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23 March 2023
Doctoral thesis (Dissertations and theses)
Observing unseen flowlines and their contribution to near stream endmembers in forested headwater catchments.
van Zweel, Karl Nicolaus


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Keywords :
End member mixing analysis; EMMA; PHREEQC; Multivariate analysis; Critical Zone; Geochemical modeling
Abstract :
[en] The general scope of the PhD research project falls within the framework of developing integrated catchment hydro-biogeochemical theories in the context of the Critical Zone (CZ). Significant advances in the understanding of water transit time theory, subsurface structure controls, and the quantification of catchment scale weathering rates have resulted in the convergence of classical biogeochemical and hydrological theories. This will potentially pave the way for a more mechanistic understanding of CZ because many challenges still exist. Perhaps the most difficult of all is a unifying hydro-biogeochemical theory that can compare catchments across gradients of climate, geology, and vegetation. Understanding the processes driving the evolution of chemical tracers as they move through space and time is of cardinal importance to validating mixing hypotheses and assisting in determining the residence time of water in CZ. The specific aim of the study is to investigate what physical and biogeochemical processes are driving variations in observable endmembers in stream discharge as a function of the hydrological state at headwater catchment scale. This requires looking beyond what can be observed in the stream and what is called ”unseen flowlines” in this thesis. The Weierbach Experimental Catchment (WEC) in Luxembourg provides a unique opportunity to study these processes, with an extensive biweekly groundwater chemistry dataset spanning over ten years. Additionally, WEC has been the subject of numerous published works in the domain of CZ science, adding to an already detailed hydrological and geochemical understanding of the system. Multivariate analysis techniques were used to identify the unseen flowlines in the catchment. Together with the excising hydrological perception model and a geochemical modelling approach, these flowlines were rigorously investigated to understand what processes drive their respective manifestations in the system. The existing perceptual model for WEC was updated by the new findings and tested on 27 flood events to assess if it could adequately explain the c − Q behaviour observed during these periods. The novelty of the study lies in the fact that it uses both data-driven modelling approaches and geochemical processbased modelling to look beyond what can be observed in the near-stream environment of headwaters.
Research center :
LIST - Luxembourg Institute of Science & Technology
Disciplines :
Earth sciences & physical geography
Engineering, computing & technology: Multidisciplinary, general & others
Author, co-author :
van Zweel, Karl Nicolaus ;  University of Luxembourg > Faculty of Science, Technology and Medecine (FSTM) ; Luxembourg Institute of Science & Technology - LIST > ERIN > CAT group > PhD student
Language :
Title :
Observing unseen flowlines and their contribution to near stream endmembers in forested headwater catchments.
Alternative titles :
[en] Observing unseen flowlines and their contribution to near stream endmembers in forested headwater catchments.
Defense date :
08 March 2023
Number of pages :
Institution :
Unilu - University of Luxembourg, Belval, Luxembourg
Degree :
Secretary :
Jury member :
Bouchez, Julien
Hrachowitz, Markus
Focus Area :
Computational Sciences
FnR Project :
FNR10623093 > Laurent Pfister > HYDRO-CSI > Towards A Holistic Understanding Of River Systems: Innovative Methodologies For Unraveling Hydrological, Chemical And Biological Interactions Across Multiple Scales > 01/03/2017 > 31/08/2023 > 2015
Name of the research project :
Funders :
FNR - Fonds National de la Recherche


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