SS3.15 Physical Forcing and Pelagic-Benthic Interactions in Aquatic Systems
Date: Thursday, June 13, 2002
Time: 3:15:00 PM
Location: Oak Bay
 
GrimmNB, Arizona State Univ., Tempe, AZ, USA, nbgrimm@asu.edu
Schade, J, D, Arizona State Univ., Tempe, AZ, USA, john.schade@asu.edu
Welter, J, R, Arizona State Univ., Tempe, AZ, USA, jill.welter@asu.edu
Lewis, D, B, Arizona State Univ., Tempe, AZ, USA, david.lewis@asu.edu
Marti, E, , Centre d'Estudis Avancats de Blanes (CSIC), Blanes, Girona, Spain, emarti@3tres3.com
 
NITROGEN RETENTION IN ARID-LAND STREAM AND RIPARIAN ZONES
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Riparian zones have been called the nutrient filters of watersheds. Arid-land streams differ from their mesic counterparts, being sites of groundwater recharge rather than discharge. Further, linkage between lateral uplands and the riparian ecosystem may occur only during intense, short-lived storms, with terrestrial and aquatic components of these watersheds normally disconnected. These features imply that 1) opportunities for retention of lateral N inputs may be episodic, 2) N retention may instead occur within the stream-riparian corridor ecosystem during downstream transport, 3) in a landscape context, overall riparian N retention may be low in arid regions. Seasonal variation in concentration and form of nitrogen within subsurface waters of two desert stream-riparian ecosystems show consistently low nitrate and higher ammonium during baseflow in riparian waters, but higher nitrate in more oxic gravel bars. During floods, this pattern disappears and nitrate enters riparian groundwater and is available to plants. Plant uptake, however, is both a temporary and a minor N retention mechanism. Denitrification is a major cause of N removal that is often localized at interfaces between oxic and anoxic subsurface zones.