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".
Original language | English (US) |
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Pages (from-to) | 68-79 |
Number of pages | 12 |
Journal | Ecosystems |
Volume | 5 |
Issue number | 1 |
DOIs | |
State | Published - Jan 1 2002 |
Keywords
- Denitrification
- Desert stream
- N mineralization
- Nitrogen retention
- Plant uptake
- Riparian zone
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics
- Environmental Chemistry
- Ecology