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| Titel |
In situ high-frequency UV-Vis spectrometer probes for investigating runoff processes and end member stability. |
| VerfasserIn |
Michael Schwab, Markus Weiler, Laurent Pfister, Julian Klaus |
| 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 |
250091233
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| Publikation (Nr.) |
 EGU/EGU2014-5512.pdf |
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| Zusammenfassung |
| In recent years, several limitations as to the application of end member mixing analysis with
isotope and geochemical tracers have been revealed: unstable end member solutions, inputs
varying in space and time, and unrealistic mixing assumptions. In addition, the
necessary high-frequency sampling using conventional methods is time and resources
consuming, and hence most sampling rates are not suitable for capturing the response
times of the majority of observed headwater catchments. However, high-frequency
observations are considered fundamental for gaining new insights into hydrological
systems.
In our study, we have used two portable, in situ, high-frequency UV-Vis spectrometers
(spectro::lyser; scan Messtechnik GmbH) to investigate the variability of several signatures in
streamflow and end member stability. The spectro::lyser measures TOC, DOC, nitrate and the
light absorption spectrum from 220 to 720 nm with 2.5 nm increment. The Weierbach
catchment (0.45 km2) in the Attert basin (297 km2) in Luxemburg is a small headwater
research catchment (operated by the CRP Gabriel Lippmann), which is completely forested
and underlain by schist bedrock. The catchment is equipped with a dense network of
hydrological instruments and for this study, the outlet of the Weierbach catchment was
equipped with one spectro::lyser, permanently sensing stream water at a 15 minutes
time step over several months. Hydrometric and meteorologic data was compared
with the high-frequency spectro::lyser time series of TOC, DOC, nitrate and the
light absorption spectrum, to get a first insight into the behaviour of the catchment
under different environmental conditions. As a preliminary step for a successful end
member mixing analysis, the stability of rainfall, soil water, and groundwater was
tested with one spectro::lyser, both temporally and spatially. Thereby, we focused on
the investigation of changes and patterns of the light absorption spectrum of the
different end members and the stream water. Besides using DOC and nitrate for
characterizing the end members, our idea is to use the light absorption spectrum as a
fingerprint of various constituents of the water. To get a better understanding on how to
handle the in situ spectro::lyser, the instrument was compared to conventionally
analysed water samples with a special focus on fundamental technical issues: Is
there a general difference between in situ and lab measurements and does it make a
difference whether the samples are analysed immediately in the field or after days
and weeks in the lab and/or again with the spectro::lyser? First results indicate
the value of using in situ spectrometers to capture high-frequency variations of
hydro-chemistry and end member mixing during runoff events in a small headwater
catchment. |
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