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