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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 7 | Copyright
Biogeosciences, 15, 2177-2188, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 13 Apr 2018

Research article | 13 Apr 2018

Diel fluctuations of viscosity-driven riparian inflow affect streamflow DOC concentration

Michael P. Schwab1,2,a, Julian Klaus1, Laurent Pfister1, and Markus Weiler2 Michael P. Schwab et al.
  • 1Catchment and Eco-Hydrology Research Group, Luxembourg Institute of Science and Technology, 4422 Belvaux, Luxembourg
  • 2Hydrology, Faculty of Environment and Natural Resources, University of Freiburg, 79098 Freiburg, Germany
  • anow at: Climate and Water Department, World Meteorological Organization (WMO), Geneva, Switzerland

Abstract. Diel fluctuations of stream water DOC concentrations are generally explained by a complex interplay of different instream processes. We measured the light absorption spectrum of water and DOC concentrations in situ and with high frequency by means of a UV–Vis spectrometer during 18 months at the outlet of a forested headwater catchment in Luxembourg (0.45km2). We generally observed diel DOC fluctuations with a maximum in the afternoon during days that were not affected by rainfall–runoff events. We identified an increased inflow of terrestrial DOC to the stream in the afternoon, causing the DOC maxima in the stream. The terrestrial origin of the DOC was derived from the SUVA-254 (specific UV absorbance at 254nm) index, which is a good indicator for the aromaticity of DOC. In the studied catchment, the most likely process that can explain the diel DOC input variations towards the stream is the so-called viscosity effect. The water temperature in the upper parts of the saturated riparian zone is increasing during the day, leading to a lower viscosity and therefore a higher hydraulic conductivity. Consequently, more water from areas that are rich in terrestrial DOC passes through the saturated riparian zone and contributes to streamflow in the afternoon. We believe that not only diel instream processes, but also viscosity-driven diel fluctuations of terrestrial DOC input should be considered to explain diel DOC patterns in streams.

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Short summary
We studied the diel fluctuations of dissolved organic carbon (DOC) concentrations in a small stream in Luxembourg. We identified an increased proportion of DOC from terrestrial sources as responsible for the peaks in DOC in the afternoon. Warmer water temperatures in the riparian zone in the afternoon increased the amount of water flowing towards the stream. Consequently, an increased amount of DOC-rich water from the riparian zone was entering the stream.
We studied the diel fluctuations of dissolved organic carbon (DOC) concentrations in a small...