toxic fertility

8/14/2019 Toxic Fertility

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Toxic Fertilityby Danielle Nierenberg

O R L D W A T C H

N S T I T U T EWIW 1776 Massachusetts Ave., NWWashington, DC 20036www.worldwatch.org

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Reprinted from WORLDWATCH, March/April 2001 Worldwatch Institute


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30 WORLDWATCH March/April 2001

b y D a n i e l l e N i e r e n b e r g

Toxic FertilityOver the past half century, the amount of biologically active

nitrogen circulating through the worlds living things hasprobably doubled. In unnatural excess, an essential nutrient is

becoming a kind of ecological poison.


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WORLDWATCH March/April 2001 31

LAST DECEMBER, talks on the climate treatyreached an impasse. The treaty process is sup-posed to result in a blueprint for reducing car-bon emissions. But when delegates met in the

Hague, in the Netherlands, for their sixth officialconference of the parties, the agenda focused not so

much on cutting fossil fuel use as on the issue ofcarbon sinks. Sinks are areas, primarily youngforests, that are absorbing more carbon than theyare releasing. Since they draw carbon from theatmosphere, sinks offer an attractive accountingoption for the United States and some other nationsthat have high carbon emissions. These nations wantto claim a carbon credit against their emissions,on the strength of their sinks. How big a creditifanyshould be allowed? In one way or another, thatquestion underlay much of the discussion, and thedelegates werent able to agree on an answer. They

failed, in other words, to agree on a way to balancethe global carbon budget.

Apart from the immediate reasons for concernover this failure, there is the matter of another unbal-anced natural budget. Nitrogen, like carbon, plays akey role in the vast biochemical cycles of life. And

increasingly, the nitrogen cycle is being reshaped byhuman activitya process that could eventuallyaffect virtually every ecosystem on earth. Oureconomies are in urgent need of a nitrogen audit.

Like carbon, nitrogen is a basic ingredient of liv-ing things. Its found, for example, in DNA, in pro-teins, and in chlorophyll, the pigment that drivesphotosynthesis. Nitrogen shares another key charac-teristic of carbon: its very common. It comprises a

whopping 78 percent of the atmosphere. But nearlyall of this atmospheric nitrogen is elemental dinitro-gen, or N2it exists in the form of two nitrogen

ILLUSTRATION BY MILAN KECMAN


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atoms linked together. Elemental nitrogen cannot bemetabolized by most living things. Nitrogenbecomes biologically active only when it is fixedthat is, incorporated into certain other molecules,primarily ammonium (NH4) and nitrate (NO3).Fixed nitrogen flows throughout the food web: it isabsorbed first by plants, then by plant-eating animals,then by their parasites and predators. Death at eachstage of the way releases nitrogen compounds tobegin the cycle anew. The fixation process is whatmakes the nitrogen cycle so different from the carboncycle. Despite the abundance of elemental nitrogen,fixed nitrogen is frequently what scientists call a lim-iting nutrient. Under normal natural conditions, itis often in short supply, so the level of available nitro-gen is a key regulator of ecological processes.

The gate-keepers to the biological part of thenitrogen cycle are certain micro-organisms capable offixing elemental atmospheric nitrogen. Some of theseorganisms live in soil, often in close association withplants that belong to the bean family. This relation-ship benefits both parties: the plants get the nitrogencompounds; the microbes get carbohydrates, whichthe plants produce through photosynthesis.(Sometimes the plants themselves are said to be nitro-gen fixing, but this is a kind of terminological short-hand.) Nitrogen fixing occurs in water as well. One ofthe biggest mysteries of the nitrogen cycle involvesmarine plankton. These microscopic plants are fixingenormous quantities of nitrogen, but their role in theglobal cycle has yet to be clearly defined. Finally, inaddition to these living portals, there is an inanimate

natural process that fixes large quantities of nitrogen:lightning fuses nitrogen and oxygen to create nitrate.

Recent human activity has greatly increased therate at which nitrogen is being fixed. Since the 1950s,the amount of nitrogen circulating through livingthings is thought to have doubled. And increasingly,in forests and fields, in rivers and along the coasts, sci-entists are blaming excess fixed nitrogen for a rangeof ecological problemssome of them obvious, oth-ers very subtle. Any one of these problems can usual-ly be linked to some local or regional cause; the nitro-gen balance of a river, for example, might be upset by

increased sewage outflow. But when you step backand look at the cycle from a global perspective, threegeneral activities emerge as the primary reasons forthe growing fixed nitrogen glut.

First, coal and oil combustion is releasing a huge,long-buried reservoir of fixed nitrogen by burningthe residues of ancient plants, in the form of coal andoil. The fossil fuel economy is disrupting not just thecarbon cycle but the nitrogen cycle as well. Second,the progressive destruction of forests and wetlands isreleasing the nitrogen contained in these naturalareas, just as it releases the carbon. Taken together,

these two activities are releasing about 90 million

tons of fixed nitrogen annually; thats about 43 per-cent of the human addition to the nitrogen cycle.(See table below.)

The remainder of the human additionsome120 million tonscomes from agriculture.Nitrogen-fixing crops produce about a third of thatamount; the rest comes from artificial fertilizer. Fixednitrogen is the basic component of fertilizer.Through its dependence on artificial fertilizer, mod-ern conventional agriculture has become, in a sense,a form of industrial nitrogen management. This is arelatively recent development in agricultural history.Low-cost techniques for synthesizing ammoniaemerged shortly after the Second World War. Cheapammonia led to mass production of artificial fertiliz-er and heralded what the ecologist and nitrogenexpert David Tilman has called the 35 most glorious

years of agricultural production.For farmers in the industrialized countriesand

increasingly, in the developing countries as wellthislimiting nutrient is now available in virtually limitlessquantities. As is typical of cheap commodities, a greatdeal of it is wasted. Fertilizer is often very inefficient-ly applied; much of it never reaches the crop. It leach-es out of the fields and into the streams, or its con-

verted into a nitrogenous gas like nitrous oxide andescapes into the atmosphere.

Nearly all crops grown in the industrialized coun-tries are now nitrogen-saturatedthat is, theyrebeing exposed to more nitrogen than they can use.But fertilizer production continues to grow, on thestrength of developing world demand. At current

rates of production, fertilizer is adding some 80 mil-lion tons of fixed nitrogen to the cycle; by 2020 that

Fertilizing the Nitrogen CycleAnnual releases of fixed nitrogen caused

by human activity

Source Millions of tons

Fertilizer 80Nitrogen-fixing crops 40Fossil fuels 20Biomass burning 40Wetland drainage 10Land clearing 20Total human releases 210Total natural fixed-nitrogen production* 140

*Terrestrial sources only; marine sources have not yet beenreliably estimated.

Source: World Resources Institute, Global Nitrogen Gluttable, available at www.wri.org/wri/wr-98-99/nutrient.htm.


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burden is expected to reach 134 million tonsjust 6million tons shy of the total input from all natural ter-restrial sources combined.

ON THE MORNING OF JUNE 22, 1995, the wall of anartificial waste lagoon gave way at a factory farm inNorth Carolina. Some 95 million liters of putrefyinghog urine and feces spilled out of the lagoon, washedacross several fields and a road, then poured into theNew River. Millions of fish and other aquatic organ-isms died in what became one of the worst incidentsof water pollution in the states history. Unfortunately,it wasnt an isolated incidentor at least not for long.

Very large livestock farms, known as concentratedanimal feeding operations or CAFOs, had become amajor part of the states agricultural sector, and theCAFOs had begun to hemorrhage waste.

A couple of weeks after the New River spill, 34million liters of poultry waste flowed down a creek andinto the Northeast Cape Fear River. In August of that

year, another 3.8 million liters of hog waste ended upin the Cape Fear Estuary, reports the January/February 2000 issue of American Scientist. But the

worst was yet to come. The hurricanes of 1998 and1999 brought a series of massive floods to NorthCarolinas seaboard and untold millions of liters ofhog waste were washed out of various CAFO lagoons.The states coastal ecosystems have yet to recover.

Like sewage, CAFO pollution is extremely high innitrogen, and most of that nitrogen comes from the

artificial fertilizer used to grow the animal feed. Youcould say that CAFOs are a consequence of chemicalfertilizer, because fertilizer has allowed for theuncoupling of livestock and crop. When farmersget their fertilizer out of a bag, they dont needmanure. And feed corn can be shipped to CAFOs justas readily as fertilizer can be shipped to corn growers.In each case, the basic input is no longer produced bythe landscape in which it is used, so the local ecologyno longer effectively limits the intensity of produc-tion. The environmental costs of this fractured sys-tem are likely to make it untenable over the long

term. But at least for the present, fertilizer is thesource of about a third of human dietary protein(from both animals and plants), according to VaclavSmil, a professor at the University of Manitoba whohas written extensively on global biochemical cycles.

The logistics of managing CAFO waste are formi-dable. Each of the 50,000 or so sows in one of thoseNorth Carolina facilities will produce about 20piglets over the course of a year. A sow and its piglets

will excrete some 1.9 tons of waste annuallythatsenough manure to fill a pick-up truck. The wastecannot simply accumulate in lagoons, since lagoon

space is obviously limited, so CAFOs require huge

amounts ofspreadable acreagecropland on near-by farms where manure can be spread, sprayed, orinjected. But crops can only use so much nitrogen.

Adding too much can actually reduce yields; likepeople, plants can overeat, and excessive nitrogenuptake tends to interfere with a plants ability tomanufacture the various chemicals needed for itsmetabolism. Too much nitrogen can also throw thesoil community out of balance by favoring only thoseorganisms that thrive in high-nitrogen conditions, atthe expense of many other organisms.

If youre trying to do a conscientious job of it,finding adequate spreadable acreage is a very difficulttask indeed. For each of those sow and piglet units, aCAFO should ideally have access to 1.2 hectares (3acres) of land. (This ratio is actually determined notby the manures nitrogen concentration but by theconcentration of phosphorus, which is also frequent-ly a limiting nutrient and therefore capable of causingsome of the same over-fertilizing effects that nitro-gen does. Sufficient spreadable acreage for the phos-phorus willat least in the case of pig manureaccommodate the nitrogen too.) A 50,000 animalCAFO would need about 60,000 spreadablehectares. Inevitably, given the size of the CAFOs,that ideal is not attained. Frequently, far too muchmanure is spread on the fields. Or the manure may bespread at the wrong times in the growing season,

when the crops cannot effectively take up the nutri-ents. Or sometimes the manure is spread on fields ofnitrogen-fixing crops like soybeans and alfalfa, whichrequire little or no additional fertilizer. In North

America, its estimated that only about half of live-stock waste is now effectively fed into the crop cycle.Much of the remainder ends up as pollutionof the

water, the air, and the soil itself.Take the water pollution first. Nitrate contamina-

tion of groundwater can create serious risks for pub-lic health. (See Groundwater Shock, January/February 2000.) For example, high nitrate levels in

wells near feedlot operations have been linked togreater risk of miscarriage. In extreme cases, nitratecontamination can cause methemoglobinemia, orblue-baby syndrome, a form of infant poisoning in

which the bloods ability to transport oxygen is great-ly reduced, sometimes to the point of death. Nitrate

water pollution is a serious ecological concern as well,even when it doesnt involve millions of liters of hogfeces. Perhaps the most obvious form of ecologicaldisruption involves algal blooms, explosive growthsof algae and cyanobacteria (so-called blue-greenalgae) that can suffocate many other aquatic organ-isms. There are more subtle wildlife effects as well;some amphibian declines, for example, appear to becaused by chronic exposure to elevated nitrate. (SeeAmphibia Fading, July/August 2000.)

But as anyone who lives near a CAFO can tell


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you, groundwater contamination is hardly the mostnoticeable environmental effect. If raw manure isexposed to air, up to 95 percent of the nitrogen in it

will escape into the atmosphere as gaseous ammonia(NH3). In the vicinity of a CAFO, the process resultsin an olfactory experience that is difficult to forget.But thats not all it does, since the nitrogen doesntusually stay airborne for longits usually deposited

within 80 to 160 kilometers of its source. In the

words of Merrit Frey, who studies factory farming forthe Clean Water Network, a coalition of U.S.-basednonprofits concerned about water quality, the ammo-nia from CAFOs is not just a localized odor nui-sance, but a regional environmental problem. Onceit falls from the sky, it tends to contribute to the sameproblems that result from the more direct forms ofsoil and water pollution.

As livestock production continues to intensify,

N2Atmosphere

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Soil Nitrates

Soil organic matter

Soil ammonium

Leachinginto rivers

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such problems are likely to become more common. Already, North Carolinas 7 million factory-raisedhogs create more waste than do the 6.5 millionhuman residents of the state. Intensive livestock pro-duction is the rule in the United States and westernEurope, and producers are increasingly interested insetting up similar operations elsewhere. In part, suchinterest is the result of the growing regulatory atten-tion that established operations are now attracting. Inthe United States, for example, CAFO waste is thetarget of new regulations recently proposed by theU.S. EPA, and of proposed amendments to the Clean

Water Act. But the export of the CAFO model is alsopartly a variation on a standard economic theme:investment in developing markets. The demand for

meat is growing in the developing world, and thecosts of producing it are generally much lower therethan in the United States or Europe.

China, for example, is interested in boostingdomestic meat production to satisfy growing domesticdemand, according to David Brubaker, an expert onfactory farming at the Johns Hopkins UniversitySchool of Public Health in Maryland. Brubaker saysthat several U.S. agribusinesses are trying to sell theChinese on CAFO production of hogs, poultry, andcattle. In the Philippines, two such corporations,Tyson Foods and Purina Mills, opened a hog breedingfacility near Manila in 1998; the facility can produce100,000 hogs per year. Richard Levins, an agricultur-al economist at the University of Minnesota, says that

Soil Nitrates

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Livestock

Leachinginto rivers

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When inert atmospheric nitrogen (N2) is fixedthat is, bonded tooxygen or hydrogenit becomes an essential plant nutrient. But too muchfixed nitrogen can upset basic physiological and ecological functions. Undernormal natural conditions, the amount of fixed nitrogen is usually fairlylimited. On land, fixation occurs naturally only in certain soil microbes andduring lightning strikes, which bond nitrogen and oxygen. (Nitrogen is fixedin the oceans as well, by some types of plankton.)

The left side of this diagram shows the terrestrial nitrogen cycle as it wouldnaturally function. The right side shows some of the ways in which humanactivity is increasing the amount of fixed nitrogen in the cycle:

Fertilizer production is artificially fixing a large amount of additional nitro-gen. Much of this is released into the environment either directly, when thefertilizer is used on crops, or indirectly, in the manure of livestock fed on thefertilized grain.

The cultivation of beans and other leguminous crops, which grow in closeassociation with nitrogen-fixing microbes, uses a natural mechanism of nitro-gen fixingbut on a scale that is unnaturally large and unnaturally intense,because it involves extensive monocultures.

The burning of coal and oil is releasing nitrogen that was naturally fixedbutmillions of years ago when these fossil fuels were living plants. Some nitrogenis also fixed directly, as a byproduct of combustion.

Finally, the destruction of forests and wetlands (not shown here), does not addfixed nitrogen to the cycle as a whole, but it releases large amounts of fixednitrogen from long-term confinement in those ecosystems.

ILLUSTRATION BY MICHAEL ROTHMAN, COURTESY LARS HEDIN, DEPARTMENT OF ECOLOGY AND EVOLUTIONARY

BIOLOGY, CORNELL UNIVERSITY.


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even Canada is becoming a prime location for hogCAFO developers looking for lots of space, few peo-ple, and relatively lax environmental regulations.

Taken globally, livestock production has become amajor outlet pipe for much of the nitrogen that human-ity is injecting into the natural cycle. The planets pop-ulation of some 2.5 billion pigs and cattle void morethan 80 million tons of waste nitrogen annually. Theentire human population, in comparison, produces justover 30 million tons. Manure, once a valuable farmresource, is now being produced in such quantities thatit might be better considered toxic waste.

HERE AND THERE, ALONG CHINAS 18,000-kilometercoastline, fishers and fish farmers have long contend-ed with an unwelcome form of marine bounty. Redtides, the toxic blooms of certain algae species, are anatural phenomenon in these waters during thespring and summer, but the frequency of the bloomsis increasing. Scientists suspect that the algae areresponding to two factors. Sea surface temperaturesin the region are risinga likely effect of climatechangeand more and more nitrogen-rich waste ispouring into Chinas coastal waters. The annual loadof such pollutionin the form of sewage, industrial

waste, and farm runoffnow exceeds 8 billion tons. Warmer, nutrient rich water is ideal habitat for

algae, and the resulting red tides have been poisoningnot just fish and shellfish, but any people unfortunateenough to consume the contaminated seafood.

Nontoxic algal blooms are on the upsurge too. Eventhough these algae produce no poisons, they use upmost of the waters available oxygen as they decom-pose. The resulting hypoxic dead zonesareas

where dissolved oxygen concentrations are too low tosupport most forms of lifecan last for months.

Algal blooms are hardly unique to China. Perhapsthe most famous of these events is the recurrentbloom in the Gulf of Mexico, off the coast of Texasand Louisiana. Almost every spring, and increasinglyat other seasons as well, thick clouds of algae form inthese waters. The Gulf dead zone is vastin 1999 it

covered 18,000 square kilometers, about the size ofthe state of New Jerseyand it does millions of dol-lars in damage to the regions fisheries every year.Here too, nitrogen is the key factor (althoughincreasing loads of phosphorus and silica are alsoapparently feeding the algae). Most of the nitrogenappears to be coming from sewage and agriculturalrunoff. According to a report by the White HouseOffice of Science and Technology Policy, manurealone contributes some 15 percent of the nitrogenthat makes its way into the Gulf. Thats more than allnonfarm industrial nitrogen sources combined.

But farm runoff and sewage arent the only com-

ponents of the nitrogen cycle that are promotingalgal blooms. In the Baltic Sea, the primary burden ofexcess nitrogen comes from fossil fuel emissions. Afull third of the nitrogen entering the Seaby far thelargest share of the excess loadconsists of nitrogenoxides produced by the combustion of coal and oil inthe surrounding countries. The Baltic is a naturallylow-nitrogen environment that supports a uniquecommunity of organisms adapted to those circum-stances. But as the nitrogen levels have increased,cyanobacteria are responding with large, eerily beau-tiful blooms. The blooms are shading out the seasforests of bladderwrack, a species of brown sea-

weed that requires clear, well lit waters. The bladderwrack is prime spawning and nursery habitat formany fish species, now threatened by the seaweedsdecline. And as the blooms decompose, they stealoxygen from the watera form of change to whichthe Baltic is especially sensitive, since its waters arerelatively low-oxygen to begin with. The drop in oxy-gen is working change in the seafloor community,

where bristleworms, which tolerate hypoxia, arereplacing the once-dominant mussels. This change,in turn, is likely to restructure the foodweb, sincemussels are an important prey item for many fish that

wont eat bristleworms.Algal blooms and dead zones are now a regular

feature of coastal life in many other places around theworldoff the coast of New England, for instance,off the west coast of India, and off Japan and Koreaas well. Most of the worlds major coastal ecosystemsappear to be suffering some degree algae-induced

hypoxia. And toxic blooms are an increasingly con-spicuous part of this problem. According to scientistsat the U.N. Food and Agriculture Organization(FAO) and the International OceanographicCommission, the 1980s and 1990s saw a globalupsurge in red tides. As these episodes have becomemore common, so has the number of algae speciesknown to be involved. In the early 1990s, only about20 species were known to produce toxic blooms;today, at least 85 have been identified.

SOME EFFECTS OF NITROGEN POLLUTION are muchmore subtle than algal blooms, but arguably evenmore dangerous. For example, the nitrogen oxidesproduced through fossil fuel combustion are a majorcomponent of the acid rain that is attacking soil andfresh water in many parts of the world. Waters thatbecome increasingly acidic support fewer forms ofaquatic life. In a similar fashion, the acidification ofsoils tends to impoverish the soil community. Thatspartly because the acid releases aluminum ions fromthe mineral matrix in which they are usually embed-

ded. Free aluminum is toxic to plantsand to many


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aquatic organisms if it washes into streams. The acidalso causes certain minerals to leach out of the soil.Calcium, magnesium, and potassium are essentialplant nutrients and are often in relatively short sup-ply. Where they become rare, plant growth is likely toslow, and the more mineral-hungry species may fadefrom the scene.

These minerals come into the soil through theweathering of rock. Since weathering is a very slowprocess, acidification could reduce the productivity ofaffected soils for centuriesor longer. The extremecase appears to involve cropland, where too muchfertilizer may perform the role of acid rain.

According to Phillip Barak, a professor of soil chem-istry and plant nutrition at the University of

Wisconsin, nitrogen-induced mineral leaching insome U.S. cropland has artificiallyaged these soilsby the equivalent of 5,000 years.

Over the past couple of decades, the industrial-ized countries have made considerable progress inreducing emissions of one main ingredient of acidrain: the sulfur dioxide produced by the combustionof sulfur-contaminated coal. The switch to low sulfurcoal and the installation of smoke stackscrubberson coal-burning powerplants have greatly reducedthis type of pollution. But incremental solutionsarent as useful in reducing the nitrogen compoundsreleased by fossil fuel combustion. The fixed nitrogenin fossil fuels cannot be readily removedandadditional nitrogen is fixed as a byproduct of thecombustion itself.

Excess soil nitrogen is sickening forests and fields

in other ways as well. Nitrogen pollution may reducecold hardiness in certain tree species, making themmore liable to injury or death during the winter. Toomuch nitrogen also tends to reduce fine root density,

which in turn restricts water and nutrient uptake,making plants more susceptible to drought.

On a community level, nitrogen loading is ahomogenizing force, because it strongly favors fast-growing plant species that can use extra nutrient, atthe expense of slower-growing species that cannot.

Affected areas may show robust growth but thatgrowth is likely to be quite uniform. Surveys in Great

Britain by the Institute for Terrestrial Ecology foundthat near major sources of nitrogen pollution, such aslarge poultry farms, the ground-layer flora of nearby

woodlands was dominated by dense stands of a fewrank, tall grass species. The farther away from thefarms the researchers went, the more varied the wood-land flora became. This homogenizing tendency isalso apparent in the heathlands of Northern Europe,particularly in the Netherlands, which has the greatestconcentration of livestock on the planet. Formerly adiverse assemblage of shrubs and herbs, these heath-lands are increasingly dominated by invasive grasses

and trees. Excess nitrogen is indeed fertilizing more

and more of the worlds wild communities. But it ispromoting the growth of a few opportunistic species,at the expense of a more diverse whole.

OVER THE PAST FEW YEARS, Indian researchers havebeen detecting substantial quantities of nitrous oxiderising out of the Arabian Sea, off Indias west coast.The Seas emissions are now thought to contributeup to 21 percent of total output of the gas from the

worlds oceans. In the upper atmosphere, nitrousoxide tends to deplete the stratospheric ozone layer,

which shields the Earth against harmful ultravioletradiation. Nitrous oxide is also a potent greenhousegas. On a molecule-per-molecule basis, its 200 timesmore effective at retaining heat than is CO2. Luckily,its far less common than CO2, but it still accountsfor 2 to 3 percent of overall greenhouse warming.

Why is the Arabian Sea exhaling so much of thisgas? Rajiv Naqvi, a researcher at Indias NationalInstitute of Oceanography sees a link with intensifyingagriculture. Over the past four decades or so, fertiliz-er use has grown substantially on Indias westerncoastal plain, as it has in most of the countrys crop-lands. (According to FAO statistics, Indian fertilizerconsumption nearly doubled from 1965 to 1998, ris-ing to over 11 million tons.) As in many of the worldscoastal waters, the resulting nitrogen-laden runoff isfeeding cyanobacteria and other plankton. Cyano-bacteria generally produce some nitrous oxide as theygrow, but their activity in these waters is affected by

another powerful factor: Indias June to Septembermonsoons. Since freshwater is lighter than salt water,the hard monsoon rainfall tends to blanket the oceansurface, reducing the aeration of the saltier waterbeneath. That drops the oxygen level, and the lack ofoxygen in turn causes the cyanobacteria to metabolizenitrogen in a way that releases larger amounts ofnitrous oxide. This effect appears to have been exac-erbated in recent years because of unusually heavymonsoon rains, a possible result of climate change.

Ice core data indicate that the atmospheric con-centration of nitrous oxide was quite stable until

about a century ago, when it began to increase. Thecurrent rate of increase is estimated at 0.2 to 0.3 per-cent per year. Atmospheric concentrations are nowabout 10 percent higher than they were at the begin-ning of the century.

In the abstract, this is what seems to be happen-ing in the Arabian Sea: an increase in fixed nitrogen,possibly combined with climate change in the form ofintensifying monsoons, is putting more pressure onthe climate system. There is a subtle connection herebetween the nitrogen and carbon cycles, but this is

just one of many such links. Pamela Matson, Director

of Stanford Universitys Earth Systems Program, puts


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it simply: In order to understand carbon and Earthsother cycles, we have to understand how nitrogen ischanging. How will the changing nitrogen cycleaffect the changing carbon cycle?

Given the climate treaty negotiations, there is anearly irresistible political impulse to look for linksthat might be increasing carbon absorption from theatmosphere. Perhaps the nitrogen glut will increasethe carbon sinks. At first glance, that looks like a rea-sonable expectation. After all, nitrogen is often a lim-iting nutrient; more of it should mean more plantgrowth, which should increase CO2 absorption. Butit doesnt seem to be that simple.

In the oceans, plankton growth out beyond thecoastal waters is often limited not by nitrogen avail-ability but by the availability of iron, another essentialnutrient. So extra nitrogen doesnt automaticallytranslate into extra CO2 absorption. (Its true thatsome scientists advocate seeding the oceans with ironto increase CO2 absorption, but given all the unfore-seen problems we ve already created with excessnitrogen and carbon, it would hardly be wise policyto interfere with yet another cycle.) And even in thecase of the coastal algal blooms, which may increaseCO2 absorption, at least periodically, its not clear

whether that extra CO2will remain in the waters overthe long term, or end up back in the atmosphere rel-atively quickly.

On land, the issue is primarily a matter of forestgrowth, since forests generally store more carbonthan other types of terrestrial ecosystems. Its truethat excess nitrogen may cause forests to grow more

rapidly over the short term. But over the long term,the prospects for such forests are fairly dismal, giventhe acidification, aluminum poisoning, and otherforms of physiological and ecological disruption thatnitrogen loading tends to cause. And a declining for-est is more likely to be releasing carbon than absorb-ing it. Despite the connections between the nitrogencycle and the carbon cycle, there is no good reason toassume that disruption of the former will partlycan-cel out disruptions in the latter.

IN TERMS OF ITS TECHNICAL DETAIL, stabilizing thenitrogen cycle is likely to be just as demanding a taskas is stabilizing the carbon cycle. But perhaps themost obvious aspect of this problem is its familiarity:the types of change that would make the most differ-ence are already standard items on the environmentalagenda. Three basic reforms appear to be necessary if

we are to achieve major reductions of our fixed nitro-gen emissions. We will need to convert the dominantmode of agricultural production from its current,high input paradigm to one that emphasizes

organic production. (See Where Have All the

Farmers Gone? September/October 2000.) We willneed to convert our fossil fuel-based energy economyto one based on sunlight, wind, geothermal, andother forms of renewable energy. And finally, we willneed to slow and eventually reverse the destruction ofthe planets remaining natural areas, especially itsremaining forests.

These are enormous goals, of course, but each ofthem shares some characteristics that can help chartthe way forward. In the first place, they all aim atbroad systemic reform, but they focus on the small-scale unit. Organic farming usually works best whenthe farms are small enough to accommodate the locallandscape. Sophisticated renewable energy systemsgenerally create networks of smaller producers ratherthan one or two enormous powerplants. And sustain-able forest use, by definition, is carefully attuned tolocal ecological realities. Theres a second commonfeature too: each of these goals emphasizes creativeuse of diversity. A polycultural cropping system, arange of renewable energy technologies, a combina-tion of agroforestry, timber, and tourismin eachcase, the idea is to replace a monoculture approach

with a system that is more diverse and therefore moreflexible, more likely to be sustainable over the longterm. Small-scale and diverse would appear to be the

way to go. You could say that the agenda pointstowards a high degree of local adaptation.

Humanity has reached a point at which we aredominatingnot just particular ecosystemsbut thecycles that regulate the basic processes on which alllife depends. Our capacity to understand the effects

of our interference is growing rapidly. But will we beable to use that understanding productively?Increasingly, it seems, progress on the global level

will depend on our ability to reinvent our relation-ships to the local levelto the particular ecosystemsand societies in which we actually live.

Danielle Nierenberg recently completed her M.S. inthe agriculture, food, and environment program atTufts University, in Massachusetts, and is currently

working with the WORLDWATCH staff.

Key Sources

GRACE Factory Farm Project website:www.factoryfarm.org.

Vaclav Smil, Cycles of Life(New York: ScientificAmerican Library, 1997).

Peter M. Vitousek, et al., Human Alteration of theGlobal Nitrogen Cycle, Issues in Ecology,vol. 1(Washington, DC: Ecological Society of America, 1997).

toxic fertility

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