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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Serie: Geophysical Monograph Series
- Sprache: Englisch
Finalist for the 2021 PROSE Award for Environmental Science! An integrated approach to understanding and mitigating the problem of excess nitrogen Human activities generate large amounts of excess nitrogen, which has dramatically altered the nitrogen cycle. Reactive forms of nitrogen, especially nitrate and ammonia, are particularly detrimental. Given the magnitude of the problem, there is an urgent need for information on reactive nitrogen and its effective management. Nitrogen Overload: Environmental Degradation, Ramifications, and Economic Costs presents an integrated, multidisciplinary review of alterations to the nitrogen cycle over the past century and the wide-ranging consequences of nitrogen-based pollution, especially to aquatic ecosystems and human health. Volume highlights include: * Comprehensive background information on the nitrogen cycle * Detailed description of anthropogenic nitrogen sources * Review of the environmental, economic, and health impacts of nitrogen pollution * Recommendations and strategies for reducing humanity's nitrogen footprint * Discussion of national nitrogen footprints and worldwide examples of mitigation policies The American Geophysical Union promotes discovery in Earth and space science for the benefit of humanity. Its publications disseminate scientific knowledge and provide resources for researchers, students, and professionals. Read the Editors' Vox: https://eos.org/editors-vox/exploring-the-widespread-impacts-of-ongoing-nitrogen-pollution
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Veröffentlichungsjahr: 2020
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Table of Contents
Cover
PREFACE
ACKNOWLEDGMENTS
1 Introduction
1.1. THE SIGNIFICANCE OF NITROGEN ON EARTH
1.2. CYCLING OF NITROGEN IN THE ENVIRONMENT
1.3. ENVIRONMENTAL CONSEQUENCES OF EXCESS REACTIVE NITROGEN
1.4. ADVERSE HUMAN HEALTH IMPACTS
1.5. LEGACY REACTIVE NITROGEN STORAGE IN THE SUBSURFACE
1.6. ECONOMIC IMPACTS OF EXCESS REACTIVE NITROGEN
1.7. PURPOSE AND SCOPE
REFERENCES
FURTHER READING
2 The Nitrogen Cycle
2.1. PREINDUSTRIAL “NATURAL” NITROGEN CYCLE
2.2. HUMAN ALTERATION OF THE NITROGEN CYCLE
REFERENCES
FURTHER READING
3 Sources of Reactive Nitrogen and Transport Processes
3.1. NATURAL SOURCES
3.2. ANTHROPOGENIC SOURCES
3.3. REACTIVE NITROGEN TRANSPORT PROCESSES
3.4. LARGE NATIONAL AND MULTINATIONAL PROGRAMS AND NITROGEN SOURCE CONTRIBUTIONS
REFERENCES
FURTHER READING
4 Methods to Identify Sources of Reactive Nitrogen Contamination
4.1. NITROGEN ISOTOPES FOR SOURCE IDENTIFICATION
4.2. DUAL ISOTOPES OF NITRATE (NITROGEN AND OXYGEN) FOR SOURCE IDENTIFICATION
4.3. OTHER CHEMICAL INDICATORS AND TRACERS OF NITRATE CONTAMINATION SOURCES
4.4. SOURCES AND IDENTIFICATION OF ANTHROPOGENIC AMMONIUM
4.5. ORGANIC WASTEWATER COMPOUNDS AND EMERGING CONTAMINANTS AS INDICATORS OF NITRATE CONTAMINATION SOURCES
4.6. STABLE ISOTOPIC MONITORING OF BIOTA IN ECOSYSTEMS
4.7. MICROBIAL INDICATORS OF NITRATE SOURCE CONTAMINATION
4.8. COMBINING NITRATE SOURCE IDENTIFICATION WITH GROUNDWATER AGE AND RESIDENCE TIME INFORMATION
4.9. USING NITRATE ISOTOPES AND OTHER INDICATORS TO ASSESS LEGACY REACTIVE NITROGEN IN SUBSURFACE STORAGE
REFERENCES
FURTHER READING
5 Adverse Human Health Effects of Reactive Nitrogen
5.1. HEALTH EFFECTS ASSOCIATED WITH REACTIVE NITROGEN IN AIR POLLUTION
5.2. HEALTH EFFECTS ASSOCIATED WITH NITRATE IN DRINKING WATER
5.3. HEALTH EFFECTS OF NITRATE AND NITRIC OXIDE IN FOODS
5.4. ECOSYSTEM DAMAGE AND POTENTIAL IMPACTS ON HUMAN HEALTH
5.5. REACTIVE NITROGEN STORAGE IN AQUIFERS AND FUTURE IMPACTS ON DRINKING WATER
5.6. CONCLUDING REMARKS
REFERENCES
FURTHER READING
6 Terrestrial Biodiversity and Surface Water Impacts from Reactive Nitrogen
6.1. WORLDWIDE TERRESTRIAL BIODIVERSITY IMPACTS FROM REACTIVE NITROGEN DEPOSITION
6.2. SOIL ACIDIFICATION AND RELATED IMPACTS ON TERRESTRIAL ECOSYSTEMS
6.3. RIVERINE EXPORT OF REACTIVE NITROGEN
6.4. NUTRIENT‐RELATED IMPAIRMENT OF SURFACE WATERS IN THE UNITED STATES
6.5. IMPACTS TO OTHER SURFACE WATER ECOSYSTEMS
6.6. HARMFUL ALGAL BLOOMS
6.7. MODELING OF REACTIVE NITROGEN TRANSPORT IN SURFACE WATER SYSTEMS
6.8. FURTHER RESEARCH NEEDS AND CONCLUDING REMARKS
REFERENCES
FURTHER READING
7 Groundwater Contamination from Reactive Nitrogen
7.1. REACTIVE NITROGEN CONTAMINATION OF GROUNDWATER IN THE UNITED STATES OF AMERICA
7.2. REACTIVE NITROGEN CONTAMINATION OF GROUNDWATER IN EUROPE
7.3. REACTIVE NITROGEN CONTAMINATION OF GROUNDWATER IN CHINA
7.4. INTERCHANGE OF REACTIVE NITROGEN BETWEEN GROUNDWATER AND SURFACE WATER
7.5. LEGACY REACTIVE NITROGEN STORAGE IN THE VADOSE ZONE AND IN AQUIFERS
7.6. NITRATE CONTAMINATION IN DRINKING WATER FROM PUBLIC SUPPLY AND DOMESTIC WELLS
7.7. MODELING NITRATE TRANSPORT AND VULNERABILITY OF GROUNDWATER TO CONTAMINATION
REFERENCES
FURTHER READING
8 Nitrate Contamination in Springs
8.1. FLORIDA'S NITRATE IMPAIRED SPRINGS
8.2. NITRATE IN SPRINGS IN THE EDWARDS AQUIFER, TEXAS
8.3. NITRATE CONTAMINATION OF SPRINGS IN NORTHEAST SPAIN
8.4. NITRATE IN SPRINGS USED FOR DRINKING WATER
8.5. SPRINGS AND WATER QUANTITY ISSUES
REFERENCES
FURTHER READING
9 Co‐occurrence of Nitrate with Other Contaminants in the Environment
9.1. NITROGEN AND PHOSPHORUS
9.2. NITRATE AND PATHOGENS
9.3. TRACE ELEMENT CONTAMINATION ASSOCIATED WITH NITRATE
9.4. NITRATE AND PESTICIDES
9.5. NITRATE AND ORGANIC CONTAMINANTS IN GROUNDWATER USED FOR DRINKING WATER
9.6. NITRATE AND EMERGING ORGANIC CONTAMINANTS
9.7. AIR POLLUTION: NITROGEN AND OTHER CONSTITUENTS
REFERENCES
FURTHER READING
10 Economic Costs and Consequences of Excess Reactive Nitrogen
10.1. ECONOMIC COSTS AND CONSEQUENCES OF REACTIVE NITROGEN IN EUROPE
10.2. ECONOMIC COSTS AND CONSEQUENCES OF REACTIVE NITROGEN IN THE UNITED STATES
10.3. ECONOMIC COSTS AND CONSEQUENCES OF REACTIVE NITROGEN IN CHINA
10.4. REDUCING ECONOMIC COSTS ASSOCIATED WITH MANAGING REACTIVE NITROGEN
10.5. CONCLUDING REMARKS
REFERENCES
FURTHER READING
11 Strategies for Reducing Excess Reactive Nitrogen to the Environment
11.1. MAJOR CHALLENGES
11.2. INCREASING NITROGEN USE EFFICIENCY (NUE) IN AGRICULTURE
11.3. NUE FOR THE FOOD PRODUCTION/CONSUMPTION CHAIN
11.4. REDUCING REACTIVE NITROGEN EMISSIONS FROM FOSSIL FUEL COMBUSTION
11.5. REDUCING AND MANAGING REACTIVE NITROGEN IN WASTEWATERS
11.6. ESTIMATING AND REDUCING NITROGEN FOOTPRINTS
11.7. CLOSING REMARKS
REFERENCES
FURTHER READING
INDEX
End User License Agreement
List of Tables
Chapter 2
Table 2.1 Ranges for biological nitrogen fixation in natural and managed ecos...
Table 2.2 Global terrestrial and ocean nitrogen fixation from various process...
Chapter 3
Table 3.1 Point‐source total nitrogen loads (2002) for all facilities, and di...
Table 3.2. Nitrogen fertilizer materials, their formulas, and percent nitroge...
Chapter 6
Table 6.1 Annual average values (kg N/ha) for modeled nitrogen fluxes and ret...
Chapter 7
Table 7.1 Percentages of samples that exceeded the drinking water MCL for nit...
Chapter 8
Table 8.1 Classification system for springs (spring magnitude) according to a...
Chapter 9
Table 9.1 Point‐source nutrient loads (2002) for all facilities, and distribu...
Chapter 10
Table 10.1 Anthropogenic nitrogen sources, systems affected, range of potenti...
Chapter 11
Table 11.1 Results of studies on EEFs.
Table 11.2 Nitrogen footprints (kg N/person/yr) calculated by Galloway et al....
List of Illustrations
Chapter 1
Figure 1.1 A conceptual diagram showing sources of anthropogenic and natural...
Figure 1.2 Plot showing increases in human population and increases in the c...
Figure 1.3 Map showing hypoxic (red circles) and eutrophic (yellow circles) ...
Figure 1.4 Conceptual diagram showing detrimental effects on human health fr...
Chapter 2
Figure 2.1 Main processes and reactions of the nitrogen cycle.
Figure 2.2 Plot showing increases in the creation of reactive nitrogen from ...
Figure 2.3 Plot showing increases in human population and increases in the c...
Figure 2.4 Various processes that create reactive nitrogen and the percentag...
Chapter 3
Figure 3.1 Nitrogen cycling in a geologic context including a summary of the...
Figure 3.2 Major river basins studied by Maupin and Ivahnenko (2011) for the...
Figure 3.3 Urban point sources from wastewater in Europe.
Figure 3.4 A conventional gravity on‐site sewage treatment and disposal syst...
Figure 3.5 Conceptual diagram showing pathways of reactive nitrogen in the a...
Figure 3.6 Map of the United States showing 2010 total deposition of nitroge...
Figure 3.7 Chemical, physical, and biological processes affecting nitrogen t...
Figure 3.8 Reactive nitrogen produced by various processes in Europe and glo...
Figure 3.9 European and global reactive nitrogen inputs from livestock manur...
Figure 3.10 Nitrogen loading onto land areas and aquatic systems as a source...
Chapter 4
Figure 4.1 Ranges of δ
15
N values of nitrate for various sources and sinks (F...
Figure 4.2 Typical ranges of δ
15
N and δ
18
O values of nitrate representing va...
Figure 4.3 Box plots showing the ranges of δ
18
O values of nitrate from nitri...
Figure 4.4 Plot showing the ratio of iodine‐sodium versus bromide concentrat...
Figure 4.5 Plot showing the relation between the Cl/Br mass ratio and the δ
1
...
Figure 4.6 δ
15
N and δ
18
O of nitrate (NO
3
–
) in precipitation, stormwate...
Figure 4.7 Nitrification, denitrification, anammox, and NH
4
+
exchange with a...
Chapter 5
Figure 5.1 Conceptual diagram showing detrimental effects on human health fr...
Figure 5.2 Upper diagram shows private drinking water wells sampled as part ...
Figure 5.3 Map showing hypoxic (red circles) and eutrophic (yellow circles) ...
Chapter 6
Figure 6.1 Distribution of categories of reactive nitrogen deposition and ex...
Figure 6.2 A plot showing the relation between increases in nitrogen loading...
Figure 6.3 Major ecological regions of North America.
Figure 6.4 (a‐f) The model predicted contribution of nitrogen sources in wat...
Figure 6.5 Pie diagram on the left shows removal of reactive nitrogen by aqu...
Figure 6.6 Map showing hypoxic and eutrophic coastal areas around the world....
Figure 6.7 Types of harmful algal bloom (HAB) events in coastal areas of the...
Figure 6.8 Map from Global Ocean Oxygen Network (https://en.unesco.org/go2ne...
Figure 6.9 Map showing the large areal extent of the dead zone (hypoxic zone...
Chapter 7
Figure 7.1 Conceptual model showing generalized groundwater flow paths and t...
Figure 7.2 Map showing the eight different lithologies for principal aquifer...
Figure 7.3 Plot showing the percentage of wells in oxic groundwater from agr...
Figure 7.4 Graph showing the increases in reactive nitrogen (Nr) leakage to ...
Figure 7.5 Conceptual diagram showing various processes affecting nitrate fa...
Figure 7.6 Conceptual diagram showing the interface of the groundwater flow ...
Figure 7.7 Conceptual diagram showing areas where submarine groundwater disc...
Figure 7.8 Map showing the PSW study areas.
Figure 7.9 Simulated contaminant response curves (to 25 years of nitrate con...
Figure 7.10 Conceptual diagram showing three different ways that preferentia...
Figure 7.11 Nolan and Hitt (2006) developed a model (GWAVA‐S) for shallow gr...
Chapter 8
Figure 8.1 Photo showing variations in porosity and underwater caverns in th...
Figure 8.2 Map showing selected springs in the UFA.
Figure 8.3 Examples of Florida springs in the Suwannee River Basin with nitr...
Figure 8.4 Photograph from USGS Circular showing how the clarity of water in...
Figure 8.5 Block diagram showing groundwater flow toward a springs in an agr...
Figure 8.6 Atmospheric input curves for tritium in rainfall (measured in Oca...
Figure 8.7 Map showing selected springsheds (approximate groundwater contrib...
Figure 8.8 Map showing generalized groundwater flowpaths in the Edwards Aqui...
Figure 8.9 Map of the major springs in the Edwards Aquifer in Texas. Map cre...
Figure 8.10 (a) Time series of nitrate concentration in Comal Springs discha...
Figure 8.11 Nitrate‐N in bottled spring waters and municipal supplies in Ala...
Chapter 9
Figure 9.1 Trends in consumption of global mineral fertilizer consumption fo...
Figure 9.2 The use of nitrogen and phosphorus fertilizers in the United Stat...
Figure 9.3 Estimated nitrogen input rate from farm and nonfarm fertilizer an...
Figure 9.4 Boxplots showing concentrations of total nitrogen and phosphorus ...
Figure 9.5 Total nitrogen and total phosphorus concentrations in streams in ...
Figure 9.6 Map showing the higher concentrations of phosphorus from natural ...
Figure 9.7 Pie charts showing the major sources contributing nitrogen and ph...
Figure 9.8 Snapshot of an interactive map of the United States showing trend...
Figure 9.9 Major river basins evaluated for nitrogen and phosphorus load cal...
Figure 9.10 Map showing concentrations of nitrate and uranium in the HP and ...
Chapter 10
Figure 10.1 Economic costs associated with damage from reactive nitrogen in ...
Figure 10.2 Estimated potential damage costs from anthropogenic inputs of re...
Figure 10.3 Estimated tributary nitrate loads to the Laurentian Great Lakes....
Figure 10.4 Spatial distribution of nitrogen loading as a stressor in the La...
Figure 10.5 Map showing location of Lake Okeechobee, Caloosahatchee River, a...
Figure 10.6 Satellite imagery from NOAA showing the progression of cyanobact...
Chapter 11
Figure 11.1 Plot showing increases in human population and increases in the ...
Figure 11.2 Map showing estimated net anthropogenic reactive nitrogen inputs...
Figure 11.3 From Sutton et al. (2013a). Our nutrient world. Trends in global...
Figure 11.4 Sutton et al. (2013a) showed the savings of reactive nitrogen fr...
Figure 11.5 A plot from EUNEP (2015) that shows conceptual model for nitroge...
Figure 11.6 Plot showing trends in the NUE
FC
estimated by Erisman et al. (20...
Figure 11.7 Variation in daily average protein intake per person based on re...
Figure 11.8 Plot from Galloway et al. (2014) showing temporal trends in glob...
Figure 11.9 Variations in the short‐term fate of reactive nitrogen consumed ...
Guide
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PREFACE
Nitrogen, an essential component of the building blocks of life (DNA, RNA, and proteins), can exist in many different forms. The various forms of nitrogen can move or cycle between the atmosphere, biosphere, and hydrosphere. The processes involved in the transfer of these different forms of nitrogen between these systems are collectively referred to as the nitrogen cycle. One form of nitrogen is di‐nitrogen gas (N2), which comprises 78% of all the gases in our atmosphere by volume. Ironically, this form of nitrogen is relatively nonreactive and not directly usable by higher life forms. Fortunately, certain specialized microorganisms can “fix” nitrogen in soils and convert nitrogen gas to inorganic nitrogen forms like ammonia that are available to plants, thereby providing sustenance to all animal life on this planet. This critical process is referred to as biological nitrogen fixation (BNF). Prior to the 19th century, the reactive nitrogen produced by microorganisms (BNF) and from nonbiological processes (e.g., lightning) was balanced by plant uptake and nitrogen losses (denitrification processes) and therefore did not accumulate in the environment. However, in the early 20th century, two scientists discovered a way to synthesize ammonia from nitrogen and hydrogen under high temperature and pressure (Haber–Bosch process). This has led to the production of artificial nitrogen fertilizers, which has grown exponentially since the 1950s and is projected to substantially grow into the future due to increasing demand and utilization. One certainly cannot discount the enormous benefits from nitrogen fertilizer use particularly in developing countries, which has led to an increase in food production and substantial reduction in malnutrition. However, the abundance of inexpensive fertilizer has led to its excessive use throughout the industrialized world, which created a surplus of nitrogen that was followed by substantial releases of reactive nitrogen to the environment.
While a considerable amount of attention has been devoted to the substantial increases in carbon dioxide in the atmosphere and its relation to climate change and alterations to the carbon cycle. Even though the carbon cycle has been impacted significantly by fossil fuel burning and other sources of carbon dioxide, we will see that the nitrogen cycle has been altered more than the carbon cycle or any other basic element cycle essential to life on earth. A better understanding of how the various forms of nitrogen are transported through the atmosphere, hydrosphere, and biosphere will ultimately lead to better management of reactive nitrogen and help to prevent further degradation of our important environmental systems.
This book discusses how human beings have substantially altered the natural nitrogen cycle and as a result how excess reactive nitrogen (e.g., ammonia, nitrate, nitrite, and nitrogen oxides) have caused widespread environmental degradation, adverse human health effects, and enormous economic costs associated with environmental and health impacts. A few brief examples of detrimental impacts to the environment include widespread harmful algal blooms, ecosystem impairment, loss of biodiversity, fish kills, contamination of drinking water aquifers and surface waters, acidification of soils and water bodies, and air pollution. These detrimental effects to the environment have resulted in various human health maladies including respiratory infections and heart disease linked to air pollution; links between nitrate in drinking water and thyroid disease, neural tube defects, several types of cancers in adults, and methemoglobinemia (blue‐baby syndrome) in infants and respiratory illnesses associated with algal blooms. Economic consequences include staggering and rising costs (in the billions of dollars annually) for treatment of human health maladies, treatment of drinking water and wastewater, removing toxins from harmful algal blooms, restoration of impaired water bodies, improvements to agricultural best management practices, and loss of jobs and revenue related to declines in fishing, ecotourism, recreation, and real estate values.
During my long career as a research hydrologist and environmental scientist, I have investigated the sources, transport, and fate of reactive nitrogen and other contaminants in groundwater and surface water systems in in a variety of environmental settings. In many areas around the world, impacts to the environment from excess reactive nitrogen compounds have continually worsened. I wrote this book because I wanted to provide a better understanding of the environmental, human health, and economic consequences associated with the continual release of excessive amounts of reactive nitrogen from multiple sources, including fertilizers, animal wastes, disposal of human wastewaters, fossil fuel combustion, atmospheric deposition, and mining. Unfortunately, many people (including students, policy makers, teachers, environmental managers, and economic strategists) are not aware of the negative impacts from excess amounts of reactive nitrogen in the environment. This is surprising given that during the past 40 years, there have been numerous national and international scientific studies that have generated hundreds of published reports and articles on various aspects of environmental degradation, human health effects, and economic consequences related to the anthropogenic alteration of the natural nitrogen cycle with an overload of reactive nitrogen species. During the past decade, a wealth of information has been published from extensive studies in the United States, Europe, and China. The material presented in this book addresses this urgent and critical need for integrating and synthesizing previous and new sources of information on environmental, human health, and economic consequences of excess reactive nitrogen in our environment.
The first three chapters of the book present background information. Chapter 1 introduces the overall purpose and scope, and a concise overview of the various issues related to environmental, health, and economic consequences associated with excess reactive nitrogen. Chapter 2 presents an overview of the natural nitrogen cycle and how this natural cycle has been dramatically altered during the past 100 years by anthropogenic activities. Chapter 3 provides detailed information on the major point and nonpoint sources that contribute reactive nitrogen to the environment and the factors that affect nitrogen transport at regional and global scales. Chapter 4 builds on this introductory information and presents information on novel and innovative tools used to identify and quantify sources of nitrate contamination. The next several chapters are devoted to ramifications (and detrimental impacts) from the anthropogenic alteration of the nitrogen cycle including adverse human health impacts (Chapter 5); degradation and contamination of surface waters, groundwater, springs, and ecosystems, and how interactions between groundwater and surface water compound these problems in lakes, streams, and estuaries (Chapters 6–8). Chapter 9 discusses other contaminants that co‐occur with nitrate contamination and originate from various anthropogenic sources. Chapter 10 presents detailed information on economic consequences and costs associated with environmental pollution, human health maladies, clean‐up costs, drinking‐water treatment costs, losses to commercial fishing, tourism, recreational activities, decreased real estate values, and cascading effects to other socioeconomic sectors. A major challenge for humanity is to reduce the significant losses of excess reactive nitrogen to the environment from agricultural activities in developed countries, while maintaining sustainable food production and food security in other parts of the world that have limited access to enough nitrogen to replenish crop uptake. The final book chapter (Chapter 11) discusses effective ways to reduce our nitrogen footprint (locally and globally) from human activities and presents practical strategies and recommendations for restoring water quality in impacted surface water bodies, groundwater and springs, and terrestrial and aquatic ecosystems. Three areas are highlighted where ongoing efforts are being focused in terms of increasing nitrogen use efficiency and sustainability in agricultural systems, reducing the per capita consumption of animal proteins, and decreasing fossil fuel combustion and replacing with alternative energy sources. Our society must be increasingly vigilant in our commitment to address the challenges associated with significantly reducing inputs of reactive nitrogen to prevent further degradation of our surface waters, aquifers, and ecosystems.
Brian G. Katz
ACKNOWLEDGMENTS
I am thankful for the opportunity to write this book, as I have been fortunate to have spent most of my career conducting research investigations on the sources, fate, and transport of reactive forms of nitrogen in a variety of environmental systems. I have received continuous editorial support from Rituparna Bose, Nithya Sechin, Bobby Kilshaw, Danielle Lacourciere, and Gunalan Lakshmipathy at Wiley. I am deeply grateful for the constructive review comments and suggestions from Jill Baron, Rick Copeland, Celeste Lyon, Kirstin Eller, J.M. Murillo, Mary Lynn Musgrove, Stephen Opsahl, Andrew O'Reilly, Carol Wicks, Ming Ye, and several anonymous reviewers. I am also thankful for the contributed figures and photos from Annette Long, Mark Long, Casey McKinlay, and John Moran.
1Introduction
1.1. THE SIGNIFICANCE OF NITROGEN ON EARTH
Nitrogen is essential to sustain life on Earth, as it is a major component of certain essential amino acids and proteins, enzymes, vitamins, and DNA and RNA. Also, nitrogen is contained in chlorophyll, the green pigment in plants that is essential for photosynthesis. Nitrogen, as dinitrogen (N2) gas is the most abundant element in the Earth's atmosphere making up 78% of all gases by volume. Galloway et al. (2003) estimated that the total amount of nitrogen in the atmosphere, soils, and waters of Earth is approximately 4 × 1021 g, which is more than the combined mass of all four other essential elements (carbon, phosphorus, oxygen, and sulfur) that are needed to sustain life. However, rather ironically, this bountiful form of nitrogen (N2 gas) is unusable by most organisms. The strong triple bond between the nitrogen atoms in nitrogen gas molecules makes N2 gas essentially unreactive. Fortunately, certain specialized nitrogen‐fixing microorganisms in soils can transform or convert nitrogen gas to forms that are available to plants (e.g., ammonium, nitrate), thereby providing sustenance to all animal life on this planet. The process by which nitrogen gas is converted by microbes into inorganic nitrogen compounds, such as ammonia, is referred to as biological nitrogen fixation (BNF). BNF accounts for approximately 90% of this transformation, which is performed by certain bacteria (e.g., genus Rhizobium) and blue‐green algae (cyanobacteria). Small amounts of nitrogen gas fixation can occur abiotically, through high temperature processes, such as lightning and ultraviolet radiation, both of which can break the strong triple bond in molecular nitrogen (N2) in the atmosphere. Denitrification is another important process in which microorganisms consume nitrate and convert it to reduced forms of nitrogen and ultimately back to nitrogen gas. This and other key processes of the nitrogen cycle are discussed in more detail in Chapter 2.
1.2. CYCLING OF NITROGEN IN THE ENVIRONMENT
Nitrogen and its various forms can move or cycle between the atmosphere, biosphere, and hydrosphere (Fig. 1.1). The processes involved in the transfer of the different forms of nitrogen between these systems or reservoirs within these systems are collectively referred to as the nitrogen cycle. Prior to the 19th century, the reactive nitrogen produced by BNF and abiotic processes was balanced by plant uptake and denitrification processes and therefore did not accumulate in the environment. As human population increased substantially during the 19th century, there were two main needs for reactive nitrogen: fertilizers and explosives. To meet these needs, large amounts of nitrogen were mined from various sources including naturally occurring nitrate deposits, guano, and coal. The overall dependence on the use of these sources in Europe has been referred to as a “fossil nitrogen economy” (Sutton et al., 2011a). By the end of the 19th century, these sources could not support the growing needs for more reactive nitrogen. Not long after the end of the 19th century, a solution to this problem was discovered. A process was developed in a laboratory in the early 20th century by Fritz Haber (who received a Nobel Prize for Chemistry in 1918) that synthesized ammonia (NH3) from nitrogen and hydrogen under high temperature and pressure. This process was industrialized by Carl Bosch (who received a Noble Prize in 1931) utilizing an iron catalyst along with high temperature (300–500°C) and high pressure (20 MPa) (Fowler et al., 2013). Thus, the combined discoveries of these two men became known as the Haber–Bosch industrial chemical process, which converts hydrogen and atmospheric nitrogen gases by chemical reactions into synthetic ammonia. This process is used mainly to create inorganic fertilizers, which started the extensive human alteration of the natural nitrogen cycle. An estimated 128 teragrams (Tg, 1 × 1012 g; 1 billion kg) of reactive nitrogen are synthetically produced annually from the Haber–Bosch process (Galloway et al., 2008) and used to make fertilizers for agriculture, lawns, and recreational turf grass. Sutton et al. (2011a) have referred to these large amounts of reactive nitrogen produced by the Haber–Bosch process as the “greatest single experiment in global geo‐engineering that humans ever made.” The production of artificial nitrogen fertilizers has grown exponentially since the 1950s and is projected to grow into the future due to increasing demand and utilization (e.g., Erisman et al., 2015; Nielsen, 2005). The abundance of inexpensive fertilizer led to its excessive use throughout the industrialized world, which created a surplus of nitrogen that was followed by substantial releases of reactive nitrogen to the environment. Global increases in reactive nitrogen have resulted from intensive cultivation of legumes, rice, and other crops that result in the conversion of nitrogen gas (N2) to organic nitrogen compounds through human‐induced BNF. The production of reactive nitrogen from Haber–Bosch process was projected to increase from 120 Tg N/yr in 2010 to about 160 Tg N/yr in 2100 (Fowler et al., 2013).
Figure 1.1 A conceptual diagram showing sources of anthropogenic and natural sources of reactive nitrogen, the various forms of nitrogen, and processes in the nitrogen cycle in the atmosphere, hydrosphere, and biosphere.
Source: Modified from Rivett et al. (2008).
The anthropogenic production of reactive nitrogen has increased steadily and significantly since the mid‐20th century as world population increased substantially (Fig. 1.2). Accompanying this increase in population are steady increases in meat and grain production, BNF, and NOx emissions. Galloway et al. (2003) estimated that reactive nitrogen inputs resulting from cultivation of legumes and other aforementioned crops (BNF) increased globally from approximately 15T g N/yr in 1860 to approximately 33 Tg N/yr in 2000. To increase productivity and crop yield per acre worldwide, increased amounts of fertilizer were being using along with fossil fuel burning machines that replace practices that involved manpower and the use of farm animals (Fig. 1.2). Throughout Europe, regional watersheds annually contribute approximately 3700 kg of reactive nitrogen per square kilometer, which is five times the background rate of natural N2 fixation (Sutton et al., 2011a). On a global scale, as a result of intensive farming practices, nitrogen and other nutrients were and are being depleted in some areas and have been concentrated in other areas, leading to a “cascade” of reactive nitrogen (Galloway et al., 2003) through the environment and creating a sequence of harmful environmental effects including ecosystem damages (loss of biodiversity, eutrophication of waters and soils, and soil acidification), increases in greenhouse gas emissions, contamination of drinking water, air pollution, human health maladies, and damages to the ozone layer (Galloway et al., 2008).
Figure 1.2 Plot showing increases in human population and increases in the creation of total anthropogenic reactive nitrogen between 1900 and 2012 (Mton, is millions of tons; kg/ha is kilograms per hectare; and Tg N is teragrams (1012 g) of reactive nitrogen).
Source: With permission from Erisman et al. (2015). Reproduced with permission of WWF.
In addition to inputs of reactive nitrogen from the use of synthetic fertilizers, there are many other point and nonpoint anthropogenic sources that release reactive nitrogen to the environment (Fig. 1.1). Additional amounts of reactive nitrogen are contributed from fossil fuel combustion, which converts both atmospheric nitrogen and fossil nitrogen to reactive oxidized forms (NOx). The amount of reactive nitrogen created from fossil fuel combustion increased from less than 1 Tg N/yr in 1860 to approximately 25 Tg N/yr in 2000 (Galloway et al., 2003; Nielsen, 2005). Anthropogenic inputs of nitrogen to the land surface from animal wastes, human wastewater (septic tanks, wastewater treatment facilities), industrial processes, and atmospheric deposition have also contributed to the substantial alteration of the cycling of nitrogen throughout the world.
The overall fate of anthropogenic reactive nitrogen in the terrestrial biosphere is not well understood. As Galloway et al. (2008) noted, the fate of only 35% of the reactive nitrogen inputs to the terrestrial biosphere were known, which included estimates of 18% exported to and denitrified in coastal ecosystems, 13% deposited to the ocean from the marine atmosphere, and 4% emitted as N2O. Although tropical forests cover only 12% of the earth's surface, it is estimated that they emit about 50% of the N2O to the atmosphere (Townsend et al., 2011). The approximately 65% of the remaining anthropogenic reactive nitrogen is potentially accumulated in soils, vegetation, and groundwater or possibly denitrified to nitrogen gas. However, these estimates have a considerable amount of uncertainty (Galloway et al., 2008).
Overall, freshwater nitrogen loadings worldwide have increased from 21 million tons in preindustrial times to 40 million tons per year in 2009 (Dodds et al., 2009), while riverine transport of dissolved inorganic nitrogen has increased from 2–3 million to 15 million tons. During the last part of the 20th century, increased nitrogen loading to the land surface has caused the natural rate of N fixation to double and the atmospheric deposition rates to increase more than tenfold. This so‐called “greatest single experiment in global geo‐engineering that human ever made” (Sutton et al., 2011a) has led to a legacy of detrimental consequences for human health, terrestrial and coastal ecosystems, and the economy. We now explore in more detail some of these adverse consequences from excess reactive nitrogen in our environment.
1.3. ENVIRONMENTAL CONSEQUENCES OF EXCESS REACTIVE NITROGEN
During the past 50 years, excess reactive nitrogen has had dire consequences for many varied types of environmental systems all over the world (Erisman et al., 2011, 2013, 2015; Payne et al., 2013; Townsend et al., 2003; B. Ward, 2012). As mentioned previously, only a small proportion of the Earth's biota can transform N2 to reactive nitrogen forms. As a result, reactive nitrogen tends to be the limiting nutrient in most natural ecosystems and typically for agricultural systems. Therefore, increased amounts of reactive nitrogen in the environment have led to shifts in plant species composition, decreases in species diversity, habitat degradation, eutrophication, decreases in water transparency, increased biomass of benthic and epiphytic algae, and changes in food‐web processes in terrestrial ecosystems and in coastal waters (Howarth et al., 2000, 2011). These effects are more prevalent in certain areas, such as the highly affected areas in Central and Western Europe, Southern Asia, the eastern United States, and parts of Africa and South America (Erisman et al., 2015).
Figure 1.3 Map showing hypoxic (red circles) and eutrophic (yellow circles) coastal areas around the world.
Source: Modified from the colored figure 4 in Erisman et al. (2015). Reproduced with permission of World Wildlife Fund.
Excess nitrogen in water bodies have led to the proliferation of harmful (toxic) algal blooms, which have been reported in every state in the United States during the past 10 years (U.S. Environmental Protection Agency (U.S. EPA), 2009), as well in as many other parts of the world (Erisman et al., 2015). Nonaquatic animals also are affected when consuming waters‐containing algae. Pets and livestock have died after drinking water containing algal blooms, including 32 cattle on an Oregon ranch in July 2017 (Flesher & Kastanis, 2017). Algal blooms have resulted in numerous beach closures in Florida and a state of emergency was declared in four coastal counties in southeast Florida in 2016. Toxic algal blooms have contaminated waterways from the Great Lakes to Chesapeake Bay, from the Snake River in Idaho to New York's Finger Lakes and reservoirs in California's Central Valley (Flesher & Kastanis, 2017). As of mid‐August 2016, the U.S. EPA noted that states across the United States have reported more than 250 health advisories due to harmful algal blooms that year. The National Aquatic Resource Surveys conducted by the U.S. EPA and state and tribal partners in 2012 found that 34% of the lakes surveyed in the United States had high levels of nitrogen associated with harmful ecological impacts. A survey of rivers and streams in 2009–2010 found that 41% had high levels of nitrogen (https://www.epa.gov/national‐aquatic‐resource‐surveys/data‐national‐aquatic‐resource‐surveys, accessed 19 October 2018). Large algal blooms occurred in the Black Sea in the 1970s and 1980s following the intensive use of fertilizers and livestock production in the Black Sea basin in the 1960s (Bodeanu, 1993; Mee et al., 2005). Most of Europe has a high potential risk of eutrophication of surface freshwaters (Grizzetti et al., 2011) as well as parts of the United States, South America, Australia, and Southeast Asia (Erisman et al., 2015) (Fig. 1.3).
Another severe impact of excessive amounts of reactive nitrogen is the depletion of oxygen (hypoxia), which has led to dead zones in estuaries and other large water bodies. In the United States more than 166 dead zones have been identified and have affected waterbodies such as the Chesapeake Bay (http://www.cbf.org/issues/dead‐zones/, accessed 18 October 2018) and the Gulf of Mexico (Rabalais et al., 2002). The Gulf of Mexico dead zone grew to approximately 5840 mile2 in 2013. This extremely large dead zone results from summertime nutrient pollution from the Mississippi River (excess reactive nitrogen most likely from fertilizers), which drains 31 upstream states (https://www.epa.gov/nutrientpollution/sources‐and‐solutions). Recent studies have indicated that there could be more than 500 coastal dead zones worldwide (Fig. 1.3), with numbers possibly doubling each decade (Breitburg et al., 2018, Conley et al., 2009, Diaz & Rosenberg, 2008). Dead zones have increased in large coastal areas of the Adriatic Sea, the Black Sea, the Kattegat, and the Baltic Sea (Diaz & Rosenberg, 2008).
Nitrogen gases, aerosols, and dissolved compounds in air that contain NO, N2O, nitrate, ammonia, and ammonium can have injurious and phytotoxic effects on the above ground parts of plants (e.g., trees, shrubs, and other vegetation). In the 1980s, foliar impacts to forests were prevalent in North America and Europe due to air pollution containing nitric and sulfuric acids; however, the situation has improved in these areas with air‐pollution control legislation and pollution reduction strategies adopted by some industries. Increased amounts of nitrogen oxides in the atmosphere could also contribute to global climate change and stratospheric ozone depletion (Galloway et al., 2004). Ironically, one potential benefit from increased nitrous oxide emissions is stimulating the sequestration of global CO2 by terrestrial and marine ecosystems. This effect could possibly lower the amounts of the greenhouse gas CO2 released to the atmosphere (Fowler et al., 2015; Zaehle et al., 2011).
Atmospheric deposition of reactive nitrogen also leads to acidification of soils and surface waters. During 2000–2010, Peñuelas et al. (2013) reported that global land had received more than 50 kg/ha accumulated N deposition. They found that nitrogen additions to the land surface significantly reduced soil pH by 0.26 on average globally. Soils in many places around the world are particularly sensitive to nitrogen deposition, with buffering likely transitioning from base cations (Ca, Mg, and K) to nonbase cations (Al and Mn), which could have a toxic impact for terrestrial ecosystems (Bowman et al., 2008; Tian & Niu, 2015). Significant decreases in forest and grassland productivity have been observed when reactive nitrogen deposition increases above threshold levels. These adverse effects could promote biodiversity changes through the food chain, affecting insects, birds, and other animals that depend on these food sources (Erisman et al., 2013). Acidification of surface waters (lakes, streams, oceans) in many places around the world also has increased and has had detrimental effects on biota (Curtis et al., 2005; Doney et al., 2007).
Ammonia emissions to the atmosphere also have increased during the past several decades (Ackerman et al., 2018) and can result in the formation of fine particulate matter through reactions with nitric and sulfuric acids. These harmful compounds in the atmosphere can be dispersed over large areas of the world, resulting in eutrophication and acidification of terrestrial, freshwater, and marine habitats (Bobbink et al., 2010; Erisman et al., 2015). Also, deposition of ammonia can damage sensitive vegetation, particularly bryophytes and lichens that consume most of their nutrients from the atmosphere (Sheppard et al., 2011). Sala et al. (2000) noted that certain biomes (particularly northern temperate, boreal, arctic, alpine, grassland, savannah, and Mediterranean) are very sensitive to reactive nitrogen deposition because of the limited availability of nitrogen in these systems under natural conditions.
1.4. ADVERSE HUMAN HEALTH IMPACTS
The widespread alteration of the nitrogen cycle from the production and use of synthetic fertilizers has both positive and negative consequences for human health. One cannot discount the huge benefits from nitrogen fertilizer use in developing countries, which has led to an increase in food production and substantial reductions in malnutrition. With better nutrition, healthier diets can lead to more efficient immune response to parasitic and infectious diseases (Nesheim, 1993). Although, shortages of food and malnutrition still exist in many large parts of the world.
Increases in reactive nitrogen compounds in the atmosphere (air pollution) and drinking water have had direct negative effects on human health. Townsend et al. (2003) show schematically how the net public health benefit from human fixation and use of reactive nitrogen has peaked and declined as a result of an exponential increase in air and water pollution and ecological feedbacks to disease (Fig. 1.4). Increased emissions of nitrogen oxides in urban areas have resulted from fossil fuel combustion. In other areas, biomass burning and volatilization of fertilizers emit large quantities of reactive nitrogen, including ammonia and nitrogen oxides. Elevated nitrogen oxides enhance the production of tropospheric ozone (O3) at low altitudes and aerosols, which can cause coughs, asthma, and other reactive airways disease, and mortality (Apte et al., 2015; Townsend et al., 2003). At high altitudes and in parts of the stratosphere, ozone can be destroyed due to the production of the catalyst NO as ultraviolet light breaks N2O apart. The destruction of ozone in the stratosphere would allow more ultraviolet light to reach the Earth's surface, possibly causing more skin cancers. Kane (1998) noted that reductions in ozone may result in a 10–20% increase in ultraviolet‐B radiation, and this could explain a 20–40% rise in skin cancer in the human population since the 1970s. Particulate air pollution has also been linked to cardiovascular diseases and overall mortality (Pope et al., 2002). N2O is a potent greenhouse gas with a long residence time in the atmosphere of 120 years (Howarth et al., 2011) and therefore its harmful effects can persist for decades.
Figure 1.4 Conceptual diagram showing detrimental effects on human health from increasing amounts of excess reactive nitrogen from human fixation.
Source: From Townsend et al. (2003). Reproduced with permission of John Wiley & Sons.
Humans are increasingly exposed to elevated levels of reactive nitrogen species (mainly nitrate) in drinking water. The U.S. EPA has set a maximum contaminant level of 10 mg/L (parts per million) for nitrate‐N in drinking water. In the United States, it is estimated that 10–20% of groundwater sources may exceed 10 mg/L for nitrate‐N (Dubrovsky et al., 2010). In 2015, the U.S. EPA reported that 183 community water systems exceeded allowable levels of nitrate in drinking water. Sutton et al. (2011a) estimated that about 3% of the population in 15 European Union countries (EU‐15) that relies on groundwater as a drinking water source is exposed to nitrate concentrations exceeding the drinking water standard of 50 mg NO3/L (equivalent to 11.2 mg N/L, expressed as nitrogen). In addition, it was estimated that 5% of the population using groundwater is chronically exposed to nitrate concentrations exceeding 5.6 mgN/L, which could double the risk of colon cancer for people that consume above median amounts of meat (Sutton et al., 2011a). In many other aquifers around the world, nitrate‐N concentrations exceed the maximum contaminant level set by the World Health Organization. Many large aquifers in China have been contaminated with elevated nitrate‐N concentrations (S. Wang et al., 2016b). About 90% of China's shallow groundwater is polluted, and nitrate is considered one of the pollutants of main concern (Qiu, 2011).
Numerous health effects have been associated with elevated nitrate levels in drinking water, including methemoglobinemia (elevated levels of methemoglobin in blood which leads to decreased oxygen availability to tissues, mostly affects babies), reproductive problems, and cancer. Recent studies during the past 20 years have reported that nitrate‐N concentrations even below the maximum contaminant level of 10 mg/L can cause other health maladies including non‐Hodgkins's lymphoma (M.H. Ward et al., 1996, 2005, 2018) and increased risk of bladder and ovarian cancers (Weyer et al., 2001).
A developing area of interdisciplinary research is investigating the links between ecosystem damages and human diseases. For example, Townsend et al. (2003) hypothesized that an increase in nutrient availability can favor opportunistic, disease‐causing organisms and could lead to changes in the epidemiology of human diseases. Johnson et al. (2010) referred to studies that showed that ecological changes related to nutrient enrichment often aggravate infection and disease caused by “generalist” parasites with direct or simple life cycles. More recently, reports of attacks to the immune systems of sport fisherman in Lake Erie were linked to algal blooms (Flesher & Kastanis, 2017). Studies have reported associations between algal blooms with cholera outbreaks and correlations between inorganic nutrient concentrations and abundances of mosquitoes that can carry pathogenic microorganisms (Camargo & Alonso, 2006).
1.5. LEGACY REACTIVE NITROGEN STORAGE IN THE SUBSURFACE
Comparably disturbing, but not widely acknowledged, are the large amounts of reactive nitrogen, mostly in the form of nitrate, that leaches below the root zone in soils to the vadose (unsaturated) zone (the material between the base of the soil to the water table at the top of the saturated zone) and eventually to groundwater (aquifers) where nitrate can be stored (Walvoord et al., 2003; L. Wang et al., 2013, 2016a). This is especially prevalent in agricultural areas where there has been a surplus of nitrogen added to cropland. Ascott et al. (2017) assessed global patterns of nitrate storage in the vadose zone by using estimates of groundwater depth and nitrate leaching for the period 1900–2000. They estimated a peak global storage of 605–1814 Tg of nitrate in the vadose zone, with the highest storage per unit area in North America, China, and Europe (areas with thick vadose zones and extensive historical agricultural activities).
Several recent studies have shown that groundwater nitrogen applied decades ago can still be found in aquifers (Basu et al., 2012; McMahon et al., 2006; Meals et al., 2010; Puckett et al., 2011; Sanford & Pope, 2013; Sebillo et al., 2013). Legacy nitrogen stored in the subsurface over long periods of time can slowly be released to streams and large rivers (Van Meter & Basu, 2015, 2017; Van Meter et al., 2016, 2017). However, even though substantial decreases in fertilizer applications have been noted in the Netherlands, Denmark, and Germany (where the nitrogen surplus is back to the level of that of 1970), concentrations of nitrate‐N in groundwater have not responded to this decrease of nitrogen surplus (Sutton et al., 2011a). Particularly noteworthy are cases in Eastern European countries where the nitrogen surplus has decreased by half (due to economic and political changes in the early 1990s), however, no improvements in water quality have been observed in streams (Sutton et al., 2011a). This is likely due to the large quantities of nitrate stored in aquifers and released very slowly over time, as a function of the groundwater residence time, which can range from weeks to several thousands of years (Alley et al., 2002; Tesoriero et al., 2013).
In arid environmental systems, an increased reliance on dryland ecosystems for agriculture may result in flushing of naturally occurring nitrate in the unsaturated zone into groundwater in regional basins due to irrigation and vegetation change (Robertson et al., 2017). Thus, the unsaturated zone, an aforementioned important reservoir for the storage and release of reactive nitrogen (mainly in the form of nitrate) over time, has significant implications for global warming, contamination of deeper aquifers used for drinking water supplies, and eutrophication of surface water bodies (Schlesinger, 2009).
1.6. ECONOMIC IMPACTS OF EXCESS REACTIVE NITROGEN
Environmental degradation from excess reactive nitrogen has led to severe economic consequences, mainly associated with treating drinking water and wastewaters, and human health issues associated with air pollution and surface water and groundwater contamination. Human‐caused eutrophication of waterways from excess nutrients has resulted in large revenue losses to the commercial fishing industry (aquaculture, fisheries, and shellfish fisheries), tourism and recreational water usage, loss of real estate values for waterfront property, and threatened and endangered species. Dodds et al. (2009) provided a detailed economic analysis of the losses associated with environmental impacts related to eutrophication in the United States and reported a conservative estimate of potential losses totaling over $2.2 billion annually. This estimate did not include additional water treatment costs related to taste and odor problems. Sobota et al. (2015) estimated reactive nitrogen leakage for large watersheds in the United States and accounted for economic costs associated with mitigation, remediation, direct damage, human health, agriculture, ecosystems, and climate. They reported estimated annual damage costs of up to $2255/ha across watersheds, with a median value of $252/ha/yr. For the entire United States, Sobota et al. (2015) estimated environmental damages from reactive nitrogen in the early 2000s that ranged from $81 to $441 billion per year.
Based on information from multiple studies conducted during 2000 through 2012, the U.S. EPA compiled extensive information on costs associated with adverse impacts of nutrient pollution in the environment and reducing nutrient pollution from various point and nonpoint sources (U.S. EPA, 2015). The following categories were identified in the report and demonstrate how costs can have cascading economic impacts through many different socioeconomic sectors. For example, losses in tourism and recreation associated with algal blooms can include decreased restaurant sales and hotel stays, loss of tourism‐related jobs, closure of lakeside businesses, and decreased tourism‐related spending. Negative impacts to commercial fishing throughout coastal areas has included reduced harvests, fishery closures, loss of jobs, and increased processing costs related to elevated risks associated with shellfish poisoning. There also have been significant losses in property values of waterfront property and nearby homes associated with decreases in water clarity, algal mats, and increased pollutant concentrations. Algal blooms have caused a variety of injurious health effects in humans and animals through direct contact with skin during recreational activities, drinking water consumption, intake of contaminated shellfish (can cause neurotoxic shellfish poisoning and other serious health effects). A study in Florida, reported that increased emergency room visits cost Sarasota County more than $130,000 (in 2012 dollars) to treat respiratory illnesses associated with increased algal blooms (Hoagland et al., 2009). Waters containing algal toxins and with taste and odor problems have significant treatment costs. The U.S. EPA 2015 report also estimated the extensive mitigation and restoration costs for coastal and inland waterways contaminated with algal blooms. Also, various organic forms of nitrogen can be stored in bottom sediments of lakes, estuaries, and other waterbodies and then be released to the water column during storms and other weather‐related events. In‐lake treatment and mitigation costs may include aeration, alum treatments, biomanipulation, and dredging. There are enormous costs to Federal, State, and local agencies associated with restoring impaired waterbodies, including developing watershed management plans, total maximum daily loads (TMDLs), nutrient trading and other programs. High costs associated with nutrient pollution control from point and nonpoint sources include upgrades to municipal wastewater treatment plants (advanced wastewater treatment to meet TMDLs for impaired waters), conversion of septic tanks to centralized wastewater treatment systems, industrial and agricultural wastewater treatment, and the control of elevated levels of nitrogen in stormwater runoff.
Over the past two decades, the State of Florida has spent hundreds of millions of dollars on restoration of large springs and their spring runs with impaired water quality and adversely affected ecosystems. More than 1000 springs have been identified in Florida, and over the past several decades, their water quality has become degraded (Katz, 2004; Scott, 2002). Elevated nitrate‐nitrogen concentrations have resulted in excessive algal growth that has depleted aquatic oxygen levels and negatively impacted the health of the spring ecosystem. About 30 of these springs have been given special status because they have been deemed by the Florida Legislature to be a unique part of the state's scenic beauty, provide critical habitat, and have immeasurable natural, recreational, economic, and inherent value. Studies have indicated that springs contribute significantly to Florida's economy, with more than 100 million dollars per year from visitor spending, jobs, and associated hotel stays and sales at restaurants, dive shops, and other expenses. In 2016, the Florida Legislature enacted the “Florida Springs and Aquifer Protection Act,” which provides continued funding ($50 million per year) and special status and protection to historic first‐magnitude springs (each discharging more than 2.8 m3/s of water from the Floridan aquifer) and to other springs of special significance. The act requires the Florida Department of Environmental Protection to set restoration targets and adopt a basin management action plan for each water‐quality impaired system to reduce nutrient loading and improve water quality over the next 20 years.
In England and Wales, Pretty et al. (2003
