HUMAN ALTERATION OF THE GLOBAL NITROGEN CYCLE: SOURCES AND CONSEQUENCES
PETER M. VITOUSEK,2 JOHN D. ABER,3 ROBERT W. HOWARTH,4 GENE E. LIKENS,5 PAMELA A. MATSON,6 DAVID W. SCHINDLER,7 WILLIAM H. SCHLESINGER,8 AND DAVID G. TILMAN9
2Department of Biological Sciences, Stanford University, Stanford,California 94305 USA Complex Systems Center, University of New Hampshire, Durham, New Hampshire 03824 USA 4Section of Ecology and Systematics, Cornell University, Ithaca, New York 14850 USA 5Institute of Ecosystem Studies, Mary Flagler Cary Arboretum, Millbrook, New York 12545 USA 6Department of Environmental Science, Policy, and Management, University of California, Berkeley, California 94720 USA7Department of Biological Sciences, University of Alberta, Edmonton, Alberta Canada T6G 2E9 8Department of Botany, Duke University, Durham, North Carolina 27709 USA 9Department of Ecology, Evolution, and Behavior, University of Minnesota, Saint Paul, Minnesota 55108 USA 3
Abstract. Nitrogen is a key element controlling the species composition, diversity, dynamics, and functioning of manyterrestrial, freshwater, and marine ecosystems. Many of the original plant species living in these ecosystems are adapted to, and function optimally in, soils and solutions with low levels of available nitrogen. The growth and dynamics of herbivore populations, and ultimately those of their predators, also are affected by N. Agriculture, combustion of fossil fuels, and other human activities have altered theglobal cycle of N substantially, generally increasing both the availability and the mobility of N over large regions of Earth. The mobility of N means that while most deliberate applications of N occur locally, their inﬂuence spreads regionally and even globally. Moreover, many of the mobile forms of N themselves have environmental consequences. Although most nitrogen inputs serve human needssuch as agricultural production, their environmental consequences are serious and long term. Based on our review of available scientiﬁc evidence, we are certain that human alterations of the nitrogen cycle have: 1) approximately doubled the rate of nitrogen input into the terrestrial nitrogen cycle, with these rates still increasing; 2) increased concentrations of the potent greenhouse gas N2Oglobally, and increased concentrations of other oxides of nitrogen that drive the formation of photochemical smog over large regions of Earth; 3) caused losses of soil nutrients, such as calcium and potassium, that are essential for the long-term maintenance of soil fertility; 4) contributed substantially to the acidiﬁcation of soils, streams, and lakes in several regions; and 5) greatly increased thetransfer of nitrogen through rivers to estuaries and coastal oceans. In addition, based on our review of available scientiﬁc evidence we are conﬁdent that human alterations of the nitrogen cycle have: 6) increased the quantity of organic carbon stored within terrestrial ecosystems; 7) accelerated losses of biological diversity, especially losses of plants adapted to efﬁcient use of nitrogen, andlosses of the animals and microorganisms that depend on them; and 8) caused changes in the composition and functioning of estuarine and nearshore ecosystems, and contributed to long-term declines in coastal marine ﬁsheries.
Manuscript received 1 November 1996. Reprints of this 14-page report are available for $2.25 each. Prepayment is required. Order reprints from the Ecological Society of America,Attention: Reprint Department, 2010 Massachusetts Avenue, NW, Suite 400, Washington, D.C. 20036. 737
PETER M. VITOUSEK ET AL.
Ecological Applications Vol. 7, No. 3
Key words: agriculture and the global N cycle; anthropogenic global change; biological diversity and the nitrogen cycle; ecosystem functioning, control by N; eutrophication of estuaries; global N-cycle alteration,...