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| Titel |
High-frequency DOC and nitrate measurements provide new insights into their export and their relationships to rainfall-runoff processes |
| VerfasserIn |
Michael Schwab, Julian Klaus, Laurent Pfister, Markus Weiler |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250108389
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| Publikation (Nr.) |
 EGU/EGU2015-11026.pdf |
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| Zusammenfassung |
| Over the past decades, stream sampling protocols for environmental tracers were often
limited by logistical and technological constraints. Long-term sampling programs would
typically rely on weekly sampling campaigns, while high-frequency sampling would remain
restricted to a few days or hours at best. We stipulate that the currently predominant sampling
protocols are too coarse to capture and understand the full amplitude of rainfall-runoff
processes and its relation to water quality fluctuations. Weekly sampling protocols are not
suited to get insights into the hydrological system during high flow conditions. Likewise, high
frequency measurements of a few isolated events do not allow grasping inter-event variability
in contributions and processes. Our working hypothesis is based on the potential of a new
generation of field-deployable instruments for measuring environmental tracers at high
temporal frequencies over an extended period. With this new generation of instruments we
expect to gain new insights into rainfall-runoff dynamics, both at intra- and inter-event
scales.
Here, we present the results of one year of DOC and nitrate measurements with the field
deployable UV-Vis spectrometer spectro::lyser (scan Messtechnik GmbH). The instrument
measures the absorption spectrum from 220 to 720 nm in situ and at high frequencies and
derives DOC and nitrate concentrations. The measurements were carried out at 15 minutes
intervals in the Weierbach catchment (0.47 km2) in Luxemburg. This fully forested
catchment is characterized by cambisol soils and fractured schist as underlying
bedrock.
The time series of DOC and nitrate give insights into the high frequency dynamics of
stream water. Peaks in DOC concentrations are closely linked to discharge peaks that occur
during or right after a rainfall event. Those first discharge peaks can be linked to fast near
surface runoff processes and are responsible for a remarkable amount of DOC export. A
special characterisation of the Weierbach catchment are the delayed second peaks a few days
after the rainfall event. Nitrate concentrations are following this second peak. We assume that
this delayed response is going back to subsurface or upper groundwater flows, with nitrate
enriched water. On an inter-event scale during low flow / base flow conditions, we observe
interesting diurnal patterns of both DOC and nitrate concentrations. Overall, the
long-term high-frequency measurements of DOC and nitrate provide us the opportunity
to separate different rainfall-runoff processes and link the amount of DOC and
nitrate export to them to quantify the overall relevance of the different processes. |
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