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| Titel |
Nitrate retention and removal in Mediterranean streams bordered by contrasting land uses: a 15N tracer study |
| VerfasserIn |
D. von Schiller, E. Martí, J. L. Riera |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 6, no. 2 ; Nr. 6, no. 2 (2009-02-11), S.181-196 |
| Datensatznummer |
250003429
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| Publikation (Nr.) |
 copernicus.org/bg-6-181-2009.pdf |
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| Zusammenfassung |
We used 15N-labelled nitrate (NO3−)
additions to investigate pathways of nitrogen (N) cycling at the whole-reach
scale in three stream reaches with adjacent forested, urban and agricultural
land areas. Our aim was to explore among-stream differences in: (i) the
magnitude and relative importance of NO3− retention (i.e. assimilatory
uptake) and removal (i.e. denitrification), (ii) the relative
contribution of the different primary uptake compartments to NO3−
retention, and (iii) the regeneration, transformation and export pathways of
the retained N.
Streams varied strongly in NO3− concentration, which was highest
in the agricultural stream and lowest in the forested stream. The
agricultural stream also showed the lowest dissolved oxygen (DO)
concentration and discharge. Standing stocks of primary uptake compartments
were similar among streams and dominated by detritus compartments (i.e. fine
and coarse benthic organic matter). Metabolism was net heterotrophic in all
streams, although the degree of heterotrophy was highest in the agricultural
stream.
The NO3− uptake length was shortest in the agricultural stream,
intermediate in the urban stream, and longest in the forested stream.
Conversely, the NO3− mass-transfer velocity and the areal
NO3− uptake rate were highest in the urban stream. Denitrification
was not detectable in the forested stream, but accounted for 9% and
68% of total NO3− uptake in the urban and the agricultural
stream, respectively. The relative contribution of detritus compartments to
NO3− assimilatory uptake was greatest in the forested and lowest in
the agricultural stream. In all streams, the retained N was rapidly
regenerated back to the water column. Due to a strong coupling between
regeneration and nitrification, most retained N was exported from the
experimental reaches in the form of NO3−.
This study provides evidence of fast in-stream N cycling, although the
relative importance of N retention and removal varied considerably among
streams. Results suggest that permanent NO3− removal via
denitrification may be enhanced over temporary NO3− retention via
assimilatory uptake in heterotrophic human-altered streams characterized by
high NO3− and low DO concentrations. |
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