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| Titel |
Application of a UV-Vis submersible probe for capturing changes in DOC concentrations across a mire complex during the snowmelt and summer periods |
| VerfasserIn |
Armine Avagyan, Benjamin Runkle, Lars Kutzbach |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250078642
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| Zusammenfassung |
| An accurate quantification of dissolved organic carbon (DOC) is crucial for understanding
changes in water resources under the influence of climate, land use and urbanization.
However, the conventionally used methods do not allow high frequency in situ analyses in
remote or hostile environments (e.g., industrial wastewater or during environmental high-flow
events, such as snowmelt or floods). In particular, missing measurements during the snowmelt
period in landscapes of the boreal region can lead to significant miscalculations in regional
carbon budgets. Therefore, the aim of the study was to test the performance of a portable,
submersible UV-Vis spectrophotometer (spectro::lyser, s::can Messtechnik GmbH, Austria)
during the snowmelt period in a boreal mire-forest catchment, and to provide a conceptual
understanding of the spatial and temporal dynamics of DOC concentrations during and after
snowmelt.
During 2011, water samples were collected from the near-pristine Ust-Pojeg mire
complex in northwestern Russia (61Ë 56’N, 50Ë 13’E). Sampling started during the spring
snowmelt period and continued until late fall. The mire presented a mosaic of different
landscape units. The mire consisted of minerogeous (fen), ombrogenous (bog), and
transitional forest-mire (lagg) zones. Water samples were taken from the surface across the
mire (22 points at 50-m intervals). DOC concentrations were analyzed directly at the study
site using a portable, submersible UV-Vis spectrophotometer, which uses high-resolution
absorbance measurements over the wavelength range 200–742.5 nm at 2.5-nm intervals
as a proxy for DOC content. Because the DOC composition of fluids varies by
site, a local calibration replaced the default settings of the spectro::lyser (Global
Calibration) to enhance the accuracy of the measurements. To evaluate the local
calibration and correct for drift, the same samples (n = 157) were additionally analyzed
using the wet persulfate oxidation method (O-I-Analytica, Aurora Model 1030,
USA).
Based on ordinary least squares regression, the local calibration showed good agreement
between the results obtained from the high-resolution absorption measurements and
the wet persulfate oxidation method (r2= 0.99, root-mean-square error = 1.7 mg
L-1). The measurement campaign revealed spatial and temporal variability of DOC
concentrations, and demonstrated that at the beginning of the snowmelt period,
surface carbon was flushed away by meltwater, whereas deeper layers remained
frozen. During this time, the surface DOC concentrations fluctuated within the range
of 8–15 mg L-1 (April 07) across the entire mire complex. After April 18, the
concentrations diverged between the sites; the DOC concentration reached 30 mg L-1in the
surface water at the lagg zone but was 15 mg L-1 at the bog site (April 25). The
DOC surface water concentration continued to increase during summer and fall,
ranging from 19 to 74 mg L-1 across the mire, with an average of 45 ± 14 mg
L-1.
The study indicates that high-resolution spectroscopic measurements provide a
simple, fast, robust and non-destructive method for measuring DOC contents, with a
short duration (17-20 seconds) and portability of the sample analysis rendering this
method particularly advantageous for in-situ measurements at remote field locations. |
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