EarthTrends: Featured Topic Title. Nutrient Overload: Unbalancing the Global Nitrogen Cycle Author(s) taff of World Resources Program Source World Resonrces 1998-99 Date written: 1998 As a basic building block of plant contribute more to the glob vegan lakes have doubled in and animal proteins, nitrogen is a supply of fixed nitrogen each year less than a decade (vitousek et al nutrient essential to all forms of than natural processes do, with 1997: 10). Although many of the life. But it is possible to have too human-generated nitrogen totaling nitrogen trouble spots tend to be luch of a good thing recent about 210 million metric tons per in North America and Europe, the studies have shown that excess year, while natural processes threat of nitrogen overload is nitrogen from human activities contribute about 140 million global in scope, as both fertilizer such as agriculture, energy (Vitousek et al use and energy use are growing 1997: 5-6). See Figure 1: Global quickly in the developing world begun to overwhelm the natural Sources of Biologically Available In fact, global nitrogen deposition itrogen cycle with a range of ill (Fixed) Nitrogen may as much as double in the next effects-from diminished soil This influx of extra nitrogen 25 years as agriculture and energy fertility to toxic algal blooms has caused serious distortions of use continue to intensify(Asner et (Vitousek et al. 1997: 2, Jordan et the natural nutrient cycle, l.1997:228 al. 1996: 665: Asner et al. especially where intensive The effects of this surfeit of 1997:232) agriculture and high fossil fuel use nutrients reach Until recently, the supply of coincide. In some parts of environmental domain nitrogen available to plants-and northern Europe, for example, threatening air and water quality ltimately to animals-has been forests are receiving 10 times the and disrupting the health of quite limited. Although it is the natural levels of nitrogen from errestrial and aquatic ecosystem most abundant clement in the airborne deposition(Pearce Natural systems may be able to atmosphere, nitrogen from the air 1997: 10), while coastal rivers in absorb a limited amount of cannot be used by plants until it is the northeastern United States and additional nitrogen by producing chemically transformed, or fixed, northern Europe are receiving as more plant mass, just as garden nto ammonium or nitrate much as 20 times the natural vegetables do when fertilized ompounds that plants can amount from both agricultural Atmospheric deposition of metabolize In nature, only certain and airborne sources(Vitousek et nitrogen emissions on some bacteria and algae(and, to a lesser al. 1997: 10). Nitrate levels in many heavily cut forests in North extent, lightning) have this ability to fix atmospheric nitrogen, an the amount that they make A Global Glut of Nitrogen available to plants is comparatively gure 1: Global Sources of Biologically Available(Fixed)Nitrogen small. Other bacteria break down nitrogen compounds in dea ANNUAL RELEASE OF matter and release it to th ANTHROPOGENIC FIXED NITROGEN atmosphere again. As a SOURCES (TERAGRAMS) ence, nitrogen is a Fertilizer precious commodity-a limiting Legumes and other plants nutrient--in most undisturbed Fossil fuels 000 Biomass burning 40 All that has changed in the 10 past several decades. Driven by a Land clearing 20 massive increase in the use of fertilizer, the burning of fossil fuels, and a surge in land clearing Total from human sources 210 and deforestation the amount of nitrogen available for uptake at NATURAL SOURCES any given time has more than Soil bacteria, algae, lightning, etc. 140 doubled since the 1940s. In other words. human activities now Source: Vitousek et al. 1997: 4-6 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. EarthTrends: Featured Topic Title: Nutrient Overload: Unbalancing the Global Nitrogen Cycle Author(s): Staff of World Resources Program Source: World Resources 1998–99 Date written: 1998 As a basic building block of plant and animal proteins, nitrogen is a nutrient essential to all forms of life. But it is possible to have too much of a good thing. Recent studies have shown that excess nitrogen from human activities such as agriculture, energy production, and transport has begun to overwhelm the natural nitrogen cycle with a range of ill effects—from diminished soil fertility to toxic algal blooms (Vitousek et al. 1997:2; Jordan et al. 1996:665; Asner et al. 1997:232). Until recently, the supply of nitrogen available to plants—and ultimately to animals—has been quite limited. Although it is the most abundant element in the atmosphere, nitrogen from the air cannot be used by plants until it is chemically transformed, or fixed, into ammonium or nitrate compounds that plants can metabolize. In nature, only certain bacteria and algae (and, to a lesser extent, lightning) have this ability to fix atmospheric nitrogen, and the amount that they make available to plants is comparatively small. Other bacteria break down nitrogen compounds in dead matter and release it to the atmosphere again. As a consequence, nitrogen is a precious commodity—a limiting nutrient—in most undisturbed natural systems. All that has changed in the past several decades. Driven by a massive increase in the use of fertilizer, the burning of fossil fuels, and a surge in land clearing and deforestation, the amount of nitrogen available for uptake at any given time has more than doubled since the 1940s. In other words, human activities now contribute more to the global supply of fixed nitrogen each year than natural processes do, with human-generated nitrogen totaling about 210 million metric tons per year, while natural processes contribute about 140 million metric tons (Vitousek et al. 1997:5–6). (See Figure 1: Global Sources of Biologically Available (Fixed) Nitrogen.) This influx of extra nitrogen has caused serious distortions of the natural nutrient cycle, especially where intensive agriculture and high fossil fuel use coincide. In some parts of northern Europe, for example, forests are receiving 10 times the natural levels of nitrogen from airborne deposition (Pearce 1997:10), while coastal rivers in the northeastern United States and northern Europe are receiving as much as 20 times the natural amount from both agricultural and airborne sources (Vitousek et al. 1997:10). Nitrate levels in many Norwegian lakes have doubled in less than a decade (Vitousek et al. 1997:10). Although many of the nitrogen trouble spots tend to be in North America and Europe, the threat of nitrogen overload is global in scope, as both fertilizer use and energy use are growing quickly in the developing world. In fact, global nitrogen deposition may as much as double in the next 25 years as agriculture and energy use continue to intensify (Asner et al. 1997:228). The effects of this surfeit of nutrients reach every environmental domain, threatening air and water quality and disrupting the health of terrestrial and aquatic ecosystems. Natural systems may be able to absorb a limited amount of additional nitrogen by producing more plant mass, just as garden vegetables do when fertilized. Atmospheric deposition of nitrogen emissions on some heavily cut forests in North A Global Glut of Nitrogen Figure 1: Global Sources of Biologically Available (Fixed) Nitrogen ANNUAL RELEASE OF ANTHROPOGENIC FIXED NITROGEN SOURCES (TERAGRAMS) Fertilizer 80 Legumes and other plants 40 Fossil fuels 20 Biomass burning 40 Wetland draining 10 Land clearing 20 Total from human sources 210 NATURAL SOURCES Soil bacteria, algae, lightning, etc. 140 Source: Vitousek et al. 1997:4-6