Control of Nitrogen Export from Watersheds by Headwater Streams
Abstract
A comparative 15N-tracer study of nitrogen dynamics in headwater streams from biomes throughout North America demonstrates that streams exert control over nutrient exports to rivers, lakes, and estuaries. The most rapid uptake and transformation of inorganic nitrogen occurred in the smallest streams. Ammonium entering these streams was removed from the water within a few tens to hundreds of meters. Nitrate was also removed from stream water but traveled a distance 5 to 10 times as long, on average, as ammonium. Despite low ammonium concentration in stream water, nitrification rates were high, indicating that small streams are potentially important sources of atmospheric nitrous oxide. During seasons of high biological activity, the reaches of headwater streams typically export downstream less than half of the input of dissolved inorganic nitrogen from their watersheds.
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This work is supported by NSF grants DEB-9628860, DEB-9810222, and OPP-9615949. More than 100 students and scientists gathered the information for this synthesis paper. We especially thank S. Johnson, L. Ashkenas, N. Grimm, S. Fisher, C. Dahm, K. Renzanka, J. Merriam, S. Findlay, C. Fellows, R. Hall, R. Holmes, C. Rensha, D. Sanzone, K. MacNeale, and E. Bernhardt for fieldwork, laboratory analyses, and discussion. K. Tholke performed all isotopic analyses.
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Published In
Science
Volume 292 | Issue 5514
6 April 2001
6 April 2001
Submission history
Received: 25 October 2000
Accepted: 1 March 2001
Published in print: 6 April 2001
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