Diel (also called diurnal) discharge patterns with minima in the afternoon are generally explained by the daily cycle of evapotranspiration, while maxima in the afternoon are often linked to freeze‐thaw cycles. In a schistose and forested headwater catchment in Luxembourg, we observed daily discharge maxima in the afternoon, although temperatures remained persistently above zero and vegetation was still in a dormant state. We show that diel water temperature fluctuations––and therefore viscosity fluctuations––in the upper layer of the riparian zone can be an explanation for the observed daily discharge maxima in the afternoon during the dormant season. In the transition period between the dormant and the growing season, the counteracting viscosity and evapotranspiration processes cancel each other out. Subsequently, during the growing season, evapotranspiration is the dominant process guiding the diel discharge pattern; nevertheless, the viscosity effect might still be present, but invisible. We believe this finding also to be of relevance when analyzing daily fluctuations of biogeochemicals in stream water.
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 (0.45 km2). 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 254 nm) 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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.