. Gentry, D.A. Kovacic, and K.M. Smith. 1997. Nitrogen balance in and export fiom an 

agricultural watershed. Journal of Environmental Quality 26:1038-1048. 

Davis, D.W. 1993. Crevasses on the lower course ofthe Mississippi River. Coastal Zone 1:360-78. 

Day, J.W., Jr., and P.H. Templet. 1989. Consequences of sea level rise: Implications fiom the Mississippi 

Delta. Coastal Management 17:241-57. 

Day, J.W., Jr., CA S. Hall, W.M. Kemp, and A Yanez-Arancibia. 1989. Estuarine ecology. New York, 

IVY: Wiley-Interscience. 

Day, J.W., Jr., D. Pont, P. Hensel, and C Ibaiiez. 1995. Impacts of sea level rise on deltas in the Gulf of 

Mexico and the Mediterranean: The importance of pulsing events to sustainability. Estuaries 18:636-47. 

Day, J.W., Jr., J.F. Martin, L. Cardoch, and P.H. Templet. 1997. System fuilctioning as a basis for sustainable management of deltaic ecosystems. Coastal Management 25:ll.S-53. 

Day, J.W., Jr., R Mach, R.R. Lane, M. Daigle, and C. Brantley. 1999. Water chemistry dynamics during 

the 1997 open?ng ofthe Bonnet Card Spillway. In Proceedings ofthe conference Recent research in coastal 

Louisiana: Natural system and response to human infiences. Louisiana Sea Grant Program, Baton 

Rouge (accepted for publication). 

Deal, S.C., J.W. Gilliam, RW. Skaggs, and K.D. Konyha. 1986. Prediction ofnitrogen and phosphorus 

losses as related to agricultural drainage system design. Agriculture Ecosystems €9 Environment 18:37-51. 

DeBarbadillo, C., L.P. Jaworski, and S.M. Kharkar. 1995. Optimal nutrient removal. Water Environment €9 Technology 7:40-44. 

DeLaune, R.D., C.N. Reddy, and W.H. Patrick. 1981. Accumulation of plant nutrients and heavy metals 

through sedimentation processes and accretion in a Louisiana salt marsh. Estuaries 4:328-34. 

DeLaune, R.D., J.H. Whitcomb, J.W.H. Patrick, J.R. Purdue, and S.R. Pezeshki. 1989. Accretion and 

canal impacts in a rapidly subsiding wetland. I. Cs and Pb techniques. Estuaries 12(4):247-59. 
' 'References 99 

Diaz, R.J., and A. Solow. 1999. Ecological and economic consequences of hypoxia. Topic 2 report for the integrated assessment on hypoxia in the GulfofMexico. NOAA Coastal Ocean Office Program Decision 

Analysis Series No. 16. Silver Spring, MD: National Oceanic and Atmospheric Administration. 

Dierberg, F.E., and P.L. Brezonik. 1984. Nitrogen and phosphorus masslbalances in a cypress dome receiving wastewater. In Cypress swamps, ed. KC. Ewe1 and H.T. Odurn, 112-18. Gainesville, FL: University Presses of Florida. 

Dierberg, F.E., and P.L. Brezonik. 1985. Nitrogen and phosphorus removal by cypress swamp sediments. 

Water,Air, and Soil Pollution 24:207-13. 

Dillaha, T.A., J.H. Sherrard, and D. Lee. 1989. Long-term effectiveness of vegetative filter strips. Water 

Environmental Technology 1(3):419-21. 

Dolan, T.J., S.E. Bayley, J. Zoltek, Jr., and A Hermann. 1981. Phosphorus dynamics of a Florida freshwater marsh receiving treated wastewater. Journal ofApplied Ecoloa 18:205-19. 

Dortch, Q T. Peterson, and RE. Turner. 1998. Algal bloom resulting fiom the opening of the Bonnet 

CarrC Spillway in 1997. In: 4th Basics of the basin research symposium, May 12-13, New Orleans. Abstract. 

Drury, C.F., C.S. Tan, J.D. Gayhor, T.O. Oloya, and T.W. Welacky. 1996. Influence of controlled drainage-subirrigation on surface and tile drainage nitrate loss.Journal of Environmental Quality 25:317-24. 

Erwin, KL. 1991. An evaluation of wetland mitigation in the South Florida Water Management District. VoZ. I. Final Report to South Florida Water Management District. West Palm Beach, FL. 

Evans, RO., J.W. Gilliam, RW. Skaggs, and W.L. Lemke. 1987. Effects of agricultural water management on drainage water quality. In Drainage design and management. Ffth national drainage symposium, December 14-15,. 210-1 9. Chicago, IL: American Society of Agricultural Engineers. 

Evans, RO., J.W. Gilliam, and RW. Skaggs. 1989. Efects of agricultural water table management on 

drainage water quality. Report no. 237. Raleigh, NC: Water Resources Research Institute of the University of North Carolina. 

Evans, RO., J.W. Gilliarn, and R.W. Skaggs. 1991. Controlled drainage management guidelines for improving water quality. AG-443. Raleigh, NC: N. C Agricultural Extension Service. 

Fail, J.L., Jr., M.J.Hamzah, B.L. Haines, and RL. Todd 1986. Above and below ground biomass, production and element accumulation in riparian forests of an agricultural watershed. In Watershed research 

perspectives,-ed. D.L. Correll, 193-224. Washington, DC: Smithsonian Institution. 

Fail, J.L., Jr., B.L. Haines, and R.L. Todd. 1987. Riparian forest communities and their role in nutrient 

conservation in an agricultural watershed. American Journal of Alternative Agriculture 2:114-21. 

Fennessy, M.S., C.C. Brueske, and W.J. Mitsch. 1994a. Sediment deposition patterns in restored freshwater wetlands using sediment traps. Ecological Engineering 3:409-28. 

Fennessy, M.S., J.K. Cronk, and W.J. Mitsch. 1994b. Macrophyte productivity and community development in,created freshwater wetlands under experimental hydrologic conditions. Ecological Engineering 

3:469-84. II 

Fetter, C.W., Jr., W.E. Sloey, and F.L. Spangler. 1978. Use of a natural marsh for wastewater polishing. 

Journal ofthe Water Pollution Control Federation 50:290-307. 

Gagliano, S., K Meyer-Arendt, and K Wicker. 1981. Land loss in the Mississippi River deltaic plain. 

Transactions ofthe ~LlfCoastAssociation of Geological Societies 31:295-300. 
100 Reducinn Nutrient Loads to Surface and Ground Waters and the Gulf 

Gale, P.M., I. Dtvai, K.R. Reddy, and DA Gratz. 1993. Denitrification potential of soils fiom constructed and natural wetlands. Ecological Engineering 2:119-30. 

Gambrell, R.P., and W.H. Patrick, Jr. 1978. Chemical and microbiological properties of anaerobic soils 

and sediments. In Plant li~5in anaerobic environments, ed. D.D. Hook ankI R.M.M. Crawford, 375-423. 

Ann Arbor, MI: Ann Arbor Science Publishers, Inc. 

Garz6n-Zuniga, MA., and M.S. Gonzilez. 1996. Biological phosphate and nitrogen removal in a 

bioh sequencingbatch reactor. Water Science €9 Technology 34:293-301. 

Gast, RG., WW. Nelson, and G.W. Randall. 1978. Nitrate accumulation in soils and loss in tile drainage 

following nitrogen applications to continuous corn. Journal of Environmental Quality 7:258-61. 

Gilliam,J.W., R.W. Skaggs, and S.B. Weed. 1978. An evaluation ofthe potential for using drainage control to reduce nitrate loss form agriculturaljields to surface waters. Report no. 128. Raleigh, NC: Water 

Resources Research Institute of the University of North Carolina. 

Giam, J.W., RW. Skaggs, and S.B. Weed. 1979. Drainage control to reduce nitrate loss form agricultural 

fields.Journal of Environmental Quality 8:137-42. -

Gilliam, J.W., Gilliam, D.L. Osmond, and RO. Evans. 1997a. Selected agricultural best management 

practices to control nitrogen in the Neuse River Basin. North Carolina Agricultural Research Service 

Technical Bulletin 311. Raleigh, NC: North Carolina State University. 

Gilliam, J.W., J.E. Parsons, and RL. Mikkelsen. 1997b. Nitrogen dynamics and buffer zones. In Buffer 

zones: Their processes and potential and water protection, ed. N.E. Haycock,, T.P. Burt, K.W.T. Goulding, 

and G. Piney, 54-61. Harpenden, United Kingdom: Qest Environmental. 

Gold, A.J., W.R DeRagon, W.M. Sullivan, and J.L. Lemunyon. 1990. Nitrate-nitrogen losses to 

groundwater from rural and suburban land uses. Journal of Soil and Water Conservation 45:305-10. 

Goodroad, L.L., and D.R. Keeney. 1984. Nitrous oxide emission hm forest, marsh, and prairie ecosystems. Journal of Environmental Quality 13:448-52. 

Goolsby, D.A., W.A. Battaglin, and R.P. Hooper. 1997. Sources and transport of nitrogen in the Mississippi River Basin. In Proceedings ofthe conference From the Corn Belt to the GuF Agriculture €9 hypoxia 

in the Mississippi River watershed,July 14-15, St. Louis, MO. 

Goolsby, D.A., W.A. Battaglin, G.B. Lawrence, R.S. Artz, B.T. Aulenbach, R.P. Hooper, D.R. Keeney, 

and G.S. Stensland. 1999. Flux and sources of nutrients in the Mississippi-Atchafalaya Basin. Topic 3 reportfor the integrated assessment on hypoxia in the GulfofMexico. NOAA Coastal Ocean Program Decision Analysis Series No. 17. Silver Spring, MD: National Oceanic and Atmospheric Administration. 

Groffman, P.M. 1994. Denitrification in freshwater wetlands. Current Topics in Wetland Biogeochemistry 1:15-35. 

Groffman, P.M., and G.C. Hanson. 1997. Wetland denitrification: Influence of site quality and relationships with wetland delineation protocols. SoilScience Society ofAmerica Journal 61:323-29. 

Gr,offman, P.M., E.A. Axelrod, J.L. Lemunyon, and WM. Sullivan. 1991. Denitrification in grass and 

forest vegetated filter strips. Journal of Environmental Quality 20571-674. 

Hallberg, G.R, J.L. Baker, and G.W. Randall. 1986. Utility of tileline effluent studies to evaluate the irnpact of agriculturalpractices on ground water. In Proceedings of the conference on agricultural impacts on 

ground water, August 11-13, Omaha, NE, 298-326. Dublin, OH: National Water Well Association. 
'-References 10 1-' 

Hammer, DA 1992. Designing constructed wetlands systems to treat agricultural nonpoint source pollution. Ecological Engineering 1:49-82. 

Hanson, G.C., P.M. Groffman, and A.J. Gold. 1994. Denitrification in riparian wetlands receiving high 

and low groundwater nitrate inputs. Journal of Environmental Quality 23:917-22. 

Hatfield,J.L. 1996. Accomplishments in watershed management: Examples fiom Walnut Creek watershed 

in Iowa. In Proceedings of the conference clean water-clean environment-2lst century. Vol.IK Accomplishments, challenges, and perspectives, March 5-8 1995, Kansas City, MO, 79-82. 

Hatton, RS., W.H. Patrick, and R.D. DeLaune. 1982. Sedimentation, nutrient accumulation, and early 

diagnoses in Louisiana Barataria Basin coastal marshes. In Estuarine comparisons. ed. V. Kennedy. New 

York, NY: Academic Press. 

Haycock, N.E., and G. Pinay. 1993. Groundwater nitrate dynamics in grass and poplar vegetated riparian buffer strips during the winter. Journal of Environmental Quality 22:273-78. 

Hemond, H.F. 1980. Biogeochemistry of Thoreau's Bog, Concord, Massachusetts. Ecological Monographs 

50:507-26. -

Hemond, H.F. 1983. The nitrogen budget of Thoreau's Bog. Ecology 64:99-109. 

Hey, D.L., and N.S. Philippi. 1995. Flood reduction through wetland restoration: The Upper Mississippi 

River Basin as a case study. Restoration Ecology 3:4-17. 

Hey, D.L., MA Cardamone, J.H. Sather, and W.J. Mitsch. 1989. Restoration of riverine wetlands: The 

Des Plaines River Wetlands Demonstration Project. In Ecological engineering: An introduction to 

ecotechnology, ed W.J. Mitsch and S.E. Jerrgensen, 159-83. New York, NY:John Wiley &Sons. 

Hey, D.L., A.L. Kenimer, and KR Arret. 1994. Water-quality improvement by four experimental wetlands. Ecological Engineering 3:381-97. 

Hickrnan, S. 1994. Improvement of habitat quality for nesting and migrating birds at the Des-Plaines 

River Wetlands Demonstration Project. Ecological Engineering 3: 485-94. 

Hill, kR 1996. Nitrate removal in stream riparian zones. Journal of Environmental Quality 25743-55. 

Iragavarapu, T.K., G.W. Randall, and MA Schmitt. 1997. Corn production and nutrient losses to tile 

drainage as influenced by source of N. In Agronomy abstracts, 31. Madison, WI: American Society of 

Agronomy. . 

Jackson, WA, L.E. Asmussen, E.W. Hauser, and AW. White. 1973. Nitrate in surface and subsurface 

flow fiom a small agricultural watershed. Journal of Environmental Quality 2:480-82. 

Jacobs, T.C., and J.W. Gilliam. 1985. Riparian losses of nitrate &om agricultural drainage waters. Journal of Environmental Quality 14472-78. 

Jenkins, M.C., and W.M. Kemp. 1984. The coupling of nitrification and denitrification in two estuarine 

sediments. Limnology and Oceanography 29:609-19. 

Johengen T.H, and P.A. LaRock. 1993. Quantifying nutrient removal processes within a constructed 

wetland designed to treat urban stormwater runoff. Ecological Engineering 2:347-66. 

Johnston, C.A. 1991. Sediments and nutrient retention by fresh-water wetlands: Effects on surface-water 

quality. CRC Critical Review in Environmental Control 21:491-565. 
.. . 

102 ReducingNutrient Loads to Surface and Ground Waters and the ~"lf 

Johnston, C.A., G.D. Bubenzer, G.B. Lee, F.W. Madison, and J.R. McHenry. 1984. Nutrient trapping by 

sedimentdeposition in a seasonally flooded lakeside wetland. Journal of Environmental Quality 13283-

90. 

J~r~ensen, S.E. 1994. A general model for nitrogen removal by wetlands. '1n Global wetlands: Old World 

and New, ed W.J. Mitsch, 575-83. Amsterdam, The Netherlands: Elsevier. 

Jury, WA 1975a. Solute travel-time estimates for tile-drained fields: I. Theory. Proceedings ofthe Soil 

Science Society oJ: America 39:1020-24. 

Jury, WA 1975b. Solute travel-time estimates for tile-drained fields: 11. Application to experimental 

studies. Proceedings ofthe Soil Science Society oJ: America 39:1024-28. 

JustiC, D., N.N. Rabalais, and RE. Turner. 1995. Stoichiometric nutrient balance and origin of coastal 

eutrophication. Marine Pollution Bulletin 30(1):41-46. 

JustiC D., N.N. Rabalais, and RE. Turner. 1996. Effects of climate change on hypoxia in coastal waters: 

A doubled C02scenario for the northern Gulf' of Mexico. Limnology and Oceanography 41:992-1003. -

Just$ D., N.N. Rabalais, and RE. Turner. 1997. Impacts of climate change on net productivity of coastal waters: Implications for carbon budgets and hypoxia. Climate Research 8:225-37. 

Kadlec, RH. 1983. The Bellaire wetlands: Wastewater alteration and recovery. Wetlands 3:4463. 

Kadlec, RH. 1994. Detention and mixing in free-water wetlands. Ecological Engineering 3:345-80. 

Kadlec, RH., and D.L. Tilton. 1979. The use of freshwater wetlands as a tertiary wastewater treatment 

alternative. CRC Critical Review in Environmental Control 9:185-212. 

Kadlec, RH., and D.L. Hey. 1994. Constructed wetlands for river water-quality improvement. Water 

Science and Technology 29:159-68. 

Kadlec, RH., and R.L. Knight. 1996. Treatment wetlands. Boca Raton, FL: Lewis Publishers. 

Kang, H., and C Freeman. 1998. Biogeochernical processes in the Olentangy River wetlands: Soil enzymes, trace gas emissions and water chemistry. In Olentangy River Wetlands at The Ohio State University: Annual report 1997, ed. W.J. Mitsch and V. Bouchard, 131-34. Columbus, OH: The Ohio State 

University, School of Natural Resources. 

Kanwar, RS., J.L. Baker, and D.G. Baker. 1987. Tillage and N-fertilizer management eflects on 

groundwater gualiq. Paper 87-2077. St. Joseph, MI: American Society of Agricultural Engineers. 

Karl, T.R, and RW. Knight. 1998. Secular trends of precipitation amount, frequency, and intensity in 

the United States. Bulletin of the American Meteorological Society 79:231-41. 

Keeney, D.R., and T.H. DeLuca. 1993. Des Moines River nitrate in relation to watershed agricultural 

practices: 1945 versus 1980s.Journal of Environmental Qualify 22:267-72. 

Kemp, G.P., andJ.W. Day, Jr. 1984. Nutrient dynamics in a Louisiana swamp receiving agriculture runoE In Cypress swamps, ed. KC. Ewe1 and H.T. Odurn, 286-93. Gainesville, FL: University Presses of 

Florida. 

Kemp, G.P., J.W. Day, D.J. Reed, D.R Cahoon, and M. Wang. In press. Predicting effects of sea level rise 

and sedimentsupply on surface elevation in an organic rich salt marsh. In Recent research in coastal Louisiana. Baton Rouge, LA: Louisiana State University, Louisiana Sea Grant Program. 
Kemp,W.M. and W.R. Boynton. 1984. Spatial and temporal coupling of nutrient inputs to estuarine primary production: The role of particulate transport and decomposition. Bulletin ofMarine Science 35522-

35. 

Kesel, R.H., E. Yodis, and D. McCraw. 1992. An approximation of the sediment budget for the Lower 

Mississippi River prior to major human modification. Earth Suface Processes and Landforms 17:711-22. 

Khalid, R.A. and W.H. Patrick. 1988. Removal of nitrogen and phosphorus by overland flow. In Proceedings of the national seminar on overland flow technology for municipal waste water, 219-45. Washington, DC: U.S. Environmental Protection Agency. 

Kitchens, W.M., Jr., J.M. Dean, L.H. Stevenson, and J.M. Cooper. 1975. The Santee swamp as a nutrient 

sink. In Mineral cycling in southeastern ecosystems, ed. F.G. Howell, J.B. Gentry, and M.H. Smith, 349-

66. ERDA Symposium Series 740513. Washington, DC: U.S. Government Printing Office. 

Kladivko, E.J., G.E. Van Scoyoc, E.J. Monke, K.M. Oates, and W. Pask. 1991. Pesticide and nutrient 

movement into subsurface tile drains on a silt loam soil in Indiana. Journal of Environmental Quality 

20:264-70. 

Klarer, D.M., and D.F. Milie. 1989. Amelioration of storm-water qualityby a freshwater estuary. Archiv 

fur Hydrobiologie 116:375-89. 

Klopatek, J.M. 1978. Nutrient dynamics of freshwater riverine marshes and the role of emergenit macrophytes. In Freshwater wetlands: Ecological processes and management potential, ed. RE. Good, D.F. 

Whigharn, and R.L. Simpson, 195-216. New York, NY: Academic Press. 

Knight, R.L. 1990. Wetland systems. In Natural systems for wastewater treatment: Manual of practice 

FD-16, ed. Task Force on Natural Systems, 211-60. Alexandria, VA: Water Pollution Control Federation. 

Knight, RL. 1992. Ancillary benefits and potential problems with the use of wetlands for nonpoint source 

pollution control. Ecological Engineering 1:97-113. 

Knight, R.L., T.W. McKim, and H.R Kohl 1987. Performance of a natural wetland treatment system for 

wastewater management. Journal of the Water Pollution Control Federation 59:746-54. 

Koerselman, W., H DeCaluwe, and W.M. Kieskamp. 1989. Denitri fication and dinitrogen fixation in 

two quaking fens in the Vechtplassen area, The Netherlands. Biogeochemistry 8:153-65. 

Koike, I., and A. Hattori. 1978. Denitrification and ammonia formation in anaerobic coastal sediments. 

Applied and Environmental Microbiology 35:278-82. 

Kovacic, D.A., M.B. David, and L.E. Gentry. 1995. Grassed detention buffer strips for reducing agricultural nonpoint-source pollution from tile drainage systems. In Proceedings of thefiph annual conference of 

the Illinois Groundwater Consortium, March 29-30, 110-15. Carbondale, IL: Southern Illinois University. 

Kroening, S.E. 1996. Nitrogen and phosphorus in streams in part of the Upper Mississippi River Basin, 

Minnesota and Wisconsin, 1984-93. In Proceedings ofthe Rivertech 96 1st international conference on 

new/emerging concepts for rivers, ed. W.H.C. Maxwell et al. Chicago,IL. 

Kunkel, K.E., K Andsager, and D.R. Easterling. 1999. Long-term trends in extreme precipitation 

events over the conterminous United States and Canada. Journal of Climate 12:2513-25. 

Lane, R.R. and J.W. Day. 1999. Water quality analysis of a freshwater diversion at Caernarvon, Louisiana. Estuaries 22(2). 
104 ReducingNutrient Loads to Surface and Ground Waters and the ~hf 

Larney, F.J., E.J. Kladivko, E.J. Monke, and J.V. Mannering. 1989. Corn growth and yield behavior 

with distance &om subsurface drains in drier-than-normal growing seasons. Transactions ofthe American Society ofAgricultzlral Engineers 32579-87. 

Lee, G.F., E. Bentley, and R. Arnundson. 1975. Effect of marshes on water quality. In Coupling of land and 

water systems, ed. AD. Hasler, 105-27. New York, NY: Springer Verlag. 

Legg, T.D., J.J. Fletcher, and K.W. Easter. 1989. Nitrogen budgets and economic efficiency: A case study of 

southeastern Minnesota. Journal of Production Agriculture 2:110-16. 

Lindau, C.W. and R.D. DeLaune. 1991. Dinitrogen and nitrous oxide emission and entrapments in 

Spartina alterniflora salt marsh soils following addition of N-15 labeled ammonium and nitrate. Estuarine, Coastal and Shelf Science 32:161-72. 

Linker, LC., RL. Dennis, and D.Y. Alegre. 1993. Impactofthe Clean Air Act on Chesapeake Bay water 

quality. In Proceedings of the international conference on the environmental management of enclosed 

coastal seas (EMECS). November 10-13. Baltimore, MD: Maryland Sea Grant College. 

Liss, P.S. 1976. Conservative and non-conservative behavior of dissolved constituents during estuarine 

mixing. In Estuarine chemistry, ed.J. Burton and P. Liss, 93-130. New York, NY: Academic Press. 

Livingston, E.H. 1989. Use ofwetlands for urban stormwater management. In Constructed wetlands for 

wastewater treatment: Municipal, industrial, and agricultural, ed. D.A. Hammer, 253-62. Chelsea, MI: 

Lewis Publishers. 

Livingston, E.H., and E. McCarron. 1992. Stormwater management: A guide for Floridians. Tallahassee, FL: Florida Department of Environmental Regulation. 

Logan, T.R., G.W. Randall, and D.R. Timmons. 1980. Nutrient content oftile drainagefrom cropland in 

the North Central region. North Central Region Research Publication 268. OARDC Research Bulletin 

1119. Wooster, OH: Ohio Agricultural Research Development Center. 

Logari, T.J., D.J. Eckert, and D.G. Beak. 1994. Tillage, crop and climatic effects on runoff and tile drainage losses of nitrate and four herbicides. Soil & Tillage Research 30:75-103. 

Loucks, O.L. 1990. Restoration of the pulse control function of wetlands and its relationship to water quality objectives. In Wetland creation and restoration, ed.J.A. Kusler and M.E. Kentula, 467-77. Washington, DC: Island Press. 

Lowrance, R, R Todd, J. Fair, Jr., 0.Hendrickson, Jr., R Leonard, and L. Asmussen. 1984. Riparian 

forests as nutrient filters in agricultural watersheds. BioScience 34:374-77. 

Lowrance, R, R Leonard, and J. Sheridan. 1985. Managing riparian ecosystems to control nonpoint 

pollution. Journal of Soil & Water Conservation 40:87-97. 

Lowrance, R, L.S. Altier, J.D. Newbold, R.R. Schnabel, P.M. Groffman, J.M. Denver, D.L. Correll, 

J.W. Gilliam,J.L. Robinson, R.B. Brinsfield, K.W. Staver, W. Lucas, and A.H. Todd. 1995. Water quality 

Jirnctions of riparian forest bufer systems in the Chesapeake Bay watershed. EPA 903-R-95-

004/CBP/I'RS 134/95. Washington, DC: U.S. Environmental Protection Agency. 

Lowrance, R, L. Altier, J.D. Newbold, R Schnabel, P.M. Groffman, J.M. Denver, D.L. Correll, J.W. 

Gilliam, J.M. Robinson, RB. Brinsfield, KW. Staver, W. Lucas, and AH. Todd. 1997. Water quality 

functions of riparian forest buffers in Chesapeake Bay watersheds. Environmental Management 21:687-

712. 

Madden, C.J., J.W. Day, and J.M. Randall. 1988. Freshwater and marine coupling in estuaries of the 

Mississippi River deltaic plain. Limnology and Oceanography 33:982-1004. 
Magdoff, F.R., D. Ross, and J. Arnadon. 1984. Asoil test for nitrogen availability to corn Soil Science Society of America Journal 48:1301-4. 

Metcalf and Eddy, Inc. 1991. Wastewater engineering, treatment, disposal and reuse. 3d ed New York., 

NY: McGraw-Hill. I 

Miller, C.V., J.M. Denis, S.W. Ator, and J.W. Brakebill. 1997. Nutrients in streams during baseflow in 

selected environmental settings of the Potomac River Basin. Journal of the American Water Resources 

Association 33:1155-71. 

Mitsch, W.J. 1977. Water hyacinth (Eichhornia crassipes) nutrient uptake and metabolism in a northcentral Florida marsh. Archivfir Hydrobiologie 81:188-210. 

Mitsch, W.J. 1990. Wetlandsfor the control of nonpoint source pollution: Preliminary feasibility study for 

the Swan Creek watershed of northwestern Ohio. Final report. Columbus, OH: Ohio Environmental 

Protection Agency. 

Mitsch, W.J. 1992. Landscape design and the role of created, restored, and natural riparian wetlands in 

controlling nonpoint source pollution. Ecological Engineering 1:27-47. -

Mitsch, W.J. 1994. A comparison of the nonpoint source pollution control hnction of natural and constructed riparian wetlands. In Global wetlands: Old World and New, ed. W.J. Mitsch, 351-61. Amsterdam, The Netherlands: Elsevier. 

Mitsch, W.J. 1995. Restoration of our lakes and rivers with wetlands-An important application of ecological engineering. Water Science and Technology 31:167-77. 

Mitsch. W.J., and L. Carmichael. 1997. Water quality and nutrient removal patterns of created riparian 

wetlands: Third year results and a 3-year summary. In Olentangy River Wetland Research Park, 1996 

annual report, ed W.J. Mitsch, 127-38. Columbus, OH: The Ohio State University, School of Natural Resources. 

Mitsch, W.J., and J.K. Cronk. 1992. Creation and restoration of wetlands: Some design considerations for 

ecological engineering. In Advances in soil science. VoZ. 17: Soil restoration, ed R Lal and B.k Stewart, 

21-59. New York, NY: Springer-Verlag. 

Mitsch, WJ., and N. Flanagan. 1997. Comparison ofstructure and function of reference freshwater 

marshes with constructed deepwater marshes at the Des Plaines River Wetland Demonstration Project in 

northeastern Illinois. Chicago,IL: Wetlands Research, Inc. 

Mitsch, W.J., and J.G. Gosselink. 1993. Wetlands. 2d ed New York, NY: J. Wdey &Sons, Inc. 

Mitsch, W.J., and H. Montgomery. 1998. Water quality and nutrient removal patterns of created riparian 

wetlands: Fourth year results. In Olentangy River Wetland Research Park, 1997 annual report, ed. W.J. 

Mitsch and V. Bouchard, 89-95. Columbus, OH:The Ohio State University, School of Natural Re sources. 

Mitsch, W.J., and B.C. Reeder. 1991. Modelling nutrient retention of a freshwater coastal wetland: Estimating the roles of primary productivity, sedimentation, resuspension and hydrology. Ecological Modelling 

54:151-87. 

Mitsch, W.J., and B.C. Reeder. 1992. Nutrient and hydrologic-budgetsof a Great Lakes coastal freshwater 

wetland during a drought year. Wetlands Ecology and Management 1(4):211-23. 

Mitsch, W.J., and R.F. Wilson. 1996. Improving the success of wetland creation and restoration with 

know-how, time, and self-design. Ecological Applications 6:77-83. 
. . 

106 Reducing Nutrient Loads to Surface and Ground Waters and the ~'&f 

Mitsch, W.J., R.H. Mitsch, and RE. Turner. 1994. Wetlands in the Old and New Worlds: Ecology and 

management. In Global wetlands: Old World and New, ed, W.J. Mitsch, 3-56. Amsterdam, The Netherlands: Elsevier. 

Mitsch, W.J., J.K. Cronk, X. Wu, RW. Nairn, and D.L. Hey. 1995. Phodphorus retention in constructed 

freshwater riparian marshes. Ecological Applications 5:830-45. 

Mitsch, WJ., X Wu,RW. Nairn, RE. Weihe, N. Wang, R. Deal, and C.E. Boucher. 1998. Creating and 

restoring wetlands: A whole-ecosystem experiment in self-design. BioScience 48:1019-30. 

Moran, M.A., and RE. Hodson. 1989. Formation and bacterial utilization of dissolved organic carbon 

derived fi-om detrital lignocellulose. Limnology and Oceanography 34:1034-47. 

Morton, T.G., A.J. Gold, and W.M. Sullivan. 1988. Influence of overwatering and fertilization on nitrogen losses fi-om home lawns. Journal of Environmental Quality 17:124-30. 

Moustafa, M.Z., M.J. Chimney, T.D. Fontaine, G. Shih, and S. Davis. 1996. The response of a freshwater wetland to long-term low-level nutrient loads-marsh efficiency. Ecological Engineering 7:15-33. -

Mulla, D.J., ed.. 1997. Minnesota River Basin water quality overview. FO-7079E. Minneapolis, MN: 

University of Minnesota Extension Service. 

National Research Council (NRC). 1992. Restoration ofaquatic ecosystems. Washington, DC: National 

Academy Press. 

Nixon, S.W. 1981. Freshwater inputs and estuarine productivity. In Proceedings of the national symposium onfieshwater inzow to estuaries, ed. R Cross and D. Williams, 31-57. FWS/OBS-81/04. Washington, DC: U.S. Department ofthe Interior, U.S. Fish and Wildlife Service, Office of Biological Services. 

Nixon, S.W., and V. Lee. 1986. Wetlands and water quality. Wetlands Research Program Technical Report y-86-2. Vicksburg, MS: U.S. Army Engineers Waterway Experiment Station. 

Nowicki, B.L., J.R. Kelly, E. Requintina, and D.V. Keuren. 1997. Nitrogen losses through sediment 

denitrification in Boston Harbor and Massachusetts Bay. Estuaries 20:626-39. 

Officer, C.B. and Ryther, J.H. 1980. The possible importance of silicon in marine eutrophication. Marine 

Ecology. Progress Series 3:83-9 1. 

Ogawa, H., and J.W. Male. 1983. Theyood mitigation potential of inland wetlands.. Water Resources 

Center Publication no. 138.Amherst, MA: University of Massachusetts. 

Olson, R.K., ed, 1992. The role of created and natural wetlands in controlling nonpoint source pollution. 

Ecological Engineering 1:l-170. 

Omernik, J.M. 1977. Nonpoint source-stream nutrient level relationships-A nationwide study. EPA600/3-P77-105. Corvallis, OR: U.S. Environmental Protection Agency. 

O'Neil, T. 1949. The muskrat in the Louisiana coastal marsh. New Orleans, LA: Louisiana Department of 

W~ldlifeand Fisheries. 

Osborne, L.L., and D.A. Kovacic. 1993. Riparian vegetated buffer strips in water-quality restoration 

and stream management. Freshwater Biology 29:243-58. 

Patini, N.K., L. Masse, and P.Y. Jui. 1996. Tile effluent quality and chemical losses under conventional 

and no-tillage Part 1:Flow and nitrate. Transactions of the American Society of Agricultural Engineers 

39:1665-72. 
.-References 1 07 -' 

Patrick, W.H., and RA. Khalid. 1974. Phosphate release and sorption by soils and sediments: Effect of 

aerobic and anaerobic conditions. Science 18653-55. 

Penland, S., and K.E. Ramsey. 1990. Relative sea-level rise in Louisiana and the Gulf of Mexico: 1908-

1988.Journal of Coastal Research 6:323-42. , I 

Penland, S., R Boyd, and J.R. Suter. 1988. Transgressive depositional systems of the Mississippi Delta 

plain: A model for barrier shoreline and shelf sand development. Journal of Sedimentary Petrology 58:932-

49. 

Peterjohn, W.T., and D.L. Correll. 1984. Nutrient dynamics in an agricultural watershed: Observations 

on the role of a riparian forest. Ecology 65:1466-75. 

Petrovic, A.M.1990. The fate of nitrogenous fertilizers applied to turfgrass. Journal of Environmental 

Quality 19:l-14. 

Peverly, J.H. 1982. Stream transport of nutrient through a wetland. Journal $Environmental Quality 

11:38-43. 

Phipps, RG., and W.G. Crumpton. 1994. Factors affecting nitrogen loss in experimental wetlands with 

different hydrologic loads. Ecological Engineering 3:399-408. 

Poirrer, M.A., andJ.M. King. 1998. Observations on Lake Pontchartrain blue-green algae blooms and 

fish kills. In 4th basics ofthe basin research symposium, May 12-13, New Orleans, LA. Abstract. 

Power, J.F., AD. Flowerday, RA. Wiese, and D.G. Watts. 1998. Agricultural nitrogen management to 

protect water quality. Washington, DC: US. Department of Agriculture, Cooperative State Research, 

Education, and Extension Service and Agricultural Research Service. 

Rabalais, N.N., R.E. Turner, W.J. Wiseman, Jr., and D.F. Bo& 1991. A brief summary of hypoxia on 

the northern Gulf of Mexico continental sheE 1985-1988. In Modern and ancient sher anoxia, ed. R.V. 

Tyson and T.H. Pearson, 35-47. SpecialPublication No. 58. London, England: Geological Society. 

Rabalais, N.N., RE. Turner, and W.J. Wiseman, Jr. 1992. Distribution and characteristics of hypoxia on 

the Louisiana shelf in 1990 and 1991. In Proceedings, nutrient enhanced coastal ocean productivity 

workshop, 15-20. Publication no. TAMU-SG-92-109. College Station, TX: Texas A&M University, 

Texas Sea Grant College Program. 

Rabalais, N.N., W.J. Wiseman, and R.E. Turner. 1994. Comparison of continuous records of near-bottom 

dissolved oxygen fi-om-thehypoxia zone along the Louisiana coast. Estuaries 17:850-61. 

Rabalais, N.N.~RE. Turner, D. JustiS QDortch, W.J. Wiseman, Jr., and B.K Sen Gupta. 1996. Nutrient changes in the Mississippi River and system responses on the adjacent continental shelf. Estuaries 

19:286-407. 

Rabalais, N.N., R.E. Turner, W.J. Wiseman, Jr., and QDortch. 1998. Consequences of the 1993 Mississippi River flood in the GulfofMexico. Regulated Rivers 14:161-77. 

Rabalais, N.N., RE. Turner, D. Justic QDortch, and W.J. Wiseman, Jr. 1999. Characterization of 

-Hypoxia. Topic 1 reportfor the integrated assessment on hypoxia in the GulfofMexico. NOM Coastal 

Ocean Program Decision Analysis Series No. 15. Silver Spring, MD: National Oceanic and Atmospheric 

Administration. 

Raisin, G.W, and D.S. Mitchell. 1995. The use of wetlands for the control of non-point source pollution. 

Water Science and Technology 32:177-86. 
108 ReducingNutrient Loads to Surface and Ground Waters and the Gulf -. 

Raisin, G.W., D.S. Mitchell, and RL. Croome. 1997. ?he effectiveness of a small constructed wetland in' 

ameliorating difhse nutrient loadings from an Australian rural catchment. Ecological Engineering 9:19-

Randall, G.W. 1998. Implications ofdry and wet cyclqon nitrate loss to subsurface tile drainage. In Proceedings of the 7t;h annual drainage symposium. Drainage in the 21st century, 53-60. March 8-10, Orlando, FL. 

Randall, G.W., and T.K. Iragavarapu. 1995. Impact of land-term tillage systems for'continuous corn on 

nitrate leaching to tile drainage. Journal of Environmental Quality 24:360-66. 

Randall, G.W., and MA Schrnitt. 1998. Advisability of fall-applying nitrogen. In Proceedings of the 

1998 Wisconsinfertilizer, aglime, andpest management conference,90-96. January 20, Middleton,WI. 

Randall, C.W., and D. Sen. 1996. Full-scale evaluation of an integrated fixed-film activated sludge 

(IFAS) process for enhanced nitrogen removal. Water Science and Technology 33:155-62. 

Randall, G.W., and J.A. Vetsch. 1995. Corn yield and nitrate loss to tile drainage as affected by N management. In Agronomy abstracts, 321. Madison, WI:American SocietyofAgronomy. 

Randall, G.W., D.R. Huggins, M.P. Russelle, D.J. Fuchs, W.W. Nelson, and J.L. Anderson. 1997. Nitrate 

losses through subsurface tile drainage in CRP, alfalfa and row crop systems. Journal of Environmental 

Quality 26:1240-47. 

Rasmussen, R.A., and M.A. Khalil. 1986. Atmospheric trace gases: Trends and distributions over the last 

decade. Science 232:1623-24. 

Reddy, K.R, and D.A. Graetz. 1988. Carbon and nitrogen dynamics in wetland soils. In The ecology and 

management ofwetlands, vol. I., ed.D.D. Hook et al., 307-18. Portland, OR: Timber Press. 

Reddy, K.R, RD. DeLaune, W.F. DeBusk, and M.S. Kock 1993. Long-term nutrient accumulation 

rates in the Everglades. Soil Science Society of America Journal 57:1147-55. 

Richard, T.L., andT.S. Steenhuis. 1988. Tile drain sampling of preferential flow on a field scale. Journal 

of Contam. Hydrology 3:307-25. 

Richardson, C.J. 1985. Mechanism controllingphosphorus retention capacity -in freshwater wetlands. Science 228:1427-27. 

Richardson, C.J., and P.E. Marshall. 1986. Processes controlling movement, storage, and export of phosphorus in a fen peatland. Ecological Monographs 56:279-302. 

Richardson, C.L., D.L. Tilton, J.A. Kadlec, J.P.M. Charnie, and W.A. Wentz. 1978. Nutrient dynamics of 

northern wetland ecosystems In Freshwater wetlands: Ecological processes and management potential, ed. 

RE. God et al., 217-41. New York, NY:Academic Press. 

Rothberg, M.R., W.F. Burks, and PA Steininger. 1993. Single basin process removes nitrogen. Water 

Environment C3 Technology 558-63. 

Russell, R.J. 1936. Physiography of the lower Mississippi River delta. In Lower Mississippi River delta, 

reports on the geology of Plaquemines and St. Bernard parishes, ed. R Russell, H Howe, J. McGuirt, C. 

Dohm,W. Hadley, F. Kniffen, and C. Brown, 3-199. Geological Bulletin no. 8. New Orleans, LA: Louisiana Geological Survey, Department of Conservation. 

Rusten, B., L Hem, and I3 Odegaard. 1995. Nitrification of municipal wastewater in moving-bed 

bioh reactors. Water Environment Research 67:75-86. 
Sanville,W., and W.J. Mitsch, eds. 1994. Creating freshwater marshes in a riparian landscape: Research 

, at the Des Plaines River Wetland Demonstration Project. Special issue of Ecological Engineering 3:315-

521. 

Schrnitt, M.A., and G.W. Randall. 1994. Developing a soil nitrogen test for improved recommendations 

for corn.Journal of Production Agriculture 7:328-34. 

Schueler,T.R., J. Galli, L. Herson, P. Kumble, and D. Shepp. 1991. Developing effective BMP strategies 

for urban watersheds. In Nonpoint source watershed workshop, September 1,69-83. Seminar Publication 

EPA/625/4-91/027. Washington, DC: U.S. Environmental Protection Agency. 

Schultz, R, J. Collem, T. Isenhart, W. Simpkins, C. Mize, and M. Thompson. 1995. Design and placement of a multispecies riparian buffer system. Agroforestry systems 29:201-26. 

Scruton, P.C. 1960. Delta building and the deltaic sequence. Recent sediments. In Proceedings of the NW 

Gulf Coast of Mexico AAPG symposium, 1960, 82-102. 

Sharp, J.H., C.H. Culberson, and T.M. Church. 1982. The chemistry of the Delaware estuary. General 

considerations. Limnology and Oceanography 27:1015-28. -

Simpson, R.L., D.F. Whigham, and RE. Good. 1978. Seasonal patterns of nutrient movement in a freshwater tidal marsh. In Freshwater wetlands: Ecological processes and management potential, ed. R.E. 

Good, D.F. Whigham, and R.L. Simpson,243-57. New York, IVY: Academic Press. 

Skaggs, R.W., and J.W. Gilliam. 1981. Effect of drainage system design on nitrate transport. Transactions 

of the American Society of Agricultural Engineers 24:929-34,940. 

Skaggs, RW., A Tabrizi, and G.R Foster. 1982. Subsurface drainage effects on erosion. Journal of Soil 

and Water Conservation 37:167-72. 

Smayda,T. 1989. Primary production and the global epidemic of phytoplankton blooms in the sea: Alinkage. In Novelalgal blooms, ed. E.M. Cosper, V.M. Bricelj, and E.J. Carpenter, 449-83. Coastal and Estuarine Studies 35. New York, NY: Springer-Verlag. 

Smayda, T. 1990. Novel and nuisance phytoplankton blooms in the sea: Evidence for global epidemic. In 

Toxic marine phytoplankton, ed E. Graneli, B. Sundstrom, R Elder, and D.M. Anderson, 29-40. New 

York, NY Elsevier Science Publishing Co. 

Smith, C.J., and R.D. DeLaune. 1983. Nitrogen loss fiom freshwater and saline estuarine sediments. 

Journal of Environmental Quality 12514. 

Smith, C.J., R.D. DeLaune, andJ.W.H. Patrick. 1982. Nitrate reduction in Spartina alternzflora marsh 

soil. Soil Science Society of America Journal 46:748-50. 

Sorenson, J. 1978. Capacity for denitrification and reduction of nitrate to ammonia in a coastal marine 

sediment. Applied and Environmental Microbiology 35(2):301-5. 

Spieles, D.J., and W.J. Mitsch. 2000. The effects of seasonal and hydrologic and chemical loading on nitrate 

retention in constructed wetlands: A comparison of low and high nutrient riverine systems. Ecological Engineering: 14. 

Stack, W.P., and KT. Belt. 1989. Modifjmg stormwater management basins for phosphorous control. 

Lake Line. May 1989, pp. 1-8. (A publication of the Virginia Regional Symposium, April 1988.) 

STAPPA & WCO. 1994. Controlling nitrogen oxides under the Clean Air Act: A menu of options. 

Washington, DC: State and Territorial Air Pollution Program Administrators and the Association of 

Local Air Pollution Control Officials. 
1 10 ReducingNutrient Loads to Surface and Ground Waters and the Gulf - -

Swenson, E., and W.-S. Chuang. 1983. Tidal and subtidal water volume exchange in an estuarine system. 

Estuarine, Coastal and Shelf Science 16:229-40. 

Tavoulareas, E.S., and J.P. Charpentier. 1995. Clean coal technologies for developing countries. World 

Bank Technical Paper No. 286, Energy Series. Washington, DC: World Bank. 

Teague, K.G., C.J. Madden, and J.W. Day. 1988. Sediment-water oxygen and nutrient fluxes in a riverdominated estuary. Estuaries 11(1):1-9. 

Turner, R.E. 1998. A comparative mass balance budget (C, N, P and suspended solids) for a natural 

swamp and overland flow systems. In Nutrient cycling and retention in natural and constructed wetlands, 

ed. J. Vymazal, 1-11. Leiden, The Netherlands: Backhuys Publishers. 

Turner, R.E., and R.L. Allen. 1982. Bottom water oxygen concentrations in the Mississippi River Delta 

Bight. Contributions in Marine Science 25:161-72. 

Turner, R.E., and N.N. Rabalais. 1991. Changes in Mississippi River water quality this century. 

BioScience 41:140-47. 

Turner, RE, N. Qureshi, N. Rabalais, QDortch, D. Just$ R Shaw, and J. Cope. 1998. Fluctuating silicate:nitrate ratios and coastal plankton food webs. Proceedings ofthe National Academy of Science USA 

95:13,048-51. 

Tyson, R 1997. Modelers take another look at Chesapeake Bay nutrient sources. Environmental Science 

and Technology 31506A. 

Urban, N.R., and S.J. Eisenreich. 1988. Nitrogen cycling in a forested Minnesota bog. Canadian Journal 

of Botany 66:435-49. 

U.S. Department ofAgriculture (USDA). 1987. Farm drainage in the United States: History, status and 

prospects. USDAMisc. Pub. No. 1455, Washington, DC. 

U.S. Department ofAgriculture (USDA). 1997. Riparian forest buffer handbook for the Chesapeake Bay 

watershed. United States Department of Agriculture, Environmental Protection Agency, Forest Service, 

and Northeastern Area State &Private Forestry, NA-TT-02-97. Washington, DC. 

U.S. Environmental Protection Agency (USEPA). 1977. Nonpoint source-stream nutrient level relationships: A nationwide study. NTIS No. PB-276 600. Washington, DC. 

U.S. Environmental Protection Agency (USEPA). 1983. Final report ofthe nationwide urban runoffprogram. Washington, DC: USEPA, Water Planning Division. 

U.S. Environmental Protection Agency (USEPA). 1993. Guidance specifying management measures for 

sources of nonpoint pollution in coastal waters. EPA-840-B-93-001c. Washington DC: USEPA, Office of 

Water. (Also available on the Internet at www.epa.gov/owow/nps/mmgi/index.html) 

U.S. Environmental Protection Agency (USEPA). 1995a. National air pollution trends. EPA-454/R-95-

011. Washington, DC. 

U.S. Environmental Protection Agency (USEPA). 1995b. Water quality functions of riparian forest 

bufer systems in the Chesapeake Bay watershed. EPA 903-R-95-004. Washington, DC: USEPA, Chesapeake Bay Program. 

U.S. Environmental Protection Agency (USEPA). 1996a. Acid rain program; nitrogen oxides emission 

reduction program. Federal Register 61:67111-64. 

U.S. Environmental Protection Agency (USEPA). 1996b. Control of NO, emissions by reburning. 

EPA/625/R-96/001. Cincinnati, OH:USEPA, National Risk Management Research Laboratory. 
.-References I I I -' 

U.S. Environmental Protection Agency (USEPA). 1997a. Performance of selective catalytic reduction on 

coal-fired steam generating units. Final report of the Ofice ofAir and Radiation, June 25, 1997. Washington, DC. 

U.S. Environmental Protection Agency (USEPA). 199%. New emission standards for heavy-duty diesel 

engines used in trucks and buses. EPA/420/F'/97/016. Washington, DC: USEPA, Office ofMobile Sources, 

Air and Radiation Program. 

U.S. Environmental Protection Agency (USEPA). 1998a. Tier 2 study, report to Congress. EPA-420-R98-008. July 1998. Washington, DC: USEPA, Air and Radiation Program. 

U.S. Environmental Protection Agency (USEPA). 1998b. Finding of significant contribution and rulemaking for certain states in the ozone transport assessment group region for purposes of reducing regional 

transport of ozone. Federal Register 6357356-57538. 

Valiela, I., G. Collins, J. Kremer, K. Lajtha, M. Geist, B. Seely, J. Brawley, and C.H. Sham. 1997. Nitrogen loading &om coastal watersheds to receiving estuaries: New method and application. Ecological Applications 7:358-8 0. 

Valigura, RA., J. Scudlar, J.E. Baker, and L.L. McConnell. 1994. Atmospheric deposi%on of nitrogen and 

contaminants to the Chesapeake Bay and its watershed. In Perspectives on Chesapeake Bay, 1994: Advances in estuarine sciences, d.S. Nelson and P. Elliott. CRC Publication no. 147. Edgewater, MD: The 

Chesapeake Research Consortium, Inc. 

Verry, E.S., and D.R. Tirnmons. 1982. Waterborne nutrient flow through an upland-peatland watershed 

in Minnesota. Ecology 63:1456-67. 

Villarrubia, C.R 1998. Ecosystem response to a freshwater diversion: The Caernarvon experience. In 

Recent research in coastal Louisiana: Natural systemfunction to human influences (symposium), February 

3-5, Lafayette, LA. 

Watanabe,Y., D.Y. Bang, K Itoh, and K, Matsui. 1994. Nitrogen removal fiom wastewaters by a bioreactor with partially aiid fully submerged rotating biofilms. Water Science and Technology 29:431-38. 

', 

Wed, D.A.J., and R.S. anwar. 1996. Nitrate and water present in and flowing &om root-zone soil. 

Journal of Environmentfl Quality 25:709-19. 

Weller, D.E., D.L. Correll, and T.E.Jordan. 1994. Denitrification in riparian forests receiving agricultural discharges. In Global wetlands: Old World and New, ed. W.J. Mitsch, 117-1331. Amsterdam, The 

Netherlands: Elsevier. 

Welsch, D.J. 1991. Riparian forest buflers: Function and designfor protection and enhancement of water 

resources. NA-PR-07-91. Radnor, PA: USDA Forest Service, Northeastern Area. 

Wieder, R.K., G. Tchobanoglous, and RW. Tuttle. 1989. Preliminaly considerations regarding constructed wetlands for wastewater treatment. In Constructedwetlands for wastewater treatment, ed. D.A. 

Hammer, 297-306. Chelsea, MI: Lewis Publishers, Inc. 

Zucker, L.A., and L.C. Brown, ds. 1998. Agricultural drainage: Water quality impacts and subsurface 

drainage studies in the Midwest. Ohio State University Extension Bulletin 871. Columbus, OH: The Ohio 

State University. 
OTHER TITLES INTHE DECISIONANALYSIS SERIES 

No. 1 Able, Kenneth W., and Susan C Kaiser. 1994. Synthesis of Summer Flounder Habitat Parameters. 

No. 2 Mattheis, Geo&eY A, and Thomas J. Minello. 1994. Technology and Success in Restoration, 

Creation and Enhancement of Spartina A(tern$ora Marshes in the United States. 2 vols. 

No. 3 Collins, Elaine V., Maureen Woods, Isobel Sheifer, and Janice.Beattie. 1994. Bibliography of 

SynthesisDocuments on Selected Coastal Topics. I 

No. 4 Hinga, Kenneth R., HeeseonJeon, and Noelle F. Lewis. 1995. Marine Eutrophication Review. 

No. 5 Lipton, Douglas W., Katherine Wehan, Isobel C Sheifer, and Rodney F. Weiher. 1995. Economic Valuation of Natural Resources: A Handbook for Coastal Policyrnakers. 

No. 6 Vestal, Barbara, Alison Reiser, et al. 1995. Methodologies and Mechanisms for Management of 

Cumulative Coastal Environmental Impacts. Part I-Synthesis with Annotated Bibliography; 

Part 11-Development and Application of a CumulativeImpacts Assessment Protocol. 

No. 7 Murphy, Michael L.1995. Forestry Impacts on Freshwater Habitat of Anadromous Salmonids in 

the Pacific Northwest and Alaska-Requirements for Protection and Restoration. 

No. 8 Wiam F. Kier Associates. 1995. Watershed Restoration-A Guide for Citizen Involvement in 

California. 

No. 9 Valigura, Richard A, WinstonT. Luke, Richard S. Artz, and Bruce B. Hicks. 1996. Atmospheric 

Nutrient Inputs to Coastal Areas-Reducing the Uncertainties. 

No. 10 Boesch, Donald F., et al. 1997. Harmful Algal Blooms in Coastal Waters: Options for Prevention, 

Control and Mitigation. 

No. 11 McMurray, Gregory R, and Robert J. Bailey, editors. 1998. Change in Pacific Northwest Coastal 

Ecosystems. 

No. 12 Fonseca, Mark S., W. Judson Kenworthy, and Gordon W. Thayer. 1998. Guidelines for the Conservation and Restoration of Seagrasses in the United States and Adjacent Waters. 

No. 13 Macklin, S. Allen, editor. 1998. Bering Sea FOCI (1991-1997)-Final Report. 

No. 14 Wiseman, Wiam, editor. 1999. Nutrient Enhanced Coastal Ocean Productivity in the Northern 

Gulf of Mexico. 

No. 15 Rabalais, N.N., RE. Turner, D. Justie QDortch, and W.J. Wiseman, Jr. 1999. Characterization of Hypoxia: Topic 1Report for the Integrated Assessment on Hypoxia in the Gulf of Mexico. 

No. 16 Diaz, R.J., and A Solow. 1999. Ecological and Economic Consequencesof Hypoxia: Topic 2 Report 

for the IntegratedAssessment on Hypoxia in the Gulf of Mexico. 

No. 17 Goolsby, D.A, WA Battaglin, G.B. Lawrence, RS. Artz, B.T. Aulenbach, R.P. Hooper, D.R. 

Keeney, and G.J. Stensland. 1999. Flux and Sources of Nutrients in the Mississippi-Atchafalaya 

River Basin: Topic 3 Report for the Integrated Assessment on Hypoxia in the Gulf of Mexico. 

No. 18 Brezonik, P.L., V.J. Bierman, Jr., R Alexander, J. Anderson, J. Barko, M. Dortch, L. Hatch, G.L. 

Hitchcock, D. Keeney, D. Mulla, V. Smith,C. Walker, T.Whitledge, and WJ. Wiseman, Jr. 1999. 

Effects of Reducing Nutrient Loads to Surface Waters within the Mississippi River Basin and the 

Gulf of Mexico: Topic 4 Report for the Integrated Assessment on Hypoxia in the Gulf of Mexico. 

No. 19 Mitsch, W.J., J.W. Day, Jr., J.W Gilliam, P.M. Groffman, D.L. Hey, G.W. Randall, and N. 

Wang. 1999. Reducing Nutrient Loads, Especially Nitrate-Nitrogen, to Surface Water, Ground 

Water, and the Gulf of Mexico: Topic 5 Report for the Integrated Assessment on Hypoxia in the 

Gulf of Mexico. 

No. 20 Doering, O.C., F. Diaz-Hermelo, C. Howard, R. Heimlich, F. Hitzhusen, R. Kazmierczak,J. 

Lee, L. Libby, W. Mion, T. Prato, and M. Ribaudo. 1999. Evaluation of the Economic Costs and 

Benefits of Methods for Reducing Nutrient Loads to the Gulf of Mexico: Topic 6 Report for the 

Integrated Assessment on Hypoxia in the Gulf of Mexico. 
U.S. Department of Commerce 

National Oceanic and Atmospheric Administration 

Coastal Ocean Program 

1315 East-West Highway 

Silver Spring, Maryland 209 1 0