Human activity has more than doubled the rate of creation of reactive nitrogen on the land surface of the earth over natural levels, with much of this change occurring in recent decades. Major drivers behind this increase are population growth, agricultural intensification, and emissions of nitrogen pollutants to the atmosphere from the combustion of fossil fuels. As a result, nitrogen is accumulating in the landscape and in water at unprecedented levels, and is connected to a host of environmental problems including effects on natural ecosystems and on human health. For example, eutrophication caused by excessive inputs of N from landscapes to the oceans is one of the greatest factors altering water quality in coastal ecosystems worldwide.
This synthesis is the final report from the International SCOPE Project on Nitrogen Transport and Transformations: A Regional and Global Analysis. SCOPE (the Scientific Committee on Problems of the Environment) authorized the Nitrogen Project because of the need to better understand how humans have altered nitrogen cycling globally and at the scale of large regions. The project has synthesized information through a series of workshops over the past 8 years, involving over 250 scientists from over 20 different nations. Papers in this volume explore the extent to which human activity has affected the nitrogen cycle in terrestrial regions and in the world's oceans, and discuss the implications of accelerated nitrogen cycling for nature and society.
Table of Contents
Foreword. International Scope Project. Towards an ecological understanding of biological nitrogen fixation; P.M. Vitousek, et al. Dinitrogen fixation in the world's oceans; D. Karl, et al. The origin, composition and rates of organic nitrogen deposition: A missing piece of the nitrogen cycle? J.C. Neff, et al. Anthropogenic nitrogen sources and relationships to riverine nitrogen export in the northeastern U.S.A.; E.W. Boyer, et al. Sources of nitrate in rivers draining sixteen watersheds in the northeastern U.S.: Isotopic constraints; B. Mayer, et al. Nitrogen retention in rivers: model development and application to watersheds in the northeastern U.S.A.; S.P. Seitzinger, et al. Forest nitrogen sinks in large eastern U.S. watersheds: estimates from forest inventory and an ecosystem model; C.L. Goodale, et al. Where did all the nitrogen go? Fate of nitrogen inputs to large watersheds in the northeastern U.S.A.; N. van Breemen, et al. A comparison of models for estimating the riverine export of nitrogen from large watersheds; R.B. Alexander, et al. Regional analysis of inorganic nitrogen yield and retention in high-elevation ecosystems of the Sierra Nevada and Rocky Mountains; J.O. Sickman, et al. Yield of nitrogen from minimally disturbed watersheds of the United States; W.M. Lewis, Jr. Nitrogen budgets for the Republic of Korea and the Yellow Sea region; V.N. Bashkin, et al. Regional nitrogen budgets for China and its major watersheds; G.X. Xing, Z.L. Zhu. Landscape, regional and global estimates of nitrogen flux from land to sea: Errors and uncertainties; P.J. Johnes, D. Butterfield. Policy implications of human-accelerated nitrogen cycling; A.R. Mosier, et al. Note added in proof.