National Science Foundation Home National Science Board Home
Environmental Science And Engineering For The 21st Century: The Role of the National Science Foundation [NSB 00-22, February 2000]

Title Page

National Science Board




1     Introduction

2    The Larger Context

3    Scope of
NSF's Current

4    Input Received About Unmet Needs and Opportunities

5    Findings and

6    Conclusion


Appendix A

Appendix B

Appendix C

Appendix D

Appendix E

Appendix F

Appendix G

Final Page

  Box 1
  Box 2
  Box 3
  Box 4
  Box 5
  BOX 6
  Box 7
  Box 8
  Box 9
  Box 10
  Box 11
  Box 12
  Box 13

BOX 6.

After thousands of years of stability, the chemistry of the surface of the Earth is changing rapidly (Schlesinger 1997). Changes in the cycles of nitrogen and phosphorus are substantial and linked in complex ways to changes in agriculture and energy (Vitousek et al. 1997a and 1997b, Carpenter et al. 1998a and 1998b).

Until the beginning of this century, microbes and lightning were the primary sources of fixed nitrogen (the form usable by plants), and human contributions were negligible. These non-anthropogenic sources currently generate approximately 140 TG fixed N/y. Humans contribute to nitrogen fixation by making fertilizers, burning fossil fuels, and planting legumes widely. Human activities now produce more than an additional 140 TG fixed N/y. As a result, the total amount of terrestrial nitrogen fixed each year has more than doubled.

Until the advent of extensive mining activity, new phosphorus was made available primarily through weathering of rock. Mining and land disturbances have now more than tripled the rate of phosphorus mobilization (from about 10 to more than 30 Tg/y) and the rate of phosphorus flow from the continents to the coastal oceans (from about 8 to 22 Tg/y).

When nitrogen and phosphorus were only scantily available to the biological world, they served as limiting factors that controlled the dynamics, biodiversity, and functioning of many ecosystems. Ecosystems now flush with excess fixed nutrients are changing rapidly. Nutrients unused by crops and lawns, livestock waste and sewage, and airborne nitrogen resulting from the burning of fossil fuels are disrupting a wide range of downstream and downwind systems. Excess nutrients stimulate the growth of algae and can lead to eutrophication, harmful algal blooms, loss of oxygen ("dead zones") in lakes and coastal waters, fish kills, loss of seagrass beds, degradation of coral reefs, and loss of commercial and sport fisheries and shellfish industries (Carpenter et al. 1998a and 1998b). In addition, the chemistry of the atmosphere is being altered by human-driven changes in the nitrogen cycle, with serious implications for the greenhouse effect, smog, and acid precipitation. Nitrate contamination is also a potential concern for human health, particularly in drinking water drawn from relatively shallow aquifers in agricultural areas (USGS 1999a).

Scientific uncertainties include the controls on nitrogen fixation and denitrification processes in ocean waters; triggers of harmful algal blooms; transport of nutrients across the landscape and among air, soil, and water; evolutionary consequences of long-term nutrient enrichment; and controls of nutrient-retention processes in ecosystems. Particularly important questions address the control points that could allow us to mitigate the flows or effects of excess nutrients. For example, how can floodplains and shorelines be configured to minimize nutrient flow to surface waters? Also, we need to understand the role of large reservoirs of nutrients in the control of regional and global cycles. For example, what is the rate of phosphorus buildup in agricultural soils, and what are the implications of this buildup for freshwaters and coastal oceans?

Back to Top

National Science Board
4201 Wilson Boulevard, Suite 1225
Arlington, Virginia 22230, USA
Telephone: (703) 306-2000
FAX: (703) 306-0181 ~ TDD: (703) 306-0090
Last Modified: