FIGURE SET 3
Figure 3A. Export of nitrate from river systems worldwide as a function of human population in
the watershed. From I. Valiela. Marine Ecological Processes, Second edition. 1995.
Springer-Verlag, N.Y. and J. J. Cole, B. L. Peierls, N. F. Caraco, and M. L. Pace. 1997.
Nitrogen loading of rivers as a human-driven process. In M. J. McDonnell and S. T. A.
Pickett, eds. Humans as components of ecosystems: the ecology of subtle human
effects and populated areas. Springer-Verlag, N.Y.
Figure 3B. Export of total N from watersheds surrounding the North Atlantic Ocean as a function of net
human-caused inputs to their watersheds. Human related inputs are synthetic N fertilizer application, N fixation by leguminous crops,
atmospheric inputs of N, and net imports of N in food and feedstock. From P. M. Vitousek, J. D. Aber, R. W. Howarth, G. E. Likens,
P. A. Matson, D. W. Schindler, W. H. Schlesinger, and D. G. Tilman, 1997. Human alteration of the global nitrogen cycle: causes
and consequences. Issues in Ecology 1: 1-15..and R.W. Howarth, G. Billen, D. Swaney, A. Townsend, N. Jaworski, K. Lajtha, A.
Downing, R. Elmgreen, N. Caraco, T. Jordan, F. Berendse, J. Freney, V. Kudeyarov, P. Murdoch, and Z. Zhao-liang. 1996. Regional
nitrogen budgets and riversine N & P fluxes for the drainages to the North Atlantic Ocean: Natural and human influences.
Biogeochemistry 35: 181-226.
For help, see the essay "Helping Your Students to Interpret Figures and Tables."