nitrogen in the nation's rain - national atmospheric deposition

NITROGENIN THE NATION’S RAIN

NATIONAL ATMOSPHERIC DEPOSITION PROGRAM

HOW TO OBTAIN NADP DATAData products are available from the National Atmospheric DepositionProgram (NADP) free of charge. The easiest way to obtain data is byvisiting our Internet site at http://nadp.sws.uiuc.edu

Our products include:

• Weekly and daily precipitation chemistry data• Monthly, seasonal, and annual precipitation-weighted mean concentrations• Annual and seasonal deposition totals• Mercury deposition data• Daily precipitation totals• Color isopleth maps of precipitation concentrations and wet deposition• Site photos and information• Quality assurance data and other information

For further information, contact:

NADP Program OfficeIllinois State Water Survey2204 Griffith DriveChampaign, Illinois 61820E-mail: [email protected]

CREDITSContributors: Ellen Porter, U.S. Fish & Wildlife Service; Kathy Tonnessen,National Park Service; John Sherwell, Maryland Department of NaturalResources; and Richard Grant, Department of Agronomy, Purdue University

Editors: Eva Kingston, Van Bowersox, and Gayle Zorrilla

Designer: Wheeler Arts

Photography: All uncredited photos are copyrighted by Nova DevelopmentCorporation and its licensors.

Computer Support: Bob Larson and Linda Hascall

4M—2000—99-2975

NADP Brochure 2000-01c (revised) 2M—05-02—02-1802—ek

Nitrogen is essential for all livingthings. Nearly 98% of the world’s nitro-gen is found in the solid earth within thechemical structure of rock, soil, and sedi-ment. The remainder moves in a dynamiccycle involving the atmosphere, oceans,lakes, streams, plants, and animals. Smallamounts of the nitrogen in soil and sedi-ment also enter this complex cycle.

Molecular nitrogen (N2) is a colorlessodorless gas that comprises 78% of ouratmosphere. Nearly 8 metric tons ofnitrogen sit atop every square meter ofthe earth’s surface. Molecular nitrogenis stable and converting it to otherchemical compounds requires consider-able energy. A lightning bolt providessufficient energy to do the job, causingsome nitrogen and oxygen in the air toform nitrogen oxides. Photosyntheticenergy in plants and chemical energy insoil microorganisms also can convertnitrogen to other chemical forms. All ofthese natural processes occur in thecycling of nitrogen in our environment.

In addition to molecular nitrogen,trace amounts of nitrogen oxides, nitricacid vapor, gaseous ammonia, particu-late nitrate and ammonium compounds,and organic nitrogen circulate throughthe atmosphere. In the United States,nitrogen contributions from human

activities rival or exceed contributionsfrom natural sources for many of thesetrace compounds.

Atmospheric nitrogen compoundscycle to the land and water throughatmospheric deposition. Wet deposition,predominantly rain and snow, carriesnitrate and ammonium. Dry depositioninvolves complex interactions betweenairborne nitrogen compounds and plant,water, soil, rock, or building surfaces.

Key issues for scientists, policy-makers, and the public are the extent towhich human activities are affecting theform and amount of nitrogen in the air,the deposition of nitrogen compoundsfrom the air, and nitrogen cycling in the environment.

Nitrogen in the Nation’s Rain 1

NITROGEN IN THE NATION’S RAIN

Atmospheric nitrogen pathways.Source: Adapted from National Science and Technology Council Committee on Environment andNatural Resources, Air Quality Research Subcommittee, 1999.

Which Human ActivitiesContribute Nitrogen?

Combustion provides high tempera-tures in which nitrogen can be oxidizedto form nitrogen oxides. It’s not surpris-ing, then, that emissions from motorvehicles, electric utilities, and industrialboilers are the largest sources of atmos-pheric nitrogen oxides in the UnitedStates. Human activities now accountfor more than 90% of U.S. nitrogenoxide emissions. According to the U.S.Environmental Protection Agency, nitro-gen oxide emissions fluctuated between20 and 23 million metric tons since1972, which is double the 1950 value.

Atmospheric chemical reactions thatoccur when sunlight is present stronglylink nitrogen oxides and other tracegases with formation of ozone. Depend-ing on atmospheric conditions, thesereactions can occur within several hun-

dred meters of the original nitrogenoxide source or after the pollutants havebeen carried several hundred kilometersdownwind — perhaps crossing state ornational borders. Ultimately, some nitro-gen oxides are converted to nitric acidvapor or particulate nitrates. Precipita-tion efficiently removes both pollutants


PrevailingWinds

Photochemistry

Cloud Processes

Chemical Transformations

Fire

Ground Water

Drinking Water

AquaticEcosystem

CulturalResources

HumanHealth

Agricultural Products

Soils

Visibility

Lightning

Agriculture Industry

Wet DepositionDry

Deposition

VerticalMixing

Sources Transport / Transformation Removal

Effects

Forest Productivity

Transportation

Estuaries

Runoff

Soils

Dispersion

SewagePlants

Nitrate

Samoa Hawaii Alaska Eastern U.S.

mill

igra

ms

per

liter

Nitrate content of precipitation in remote and highly populated locations

0

0.2

0.4

0.6

0.8

1.0

1.2

Source: National Atmospheric Deposition Program National Trends Network(after J.N. Galloway, G.E. Likens, and M.E. Hawley, 1984. Science 226:829).

1998 wet deposi-tion of nitrogenfrom nitrate andammonium.Source: NationalAtmospheric Deposi-tion Program NationalTrends Network.

from the air. As a consequence, nitratesin precipitation tend to be highest wherethe air is most polluted with nitrogenoxides. These areas are likely to havehigh population densities, numerousmotor vehicles, and many power plantsor industrial boilers.

Ammonia and ammonium are otherforms in which nitrogen occurs. Ammo-nia is a gas that becomes ammoniumwhen dissolved in water or when pre-sent in soils or airborne particles. Unlikenitrogen oxides that form during com-bustion, soil microorganisms naturallyform ammonia and ammonium, com-pounds of nitrogen and hydrogen. Otherprocesses also form these compounds.

Today, farmers apply millions of tonsof nitrogen fertilizers to the soil. TheU.S. Environmental Protection Agencyestimates that half a million metric tonsof ammonia were emitted to the atmos-phere from fertilizer applications alonein 1997. More than three times as muchwas emitted from livestock waste(manure and urine). These two sourcesaccount for almost 80% of ammoniaemissions in the United States.

Precipitation readily removes ammo-nia and ammonium from the air. Wetdeposition of these compounds and

nitrate could be viewed as anothersource of fertilizer for agricultural crops(see sidebar on agriculture). It can alsobe an unwanted input of fertilizer to sen-sitive ecosystems.

The U.S. map below shows the totalinorganic nitrogen deposited in precipi-tation in 1998. Total inorganic nitrogenincludes the nitrogen from nitrateammonium. Wet inorganic nitrogendeposition was highest in the intenselycultivated upper Midwest. Parts of eightstates from eastern Nebraska to westernOhio received 7 kilograms per hectare(6.2 pounds per acre) or higher. One-half to three-quarters of the total inor-ganic nitrogen deposited in this area isfrom ammonium deposition, whichpeaks in this same area.

A U.S. Environmental ProtectionAgency map shows that atmosphericammonia emissions also peak there.Ammonium-nitrogen dominates thetotal inorganic nitrogen deposition in theupper Midwest, while nitrate-nitrogengenerally dominates in the Northeast.

Areas with the highest nitrogen emis-sions do not necessarily experience thegreatest deposition effects, which canoccur far from the original nitrogensource. Scientists have found that some


Alaska

Puerto Rico

Virgin Islands

N(kg/ha)

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GRAPHIC COURTESY OF

JOHN DEERE - NAAMC.With advances insatellite, computer,and electronics,crop production ismoving into a new age.


The Role of Agriculture Persons engaged in the business of agriculture have a multifaceted interest in

nitrogen deposition. Applying nitrogen-based fertilizers has proven very effec-tive in increasing crop yields, but these same fertilizers may be detrimental to thegoal of sustainable agriculture and may raise the amount of nitrogen in groundwater and surface water downstream of the farmland, contributing to the degra-dation of aquatic ecosystems. Therefore, one of the major challenges facingenvironmentally conscious crop producers today is the fertilizer application ratesthat will optimize crop yield and profit and minimize potential environmentaldamage. Availability of nitrogen for plant growth and crop yield depends onnumerous factors: historical land use, crop type, residual nitrogen from legumessuch as soybeans, soil type and condition, amount of nitrogen released by soilorganic matter, and amount of nitrogen deposited by atmospheric deposition.

Precision farming addresses this complex problem by providing real-timevariable-rate fertilizer application that takes into consideration the crop, soiltype, soil fertility, and other factors within an individual field. This maximizesthe efficiency of fertilizer application, minimizes waste, and reduces surfacewater contamination. On a larger scale, the management guidelines of statewidefertilizer use for a given crop can be adjusted for the spatial variation of plant-available atmospheric nitrogen deposition. For instance, precipitation over theMidwest annually contributes 3 to 7 kilograms per hectare of inorganic nitrogento the soil, representing less than 5% of the inorganic nitrogen needs of corn andup to 15% of the nitrogen needs of wheat, depending on the target yield of thecrop and on soil quality. Estimated atmospheric nitrogen deposition for the east-ern United States could account for at least 10% of the nitrogen needs of major,nonnitrogen-fixing crops.

All of us benefit as science and technology continue to work together to opti-mize farmland crop production and safeguard the water supply and terrestrialand aquatic ecosystems.


Bristlecone pinesare among theoldest living orga-nisms. Increasesin the amount ofnitrogen thatreaches this treemay reduce itschances of survi-val in such a harshenvironment.

PHOTO BY GARY LEAR

ecosystems are more sensitive to addednitrogen than others: certain high-eleva-tion eastern forests and streams, Eastand Gulf Coast estuaries, and westernalpine areas and high-elevation forests.

What Effects Are Associated with Nitrogen Deposition?

Depending on the chemical form andamount in the environment, nitrogen canserve as a nutrient, enhancing growthand productivity, or as a toxin, causingecological damage or harming humanhealth. Scientists often refer to nitrogenas a macronutrient because plants andanimals require it in relatively large pro-portions compared to other essentialnutrients such as iron or copper.

Nitrogen needs vary, depending onthe ecosystem and on the plant or ani-mal species. Different life forms withinthe same ecosystem do not have thesame nitrogen requirements.

Many ecosystems and crops are lim-ited by the availability of nitrogen.That’s why the advent of synthetic fertil-izers earlier in the 20th century has beensuch a boon to agricultural productivity.That’s also why atmospheric depositionof nitrogen in some ecosystems maystimulate unhealthy growth or causegrowth of some plants at the expense of others.

Air quality and atmospheric deposi-tion are closely linked. Nitrogen oxidescontribute to the formation of ozone, alung irritant. Many studies have shownthat elevated ozone levels also damageplant leaves and reduce crop yields.Near urban or industrial air pollutionsources, high nitrogen dioxide concen-trations can irritate human lung tissuesand lower resistance to influenza orother respiratory infections.

Visibility degradation and acidicdeposition are also linked. Too manyfine particles in the air create the

unsightly haze that reduces visibility inmany U.S. cities and even occasionallyshrouds the beautiful vistas in nationalpark and wilderness areas. These fineparticles contain nitrogen compounds(nitrate, ammonium, or both) and otherpollutants (sulfate and carbon com-pounds). Sulfate is often more importantthan nitrogen in degrading visibility,especially in the eastern United States.When sunlight is present, nitrogen diox-ide gas may also contribute to degrada-tion of visibility .

While precipitation cleans the air,rain and snow contain nitrates and sul-fates, making them more acidic. Statues,monuments, and the exteriors of build-ings are all subject to acid rain damage.Acidic precipitation also affects sensi-tive streams, lakes, and soils, which areeasily altered by chemical inputs. Acidicprecipitation can disturb the delicate bal-ance in these sensitive ecosystems.

Stream acidifica-tion in Shenan-doah NationalPark has hadeffects on somenative species,such as thisbrook trout.

Stream-waternitrogen oftenreaches a peakduring the springwhen snowmelt orrainstorms canflush nitrate fromthe soils.

Nitrogen deposition also may have afertilizer effect. In estuaries and coastalecosystems, this can lead to eutrophica-tion, a condition characterized by algaeblooms, low dissolved oxygen, and lossof invertebrates, fish, and other wildlife.

Effects on Freshwater and Terrestrial Systems

Freshwater streams, ponds, and lakesrespond to the water and chemicalinputs from rainstorms and snowmelt.On rare occasions when the ground isfrozen, some headwater streams carry asurge of nitrate, sulfate, and acidity pro-vided directly by rain or melting snow.

More typically, precipitation soaksinto the ground adding nitrate and am-monium to the nitrogen cycle, whichalso involves soils, decaying plant andanimal matter, microbes, and livingplant roots. Many factors control therate at which nitrogen enters and leavesthis complex cycle, including soil type,temperature, microbial activity, andplant needs. Precipitation is just onesource of the nitrogen in soils.

Scientists have found that the cu-mulative effect of years of nitrogendeposition does increase the amount ofnitrogen carried by streamflow fromsome watersheds. Rainstorms and snow-melt can flush accumulated nitrate fromsoils into these streams.

Nitrogen deposition, especially incombination with sulfate, can contribute

to episodic acidification of streams. Notall aquatic organisms have the same tol-erance for these episodes, which cancause a decline in acid-sensitive fish,amphibian, and invertebrate populations.

Nitrogen deposition to forest andalpine soils can affect plant populationsand overall forest health. Decades ofacidic nitrate and sulfate deposition hasdepleted the supply of calcium andmobilized aluminum in some forestsoils. Calcium is essential for treegrowth, but aluminum interferes withthe uptake of this nutrient by tree roots.

Low soil calcium has been linked tothe dieback of sugar maples in somenortheastern forests. Researchers arestudying nitrogen-saturated, high-eleva-tion spruce/fir forests in the Great Smo-ky Mountains National Park. They findthat as aluminum in soil water increases,the calcium in spruce trees decreases,

Nitrogen in the Nation’s Rain 6PHOTO BY KATHY TONNESSEN

possibly making trees more vulnerableto drought and insect infestations.

Experiments have shown that addingnitrogen to alpine forest and grass com-munities alters the species mix. Thoseplants that can store and use the addednitrogen become predominant.

Effects on Estuarine SystemsThe numerous estuaries along the

U.S. coastline have great economic, aes-thetic, and ecological value. Watershedscollect water and direct its flow intoestuaries and other water bodies. Atmos-pheric deposition delivers nitrogen toestuaries and their watersheds. Nitrogenfrom many sources enters an estuary;only a portion is from atmosphericdeposition (see sidebar on ChesapeakeBay). Estuary and watershed size areimportant in evaluating the atmosphericcontribution to the total nitrogen enter-ing an estuary.

Soils, plants, and animals retainmuch of the nitrogen deposited in estu-arine watersheds. Much of the remain-der leaves these watersheds in runoff tostreams and rivers. Subsurface watercarrying nitrogen can also enter thesewaterways, which feed into estuaries.

Nitrogen has unique effects on indi-vidual estuaries. Along the East andGulf Coasts, nitrogen promotes growthof algae. These microscopic waterborneplants cloud water and block sunlight,which can interfere with aquatic plantand animal productivity and affect watertemperature and currents. For example,algae can inhibit growth of sea grassesthat offer habitat for fish and shellfish.

While living algae can degrade habi-tat, decaying algae also can have effectsas they complete their life cycle, sink tothe bottom, and decompose. Decompo-sition of algae and other dead matterremoves oxygen from bottom watersand can lead to hypoxia, a low-oxygencondition. Hypoxia has negative impactson populations of bottom dwellers suchas crabs, oysters, mussels, and clams.


How is NitrogenDeposition Measured?

Nitrogen deposition occurs as bothwet and dry deposition. The NationalAtmospheric Deposition Program(NADP) National Trends Network(NTN) measures nitrate and ammoniumin one-week rain and snow samples atnearly 240 regionally representativesites in 48 states. Nitrate and ammoniumare measured in daily samples at another10 sites in NADP’s Atmospheric Inte-grated Research Monitoring Network(AIRMoN). These two NADP networksmeasure the wet deposition of inorganicnitrogen (see NADP sidebar).

Two networks measure atmosphericconcentrations of gaseous nitric acid andparticulate ammonium and nitrate atrural locations across the United States.The U.S. Environmental ProtectionAgency Clean Air Status and TrendsNetwork (CASTNet) operates 84 sites.The National Oceanic and AtmosphericAdministration operates the 5 sites inthe AIRMoN dry deposition program.Dry deposition rates are calculated using

PHOTO BY KATHY TONNESSENBioassays canassess the healthof fish.


Sources of nitrogen to theChesapeake Bay.Source: Chesa-peake Bay Program,The State of theChesapeake Bay,CBP/TRS 222/108,October 1999.

A water qualityanalysis of nitrateas N in the Chesa-peake Bay.Source: ChesapeakeBay Program.

The Chesapeake Bay The Chesapeake Bay, located in coastal Maryland and Virginia, is the largest

of 130 estuaries in the nation. The Bay’s most troubling problem is an overabun-dance of nutrients. Excess nutrients lead to increased algal production andorganic matter, a process known as eutrophication. Nitrate accumulates in theBay during winter and spring. As temperatures rise, this nitrate promotes exces-sive algal growth. By mid-summer the decay of algae and other dead matter leadto hypoxia in the bottom waters of the Bay (see “Effects on Estuarine Systems”).

Researchers are using NADP data to compute the amount of nitrogen depos-ited by precipitation in Chesapeake Bay and its watershed. Scientists are usingcomputer modeling to simulate the complex cycling of nitrogen through this ter-restrial watershed, which has a far greater area than the Bay itself. ChesapeakeBay Program models were used to estimate the contributions of the primarysources of nitrogen to the Bay (see pie chart).

The Chesapeake Bay Program seeks ways to reduce the amount of nitro-gen entering the Bay (see map). High-quality data from NADP measurementsgive cooperating scientists and policymakers the information they need tomeet this goal.

Nitrate as N

Point SourcesWater

Land

Nonpoint Sources

Atmospheric Deposition

N

these concentration data and depositionvelocities simulated by a computermodel. The model uses meteorologicalmeasurements, and information on landuse, vegetation, and surface conditions.Calculating the dry deposition of inor-ganic nitrogen requires summing theindividual rates for nitric acid, nitrate,and ammonium.

The amount of nitrogen deposited byprecipitation can be calculated for loca-tions without NTN or AIRMoN sites.One approach uses NADP rainfall,nitrate and ammonium concentrationdata, and digital terrain maps. Thesemaps make it possible to generate plotsthat account for terrain effects on wetdeposition. The map generated for theChesapeake Bay watershed using thistechnique includes important informa-tion for planners, policymakers, and thescientific community about the complexrelationship between the atmosphereand the ecological health of the nation’sestuarine systems.


A headwaterstream.

SummaryNitrogen is a macronutrient that is

essential for all living things. Fossilfuel combustion, animal husbandrypractices, nitrogen fertilizer produc-tion and application, and other humanactivities add substantial amounts ofnitrogen compounds to the atmos-phere every year. Higher airbornenitrate and ammonium concentrationsfrom these activities increase the wetand dry deposition rates of nitrogen.Increased atmospheric deposition canaffect natural and agricultural systems.

Information on nitrogen deposition,such as that collected by the NADP, isimportant to regulators, policymakers,and land managers responsible for theprotection of air and water quality innatural and managed ecosystems.

Nitrogen (kg/ha)

Estimated 1997wet deposition ofnitrogen in theChesapeake Baywatershed. Source: J. W. Grimmand J. A. Lynch,Pennsylvania StateUniversity.


About the National AtmosphericDeposition Program

Evaluating nitrogen deposition from the atmosphere is a major role of theNational Atmospheric Deposition Program (NADP) — a partnership of StateAgricultural Experiment Stations, federal, state, and local government agencies,universities, public institutions, Native American organizations, and industries.Continued commitments by these organizations make it possible for NADP toprovide the only long-term record of precipitation chemistry in the UnitedStates. This information is used by scientists, policymakers, and the public inaddressing the health, environmental, and agricultural issues facing the nation,including policy decisions related to the Clean Air Act amendments.

NADP was initiated in 1977 to address the problem of atmospheric deposi-tion and its effects on agricultural crops, forests, rangelands, surface waters, andother natural resources. NADP coordinates approximately 240 sites in theNational Trends Network, which collects weekly precipitation samples forchemical analysis. Samples are analyzed at the program’s Central AnalyticalLaboratory in Champaign, Illinois, to determine the amounts of certain chemi-cals, including nitrate and ammonium.

Two additional networks joined NADP in the 1990s: the AtmosphericIntegrated Research Monitoring Network (AIRMoN) in 1992 and the MercuryDeposition Network (MDN) in 1996. The AIRMoN wet deposition programevaluates the effect of emission changes on precipitation chemistry, combiningmeasurements with atmospheric models. MDN is investigating the importanceof atmospheric deposition as a source of mercury in lakes and streams.

A number of federal agencies support NADP, including the Tennessee ValleyAuthority; U.S. Department of Agriculture (Cooperative State Research, Educa-tion, and Extension Service, and Forest Service); U.S. Department of Commerce(National Oceanic and Atmospheric Administration); U.S. Department of Inter-ior (Bureau of Land Management, National Park Service, U.S. Fish & WildlifeService, and U.S. Geological Survey); and U.S. Environmental Protection Agen-cy. Additional support comes from various other federal agencies, State Agri-cultural Experiment Stations, state and local government agencies, universities,Native American organizations, and public and private research organizations.

For more information, contact:NADP Program OfficeIllinois State Water Survey2204 Griffith DriveChampaign, IL 61820E-mail: [email protected] Internet: http://nadp.sws.uiuc.edu

The Illinois State Water Survey is an Affiliated Agencyof the University of Illinois and a Division of the IllinoisDepartment of Natural Resources.

NATIONAL ATMOSPHERIC DEPOSITION PROGRAMA Cooperative Research Support Program of theState Agricultural Experiment Stations (NRSP-3)

Federal and State Agenciesand Private Research Organizations

N A T U R A LRESOURCES

DEPARTMENT OF

I L L I N O I S


Ammonia/AmmoniumCompounds of nitrogen and hydrogenthat readily dissolve in water. In oxy-gen-rich water, ammonium is easilytransformed to nitrate and in oxygen-poor water to molecular nitrogen. Am-monium and nitrate comprise most ofthe inorganic nitrogen in precipitation.

Atmospheric Deposition The process whereby airborne particlesand gases are deposited on the earth’ssurface by wet deposition (precipitation)or by dry deposition (processes such assettling, impaction, and adsorption).

Dry Deposition Atmospheric deposition that occurswhen particles settle to a surface, collidewith and attach to a surface, or whengases stick to a surface (adsorption) orare absorbed.

Estuary An arm of the sea at the mouth of astream or river where freshwater andsalt water meet.

EutrophicationA process in which nutrients degradewater quality due to excessive growth ofmicroscopic plants and animals. As thismatter dies and decays, it sometimesremoves so much dissolved oxygenfrom the water that fish and other organ-isms cannot survive.

Hypoxia A low-oxygen condition wherebydecaying microscopic plants and ani-mals in estuarine waters remove oxygento a level below which most aquatic ani-mals can survive. Although fish andshrimp can migrate from hypoxic zones,less mobile bottom dwellers cannot.

Nitrate A compound of nitrogen and oxygenthat is highly soluble in water. Nitrate isstable over a wide range of environmen-tal conditions and is readily transportedin surface and ground water.

Nitrogen Molecular nitrogen (N2), an extremelystable gas, comprises 78% of theatmosphere. Converting this gas toother chemical compounds requireslots of energy. Other compounds ofnitrogen include nitrate and ammonia/ammonium.

Watershed A land surface from which water drainsto a lake, stream, river, estuary, or bay.

Wet Deposition Atmospheric deposition that occurswhen rain, snow, or fog carry gases andparticles to the earth’s surface.

KEY TERMS


Fenn, M.E., M.A. Poth, J.D. Aber, J.S. Baron, B.T.Bormann, D.W. Johnson, A.D. Lemly, S.G. McNulty,D.F. Ryan, and R. Stottelmeyer. 1998. Nitrogen Excessin North American Ecosystems: a Review of Geo-graphic Extent, Predisposing Factors, EcosystemResponses, and Management Strategies. Ecol. Appl.8:706-733.

Galloway, J.N., H. Levy III, and P.S. Kasibhatla. 1994.Year 2020: Consequences of Population Growth andDevelopment on the Deposition of Oxidized Nitrogen.Ambio 23:120-123.

National Science and Technology Council Committeeon Environment and Natural Resources Air QualitySubcommittee. 1999. The Role of Monitoring Networksin the Management of the Nation’s Air Quality. Wash-ington, D.C.: U.S. Government Printing Office.(http://www.nnic.noaa.gov/CENR/cenr.html)

Stoddard, J. 1994. Long-term Changes in WatershedRetention of Nitrogen; Its Causes and AquaticConsequences. In Baker, L.A. (ed.). EnvironmentalChemistry of Lakes and Reservoirs. Washington, D.C.:American Chemical Society: pp. 223-284.

Vitousek, P.M., J.D. Aber, R.W. Howarth, G.E. Likens,P.A. Matson, D.W. Schindler, W.H. Schlesinger, andD.G. Tilman. 1997. Human Alteration of the GlobalNitrogen Cycle: Sources and Consequences. Ecol.Appl. 7(3):737-750.

Williams, J.N., J. Baron, R. Caine, R. Sommerfeld, andJ.R. Sanford. 1996. Nitrogen Saturation in the RockyMountains. Environ. Sci. & Tech. 30:640-646.

RESOURCES

Web Site ResourcesChesapeake Bay Program: www.chesapeakebay.net

Ecological Society of America: www.esa.org

National Acid Precipitation Assessment Program:www.oar.noaa.gov/organization/napap.html

National Atmospheric Deposition Program: nadp.sws.uiuc.edu

National Oceanic and Atmospheric Administration AIRMoN DryDeposition Program:www.arl.noaa.gov/research/projects/airmon_dry.html

National Park Service Air Resources Division: www2.nature.nps.gov/ard

U.S. Environmental Protection AgencyClean Air Status and Trends Network: www.epa.gov/castnetEnvironmental Monitoring and Assessment Program:

www.epa.gov/emapGulf of Mexico Program: pelican.gmpo.govNational Estuary Program: www.epa.gov/nepOffice of Air & Radiation: www.epa.gov/oar

U.S. Geological Survey Acid Rain Program:bqs.usgs.gov/acidrain/index.htm

NADP COOPERATORS

State Agricultural Experiment StationsAuburn Univ.-Black Belt Substa.; Auburn Univ.-Sand Mtn. Substa.;Colorado State Univ.-Central Plains Experimental Range; Cornell Univ.-Aurora Res. Farm; Iowa State Univ.-McNay Res. & Demonstration Farm;Kansas State Univ.-Konza Prairie; Louisiana State Univ.-Iberia Res. Sta.;Louisiana State Univ.-Southeast Res. Sta.; Montana State Univ.-NorthernAg. Res. Ctr.; North Carolina State Univ.-Finley Farm; North CarolinaState Univ.-Horticultural Crops Res. Sta.; North Carolina State Univ.-Peanut Belt Res. Sta.; North Carolina State Univ.-Piedmont Res. Sta.;Ohio State Univ.-Eastern Ohio R&D Ctr.; Ohio State Univ.-Ohio Ag. R&D Ctr.; Oklahoma State Univ.-Goodwell Res. Sta.; Oregon State Univ.-Hyslop Farm; Pennsylvania State Univ.-School of Forest Resources;Pennsylvania State Univ.-Fruit Res. & Extension Ctr.; Purdue Univ.-Purdue Ag. Res. Ctr.; Purdue Univ.-Southwest-Purdue Ag. Ctr.; SouthDakota State Univ.-Cottonwood Range Livestock Field Sta.; Texas A&MUniv.-Texas A&M Ag. Res. Sta.-Beeville; Texas A&M Univ.-Texas A&MAg. Res. Sta.-Sonora; Univ. of Arkansas-Ag. Res. & Extension Ctr.; Univ.of California-Davis; Univ. of California-Hopland Field Sta.; Univ. ofFlorida-Bradford Forest; Univ. of Georgia-Coastal Plain Exp. Sta.; Univ.of Georgia-Georgia Exp. Sta.; Univ. of Illinois-Dixon Springs Ag. Ctr.;Univ. of Illinois-Northern Illinois Agron. Res. Ctr.; Univ. of Illinois-Northwestern Illinois Ag. Res. & Demonstration Ctr.; Univ. of Maine-Greenville Sta.; Univ. of Maryland-Wye Res. & Education Ctr.; Univ. ofMassachusetts-Suburban Exp. Sta.; Univ. of Michigan-Biological Sta.;Univ. of Michigan-Kellogg Biological Sta.; Univ. of Minnesota-SouthwestRes. & Outreach Ctr.; Univ. of Missouri-Baskett Wildlife Area; Univ. ofMissouri-Univ. Forest; Univ. of Nebraska-Ag. R&D Ctr.; Univ. ofNebraska-North Platte Ag. Exp. Sta.; Univ. of Vermont-Proctor Maple Res.Ctr.; Univ. of Wisconsin-Spooner Ag. Res. Sta.; Utah State Univ.-Utah Ag.Exp. Sta.; Virginia Polytechnic Inst. & State Univ.-Horton Res. Ctr.;Washington State Univ.-Palouse Conservation Farm

UniversitiesAlfred Univ.; Colorado State Univ.; Cornell Univ.; Eastern KentuckyUniv.; Miami Univ. of Ohio; Murray State Univ.; New Mexico State Univ.;North Carolina State Univ.-Southern Oxidant Study; Pennsylvania StateUniv.; State Univ. of New York-Albany; State Univ. of New York-Fredonia; State Univ. of New York-Oswego; State Univ. of New York-Syracuse; Texas A&M Univ.; Univ. of Alaska, Fairbanks-Water &Environmental Res. Ctr.; Univ. of Arkansas-Monticello; Univ. ofColorado-Inst. of Arctic & Alpine Res.; Univ. of Delaware; Univ. ofKentucky-Ctr. for Applied Energy Res.; Univ. of Massachusetts; Univ. ofMichigan-Biological Sta.; Univ. of Minnesota; Univ. of Missouri; Univ. ofNew Hampshire; Univ. of Oklahoma; Univ. of Puerto Rico; Univ. of SouthCarolina-Baruch Inst. for Marine Biology & Coastal Res.; Univ. ofVermont; Univ. of Virginia; Washington Univ.-Tyson Res. Ctr.

United States Government AgenciesNational Aeronautics & Space Admin.; National Science Foundation-Long-Term Ecological Res. Program; Tennessee Valley Authority; U.S.Dept. of Agriculture (Ag. Res. Service, Cooperative State Res. Education& Extension Service, Science & Education Admin.); U.S. Dept. ofAgriculture/Forest Service (Wildlife, Fish, Water & Air Res., BitterrootNat’l Forest, Bridger-Teton Nat’l Forest, Coweeta Hydrologic Lab., ForestSciences Lab.-Delaware, Ohio, Fremont Nat’l Forest, Gifford Pinchot Inst.for Conservation Studies, Hiawatha Nat’l Forest, H.J. AndrewsExperimental Forest, Hubbard Brook Experimental Forest, Huron-Manistee Nat’l Forest, Kane Experimental Forest, Medicine Bow-RouttNat’l Forest, North Central Res. Sta., Northeastern Res. Sta., PacificNorthwest Res. Sta., Pacific Southwest Res. Sta., Rocky Mtn. Res. Sta., SanJuan Nat’l Forest, Shoshone Nat’l Forest, Southern Res. Sta., SuperiorNat’l Forest, White River Nat’l Forest); U.S. Dept. of Commerce/NationalOceanic & Atmospheric Admin. (Air Resources Lab., AtmosphericTurbulence & Diffusion Div., Nat’l Weather Service); U.S. Dept. ofDefense/U.S. Military Academy; U.S. Dept. of Energy (Argonne Nat’lLab., Los Alamos Nat’l Lab., Nat’l Energy Tech. Lab., Oak Ridge Nat’lLab.); U.S. Dept. of Interior/Bureau of Land Mgt. (Nat’l Applied ResourceSciences Ctr., Lander Field Ofc.-Wyoming, Las Vegas Field Ofc.-Nevada,Little Snake Field Ofc.-Colorado, Safford Field Ofc.-Arizona); U.S. Dept.

of Interior/Bureau of Reclamation; U.S. Dept. of Interior/National ParkService (Air Resources Div., Acadia Nat’l Park, Allegheny PortageRailroad Nat’l Historic Site, Assateague Island Nat’l Seashore, BandelierNat’l Monument, Big Bend Nat’l Park, Bryce Canyon Nat’l Park, BuffaloNat’l River, Canyonlands Nat’l Park, Cape Cod Nat’l Seashore, CapulinVolcano Nat’l Monument, Chiricahua Nat’l Monument, Craters of theMoon Nat’l Monument, Death Valley Nat’l Park, Denali Nat’l Park,Everglades Nat’l Park, Glacier Nat’l Park, Grand Canyon Nat’l Park,Great Basin Nat’l Park, Great Smoky Mtns. Nat’l Park, Guadalupe Mtn.Nat’l Park, Hawaii Volcanoes Nat’l Park, Indiana Dunes Nat’l Lakeshore,Isle Royale Nat’l Park, Joshua Tree Nat’l Park, Lassen Volcanic Nat’lPark, Little Big Horn Battlefield Nat’l Monument, Mesa Verde Nat’l Park,Mt. Rainier Nat’l Park, North Cascades Nat’l Park, Olympic Nat’l Park,Organ Pipe Cactus Nat’l Monument, Pinnacles Nat’l Monument, RockyMtn. Nat’l Park, Sequoia Nat’l Park, Shenandoah Nat’l Park, TheodoreRoosevelt Nat’l Park, Valley Forge Nat’l Historical Park, Virgin IslandsNat’l Park, Voyageurs Nat’l Park, Yellowstone Nat’l Park, Yosemite Nat’lPark); U.S. Dept. of Interior/U.S. Fish & Wildlife Service (Air QualityBranch, Attwater Prairie Chicken Nat’l Wildlife Refuge, Cape RomainNat’l Wildlife Refuge, Chassahowitzka Nat’l Wildlife Refuge, Edwin B.Forsythe Nat’l Wildlife Refuge, Hatchie Nat’l Wildlife Refuge, Mingo Nat’lWildlife Refuge, Muleshoe Nat’l Wildlife Refuge, Okefenokee Nat’l WildlifeRefuge, Salt Plains Nat’l Wildlife Refuge, Santee Nat’l Wildlife Refuge,Seney Nat’l Wildlife Refuge); U.S. Dept. of Interior/U.S. GeologicalSurvey; U.S. Environmental Protection Agency (Ofc. of Air & Radiation-Clean Air Markets Div., Ofc. of Wetlands, Oceans, and Watersheds, Nat’lHealth & Environmental Effects Res. Lab.-Western Ecology Div.)

State & Local Government AgenciesAlabama Dept. of Environmental Mgt.; Arkansas Dept. of EnvironmentalQuality; Delaware Dept. of Natural Resources & EnvironmentalConservation Trap Pond State Park; Florida Dept. of EnvironmentalProtection; Fort Worth, Texas, Dept. of Environmental Mgt.; Illinois StateWater Survey; Indiana Dept. of Environmental Mgt.; Iowa ConservationCommission; Kansas Dept. of Wildlife & Parks; Louisiana Dept. ofEnvironmental Quality; Maine Dept. of Environmental Protection;Maryland Dept. of Natural Resources; Massachusetts Dept. ofEnvironmental Protection; Minnesota Pollution Control Agency; MissouriDept. of Natural Resources; New Hampshire Dept. of EnvironmentalServices; New Jersey Dept. of Environmental Protection; New MexicoEnvironment Dept.; North Carolina Dept. of Environment, Health, &Natural Resources; North Dakota State Parks & Recreation-Icelandic StatePark; Northeast States for Coordinated Air Use Mgt.; OklahomaConservation Commission; Pennsylvania Dept. of Conservation & NaturalResources; Pennsylvania Dept. of Environmental Resources; Portland,Oregon, Water Bureau; San Francisco Estuary Inst.; San JoseEnvironmental Services Dept.; Siskiyou County, California-Air PollutionControl Dist.; South Carolina Dept. of Health & Environmental Control;South Carolina Dept. of Natural Resources; South Florida Water Mgt.Dist.; St. Johns River Water Mgt. Dist.; Texas Natural ResourceConservation Commission; Vermont Dept. of EnvironmentalConservation; Wisconsin Dept. of Natural Resources

IndustryAdvance Tech. Systems, Inc.; Atmospheric Res. & Analysis, Inc.; BPAmoco; Constellation Energy Group; Dynamac Corp.; Exxon MobilCorp.; Florida Power & Light Co.; Frontier Geosciences, Inc.; HardingESE, Inc.; Lockheed Martin Energy Res.; SF Phosphates, Ltd.; SouthernCompany; Union Camp Corp.; Westinghouse Savannah River Co.

Native American Tribes and OrganizationsFond du Lac Reservation; Fort Peck Tribes; Grand Traverse Band; LacCourte Oreilles Tribe; Menominee Indian Tribe; Mille Lacs Band ofOjibwe; Penobscot Nation; St. Regis Mohawk Tribe

Other Research OrganizationsBlack Rock Forest Inst.; Electric Power Res. Inst.; Environment Canada-Atmospheric Environment Branch; Environment Canada-Air Quality Res.Branch; Environment Canada-Environmental Conservation Service;Environment Canada-Meteorological Service of Canada; Green RiverHigh School, Utah; Huntsman Marine Science Centre, Canada; Ministerede l’Environnement du Quebec; New Brunswick Dept. of Environment;North Woods Audubon Nature Ctr., Minnesota; Wolf Ridge EnvironmentalLearning Ctr., Minnesota


nitrogen in the nation's rain - national atmospheric deposition

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