An Interview with Matthias Sprenger and Sylvain Kuppel

March 4, 2023

The Colorado River is one of the major rivers in the United States and Northern Mexico, going through more than seven states and is the major water supply for many communities across Southwestern America. This is what pushed both Matthias Sprenger (Research Scientist at the Earth & Environmental Area of the Lawrence Berkeley National Laboratory) and Sylvain Kuppel (Research Scientist at the French National Research Institute for Sustainable Development (IRD)) to focus on the water components of this infamous watercourse. We sat down with them to learn more about the motivations behind their project, what their research consists of, and what opportunities the France-Berkeley Fund gave them. 

Matthias Sprenger and Sylvain Kuppel

Can you both introduce yourselves and talk about your academic journeys that lead you to this project? 

MS: I am Matthias Sprenger, a Research Scientist at the Earth & Environmental Area of the Lawrence Berkeley National Laboratory. Before coming to the national lab in 2020, I did my B.Sc., M.Sc., and PhD at three different German universities and worked as a Postdoc in Aberdeen in Scotland, Barcelona in Spain, and Raleigh in North Carolina. In Aberdeen, Sylvain and I crossed paths briefly. However, since we never worked together, the France-Berkeley Fund appeared to as a great opportunity to get a collaboration going.

SK: I am Sylvain Kuppel, a Research Scientist at the French National Research Institute for Sustainable Development (IRD), based at the Géosciences Environnement Toulouse laboratory in France. I studied engineering and plasma physics, and then I realized I was most interested in studying Earth functioning rather than "harnessing its power". So, I embarked in a PhD on the terrestrial carbon cycle, and slowly drifted towards hydrology and critical zone science during my postdoc time in Argentina, Scotland, and France. As Matthias said, we never formally collaborated, although we knew each other's work quite well. 

What made you interested in the mountainous region of the Upper Colorado River and in the water components of it? 

MS: The Colorado River is essential for the water supply of about 40 million people in the Western US. The water scarcity in the Colorado River basin that we observe is a great challenge and mountains play a special role in that regard, because the snow sustains most of the flow in the river. It is therefore crucial to better understand how much of the water from the mountains is used by the trees for their transpiration and how much is recharging the groundwater or flowing to the rivers. Only if we understand the interplay between snow, plant water use, and storage and release of water in mountainous watersheds, we will be able to predict how changes of the snowmelt timing and amount will affect forest health and water quantity and its quality.

SK: The insights gained in Colorado may also serve to better understand the water cycle in many other mountainous parts of the world, where water availability for ecosystems and societies is being altered in a changing environment.

How and why did you decide to work together on your research? 

MS: I followed Sylvain's efforts in developing a hydrological model that makes use of tracer data for its calibration. Most spatially explicit hydrological models simulate only how much water is in the soil, taken up by trees and routed to the stream. However, adding tracer data (like stable isotopes of water) better constrains the model and therefore should give a better representation of the hydrological processes. In the DOE funded Watershed Scientific Focus Area, we have an extensive data set that we can use to inform such modeling efforts. This is why I wanted to get Sylvain involved.

SK: The model I helped to develop connects the simulation of water transit in various compartments (plants, shallow soil, deeper weathered fractured bedrock) across and within a landscape. However, reducing uncertainties around the various quantities the model can estimate at multiple scales (e.g., snowmelt contribution to groundwater recharge, water content available for plants transpiration, groundwater contribution of stream flow) is commensurate with a thorough evaluation of contemporary simulations with a diverse set of measurements: water stores, fluxes and (as Matthias pointed out) tracer content. The exceptional breadth of hydrological datasets at the East River watershed makes this model-data approach very promising to address the scientific questions driving our research.

Can you explain a bit more in detail what your research focuses on?  

MS & SK: In the FBF supported work, we focus on the estimation of water ages in the snow dominated catchments of the Upper Colorado River. The previously mentioned modeling efforts will provide information about how long a water droplet, for example of the snowmelt in spring or the monsoon rains in the summer, will take to either end up in the stream water or be used by plants and evaporated back to the atmosphere. As such, this water age provides crucial cues on the resilience or vulnerability of ecosystems to water availability. The time water spends in the soil and rock will also impact the weathering of rocks and the transport processes of water solutes (e.g., nutrients) within and outside of the landscapes. Thus, we are working on connecting the water age estimations with solute transport simulations.

What are the next steps within your research? 

MS: We're currently in the process of "fine tuning" the simulations using comparison of the model results with various observations. This calibration will improve the model realism and then we'll use the model results of water flows in the East River and add simulations of biogeochemical processes to it.

What are the reasons that pushed you to apply for the FBF (France-Berkeley Fund)? 

MS: My motivation to apply for the FBF was the opportunity to get an international collaborator involved in the work we're doing in Colorado. With Sylvain, we were able to make very good use of the data sets that have been gathered over seven years now. Additionally, the proposal submission is relatively straightforward, but also the money available is very limited.

SK: Also, the deadline for proposal submission in 2021 fell on the exact day I became eligible to apply to the FBF by starting my permanent position in Toulouse, so the application seemed only fitting!

What has the FBF done for your research?  What type of opportunities did it open for you? 

MS & SK: The FBF funding allowed Sylvain to visit the research catchment in Colorado for a week, help Matthias with field work, and get a hands-on insight into the catchment characteristics and conditions during summer. The funding further enabled us to organize a workshop for early career scientists to discuss how we can better connect the travel time research with biogeochemical research.

We want to thank both Matthias Sprenger and Sylvain Kuppel for their time to answer our questions, wish them of all luck for the rest of the rest of their study. You can learn more about their project here