suffered the most so far. They are troubling aspects of this nutrient the ultimate receptacles of much assault on aquatic systems has f the nutrient overload, which been a steady rise in toxic alg ends to accumulate in runoff blooms which can take a heay be delivered directly in the oll on fish, seabirds, and marine form of t treated mammals(Anderson 1994: 62-68) ewage is very high in nitrogen The nitrogen glut also from protein in the human diet. impinges on the health of the South Florida Water Management District In these aquaticsystems, excess atmosphere when the nitrogen- have spurred additional growth in When this extra plant matter dies the air, either from fossil fuey 9 nitrogen can often stimulate the containing gases-nitric oxide and America and Europe seems to growth of algae and other plants. nitrous oxide-are released this manner. But there is a limit to and decays, it can rob the water of burning, land clearing, or the amount of nitrogen that its dissolved oxygen, suffocating agriculture-related activities. Nitric natural systems can take up; many aquatic organisms oxide, for example, is a potent beyond this level, serious harm This overfertilization proces precursor of smog and acid rain can ensue. In terrestrial called eutrophication, is one of the and nitrous oxide is a long-lived ecosystems, nitrogen saturation most serious threats to aquatic greenhouse gas that traps some can disrupt soil chemistry, leading environments today, particularly 200 times more heat than carbon to loss of other soil nutrients such as calcium, magnesium, and waters where most commercial play a role in depleting the potassium and ultimately to a fish and shellfish species breed stratospheric ozone layer decline in fertility (Vitousek et al. (Vitousek et al. 1997: 11; Diaz et concentrations in the atmosphere 1997:7-9 al. 1995: 245). Partially enclosed are rising rapidly-about 0.2 to Excess nitrogen can also seas such as the Baltic Sea, the 0.3 percent per year Socci 1997, reak havoc with the structure of Black Sea, and even the Vitousek et al. 1997: 6-7) ecosystems, affecting the number Mediterranean have also been Curbing the world,'s nitroger nd kind of species found. hard hit by nitrogen-ca overload will mean acting on Researchers in the united eutrophication, and an extensive several fronts. Making fertilizer Kingdom and the United States ' dead zone of diminished applications more efficient is one have found that applying nitrogen productivity has developed at the of the most promising options fertilizer to grasslands enables a mouth of the Mississippi River in Agriculture accounts for by far th ew nitrogen-responsive grass the Gulf of Mexico because of the largest amount of human species to dominate, while others large influx of nitrogen from generated nitrogen-some 86 disappear. In one British agricultural runoff (Warrick percent (ordan et al. 1996: 655) experiment, this effect led to a 1997: A1). One of the more Fertilizer use was scant until the fivefold reduction in the number of species in the most heavily fertilized plots(Vitousek et al. More fertilizer: more food, But more pollution too 1997:9-10: Wedin et al Figure 2: Trends in Fertilizer Consumption, 1961-1997 1996:1720-1721). In the Netherlands, where nitroger 120 deposition rates are among the ighest in the world, whole 100 ecosystems have been altered because of this shift in dominant plants, with species-rich heathlands being converted to species-poor forests and grasslands that better accommodate the nitrogen load (Vitousek et al. 1997: 9-10) Although terrestrial 196119651970197519801985199019951997 ecosystems are vulnerable to the global nitrogen glut, aquatic ecosystems in lakes, rivers, and OUTH AMERIC -O OCEANIA coastal estuaries have probably ood and Agriculture Organization of the United Nations(FAO) CEarthTrends 2001 World Resources Institute. All nights reserved. Fair use is permitted on a limited scale and for educational purposes.©EarthTrends 2001 World Resources Institute. All rights reserved. Fair use is permitted on a limited scale and for educational purposes. 2 South Florida Water Management District America and Europe seems to have spurred additional growth in this manner. But there is a limit to the amount of nitrogen that natural systems can take up; beyond this level, serious harm can ensue. In terrestrial ecosystems, nitrogen saturation can disrupt soil chemistry, leading to loss of other soil nutrients such as calcium, magnesium, and potassium and ultimately to a decline in fertility (Vitousek et al. 1997:7–9). Excess nitrogen can also wreak havoc with the structure of ecosystems, affecting the number and kind of species found. Researchers in the United Kingdom and the United States have found that applying nitrogen fertilizer to grasslands enables a few nitrogen-responsive grass species to dominate, while others disappear. In one British experiment, this effect led to a fivefold reduction in the number of species in the most heavily fertilized plots (Vitousek et al. 1997:9–10; Wedin et al. 1996:1720–1721). In the Netherlands, where nitrogen deposition rates are among the highest in the world, whole ecosystems have been altered because of this shift in dominant plants, with species-rich heathlands being converted to species-poor forests and grasslands that better accommodate the nitrogen load (Vitousek et al. 1997:9–10). Although terrestrial ecosystems are vulnerable to the global nitrogen glut, aquatic ecosystems in lakes, rivers, and coastal estuaries have probably suffered the most so far. They are the ultimate receptacles of much of the nutrient overload, which tends to accumulate in runoff or to be delivered directly in the form of raw or treated sewage. (Sewage is very high in nitrogen from protein in the human diet.) In these aquaticsystems, excess nitrogen can often stimulate the growth of algae and other plants. When this extra plant matter dies and decays, it can rob the water of its dissolved oxygen, suffocating many aquatic organisms. This overfertilization process, called eutrophication, is one of the most serious threats to aquatic environments today, particularly in coastal estuaries and inshore waters where most commercial fish and shellfish species breed (Vitousek et al. 1997:11; Diaz et al. 1995:245). Partially enclosed seas such as the Baltic Sea, the Black Sea, and even the Mediterranean have also been hard hit by nitrogen-caused eutrophication, and an extensive “dead zone” of diminished productivity has developed at the mouth of the Mississippi River in the Gulf of Mexico because of the large influx of nitrogen from agricultural runoff (Warrick 1997:A1). One of the more troubling aspects of this nutrient assault on aquatic systems has been a steady rise in toxic algal blooms, which can take a heavy toll on fish, seabirds, and marine mammals (Anderson 1994:62–68). The nitrogen glut also impinges on the health of the atmosphere when the nitrogen￾containing gases—nitric oxide and nitrous oxide—are released into the air, either from fossil fuel burning, land clearing, or agriculture-related activities. Nitric oxide, for example, is a potent precursor of smog and acid rain, and nitrous oxide is a long-lived greenhouse gas that traps some 200 times more heat than carbon dioxide. Nitrous oxide can also play a role in depleting the stratospheric ozone layer; concentrations in the atmosphere are rising rapidly—about 0.2 to 0.3 percent per year (Socci 1997; Vitousek et al. 1997:6-7). Curbing the world's nitrogen overload will mean acting on several fronts. Making fertilizer applications more efficient is one of the most promising options. Agriculture accounts for by far the largest amount of human￾generated nitrogen—some 86 percent (Jordan et al. 1996:655). Fertilizer use was scant until the Figure 2: Trends in Fertilizer Consumption, 1961-1997 More Fertilizer: More Food, But More Pollution, Too 0 20 40 60 80 100 120 140 1961 1965 1970 1975 1980 1985 1990 1995 1997 million metric tons ASIA (EXCL. MIDDLE EAST) EUROPE MIDDLE EAST & N. AFRICA SUB-SAHARAN AFRICA NORTH AMERICA C. AMERICA & CARIBBEAN SOUTH AMERICA OCEANIA WORLD Source: Food and Agriculture Organization of the United Nations (FAO)