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

Abstract

Abstract. Diel fluctuations of streamwater 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 highfrequency by means of a UV-Vis spectrometer during 18 months at the outlet of a forested headwater catchment in 10 Luxembourg (0.45 km 2 ). We generally observed diel DOC fluctuations with a maximum in the afternoon during days thatwere 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 254 nm) index, which is a good indicator for the aromaticity of DOC. In the studied catchment, the only possible process that can explain the diel DOC input variations towards the stream is the so-called viscosity effect. 15The water temperature in the upper parts of the 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 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 for explaining diel DOC patterns in streams. 20Biogeosciences Discuss., https://doi

Saturated areas through the lens: 2. Spatio‐temporal variability of streamflow generation and its relationship with surface saturation

“…Until now, previous research carried out in the Weierbach catchment has led to considerable advancement in our level of understanding of how its hydrological response is generated. Through modelling and tracer‐based studies (Fenicia et al, ; Glaser et al, ; Klaus, Wetzel, Martínez‐Carreras, Ector, & Pfister, ; Martínez Fernández et al, ; Martínez‐Carreras et al, ; Schwab, Klaus, Pfister, & Weiler, ; Wrede et al, ), it has been possible to develop a solid perceptual model of the catchment, being able to explain its dual hydrological behaviour and related water sources. With the exception of the parallel modelling study by Glaser, Antonelli, Hopp, and Klaus () on surface saturated areas, all the observations made until now have been based on the hydrological response of the catchment observed at its outlet.…”

Delineating Source Contributions to Stream Dissolved Organic Matter Composition Under Baseflow Conditions in Forested Headwater Catchments

“…DOC concentration and DOM quality are often monitored with spectroscopic techniques integrated in field deployed sensors (Hood et al, 2006;Jaffé et al, 2008). In headwater streams, spectroscopic sensors have been used to reveal temporal variability of DOC concentration and DOM quality during periods of drought, storm events (Broder et al, 2017;Strohmeier et al, 2013), and across seasons (Schwab et al, 2018;Werner et al, 2019). Absorption indices have emerged as an efficient way of characterizing the structure and reactivity of DOM (Ågren et al, 2008;Hansen et al, 2016;Jaffé et al, 2008).…”

Saturated areas through the lens: 1. Spatio‐temporal variability of surface saturation documented through thermal infrared imagery

“…The Weierbach catchment has a well‐developed riparian zone, characterized by variable morphology (e.g., riparian width and elevation) and the presence of perennial and/or temporary groundwater exfiltration points. Although there is a reasonable understanding of how the overall hydrological response of the catchment is generated (Fenicia et al, ; Glaser et al, ; Klaus, Wetzel, Martínez‐Carreras, Ector, & Pfister, ; Martínez‐Carreras et al, ; Schwab, Klaus, Pfister, & Weiler, ; Wrede et al, ), there is still a lack of understanding of the dynamics of small‐scale riparian processes, like the spatial and temporal variability of riparian surface saturation, and of how these dynamics are related to the hydrological response (Scaini et al, ).…”