Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen
Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen I Published by the Ecological Society of America Number 3, Summer 1998 ssues in Ecology Photo by Brett Johnson
Issues in Ecology Number 3 Summer 1998 Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen SUMMARY Runoff from our farms and cities is a major source of phosphorus(P)and nitrogen (N)entering rivers,lakes,and coastal waters.Acid rain and airbomne pollutants generated by human activities also supply N to surface waters.These nutrient sources are called"nonpoint"because they involve widely dispersed activities.Nonpoint inputs are difficult to measure and potion in the nited Statest acts nd.In nrichment ith wide range of probl over ms,including toxic alga blooms,k sof xyen.fish kills s seagrass beds and other aquatic vegetation,degradation of coral reefs,and loss of biodiversity- -including species important to commercial and sport fisheries and shellfish industries.Thus,nutrient fouling seriously degrades our marine and freshwater resources and impairs their use for industry.agriculture.recreation.drinking water,and other purposes. Based on our review of the scientific literature,we are certain that Eutrophication caused by over-enrichment with P and N is a widespread problem in rivers,lakes,estuaries,and coastal oceans. .Nonpoint pollution is a major source of P and N to surface waters of the United States.The major sources of non point pollution are agriculture and rban activity,incuding industry and transportation. In the U.S. and of P ar d N to agri n the form of fertilizers exceed outputs of nutrients in th form of crops Htehdknsisofthcesiotkaecealeisusiomsnwhdhmaurepoteionecetsthenedbsofcepowhdhthke manure is applied.The density of animals on the land is directly related to nutrient flows to aquatic ecosystems. Excess fertilization and manure production cause a P surplus,which accumulates in soil.Some of this surplus is transported in soil runoff to aquatic ecosystems. Excess fertilization and manure production create a N surplus on agricultural lands.Surplus N is mobile in many soils.and much leaches int rface wate r perc olatilize to the atm redeposited far downwind as acid rainor dry pollutants that may eventually reach distant aquaticecosystems contin not inevitable,ho available that can decrease the flow of nonpoint P and N into surface waters. From our review of the available scientific information,we are confident that: Nonpoint pollution of surface waters with P and N coud be decreased by reducing excess nutrient flows in agricultural systems,reducing farm and urban runoff.and reducing N emissions from fossil fuel burning. Eutrophication of aquatic ecosystems can be reversed by decreasing input rates of P and N.However,rates of recovery are highly variable,and recovery is often slow. The panel finds that the roots of the problem of nonpoint pollution and eutrophication are well understood scientifically. There is a critical need for creative efforts to translate this understanding into effective policies and practices that will lead to protection and recovery of our aquatic resources
1 Issues in Ecology Number 3 Summer 1998 Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen SUMMARY Runoff from our farms and cities is a major source of phosphorus (P) and nitrogen (N) entering rivers, lakes, and coastal waters. Acid rain and airborne pollutants generated by human activities also supply N to surface waters. These nutrient sources are called nonpoint because they involve widely dispersed activities. Nonpoint inputs are difficult to measure and regulate because of their dispersed origins and because they vary with the seasons and the weather. Yet nonpoint inputs are the major source of water pollution in the United States today, and their impacts are profound. In aquatic ecosystems, overenrichment with P and N causes a wide range of problems, including toxic algal blooms, loss of oxygen, fish kills, loss of seagrass beds and other aquatic vegetation, degradation of coral reefs, and loss of biodiversity including species important to commercial and sport fisheries and shellfish industries. Thus, nutrient fouling seriously degrades our marine and freshwater resources and impairs their use for industry, agriculture, recreation, drinking water, and other purposes. Based on our review of the scientific literature, we are certain that: • Eutrophication caused by over-enrichment with P and N is a widespread problem in rivers, lakes, estuaries, and coastal oceans. • Nonpoint pollution is a major source of P and N to surface waters of the United States. The major sources of nonpoint pollution are agriculture and urban activity, including industry and transportation. • In the U.S. and many other nations, inputs of P and N to agriculture in the form of fertilizers exceed outputs of those nutrients in the form of crops. • High densities of livestock have created situations in which manure production exceeds the needs of crops to which the manure is applied. The density of animals on the land is directly related to nutrient flows to aquatic ecosystems. • Excess fertilization and manure production cause a P surplus, which accumulates in soil. Some of this surplus is transported in soil runoff to aquatic ecosystems. • Excess fertilization and manure production create a N surplus on agricultural lands. Surplus N is mobile in many soils, and much leaches into surface waters or percolates into groundwater. Surplus N can also volatilize to the atmosphere and be redeposited far downwind as acid rain or dry pollutants that may eventually reach distant aquatic ecosystems. If current practices continue, nonpoint pollution of surface waters is virtually certain to increase in the future. Such an outcome is not inevitable, however, because a number of technologies, land use practices, and conservation measures are available that can decrease the flow of nonpoint P and N into surface waters. From our review of the available scientific information, we are confident that: • Nonpoint pollution of surface waters with P and N could be decreased by reducing excess nutrient flows in agricultural systems, reducing farm and urban runoff, and reducing N emissions from fossil fuel burning. • Eutrophication of aquatic ecosystems can be reversed by decreasing input rates of P and N. However, rates of recovery are highly variable, and recovery is often slow. The panel finds that the roots of the problem of nonpoint pollution and eutrophication are well understood scientifically. There is a critical need for creative efforts to translate this understanding into effective policies and practices that will lead to protection and recovery of our aquatic resources.
Issues in Ecology Number 3 Summer 1998 Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen by Stephen Carpenter,Chair,Nina F.Caraco. David L.Correll.Robert W.Howarth, AndrewN.Sharpley.and Val H.Smith INTRODUCTION component species as well as the ame nities that these From ancient times.people have chosen to live ecosystems once provided to society.Water shortages. near water,settling in river valleys,beside lakes,or along for instance,are increasingly common and likely to be coastlines.The attractions of water are as diverse as hu- come more severe in the future.Water shortages and man needs and aspirations.Clean water is a crucial re. poor water quality are linked,because contamination re. source for drinking.irrigation,industry,transportation. duces the supply of water and increases the costs of treat recreation.fishing hu support of biodiv ing w ake it safe for hu ven sheer esthetic enjoyment For as long as umans hav lived near waterways.they have also used them to wash increasing water supplies. away and dilute society's wastes and pollutants.But with The most common impairment of surface waters growing populations and increased production and con- in the U.S.is eutrophication caused by excessive inputs sumption,this long tradition of flushing wastes down- of phosphorus(P)and nitrogen (N).Impaired waters are defined as those that are not suitable for designated uses ased in reation.or fish recent decades .and the ing. Counts water quality in many rivers,lakes and coastal oceans paired lake area and 6%of the impaired river reaches ir This degradation shows up in the disruption of natural the U.S.and is also the most widespread pollution prob Inputs Outputs Transport processes N Dissolved】 Figure I-Nutrients inm ure and fertilizers are tra rted tolakes,rivers,and cea Excessive nutrient inputs result in degradation of water quality,causing the disruption of aquatic ecosystems
Issues in Ecology Number 3 Summer 1998 2 by Stephen Carpenter, Chair, Nina F. Caraco, David L. Correll, Robert W. Howarth, Andrew N. Sharpley, and Val H. Smith Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen INTRODUCTION From ancient times, people have chosen to live near water, settling in river valleys, beside lakes, or along coastlines. The attractions of water are as diverse as human needs and aspirations. Clean water is a crucial resource for drinking, irrigation, industry, transportation, recreation, fishing, hunting, support of biodiversity, and sheer esthetic enjoyment. For as long as humans have lived near waterways, they have also used them to wash away and dilute societys wastes and pollutants. But with growing populations and increased production and consumption, this long tradition of flushing wastes downstream has begun to overwhelm the cleansing capacities of the Earths waters. Pollutant inputs have increased in recent decades, and the result has been degradation of water quality in many rivers, lakes and coastal oceans. This degradation shows up in the disruption of natural aquatic ecosystems, and the consequent loss of their component species as well as the amenities that these ecosystems once provided to society. Water shortages, for instance, are increasingly common and likely to become more severe in the future. Water shortages and poor water quality are linked, because contamination reduces the supply of water and increases the costs of treating water to make it safe for human use. Thus, preventing pollution is among the most cost-effective means of increasing water supplies. The most common impairment of surface waters in the U.S. is eutrophication caused by excessive inputs of phosphorus (P) and nitrogen (N). Impaired waters are defined as those that are not suitable for designated uses such as drinking, irrigation, industry, recreation, or fishing. Eutrophication accounts for about half of the impaired lake area and 60% of the impaired river reaches in the U.S. and is also the most widespread pollution probFigure 1 - Nutrients in manure and fertilizers are transported to lakes, rivers, and oceans. Excessive nutrient inputs result in degradation of water quality, causing the disruption of aquatic ecosystems. Artwork by W. Feeny
Issues in Ecology Summer 1998 Sources of Point and Nonpoint Pollution POINT SOURCES NONPOINT SOURCES Wastewater efuent.both municipal and indus ff and leachate from waste disposal site Runoff and infiltration from animal feed lots Runoff from mines.oil fields.and unsewered indus nal sites nofromcotruction sites arger than w Atmospheric deposition over a water surface hectar Activities on land that generate contaminants, such a ows of combined storm and sanitary ogging. ersion,construction and devel sewer opment of land or waterways Figure 2.Sources of point and nonpoint chemical inputs to lakes,rivers.and oceans recognized by statutes. Pollutant discharges from point sources tendto be continous and therefore relatively simple to identify and monitor Nonpoint source owever,arise fror suite of activi arge areas re difficult to control lem of U.S.estuaries Other important causes of sur- many cases over recent decades,point sources face water degradation are siltation caused by ero- of water pollution have been reduced,owing to their relative sion from agricultural,logging,and construction ac- ease of identification and control.However.point sources tivities (silt also carries nutrients.contributing to are still substantial in some parts of the world and may in- eutrophication):acidification from atmospheric sources and crease with future expansion of urban areas.aquaculture mine drainage contamination by toxins:introduction o and factory"farms,"such as hog factories.This report species such as zebra sels and sea lampreys;an focuses on nonp int ources,not because point source hydrologic changescreated by dams.drain- are unimportant.but because nonpoint inputs are ofter ing of wetlands,and other waterworks. overlooked and pose a significant environmental challenge Chemical inputs to rivers,lakes,and oceans origi- Nonpoint inputs are the major source of water pol nate either from point or nonpoint sources.Point sources lution in the U.S.today.The National Water Quality Inven include effluent pipes from municipal sewage treatment tory stated in 1988 that"the more we look.the more we Pollutant discha rges from such find.”For exar %to%of eutro ophic lakes would variability ove req water quality often t they can be asuring di even if point inputs were reduced to zero charge and chemical concentrations periodically at a single This report primarily addresses nonpoint pollution place.Consequently,point sources are relatively simple of water by P and N because: to monitor and regulate,and can often be controlled by Eutrophication is currently the most widespread water treatment at the source.Nonpoint inputs can also be quality problem in the U.S.and many other nations. ofte and linked Restoration of most eutrophic waters requires the ity such asp nting and plov reduc of nonpoint i ing or irregular events such heavy rains or major con A sound scie struction.Nonpoint inputs often arise from a varied suite nonpoint nutrient pollution exists.In many cases,we of activities across extensive stretches of the landscape have the technical knowledge needed to decrease and materials enter receiving waters as overland flow nonpoint pollution to levels compatible with water underground seepage,or through the atmosphere.Con quality standards. sequently,nonpoint sources are difficult to measure a The most important barriers to control of nonpoin regulate. Control l of non oint pollutio ters on land appe to be social political,and management practices and regulation of the release of We hope that ou summary of the sci pollutants to the atmosphere.Such controls may affect entific basis of the problem will inform and support the daily activities of millions of people. debate about solutions
3 Issues in Ecology Number 3 Summer 1998 lem of U.S. estuaries. Other important causes of surface water degradation are siltation caused by erosion from agricultural, logging, and construction activities (silt also carries nutrients, contributing to eutrophication); acidification from atmospheric sources and mine drainage; contamination by toxins; introduction of exotic species such as zebra mussels and sea lampreys; and hydrologic changes created by dams, channelization, draining of wetlands, and other waterworks. Chemical inputs to rivers, lakes, and oceans originate either from point or nonpoint sources. Point sources include effluent pipes from municipal sewage treatment plants and factories. Pollutant discharges from such sources tend to be continuous, with little variability over time, and often they can be monitored by measuring discharge and chemical concentrations periodically at a single place. Consequently, point sources are relatively simple to monitor and regulate, and can often be controlled by treatment at the source. Nonpoint inputs can also be continuous, but are more often intermittent and linked to seasonal agricultural activity such as planting and plowing or irregular events such as heavy rains or major construction. Nonpoint inputs often arise from a varied suite of activities across extensive stretches of the landscape, and materials enter receiving waters as overland flow, underground seepage, or through the atmosphere. Consequently, nonpoint sources are difficult to measure and regulate. Control of nonpoint pollution centers on land management practices and regulation of the release of pollutants to the atmosphere. Such controls may affect the daily activities of millions of people. In many cases over recent decades, point sources of water pollution have been reduced, owing to their relative ease of identification and control. However, point sources are still substantial in some parts of the world and may increase with future expansion of urban areas, aquaculture, and factory farms, such as hog factories. This report focuses on nonpoint sources, not because point sources are unimportant, but because nonpoint inputs are often overlooked and pose a significant environmental challenge. Nonpoint inputs are the major source of water pollution in the U.S. today. The National Water Quality Inventory stated in 1988 that the more we look, the more we find. For example, 72% to 82% of eutrophic lakes would require control of nonpoint P inputs to meet water quality standards, even if point inputs were reduced to zero. This report primarily addresses nonpoint pollution of water by P and N because: • Eutrophication is currently the most widespread water quality problem in the U.S. and many other nations. • Restoration of most eutrophic waters requires the reduction of nonpoint inputs of P and N. • A sound scientific understanding of the causes of nonpoint nutrient pollution exists. In many cases, we have the technical knowledge needed to decrease nonpoint pollution to levels compatible with water quality standards. • The most important barriers to control of nonpoint nutrient pollution appear to be social, political, and institutional. We hope that our summary of the scientific basis of the problem will inform and support debate about solutions. Figure 2 - Sources of point and nonpoint chemical inputs to lakes, rivers, and oceans recognized by statutes. Pollutant discharges from point sources tend to be continous and therefore relatively simple to identify and monitor. Nonpoint sources, however, arise from a suite of activities across large areas and are much more difficult to control. POINT SOURCES • Wastewater effluent, both municipal and industrial • Runoff and leachate from waste disposal sites • Runoff and infiltration from animal feed lots • Runoff from mines, oil fields, and unsewered industrial sites • Storm sewer outfalls from cities with a population of greater than 100,000 • Runoff from construction sites larger than two hectares • Overflows of combined storm and sanitary sewers NONPOINT SOURCES • Runoff from agriculture (including return flow from irrigated agriculture) • Runoff from pasture and range • Urban runoff from unsewered areas and sewered areas with a population of less than 100,000 • Septic leachate and runoff from failed septic systems • Runoff from construction sites smaller than two hectares • Runoff from abandoned mines • Atmospheric deposition over a water surface • Activities on land that generate contaminants, such as logging, wetland conversion, construction and development of land or waterways Sources of Point and Nonpoint Pollution
Issues in Ecology Number 3 Summer 1998 WHY IS NONPOINT P AND N POLLUTION A CONCERN? reand rinkingAsv nuisance pl as they work to break do omposers prolife erate wn this plant matter.the bac Eutrophication:Scope and Causes teria consume more dissolved oxygen from the water. Eutrophication means the fertilization of sur- The result can be oxygen shortages that cause fish face waters by nutrients that were previously scarce kills.Eutrophication can lead to loss of habitats such Over geologic time,eutrophication through nutrient as aquatic plant beds in fresh and marine waters and and sed inflow is a nat ral a s by which coral reefs along tropical coasts.Thus,eutre rophica warn y hun tion plays a role in th loss of aquatic biodiversity. activities are greatly accelerating the process.Fresh Explosive growths of nuisance algae are among water eutrophication has been a growing problem for the most pernicious effects of eutrophication.These al decades.Both p and n gae produce structures or supplies contribute to it, chemicals that are harm although for many lakes Lake Aging ful to other organisms.in nputs are Natural Accelerated cluding livestock or hu Eutrophication is Process by Land Use mans rine ecosys tems.algal blooms known also widespread and rap- as red or brown tide: idly expanding in estuar cause widespread prob ies and coastal seas of lems by releasing toxins the developed world.For and by spurring oxygen depletion a th y die decompose [ha tems, dence of harmful alga most limiting to produc blooms in coastal ocean tion of plant material such as algae (primary UR has increased in recent vears This increase is productivity).and so N E linked to coastal eutrophi inputs are the most prob- Cation and other factors Alt ough N is such as changesin arin the major factor in food webs that may in eutrophication of most crease decomposition and estuaries and coastal nutrient recvcling or re seas p is also an essen duce populations of algae tial element that contrib grazing fish.Algal bloo utes to coastal eutronhi tion.It is,in fact,the negative im dominant control on pri Figure 3-Over extended periods of time.lakes tend to fill with sheries They caus mary production in some nent through natu al processes (l shellfish poisoning in hu coastal ecosystems. nd use and nutrient inp are accelerating this proce mans.and have caused lakes with sediments and algal blooms in just a few years(night). significant mortality in Consequences marine mammals A toxic Eutrophication has many negative effects on dinoflagellate known as Pfiesteria has been associated aquatic systems. the most visible conse ith mo tality finfish the U.S.Atlantic oast.The quence is th proliferation of algae,which can turr highly toxic,volatile chemi al produ ced by this di lage water a turbid green and coat shallower surfaces with late can also cause neurological damage to people who "pond scum."This increased growth of algae and also come in contact with it. aquatic weeds can degrade water quality and inter- In freshwater,blooms of cyanobacteria(formerly fere with use of the water for fisheries.recreation called blue-green algae)are a prominent symptom of
Issues in Ecology Number 3 Summer 1998 4 WHY IS NONPOINT P AND N POLLUTION A CONCERN? Eutrophication: Scope and Causes Eutrophication means the fertilization of surface waters by nutrients that were previously scarce. Over geologic time, eutrophication through nutrient and sediment inflow is a natural aging process by which warm shallow lakes evolve to dry land. Today human activities are greatly accelerating the process. Freshwater eutrophication has been a growing problem for decades. Both P and N supplies contribute to it, although for many lakes excessive P inputs are the primary cause. Eutrophication is also widespread and rapidly expanding in estuaries and coastal seas of the developed world. For most temperate estuaries and coastal ecosystems, N is the element most limiting to production of plant material such as algae (primary productivity), and so N inputs are the most problematic. Although N is the major factor in eutrophication of most estuaries and coastal seas, P is also an essential element that contributes to coastal eutrophication. It is, in fact, the dominant control on primary production in some coastal ecosystems. Consequences Eutrophication has many negative effects on aquatic ecosystems. Perhaps the most visible consequence is the proliferation of algae, which can turn water a turbid green and coat shallower surfaces with pond scum. This increased growth of algae and also aquatic weeds can degrade water quality and interfere with use of the water for fisheries, recreation, industry, agriculture, and drinking. As overabundant nuisance plants die, bacterial decomposers proliferate; as they work to break down this plant matter, the bacteria consume more dissolved oxygen from the water. The result can be oxygen shortages that cause fish kills. Eutrophication can lead to loss of habitats such as aquatic plant beds in fresh and marine waters and coral reefs along tropical coasts. Thus, eutrophication plays a role in the loss of aquatic biodiversity. Explosive growths of nuisance algae are among the most pernicious effects of eutrophication. These algae produce structures or chemicals that are harmful to other organisms, including livestock or humans. In marine ecosystems, algal blooms known as red or brown tides cause widespread problems by releasing toxins and by spurring oxygen depletion as they die and decompose. The incidence of harmful algal blooms in coastal oceans has increased in recent years. This increase is linked to coastal eutrophication and other factors, such as changes in marine food webs that may increase decomposition and nutrient recycling or reduce populations of algaegrazing fish. Algal blooms have severe negative impacts on aquaculture and shellfisheries. They cause shellfish poisoning in humans, and have caused significant mortality in marine mammals. A toxic dinoflagellate known as Pfiesteria has been associated with mortality of finfish on the U.S. Atlantic coast. The highly toxic, volatile chemical produced by this dinoflagellate can also cause neurological damage to people who come in contact with it. In freshwater, blooms of cyanobacteria (formerly called blue-green algae) are a prominent symptom of Figure 3 - Over extended periods of time, lakes tend to fill with sediment through natural processes (left). Currently, changes in land use and nutrient inputs are accelerating this process, filling lakes with sediments and algal blooms in just a few years (right). Artwork by W. Feeny
Issues in Ecology Number 3 Summer 1998 Adverse Effects of Eutrophication Increased biomass of phytoplankton Shifts in phytopankton to blomfoming ecies which may be toxirind ncreasesboo lainonont) omass c Taste.odo Decreases in perceived esthetic value of the water body Figure 4-Eutrophication,caused by excessive inputs of phosphorus(P)and nitrogen(N).has many adverse effects on lakes.reservoirs.rivers,and coastal oceans(modified from Smith 1998) eutrophication.These blooms contribute to a wide range remain the primary source of N inputs.And although of water-related problems including summer fish kills,foul nonpoint inputs of P are often significant,point sources odors,and unpalatable tastes in drinking water.Further. supply the highest inputs of P in many marine environ- more.when such water is processed in water treatment ments. mntpioEog itu sreacts with chlo mm carcinogens known as trihalomethanes.Wa Remediation Reversal of eutrophication requires the reduction liver are released when cyanobacterial blooms die or are of P and N inputs,but recovery can sometimes be accel ingested.These can kill livestock and may pose a serious erated by combining input controls with other manage health hazard to humans. ment methods.In fact,active human intervention may be necessary in some cases because the eutrophic state is stable in lakes chani npoint sou are now the dominant inputs nper recovery from this degra ded s surface waters. Nonpoint in- clude continuing release of P from accumulations in lake puts of P cause eutrophication across a large area of bottom sediments,loss of submerged plants whose roots lakes and reservoirs in the U.S.Nonpoint sources are served to stabilize sediments,and complex changes in also the dominant contributors of P and N to most the food web such as decreases in grazing fish or zoop rivers in the U.S..although point sources still gen lankton that helped to control growth of nuisance algae more than half of the P a into rivers fron Less is knowr the stabili y of eutrophication ines urbanized areas In one study of 86 ers, tuaries and coastal ocea ns.but the trophic state may N sources were responsible for more than 90%of N be more easily disrupted and remedied there because in inputs to more than half these rivers. Nonpoint P open,well-mixed coastal oceans nutrients may be diluted sources contributed over 90%of the P in a third of and flushed away rapidly.However,in relatively confined. these rivers. shallow marine waters such as the Baltic Sea,nutrients may be trapped and eutrophication may be as persistent sources re the do as it is in lakes. coastineoft entire for instance nonpoint soures of Naresome greater tha Direct Health Effects inputs from wastewater treatment plants.In some Phosphorus in water is not considered directly coastal areas,however,wastewater treatment plants toxic to humans and animals,and because of this,no
5 Issues in Ecology Number 3 Summer 1998 remain the primary source of N inputs. And although nonpoint inputs of P are often significant, point sources supply the highest inputs of P in many marine environments. Remediation Reversal of eutrophication requires the reduction of P and N inputs, but recovery can sometimes be accelerated by combining input controls with other management methods. In fact, active human intervention may be necessary in some cases because the eutrophic state is relatively stable in lakes. Some internal mechanisms that may hamper recovery from this degraded state include continuing release of P from accumulations in lakebottom sediments, loss of submerged plants whose roots served to stabilize sediments, and complex changes in the food web such as decreases in grazing fish or zooplankton that helped to control growth of nuisance algae. Less is known about the stability of eutrophication in estuaries and coastal oceans, but the eutrophic state may be more easily disrupted and remedied there because in open, well-mixed coastal oceans nutrients may be diluted and flushed away rapidly. However, in relatively confined, shallow marine waters such as the Baltic Sea, nutrients may be trapped and eutrophication may be as persistent as it is in lakes. Direct Health Effects Phosphorus in water is not considered directly toxic to humans and animals, and because of this, no eutrophication. These blooms contribute to a wide range of water-related problems including summer fish kills, foul odors, and unpalatable tastes in drinking water. Furthermore, when such water is processed in water treatment plants, the high load of organic detritus reacts with chlorine to form carcinogens known as trihalomethanes. Water-soluble compounds toxic to the nervous system and liver are released when cyanobacterial blooms die or are ingested. These can kill livestock and may pose a serious health hazard to humans. Contribution of Nonpoint Pollution Nonpoint sources are now the dominant inputs of P and N to most U.S. surface waters. Nonpoint inputs of P cause eutrophication across a large area of lakes and reservoirs in the U.S. Nonpoint sources are also the dominant contributors of P and N to most rivers in the U.S., although point sources still generate more than half of the P and N flowing into rivers from urbanized areas. In one study of 86 rivers, nonpoint N sources were responsible for more than 90% of N inputs to more than half these rivers. Nonpoint P sources contributed over 90% of the P in a third of these rivers. For many estuaries and coastal seas, nonpoint sources are the dominant N inputs. Along the entire coastline of the North Atlantic Ocean, for instance, nonpoint sources of N are some 9-fold greater than inputs from wastewater treatment plants. In some coastal areas, however, wastewater treatment plants Figure 4 - Eutrophication, caused by excessive inputs of phosphorus (P) and nitrogen (N), has many adverse effects on lakes, reservoirs, rivers, and coastal oceans (modified from Smith 1998). u Increased biomass of phytoplankton u u Shifts in phytoplankton to bloom-forming species which may be toxic or inedible u u Increases in blooms of gelatinous zooplankton (marine environments) u u Increased biomass of benthic and epiphytic algae u u Changes in macrophyte species composition and biomass u u Death of coral reefs and loss of coral reef communities u u Decreases in water transparency u u Taste, odor, and water treatment problems u u Oxygen depletion u u Increased incidence of fish kills u u Loss of desirable fish species u u Reductions in harvestable fish and shellfish u u Decreases in perceived esthetic value of the water body u Adverse Effects of Eutrophication
Issues in Ecology Summer 1998 Figure 5.Nitrogen and phospho rus pollution causes increased inci- dents of fish kills.Fish die because of toxic algal blooms or the removal drinking water standards have been established for P. to protect babies under 3 to 6 months of age.This Any toxicity caused by P pollution in fresh waters is age group is most sensitive because bacteria that indirect,through stimulation of toxic algal blooms or live in an infant's digestive tract can reduce nitrate to nitrite.which oxidizes hemoglobin and interferes ntrast nitrate pollution poses a direct with the oxy health threat to other mar toxic causes a s ar type of anemia as well as abortions has been linked to toxic effects on livestock and Levels of 40-100 milligrams of nitrate-N per liter also to "blue baby disease"(methemoglobinemia) in livestock drinking water are considered risky un- in infants.The Environmental Protection Agency has less the animals'feed is low in nitrates and forti- established a Maximum Contaminant Level for ni- fied with vitamin A. trate-N in drinking water of 10 milligrams per liter 2 n can lead to the loss of habitats versity. the healthy growth d coverage of ard soft corals resulting from human disturbance,including increased turbidity.in the area of the reef shown on the right
Issues in Ecology Number 3 Summer 1998 6 drinking water standards have been established for P. Any toxicity caused by P pollution in fresh waters is indirect, through stimulation of toxic algal blooms or resulting oxygen depletion. In contrast, nitrate pollution poses a direct health threat to humans and other mammals. Nitrate in water is toxic at high concentrations and has been linked to toxic effects on livestock and also to blue baby disease (methemoglobinemia) in infants. The Environmental Protection Agency has established a Maximum Contaminant Level for nitrate-N in drinking water of 10 milligrams per liter to protect babies under 3 to 6 months of age. This age group is most sensitive because bacteria that live in an infants digestive tract can reduce nitrate to nitrite, which oxidizes hemoglobin and interferes with the oxygen-carrying ability of blood. In cattle, nitrate reduced to nitrite can also be toxic and causes a similar type of anemia as well as abortions. Levels of 40-100 milligrams of nitrate-N per liter in livestock drinking water are considered risky unless the animals feed is low in nitrates and fortified with vitamin A. Figure 5 - Nitrogen and phosphorus pollution causes increased incidents of fish kills. Fish die because of toxic algal blooms or the removal of oxygen from the water as algal blooms decay. Figures 6 and 7 - Eutrophication can lead to the loss of habitats such as coral reefs, therefore contributing to the loss of aquatic biodiversity. Note the healthy growth and coverage of hard corals in the figure on the left, versus the less diverse soft corals resulting from human disturbance, including increased turbidity, in the area of the reef shown on the right. Photos by R.W. Buddemeier, Kansas Geological Survey Photo by Chris Luecke
Issues in Ecology Number 3 Summer 1998 WHAT ARE THE SOURCES OF remain in soils or be exported to surface waters by erosion NONPOINT POLLUTION? or leaching.The majority of applied P remains on crop with only 3 to 20%leaving b Nonpoint P and N pollution isca d primarily by is likely.the ore.that metric tons of P agricultural and urban activities.n the U.S.agriculture has accumulated in the world'scroplands.The standing stock is the predominant source of nonpoint pollution.Wind or of P in the upper lo centimeters of soil in the world's crop rain-bomne deposits from a variety of sources,including lands is roughly 1,300 million metric tons.That means that agriculture and fossil fuel burning.can add significant a net addition of 350 million metric tons between 1950 amounts of N to surface waters. and 1995 would have increased the P content of agricul about 25%.In the U.S.and Eur only abou Agriculture 30%of th Pinput in fertilizers ends up being in orporate On the world's croplands,human additions and into crop plants.resulting in an average accumulation rateof removals of nutrients have overwhelmed natural nutrient 22 kilograms of surplus P per hectare each year.Across cycles.Globally.more nutrients are added as fertilizers whole watersheds.the amount of P applied to agricultural than are removed as produce.fertilizers are moved from soils in excess of what plants can use is closely linked to areas of manufacture to eutrophication of surface area crop produc Is in the Global industria fertilizer are only partly production of N fertilizers incorporated into crops. has increased steeply from which are then har nearly zero in the 1940s vested and transported to roughly 80 million met to other areas for con ric tons per year.In the peop and Fu only 8%of the N input produce,meaning tha from sites of fertilizer on average.174 kilo manufacture to sites of orams ner hectare of sur fertilizer deposition and olus N is left behind on rep Figure 8-Intensive animal production,where large numbers of ani Thi flux creates a mals are concentrated in small feedlots.creates enormous amounts surplus on croplands of waste.causing excess nutrients to build up in the soil.run off.or in soils.erodeor leach t and this surplus is the un nfiltrate water supplies. surface and ground wa derlving cause of ters.or enter the atmo nonpoint pollution from agriculture. sphere.N is added to the atmosphere through volatiliza tion of ammonia and microbial generation of nitrous ox Fertilizer ide gas from soils.Nitrous oxide contributes to global wam Phosphorus is ac umulati ng in the world's agricul ing and c lyze the uction of stratospheri tural soils.Between 1950 and 1995.about 600 million ozone.Much of the N volatilized to the atmosphere in metric tons of fertilizer P were applied to Earth's surface these forms is rained out or redeposited in dry forms on primarily on croplands.During the same time period.roughly land or water and eventually enters rivers.lakes.and other 250 million metric tons of P were removed from croplands aquatic ecosystems. fed to livestock and a porti of the from Manure Intensive animal production generally involve feeding large numbers inmal areas. the net addition of P to cropland soils over this period was example,4%of the cattle feedlots in the U.S.produce about 400 million metric tons.This excess P may either 84%of the cattle.Such large concentrations of animals
7 Issues in Ecology Number 3 Summer 1998 WHAT ARE THE SOURCES OF NONPOINT POLLUTION? Nonpoint P and N pollution is caused primarily by agricultural and urban activities. In the U.S., agriculture is the predominant source of nonpoint pollution. Wind or rain-borne deposits from a variety of sources, including agriculture and fossil fuel burning, can add significant amounts of N to surface waters. Agriculture On the worlds croplands, human additions and removals of nutrients have overwhelmed natural nutrient cycles. Globally, more nutrients are added as fertilizers than are removed as produce. Fertilizers are moved from areas of manufacture to areas of crop production. The nutrients in the fertilizer are only partly incorporated into crops, which are then harvested and transported to other areas for consumption by people or livestock. Thus on balance, there is a net transport of P and N from sites of fertilizer manufacture to sites of fertilizer deposition and manure production. This flux creates a nutrient surplus on croplands, and this surplus is the underlying cause of nonpoint pollution from agriculture. Fertilizer Phosphorus is accumulating in the worlds agricultural soils. Between 1950 and 1995, about 600 million metric tons of fertilizer P were applied to Earths surface, primarily on croplands. During the same time period, roughly 250 million metric tons of P were removed from croplands in the form of harvested crops. Some of this produce was fed to livestock and a portion of the manure from these animals was reapplied to croplands, returning some of the harvested P (about 50 million metric tons) to the soil. Thus the net addition of P to cropland soils over this period was about 400 million metric tons. This excess P may either remain in soils or be exported to surface waters by erosion or leaching. The majority of applied P remains on croplands, with only 3 to 20% leaving by export to surface waters. It is likely, therefore, that about 350 million metric tons of P has accumulated in the worlds croplands. The standing stock of P in the upper 10 centimeters of soil in the worlds croplands is roughly 1,300 million metric tons. That means that a net addition of 350 million metric tons between 1950 and 1995 would have increased the P content of agricultural soils by about 25%. In the U.S. and Europe, only about 30% of the P input in fertilizers ends up being incorporated into crop plants, resulting in an average accumulation rate of 22 kilograms of surplus P per hectare each year. Across whole watersheds, the amount of P applied to agricultural soils in excess of what plants can use is closely linked to eutrophication of surface waters. Global industrial production of N fertilizers has increased steeply from nearly zero in the 1940s to roughly 80 million metric tons per year. In the U.S. and Europe, only 18% of the N input in fertilizer leaves farms in produce, meaning that on average, 174 kilograms per hectare of surplus N is left behind on croplands each year. This surplus may accumulate in soils, erode or leach to surface and ground waters, or enter the atmosphere. N is added to the atmosphere through volatilization of ammonia and microbial generation of nitrous oxide gas from soils. Nitrous oxide contributes to global warming and can also catalyze the destruction of stratospheric ozone. Much of the N volatilized to the atmosphere in these forms is rained out or redeposited in dry forms on land or water and eventually enters rivers, lakes, and other aquatic ecosystems. Manure Intensive animal production generally involves feeding large numbers of animals in small areas. For example, 4% of the cattle feedlots in the U. S. produce 84% of the cattle. Such large concentrations of animals Figure 8 - Intensive animal production, where large numbers of animals are concentrated in small feedlots, creates enormous amounts of waste, causing excess nutrients to build up in the soil, run off, or infiltrate water supplies. Photo by Stephen R. Carpenter
Issues in Ecology Number 3 Summer 1998 Figure 9-Runoff from urban activities such as lawn fertilizers and pet wastes is a significant soure of nonpoint lution that we can all helpto create enormous amounts of waste.The disposal prob and manure are influenced by the rate.season,chemica lems are comparable to those for raw human sewage. form,and method of nutrient application:amount and and yet the regulatory standards for disposing of animal timing of rainfall after application;and the plant cover. wastes are generally far less stringent than the standards The greater proportional losses of P and N from manure cities and towns must meet for treating human sewage. than from industrially produced fertilizers may result from Nutrients in manure can be higher P and N concer rtions in manure and less flexibil the amount of ma ity in the timin applicatio nure must be nure generated by concentrated live ock opera tions of worked into so ten far exceeds the capacity of nearby croplands to use rather than at the time growing crops require P and N. and retain the nutrients.At typical stocking rates for feed The amount of p lost to surface waters increases lots,for instance,an area of cropland roughly 1,000 times with the p content of the soil the loss can come in the form greater than the feedlot area itself is required to distribute of dissolved P but even more P is transported as particles. manure nutrients at levels equal to what the crops on that In the long term,this particulate P can be com verted to land ca an use. This much accessible cropland may not be phosphate and made vailable to aquaticorgani available.soexcess quantities of manure are applied to Ntransport to the eans has increased in reent de smaller land areas.The excess nutrients then build up in cades and the increase can be comrelated to a number of human soil,run off,or infiltrate to water supplies.Or,in the case activities that increase N inouts into watersheds.Similarly.th of N.they may enter the atmosphere. amount of p camed in nvers to the oceans is nositiely come lated with human population density in watersheds.Globally.the Transport to Aquatic Ece ment oastal oceans has ind ased from ar of P and N to surface waters mated pri rate of have been measure d after application of fertilizeror ma rent rate f33 me tric tons per year. ut30 nure to farm land.Fertilizer P and N losses in runoff are this increase is attributed to P enrchment of agrcultural soils generally less than 5%of the amount applied.Losses and the remainder to increasing rates of erosion. from manure can be slightly higher(up to 20%if rain falls immediately after application).However.these percent- Urban Runoff ate total n flux to aqu tic ecosy Asignificant amount of P and Nenters lakes,riv they do ot include n and leachi ers,andcoa ters fro n nonpoint sources tely carry N to ground and surface waters N ex as construction sites,run f lawn fertili and pe port from agricultural ecosystems to water,as a percent wastes,septic systems and developed areas that lack sew age of fertilizer inputs.ranges from 10%to 40%for ers.Urban runoff is the third most important cause of loam and clay soils to 25%to 80%for sandy soils.In lake deterioration in the U.S.,affecting about 28%of eeneral.the rates of nutrient loss to water from fertilizer the lake area that does not meet water quality standards
Issues in Ecology Number 3 Summer 1998 8 create enormous amounts of waste. The disposal problems are comparable to those for raw human sewage, and yet the regulatory standards for disposing of animal wastes are generally far less stringent than the standards cities and towns must meet for treating human sewage. Nutrients in manure can be recycled by applying the manure to cropland. However, the amount of manure generated by concentrated livestock operations often far exceeds the capacity of nearby croplands to use and retain the nutrients. At typical stocking rates for feedlots, for instance, an area of cropland roughly 1,000 times greater than the feedlot area itself is required to distribute manure nutrients at levels equal to what the crops on that land can use. This much accessible cropland may not be available, so excess quantities of manure are applied to smaller land areas. The excess nutrients then build up in soil, run off, or infiltrate to water supplies. Or, in the case of N, they may enter the atmosphere. Transport to Aquatic Ecosystems Increased fluxes of P and N to surface waters have been measured after application of fertilizer or manure to farm land. Fertilizer P and N losses in runoff are generally less than 5% of the amount applied. Losses from manure can be slightly higher (up to 20% if rain falls immediately after application). However, these percentages underestimate total N flux to aquatic ecosystems because they do not include infiltration and leaching which ultimately carry N to ground and surface waters. N export from agricultural ecosystems to water, as a percentage of fertilizer inputs, ranges from 10% to 40% for loam and clay soils to 25% to 80% for sandy soils. In general, the rates of nutrient loss to water from fertilizer and manure are influenced by the rate, season, chemical form, and method of nutrient application; amount and timing of rainfall after application; and the plant cover. The greater proportional losses of P and N from manure than from industrially produced fertilizers may result from higher P and N concentrations in manure and less flexibility in the timing of applications, since manure must be worked into soils before or after the growing season rather than at the time growing crops require P and N. The amount of P lost to surface waters increases with the P content of the soil. The loss can come in the form of dissolved P, but even more P is transported as particles. In the long term, this particulate P can be converted to phosphate and made available to aquatic organisms. N transport to the oceans has increased in recent decades and the increase can be correlated to a number of human activities that increase N inputs into watersheds. Similarly, the amount of P carried in rivers to the oceans is positively correlated with human population density in watersheds. Globally, the movement of P to coastal oceans has increased from an estimated pristine flux rate of 8 million metric tons per year to the current rate of 22 million metric tons per year. About 30% of this increase is attributed to P enrichment of agricultural soils, and the remainder to increasing rates of erosion. Urban Runoff A significant amount of P and N enters lakes, rivers, and coastal waters from urban nonpoint sources such as construction sites, runoff of lawn fertilizers and pet wastes, septic systems and developed areas that lack sewers. Urban runoff is the third most important cause of lake deterioration in the U. S., affecting about 28% of the lake area that does not meet water quality standards. Figure 9 - Runoff from urban activities, such as lawn fertilizers and pet wastes, is a significant source of nonpoint pollution that we can all help to control. Photo by S.C. Delaney/EPA
Issues in Ecology Summer 1998 Urban point sources of water pollution.such as sewage organic fertilizers and the planting of n-fixing crops such and industrial discharges,are also significant,but unlike as ovbeans and other legumes.nonetheless.n from fossi nonpo nt sources,the often fuel combustion may co ntribute substantially to the Construction sites are a critical concem as sources nonpoint-soure polution ce waters of nonpoint pollution.Although construction sites may oc- A comparative study of N fluxes from 33 rivers in cupy a relatively small percentage of the land area.their the northeastem U.S.found that the amounts of both nitrate erosion rates can be extremely high and the total nonpoint and total N in the rivers were correlated with the atmospheric pollution vield quite large.Erosion rates from watersheds deposition of oxidized N-which comes largely from fossil under development appr ach 50.000 me trie tons ne rsquare fuel combustion. onto the watersheds of these rivers for kilometer a yea to1.000to4.00 asmall subset of these rivers .historical data showed an in tons per r square ter lands and les crease in rom the early 1900s t than 10O metric tons for lands with undisturbed plant cover. the present. Eroded material from construction sites contributes to lates with estimates for increased fossil fuel emissions of N siltation of water bodies as well as eutrophication. during the same period. We still have much to learn about the transport Atmospheric Deposition of N of atmospherically-derived N from land to water.Clearly sited to surface waters from the atmo be a signific nt soure of Nto lake sphere arises from sev al sources including trace gase large contrib released from farm soils and the burning of fossil fuels coastal eutrophication.And we know that volatilization Combustion of fuels such as coal and oil releases signifi of nitrogen-based gases from agricultural land supplies a cant quantities of nitrogen-based trace gases into the at- significant fraction of this N. mosphere.both by oxidizing organic N stored in the fuels themselves and by directly"fixing"molecular N from the WHAT CAN BE DONE ABOUT IT? dur high dingit t Unless current practices are changed,nonpoin hydrogen or oxygen to form compounds that plants and pollution of surface waters will increase in the future other organisms can use.Currently,some 20 million met Some factors that drive this expectation are the substan ric tons of fixed N per year are released globally from tial and growing buildup of P and N in agricultural soils; fossil fuel combustion by automobiles,factories,and power an increasing human population:people's preference for epresents only one-fourth of the meat-rich diets.which mandates increasing livestock pro N fo and develop nth of the mer ed fixatio Figure 0-The high erosion rate of con tion sites is off from developing areas. terials contribute to siltation and eutrophi cation of lakes,rivers,and coastal oceans. PO'SAg
9 Issues in Ecology Number 3 Summer 1998 Urban point sources of water pollution, such as sewage and industrial discharges, are also significant, but unlike nonpoint sources, they are often managed intensively. Construction sites are a critical concern as sources of nonpoint pollution. Although construction sites may occupy a relatively small percentage of the land area, their erosion rates can be extremely high and the total nonpoint pollution yield quite large. Erosion rates from watersheds under development approach 50,000 metric tons per square kilometer a year, compared to 1,000 to 4,000 metric tons per square kilometer for agricultural lands and less than 100 metric tons for lands with undisturbed plant cover. Eroded material from construction sites contributes to siltation of water bodies as well as eutrophication. Atmospheric Deposition of N N deposited to surface waters from the atmosphere arises from several sources, including trace gases released from farm soils and the burning of fossil fuels. Combustion of fuels such as coal and oil releases significant quantities of nitrogen-based trace gases into the atmosphere, both by oxidizing organic N stored in the fuels themselves and by directly fixing molecular N from the air during high temperature, high pressure combustion. (Fixing N involves pulling it from the air and bonding it to hydrogen or oxygen to form compounds that plants and other organisms can use.) Currently, some 20 million metric tons of fixed N per year are released globally from fossil fuel combustion by automobiles, factories, and power plants. However, this represents only one-fourth of the amount of N used in inorganic N fertilizer and perhaps one-seventh of the total amount of N fixed globally through human activity, including the manufacture of inorganic fertilizers and the planting of N-fixing crops such as soybeans and other legumes. Nonetheless, N from fossil fuel combustion may contribute substantially to the nonpoint-source pollution of surface waters. A comparative study of N fluxes from 33 rivers in the northeastern U.S. found that the amounts of both nitrate and total N in the rivers were correlated with the atmospheric deposition of oxidized N which comes largely from fossil fuel combustion onto the watersheds of these rivers. For a small subset of these rivers, historical data showed an increase in nitrate concentrations from the early 1900s to the present. The increase in nitrate concentrations correlates with estimates for increased fossil fuel emissions of N during the same period. We still have much to learn about the transport of atmospherically-derived N from land to water. Clearly the atmosphere can be a significant source of N to lakes and rivers and make potentially large contributions to coastal eutrophication. And we know that volatilization of nitrogen-based gases from agricultural land supplies a significant fraction of this N. WHAT CAN BE DONE ABOUT IT? Unless current practices are changed, nonpoint pollution of surface waters will increase in the future. Some factors that drive this expectation are the substantial and growing buildup of P and N in agricultural soils; an increasing human population; peoples preference for meat-rich diets, which mandates increasing livestock production; growth of urban areas with associated development and erosion; and increased fixation of N by human activities such as fertilizer production and fossil fuel burnFigure 10 - The high erosion rate of construction sites is a major source of runoff from developing areas. Eroded materials contribute to siltation and eutrophication of lakes, rivers, and coastal oceans. Photo by S.C. Delaney/EPA