Luxembourg: A unique place in the world to solve the mysteries of water cycle

Published on 21/11/2019

In the light of global change impacts on water resources, there is a pressing need for a better understanding of hydrological processes: Where does water go when it rains? What flowpath does it take to the stream? How old is the water in the stream? Answering these questions is essential to ensure an efficient water management regarding the sustainability use and quality of water resources. From the amount of drinking water reservoirs to the quality of water in the streams, the water cycle balance plays a key role. As example, vine-growing, or any form of agriculture, will depend on the water cycle and the time water spends in the ground. It not only affects a wide range of sectors, but also the ecosystems’ balance.

In order to tackle these fundamental questions that are going to define outcomes to climate change, land use change or chemicals in the environment, LIST performs groundbreaking researches and monitors the situation in the country. With a strong expertise in hydrology and a unique natural experimental field, LIST constitutes an attractive place for prominent international researchers. Jeffrey McDonnell, professor of hydrology at the University of Saskatchewan (CA) and associate director of the Global Institute for Water Security, came to Luxembourg as a visiting researcher for the past ten months in Laurent Pfister’s group and answered our three questions: 

Why is Luxembourg a place internationally coveted by hydrologists?

Hydrologists from all around come to Luxembourg to study its  natural environment where river basins, with a diverse and varied geology, are located in a homogenous climate and land use. It is a unique experimental design where sandstones shales and marls sit next to each other in neighboring catchments. Like  sponges with very different properties, sandstones can store an enormous amount of water, whereas very tight rocks like marl are almost impermeable to water. Consequently, the underground water storage varies considerably from watershed to watershed. Hydrologists are thus able to begin answer global research questions in such an unusual place. In order to understand how landscapes are going to respond to climate change, Laurent Pfister (LIST) and I work closely on watershed storage and release of water through the lens of these different rock types.

How Luxembourgish stream flows variations are monitored?

We can track the water molecule and its movement in the hydrologic cycle using the stable isotopes of oxygen and hydrogen—both  part of the water molecule. These tracers  record the stream flow signature and response to past rainfall and snowmelt events. Indeed, those stable isotopes will be slightly different depending on the water source (e.g. snowmelt; groundwaters). However, the current records are very short. A promising area of research, built on many years of work by LIST scientists, aims to use mussels as recorder of the isotope composition of the stream water in their shell material. If researchers could refine this methodology for understanding the annual or sub-annual variations in the isotope record in the shell ( linked directly to the stream environment), then it would open up new windows to learn about how our systems are behaving.

How to ensure the sustainable management of water resources?

When it comes to sustainable management of water resources, it is essential to take into account not only the stream flow, but also the groundwater, its age and the source of vegetation water uptake. In Luxembourg’s sandstones aquifers, some waters have been age-dated at 33,000 years old. This water was certainly recharged before modern societies, with a different climate and another geological period. Knowing the aquifers’ water age is thus of great importance to guarantee a sustainable use of water resources. With probably half of the water that leaves the watershed via evapotranspiration through the trees, the vegetation also  plays a key role in water cycling. If one is managing rivers for flow or thinking about rates of groundwater recharged, the movement of water by the vegetation out of the ground and in the atmosphere has a big impact. The LIST group is world-leading in this area and it has been a distinct pleasure and honor to be part of the group for 2019. I look forward to many more years of fruitful collaboration.

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Dr habil. Laurent PFISTER
Dr habil. Laurent PFISTER
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