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| Titel |
Amount, composition and seasonality of dissolved organic carbon and nitrogen export from agriculture in contrasting climates |
| VerfasserIn |
Daniel Graeber, Mariana Meerhof, Elke Zwirnmann, Niels Ovesen, Jörg Gelbrecht, Franco Teixeira de Mello, Ivan González-Bergonzoni, Erik Jeppesen, Brian Kronvang |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093076
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| Publikation (Nr.) |
 EGU/EGU2014-7458.pdf |
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| Zusammenfassung |
| Agricultural catchments are potentially important but often neglected sources of dissolved
organic matter (DOM), of which a large part is dissolved organic carbon (DOC) and nitrogen
(DON). DOC is an important source of aquatic microbial respiration and DON may be an
important source of nitrogen to aquatic ecosystems. However, there is still a lack of
comprehensive studies on the amount, composition and seasonality of DOM export from
agricultural catchments in different climates. The aim of our study was to assess the amount,
composition and seasonality of DOM in a total of four streams in the wet-temperate and
subtropical climate of Denmark and Uruguay, respectively. In each climate, we investigated
one stream with extensive agriculture (mostly pasture) and one stream with intensive
agriculture (mostly intensively used arable land) in the catchment. We sampled each
stream taking grab samples fortnightly for two years and measured DOC and DON
concentration, as well as molecular composition by size-exclusion chromatography.
We used absorbance, fluorescence and parallel factor analysis to gather additional
information on the sources and composition of the DOM. The results were coupled to
measurements of precipitation, water temperature, discharge, water residence time and
physicochemical data measured at each study site to investigate the effects these
environmental variables have on the amount and composition of DOM in the streams.
Average annual DOM concentration and seasonality were highest in the stream with
intensive agriculture in Uruguay and lowest in the stream with extensive agriculture in
Denmark. In all streams, the molecular-size composition of DOC and DON were
similar and most DOC and DON were exported as humic substances with low C:N
ratio, which indicates high bioavailability. Moreover, DON was of higher relative
importance in the Uruguayan streams than in the Danish streams, as can be seen from the
lower dissolved inorganic to total dissolved nitrogen ratios. The high seasonality of
DOM, especially in the Uruguayan streams implies high influence of variation
of the environmental conditions, both temperature and precipitation. Our study
shows the importance of agriculture as DOM source in both climate zones, with
a high seasonality particularly in Uruguayan streams. Future investigations and
models of DOC and DON export in agricultural catchments need to include this
seasonality to give correct information on the catchment export. Moreover, our
results clearly show that DON is increasingly important for the nitrogen export
from agricultural catchments when moving from a temperate to a warmer climate. |
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