Sources of Nitrogen to the Riparian Zone of a Desert Stream: Implications for Riparian Vegetation and Nitrogen Retention |
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Authors: | John D Schade Eugenia Marti Jill R Welter Stuart G Fisher Nancy B Grimm |
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Institution: | 1.Biology Department, Arizona State University, Tempe, Arizona 85287-1501, USA; and,US;2.Centre d'Estudis Avan?ats de Blanes (CSIC), 17300 Blanes, Spain,ES |
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Abstract: | Riparian zones effectively remove nitrogen (N) from water flowing through riparian soils, particularly in agricultural watersheds.
The mechanism of N removal is still unclear, especially the role of vegetation. Uptake and denitrification are the two most
commonly studied mechanisms. Retention of groundwater N by plant uptake is often inferred from measurements of N in net incremental
biomass. However, this assumes other sources of N are not contributing to the N demand of plants. The purpose of this work
was to investigate the relative importance of three sources of available N to riparian trees in a desert stream—input in stream
water during floods, input during baseflow, and mineralization of N from soil organic matter. Two approaches were used; a
mass balance approach in which the mass of available N from each source was estimated, and a correlational approach in which
indexes of each source were compared to leaf N for individual willow trees. Total N from all sources was 396 kg ha−1 y−1, with 172 kg ha−1 y−1 from mineralization, 214 kg ha−1 y−1 from the stream during baseflow, and 9.6 kg ha−1 y−1 from floods. Leaf N was significantly related to N mineralization rates and flood inputs; it was not related to baseflow
inputs. We conclude that mineralization is a major source of available N for willow trees, subsidized by input of N from floods.
Baseflow inputs are most likely removed by rapid denitrification at the stream–riparian edge, while higher rates of flood
supply exceed the capacity of this “filter.”
Received 18 January 2001; accepted 15 June 2001. |
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Keywords: | : riparian zone nitrogen retention denitrification plant uptake N mineralization desert stream |
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