WWORLDORLD••WWATCHATCH Working For A Sustainable Future

P Soup (the global cycle)

by Elena Bennett and Steve Carpenter

Excerpted from March/April 2002 WORLD WATCH magazine

© 2002, Worldwatch Institute

For more information about Worldwatch Institute and its programs and publications, please visit our website at www.worldwatch.org

ORLDWATCH NSTITUTE WW 1776 Massachusetts Ave., NW Washington, DC 20036 I www.worldwatch.org Soup

It’s green, but it’s not good for you. That benign- looking pond scum signifies a far-reaching shift in the global phosphorus cycle.

by Elena Bennett and Steve R. Carpenter

hink of global environmental change, and that the movement of phosphorus is indeed a global you’ll probably think most immediately of phenomenon—and that that patch of algae you see in Tsuch sweeping atmospheric phenomena as the pond at your feet may be affected by changes in global warming or . Many of the the hundreds or thousands of miles away. other environmental disruptions we’re familiar Both nitrogen and phosphorus are essential nutri- with—toxic dumps, decimated forests, eroded ents for plants and are therefore present in most fer- fields—seem largely confined to particular localities. tilizers in addition to being present in agricultural Yet there are some environmental changes that, while and municipal waste products. As a result, the move- appearing to be locally confined, are in fact manifes- ment of large amounts of around the plan- tations of worrisome global patterns. Look at the et can also mean the movement of excessive nutrients algae forming on a local farm pond, for example, and from one place to another. Typically, some of the fer- you’re seeing the result of a process—the phosphorus tilizer used on a farm does not stay there but moves cycle—that extends far beyond that farm. downhill where it can get into a downstream aquatic Algae thrives (literally “blooms”) on runoff of ecosystem—a river, lake, or bay. Concentrations of waste or other materials containing phos- excess nutrients in these bodies of water cause the phorus. While human-caused changes in the closely patches of algae to expand prolifically. Such related have been widely publicized “,” as the green blanketing of the (see “Toxic Fertility” in the March/April 2001 water is called, can be a crippling process: it suffo- WORLD WATCH), impacts on the phosphorus cycle cates the life under the slime—killing fish, diminish- ✦ are less well known. Our research suggests, however, ing , and emitting noxious odors. It

24 WORLD•WATCH March/April 2002 19th-century engraving of a phosphorescent sea creature.

reduces the value of the water for most human uses— have been common here since the 1880s. Along with whether for drinking, fishing, swimming, or even these blooms came dramatic changes in the food boating. web, including loss of some native species and Lake Mendota, in Madison, Wisconsin is a classic increased populations of non-native species such as example of a eutrophic lake in an urbanizing, but Eurasian milfoil and carp. Eutrophication has greatly primarily agricultural setting. The lake has exhibited diminished the lake’s recreational value. many of the symptoms associated with eutrophica- Historically, Madison has never developed public tion since agriculture became the primary land cover swimming pools, because people were always able to in the surrounding watershed, in place of the native swim in the area’s plentiful lakes. Now, as eutrophi- prairie and oak savannah. Blooms of blue-green algae cation worsens, there is increasing public pressure to ✦

WORLD•WATCH March/April 2002 25 develop pools because many of the lakes are no ization, the natural cycle was in some respects short- longer swimmable. For Lake Mendota alone, the cost circuited. Technological advances, especially in the of eutrophication has been estimated to be about $50 past 50 years, enabled us to mine phosphorus on a million in lost recreation and property values. Even large scale, make fertilizer and other products from it, so, what happened to this lake is seen as a local and transport these products around the world, dra- story—of little interest to someone in North Caroli- matically accelerating the now not-so-natural phos- na or South China. If the people in Madison want to phorus cycle. Globally, we estimate that the annual deal with this problem, obviously it is their own local accumulation of phosphorus in the Earth’s freshwa- farms and sewer pipes they have to deal with. What’s ter and terrestrial ecosystems has almost quadrupled, not so obvious is that what has happened here results from around 3.5 terragrams per year before humans from massive changes in the flow of phosphorus began mining and farming on a large scale, to around around the globe. 13 terragrams per year now. To understand the cycle as it was before human Human Impact on the Global interventions began, it is useful to think of the cycle Phosphorus Cycle as a flow from the earth’s crust back to earth’s crust, through four main compartments (see figure, page Long before humans arrived on the scene, phos- 31). First, phosphorus-containing rock is weath- phorus was moving around the planet in a natural ered—worn by wind, rain, freezing and thawing, cycle that probably took millions of years to com- etc.—until it becomes soil. With the soil, it moves plete. A phosphorus molecule might be trapped in into lakes and rivers, which transport it to the . rock, then released by to start its gravity-driv- Some of it is dissolved in water, and some adsorbed en journey to the ocean. Along the way, it might be to soil particles that are carried by erosion down to taken up by plants and then animals, then returned to the sea and, ultimately, to the ocean bottom. There it the soil or water via dead vegetation or urine, to con- awaits the tectonic movement that will lift up the tinue its slow trek downhill until it finally reached the rock and make it part of the land again. The cycle is ocean. Once in the ocean—probably after taking described by Aldo Leopold in his essay, “Odyssey,” in more detours through plants and animals along the A Sand County Almanac: way—it would sink into the sediment. In time, geo- “X had marked time in the limestone ledge since logical processes would turn this sediment to terres- the Paleozoic seas covered the land. Time, to an atom trial rock—reincorporating the phosphorus locked in a rock, does not pass. The break came when molecule. The cycle would begin again. a bur-oak root nosed down a crack and began prying With the advent of human agriculture and urban- and sucking. In the flash of a century the rock

A Brief History of Phosphorus

In his book The 13th Element: The as suggested by Emsley’s account seen. Unwittingly he unleashed Sordid Tale of Murder, Fire, and of its discovery, the users of phos- upon an unsuspecting world one Phosphorus, science writer John phorus had little inkling of the of the most dangerous materials Emsley tells the story of a material damage its disruption might ever to have been made. that acquired a notorious reputa- ultimately do: On that dark night our lone tion over three centuries—in mak- alchemist was having no luck with ing the nerve gas ethyl S-2 Uncertainty still surrounds the his latest experiments to find the diisopropylaminoethyl methyl- date on which phosphorus was philosopher’s stone. Like many phosphrothiolate (VX); in the first made. We can be fairly sure before him he had been investi- organophosphate insecticides the place was Hamburg in Ger- gating the golden stream, urine, Tetraethyl diphosphate, Parathion, many, and that the year was prob- and he was heating the residues and Malathion; in mortar and how- ably 1669, but the month and day from this which he had boiled itzer shells; in the bombs Hitler are not recorded, though it must down to a dry solid. He stoked his rained on Britain; in the execution have been night time. The small furnace with more charcoal of numerous murders; and— alchemist who made the discov- and pumped the bellows until his allegedly—in the infliction of Gulf ery stumbled upon a material the retort glowed red hot. Suddenly War Syndrome. But from the start, like of which had never been something strange began to hap- ✦

26 WORLD•WATCH March/April 2002 decayed, and X was pulled out and up into the world they are incorporated into the soil, either directly as of living things. He helped build a flower, which fertilizers or indirectly as excess phosphorus in became an acorn, which fattened a deer, which fed an manure resulting from the use of high- ani- Indian, all in a single year….” The narrative continues mal feeds. Poor land-use practices further increase through a journey of many adventures involving a erosion of this phosphorus-laden soil. bluestem, a plover, some phlox, a fox, a buffalo, a spi- Human actions thus accelerate the natural cycle at derwort, a prairie fire, another fox, another Indian, a two key points: in the entry of phosphorus into the beaver, a bayou, and a riverbank. Then, “One spring from rock, and in the movement from soil an oxbow caved the bank and after one short week of into aquatic ecosystems. Additionally, by moving freshet X lay again in his ancient prison, the sea.” phosphorus away from certain spots on the Earth’s Within each of the four compartments of this surface (those where it is mined) and to others (pri- cycle—the Earth’s crust, the soil, aquatic systems and marily where it is used as fertilizer and animal feed), the —there are more rapid cycles of phospho- we radically alter the distribution of this element on rus through the biosphere. In the soil phase, the the planet’s surface. The effect of shifting large quan- phosphorus does not all just stay put in the ground. tities to places where it would not naturally be found Some of it is taken up from the soil by plants, which in high concentration has become a growing concern are eaten by animals, which may in turn be eaten by to aquatic ecologists and others who care about other animals, before the phosphorus is eventually maintaining supplies of clean . returned to the soil in manure or through decompo- Most phosphorus moves downhill attached to sition of the animals’ bodies after they die. Of course, eroded soil particles—whether over the ground as the phosphorus molecule can go through several muddy runoff or in rain-swollen streams or rivers. As more of these rapid biospheric cycles before moving people increase the amount of phosphorus in the soil to the next compartment of the global cycle. Similar through use of fertilizers, the amount of phosphorus biospheric cycles may then take place in the ocean. carried downhill per kilogram of soil also increases. People do several things that impact both the larg- The higher the concentration in the soil at the outset, er global cycle and the smaller, more rapid cycles of the more is available to release downhill. And although phosphorus through the biosphere. Most phosphorus it is likely that less than 5 percent of the phosphorus mining takes place in only a few locations around the used as fertilizer in temperate areas makes its way into world—primarily in Florida, West and North Africa, aquatic ecosystems each year, that is enough to cause and Russia. Mined phosphorus is then made into fer- major changes in those environments. tilizers, animal feeds, and other products and trans- Understanding what is happening in the upland ported to agricultural areas all over the world. There soil provides a window on the future of downhill water

pen. Glowing fumes filled the was all but spent. Magical though vessel and from the end of the it was, his phosphorus stub- retort dripped a shining liquid bornly refused to bring the that burst into flames…. riches of which he dreamed. That Hamburg alchemist was Today we know his was a vain Hennig Brandt, a rather pompous hope, but the luminescent man who insisted on being called material he had made was to Herr Doktor Brandt. His first create great wealth for a few thought was that he had at last in the centuries ahead. It was found what he had been search- to create untold misery for ing for. Surely this wondrous new many more. material was the philosopher’s stone? If so, he had better keep the secret to himself while he made his fortune. And so for six long years he hid his discovery from the world, until his wealth ✦

WORLD•WATCH March/April 2002 27 bodies. If we study soil uphill from lakes and rivers, we rapidly because all the necessary nutrients are now know more about the possibilities for the future of present. But the excessive growth of one organism those same lakes, rivers, and the estuaries they flow may mean the death of another. When thick blooms into. Studying changes in the phosphorus cycle and of algal growth block sunlight from reaching the upland on a global scale can help us know where plants below, the decay of dead algae uses up the to expect problems in the future and may help us available oxygen in the water, suffocating fish and reduce excess phosphorus before it is a problem. sometimes causing whole populations of species to be lost. Eutrophication not only makes a lake look and Messing with Eutrophication smell putrid; it also substantially changes the way the aquatic ecosystem works. It can change the plant Under natural conditions, eutrophication can be community, the food web, and the chemistry of a a centuries-long aging process for some lakes. When lake beyond recognition. human caused (scientists call this “cultural” eutroph- Although scientists have been studying eutrophi- ication), it can happen in a few years. In many cases, cation since the turn of the twentieth century, cultur- cultural eutrophication can be reversed by greatly al eutrophication was not recognized as a widespread reducing the amount of phosphorus entering the international problem until the 1950s and 60s, when water. it became a matter of growing concern in both North Phosphorus is just one of many nutrients that America’s Great Lakes region and in much of plants need to survive and grow. However, it is par- Europe. “Lakes became green and smelly, devoid of ticularly important to lake systems because it is the fish, unfit as sources of drinking water and unimagin- limiting nutrient. In other words, even when plants able as places of recreation,” writes John Emsley in have all other nutrients in sufficient quantities, they The Thirteenth Element: A Sordid Tale of Murder, will often lack phosphorus. When phosphorus is Fire, and Phosphorus. added to lake water, plants may suddenly grow very Scientists did not always know that phosphorus

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28 WORLD•WATCH March/April 2002 was the culprit in situations Terragrams (millions of tons) per year of cultural eutrophication. 16 But in the late 1960s, a 400 research team headed by David Schindler, a professor 12 of Ecology at the University 300 of Alberta in Edmonton, Annual Accumulation Canada, conducted a reveal- (left axis) ing experiment on a lake— 8 known as “Lake 227”—in 200 northwestern Ontario. The team divided the lake into Cumulative Accumulation two halves. They enriched 4 (right axis) 100 one half with nitrogen and carbon, and the other half with phosphorus and car- 0 0 bon. The phosphate- 1960 1965 1970 19751980 1985 1990 1995 enriched basin rapidly became eutrophic, while the The Rising Phosphorus Content of Terrestrial and other basin remained Fresh Water Ecosystems unchanged. Phosphorus became widely recognized as the The growing recognition that eutrophication is source of fresh water eutrophication problems, and more widespread than we might have initially imag- efforts were begun to reduce phosphorus inputs to ined led us to look for a larger-scale perspective on aquatic ecosystems. In most of the developed world, the issue and its causes. We knew that the immediate sewage was diverted around lakes, and most “point” cause is human impact on phosphorus cycling: sources (direct outflows of phosphorus-rich effluents increased phosphorus in soils and increase erosion from specific farms or processing plants) were cut off. causes increased erosion to lakes. However, we want- By the 1990s, had been removed from ed to understand the eutrophication problem from a most detergents, as well. Yet eutrophication persist- global perspective because we believed that this per- ed, in part because lakes are efficient recyclers of spective might lead to more effective long-term poli- phosphorus. Under conditions of low oxygen at the cies to reduce phosphorus load to aquatic lake bottom, phosphorus lying in the sediment reen- ecosystems. Studying phosphorus increase in soils, as ters the water column and is once again available to opposed to waiting until fish begin dying off in lakes, be used by algae. The problem also remained because can be an effective preventive measure. So far, the scientists had overlooked another source of phospho- systematic assessment of phosphorus in upland soils rus entering lakes—the non-point source runoff from has not become a standard of the eutrophication surrounding lands—which proves much more diffi- management process. cult to control. Currently, non-point runoff from uplands is the main source of phosphorus to most Management: The Global Picture aquatic systems in the developed world. Worldwide, eutrophication in lakes, rivers, and Despite widespread controlling of point source estuaries appears to be increasing. In the Gulf , treatment of sewage, and elimination of of Mexico, there is now a large hypoxic zone, or phosphates from most soaps and detergents, “dead” zone, where the low oxygen content of the eutrophication continues to worsen as a result of water has led to massive die-offs in ocean species. The human activity worldwide. What to do? cause has been traced to nutrient runoff from the The phosphorus in agricultural soils could take grain-growing states of the midwestern United States, decades to draw down by reducing use of fertilizers. carried to the Gulf by the Mississippi River. In New During that time, changes in farm practices, urban Zealand, an increase in dairy farming and fertilizer use expansion, or could accelerate erosion has worsened nutrient pollution in hundreds of shal- and—despite the lower input of phosphorus to soil— low lakes and streams. By 1994, the most recent date increase the rate at which phosphorus moves from for which we have worldwide data, significant eutroph- the soil into aquatic ecosystems. By the time author- ication problems were being reported in 54 percent of ities see enough impairment of lakes to want to take all lakes and reservoirs in Southeast Asia, 53 percent of action upstream, the fate of the lakes downstream those in Europe, 48 percent in North America, 41 per- may already have been sealed. By the same logic, cent in South America, and 28 percent in Africa. however, the long time lags associated with soil phos- ✦

WORLD•WATCH March/April 2002 29 How we studied the global cycle

Although there is not much phos- to find out how much phosphorus We completed a similar calcula- phorus on Earth (only about 0.1 is accumulating in the soil compart- tion for soil accumulation of phos- percent of the Earth’s crust is ment of the global model each phorus before widespread human phosphorus), it is an essential nutri- year. We wanted to get a large- impact. In the millennia before civi- ent for all life forms on our planet. It scale picture because we thought lization began, of course, there was is found primarily in solid or liquid we might have more options for no mining of phosphorus—only state and it plays a key role in DNA management if eutrophication was natural , which released (the genetic material of most life) recognized as a global, rather than between 1 and 6 million metric tons and the energy-releasing molecule just local, problem. per year. ATP. We calculated phosphorus By making separate calcula- Phosphorus is mined in only a accumulation in soils by determin- tions for agricultural areas and non- few countries, including the United ing how much phosphorus enters agricultural, we found that although States, the former Soviet Union, soils each year and how much is agricultural areas occupy only a Morocco, and China; however, removed. We found values for the small fraction of the Earth’s surface phosphorus-containing products amount of mined phosphorus that (about 11 percent), most of the are consumed in most countries. is used for animal feeds, fertilizer, phosphorus accumulation occurs About 90 percent of the phospho- and other easily biodegradable there. Year by year, phosphorus rus mined annually is used to pro- products annually, and added that continues to build up in the world’s duce fertilizers and animal feeds. to the amount of naturally weath- farmland. Globally, we knew that by mining ered phosphorus. These are the Separating calculations for poor phosphorus in order to put it on inputs to Earth’s soil. We also cal- and rich countries, we found that farms and lawns, we were likely to culated how much was leaving while poor countries once had a be creating new areas of high con- Earth’s soils each year, by estimat- net loss of phosphorus, they now centration. However, scientists ing how much phosphorus moved account for more accumulation knew little about where accumula- into the ocean and other aquatic than rich countries do. Lakes in tion might be most severe. Answer- ecosystems. The difference these countries are probably ing this question would help between the inputs and the outputs becoming more susceptible to managers prepare for future is the amount that accumulates in eutrophication, which is likely to eutrophication problems. soils on an annual basis, which we worsen the quality of life of these We made a budget (analogous estimated to be between 10.5 and countries in the future. ✦ to a household’s financial budget) 15.5 million metric tons per year.

phorus buildup also mean that action now can pre- the phosphorus stored in upland soil is more difficult. vent expensive and persistent eutrophication prob- Because upland runoff originates from more dis- lems in the future. persed sources, it is very difficult to pinpoint the Efforts to control phosphorus runoff have landowners who are responsible. One consequence is increased dramatically in recent years. Still, most poli- that in the United States, programs are usually vol- cies and regulations have approached such runoff as a untary rather than mandatory. Effectiveness is limit- problem of the particular lake, river reach, or estuary, ed, especially if the incentives for participation are not rather than as part of a larger pattern. These efforts great enough. In some cases, local water authorities have generally involved reducing nearby fertilizer and attempt to help farmers (and others) to limit phos- manure use, limiting erosion, or removing algae from phorus use or reduce erosion by offering cost sharing the water directly. In Lake Mendota, the city regular- from the government. For example, if manure stor- ly runs a floating lawn mower-like machine that strips age pits are needed, the government may offer to pay algae and other aquatic plants from the water. a share of the cost of creating a manure storage pit. To implement the long-term solution by reducing In other countries such as the Netherlands, ✦

30 WORLD•WATCH March/April 2002 The Human Impact on the Phosphorus Cycle

The global phosphorus cycle is made up of four “compartments” of the Earth EARTH’S CRUST Mining (crust, soil, freshwater systems, and the ocean), through which—due Fertilizer to the slow process of rock for- mation in the ocean bottom, subsequent tectonic upheaval, and weathering of rock into soil—it takes mil- lions of years to complete. millions of years SOIL SEAFLOOR plants & Along the way, an atom of days to years animals phosphorus may go through many more rapid, biological, cycles as it is incorporated into animals or plants in the soil, aquatic, or ocean compartments. Human activity, however, has radically accelerated some parts of Erosion the movement. Mining phosphorus LAKES & RIVERS Clearing land (exposing soil) for fertilizer speeds up the release for farming, timbering, and from crust to soil, and clearing development land speeds up the movement from soil to aquatic systems. The result has been a more days to years rapid buildup of phosphorus in soils, and a more widespread eutrophication of lakes and rivers, than occurred in the past. plants & animals

restrictions on phosphorus use are more severe and phenomenon, we notice that around the world, water enforced by law rather than enacted voluntarily. subsidizes agricultural systems. Because we do not Eutrophication is a major concern for the Nether- account for the cost of water pollution when we add lands, due to the country’s high up the cost of agricultural production, food produc- and intensive agriculture—combined with the fact tion seems cheaper than it actually is. In economic that the Rhine River water that flows into the terms, the cost of water pollution caused by agricul- Netherlands from other European countries is tural production is an externality to the agricultural already high in phosphorus content. Therefore, production system. If this worked in the past because Dutch farmers are subject to manure quotas: for each clean fresh water seemed infinite, it no longer makes acre of land, they may only spread a certain amount sense to take fresh water supply for granted. Since of manure. (The amount allowed per acre often both food and water are necessary for human sur- depends on the location, size, and type of farm.) For vival, it might appear that we are facing a difficult any manure used beyond that amount, the farmer choice between producing food and protecting must pay the costs of removal and processing. aquatic resources. However, just as we cannot afford As we begin to look at eutrophication as a global to ignore water pollution, we cannot afford to solve ✦

WORLD•WATCH March/April 2002 31 the problem simply by reducing agricultural produc- lion to build a water filtration plant to clean the tion. The growing human population and increasing water. Instead, they were able to purchase watershed demand for food, along with the lack of vacant arable land in the Catskills sufficient to naturally filter the land for use in agricultural expansion, mean that agri- water for only $1.5 billion. Quality of the water sup- cultural production will probably have to become ply was increased and money was saved. more intense and efficient on land already in produc- Comparable solutions may be feasible at national tion. and global scales, making it possible to conserve fer- Win-win solutions would change regulations and tilizer, stabilize soils, and improve water quality while incentives to bring the costs and benefits of agricul- reducing costs. Effective policies might include the tural production and water quality protection into establishment of national or international phospho- better balance. For example, governments could cre- rus markets and better tracking of phosphorus ate markets for nitrogen and phosphorus runoff. around the world, in order to ensure that some areas Each farm would be allotted a certain amount of per- are not being overwhelmed by excess nutrients. missible pollution or runoff. If the farmer could find Phosphorus markets could ensure that products such a way to emit less pollution, he could then sell some as manure are moved to where they can be used. of his pollution rights to another farm. If set up cor- rectly, the market would quickly adjust to the value of Steve R. Carpenter is Halverson Professor of Lim- water—thereby internalizing the cost of water pollu- nology and Professor of Zoology at the University of tion. Alternatively, governments could tax fertilizer Wisconsin, and a past president of the Ecological use to create an incentive for conservation, using the Society of America. Elena Bennett is doing post- tax revenues to improve water quality. doctoral research in fresh water ecology at the Such methods can prove economically as well as University of Wisconsin. The data in this article are environmentally beneficial. A few years ago, New based on E.M. Bennett, S.R. Carpenter, and N.F. York City, which gets its water supply from the Caraco, 2001, “Human Impact on Erodable Phos- Catskill mountain area, found that its water was no phorus and Eutrophication: A Global Perspective,” longer meeting EPA standards due to fertilizers and BioScience 51:227–234 pesticides in the soil. City officials realized they would have to spend between $6 billion and $8 bil-

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32 WORLD•WATCH March/April 2002