Projects on cross-cutting themes are selected witihin the framework of an annual call launched since 2019. These projects should promote collective research actions, by pooling sites, technics and know-how, according to a systemic and holistic approach aimed at better understanding the coupling between physical, chemical, biological and human processes within the Critical Zone, integrating time and space scale (cf. publication Gaillardet et al. 2018 – https://doi.org/10.2136/vzj2018.04.0067).
Collective and systemic research actions
The projects are built on an original scientifique question or issue, with an unifying and interdiciplinary nature and involve several observatories. Transversal themes, multi-year research actions or workshops for transverse exchange on a scientific issue, are a springboard for the emergence of multidisciplinary research projects.
Collaborations with the Zones Ateliers (https://www.za-inee.org) are stongly encouraged, as well as the study of socio-ecolosystems aimed at structuring the eLTER France community. Since this call for ideas has been launched, 34 cross-cutting projects have been supported (8 projects in 2019, 6 projects in 2020, 6 projects in 2021, 9 projects in 2022 and 6 projects in 2023). The feedbacks from the funded themes show that a real collective dynamic is in place using the data of OZCAR-RI. This dynamic has to be maintained and to be improved through the support of new projets.
Active projects
Cross-cutting themes 2019
Chemical erosion fluxes in OZCAR observatories (Julien Bouchez, IPGP)
This theme aims to synthesise existing data on the chemical composition of OZCAR RI rivers and to calculate dissolved transport and chemical erosion fluxes in OZCAR RI catchments along the geological, climatic and land-use gradients explored by the network.
Long-term erosion fluxes in OZCAR observatories (Vincent Regard, GET Toulouse)
This theme is a research project focusing on the analysis of beryllium isotopes in the quartz sands at the bottom of the OZCAR RI rivers. The isotope 10 of beryllium is formed when the Earth’s surface is irradiated by cosmic rays and provides information on long-term erosion rates. Its measurement can be used to deduce erosion rates that can be compared with the more conventional estimates made in the OZCAR RI observatories (next project) under varying land-use conditions.
Particulate fluxes in OZCAR observatories (Cédric Legout, IGE Grenoble)
This theme aims to bring together the OZCAR RI communities interested in solid transport, in the form of a workshop focusing on methodological and instrumental developments – sampling of SS and calculation of fluxes, harmonisation of protocols – and on the modelling of particle transfer. The data will be compared with the long-term estimates made in the previous project. Soil solid matter loss is a very important social issue for the OZCAR network. For the time being, this topic has led to the comparison of several turbidimeters for assessing the concentration of suspended solids (SS), which is described in Bakker et al (2024).
Evolution of water resources and adaptation to climate change (Florence Habets, ENS Paris)
The aim of this workshop is to identify the contribution of climate change and that of human activities, and to quantify the potential for adaptation, in the data series acquired by the OZCAR RI observatories. An internship in 2020 enabled an initial trend analysis to be carried out on the long data series acquired by RI OZCAR.
Intermittent streams and rivers (Ophélie Fovet, SAS, Rennes, Thibault Datry, RiverLy, Inrae Lyon)
A workshop entitled “intermittent rivers and streams” was organized as part of the RI OZCAR cross-disciplinary workshops. This one-and-a-half-day seminar was a first event to:
1) Review and share the panorama of studies conducted on the subject: sites, techniques and know-how;
2) Identify persistent barriers on the theme, identify possible links and collaborations between teams, and discuss strategies for dealing with these barriers. It resulted in a joint publication currently under review in the WiRES journal (Fovet et al., 2020).
Cross-cutting themes 2020
“PAPAYES”: Integrated Particulate Sampling and Analysis of Suspended Solids (Annaëlle Simonneau, ISTO Orléans)
This cross-disciplinary theme focuses on the quantification of particulate biogeochemical fluxes on a watershed scale. Twelve OZCAR/RZA sites of varying size (5 km² to 42 km²) are involved. The project comprises three stages: installation of GEACOS (a new “low-cost” sediment trap developed at UMR ISTO in Orléans by Anaëlle Simonneau and her team: the GranulomEtric pAssive Capture of dissOlved matter & Sediment licensed under creative commons CNRS), collection and analysis of bio-geochemical characterization data on suspended matter. This project is linked to the 2019 particulate flux project.
UV-vis and DOM: characterization of dissolved organic matter in OZCAR rivers using UV-vis spectrophotometry (Mathieu Masson, RiverLy, Inrae Lyon)
This project focuses on the use of UV-visible spectrophotometry in OZCAR RI observatories to determine the sources and nature of dissolved organic matter in watersheds, using low-cost commercial probes. As a first step, a workshop is planned to take stock of the current situation.
Feedback loops and tipping points in OZCAR (Christophe Peugeot, HSM Montpellier)
This project, which was submitted in 2019, is scheduled for completion in 2020. It proposes to describe the temporal trajectories of critical zone evolution based on available OZCAR RI data and the possibility of systems showing tipping points as a function of perturbations. An interdisciplinary workshop on feedback loops and their influence on the dynamics of the Critical Zone will be organized in 2021, to take stock of the current configuration of observatories in terms of data and how they are taken into account in modeling. The subject is the subject of an ANR collaborative research project “TipHyc” -Exploration of tipping points in the West African hydrological cycle, selected in the latest 2020 generic call.
Cross-cutting themes 2021
Contribution of superconducting gravimetry to the estimation of evapotranspiration – multisite approach: Observatoire du Larzac, BV du Strengbach, Fontaine du vaucluse-LSBB (Simon Carrière, METIS, Paris)
The aim of this interdisciplinary project is to identify the relationships between the temporal dynamics of the gravimetric signal and the dynamics of evapotranspiration from daily to seasonal time steps on different sites of the OZCAR research infrastructure. The aim is therefore to work on sites already equipped with superconductor gravimeters and flux towers, to add sap flow sensors and implement an evapotranspiration model. Finally, the results from the various sites will be compared. Ultimately, this project should lead to the preparation of a more ambitious project (i.e. ANR).
High-frequency monitoring of 3 contrasting rivers in the critical zone (mountain and agricultural sites). Contribution of multi-element chemical concentrations to understanding hydrosystems and their responses to anthropogenic forcing (Marie-Claire Pierret, Lhyges (ITES Strasbourg))
The three sites are the watersheds of Orgeval (Paris basin, agricultural, 45 km2, BVRE ORACLE), Kervidy-Naizin (Brittany, 4.9km2, agricultural – ORE AgrHys) and Strengbach (Vosges mountains, mid-mountain, forestry, 0.8 km2, SNO-OHGE). Their characteristics vary widely in terms of size, geology, climate, land use, anthropization and, consequently, hydrodynamic and biogeochemical functioning, as well as responses to human activities and climatic forcings. This is where the OZCAR structure comes into its own, enabling cross-site connections and collaborations. The completion of the project is a springboard for the preparation of new projects, particularly within the framework of ANR calls for proposals. The project is also complementary to the cross-cutting theme projects “intermittent rivers”, “material flows in BVs” and “river metabolism, organic matter dynamics”, as well as to the activities developed by the post-doctoral student in modeling. The analysis of RiverLab data has led to several publications (Brekkenfeld et al., 2024a; Brekenfeld et al., 2024b; Floury et al., 2024).
Monitoring eDNA in critical zone observatories (Jérôme Murienne, EDB – Evolution et Diversité Biologique, Toulouse)
The aim of the project is to measure the impact of water quality and anthropogenic disturbances on the seasonal variation of eDNA (analysis of essential hydrological variables every 2 months). As part of this project, we plan to develop the 1st spatio-temporal database including data on environmental DNA (eDNA) in tropical waters/soils in the critical zone (major parameters of the critical zone: hydrology, sedimentary, geochemistry). The development of this DBD will focus in year 1 on data from the Nouragues station, French Guiana (pristine tropical forest ecosystem) and on the Maroni site of the Hybam station (significant impact on biodiversity – 240% increase in turbidity over the last 15 years due to illegal mining). And plan to include at least one other CZO site in year 2. Recent studies have shown the importance of using environmental DNA as a technological tool for ecological monitoring (i.e. tropical aquatic ecosystems). The project responds to an overriding challenge, that of preserving species and biodiversity, a recent IPBES report having concluded on the importance of preserving biodiversity.
Landscape heritage: impact of societal and climatic mutations on the critical zone (Claire Marais Sicre, CESBIO Toulouse)
In the Montoussé watershed, this project aims to study the impact of past land-use changes in an agricultural watershed on soil erosion and water quality, and to gain a better understanding of the spatial and temporal evolution of the landscape. The aim is to propose a generic methodology for past landscape evolution that can be transposed to other OZCAR sites. It will also enable links to be made between OZCAR and RZA sites, as has already been done with the Baget observatory site (SNO Karst, OZCAR) and the Pyrenees workshop site of the PYGAR ZA.
Cross-cutting themes 2022
Gravimetry and evapotranspiration (Nolwenn Lesparre, ITES Strasbourg)
The aim is to refine the estimation of evapotranspiration by combining measurements (evapotranspiration flux by eddy-covariance, sap flux and spontaneous potential sensors, gravimetry) and modeling (SimpleKcET model) on three sites equipped with gravimeters (Strengbach, LSBB-Fontaine de Vaucluse, H+/Larzac). The instrumentation will be completed in 2022, and a master’s degree course planned for 2023 will enable data to be cross-analyzed. A workshop on “Passive geophysics for critical zone studies” is also planned for 2022.
Soil moisture in OZCAR RI observatories (Flora Branger et al., RiverLy, Lyon)
Soil moisture is a key variable for critical zone observatories. However, this information remains largely under-exploited in IR, as many questions linked to the measurement process itself, and to the exploitation and valorization of the data acquired, have yet to be addressed. The aim of this cross-disciplinary theme is to share, in the form of workshops, the experience acquired in OZCAR observatories on the following topics: choice of sensors, deployment and installation protocols; sensor calibration and data validation procedures; state of the art in terms of data sharing and availability; different ways of exploiting and using data (data analysis, modeling), on the local scale of observatories, or on cross-disciplinary spatial scales. An initial survey of soil moisture monitoring practices has been carried out. A summary of this survey is available here.
Back-observation of the critical zone (Pierre Sabatier et al., EDYTEM, Le Bourget du Lac)
The approach based on retro-observation enables us to retrace the evolutionary trajectories of the critical zone on different timescales, reconstructing both its functioning and the associated forcings. The underlying hypothesis is that each process at work within the critical zone results in a transfer of matter that carries and transmits information relating to the process that generated it. The study of these products, subsequently trapped in sedimentary archives, therefore enables us, in theory, to faithfully reconstruct the processes at work within the critical zone. The aim of the proposed theme is to identify observatories where it would be possible to carry out lake or other sedimentary coring in the network’s observatories, which, after dating, would make it possible to extend into the recent past (last century) the observation chronicles and information available on the evolution of the critical zone. The idea behind focusing on the last century is that archives can be precisely dated using the short-period radioelements 210Pb/137Cs, leaving the possibility of calibrating variable reconstructions from sediments with instrumental data acquired in associated observation. The indicators (proxies) that could potentially be mobilized to reconstruct the various parameters along the core are sedimentological, physical, geochemical (organic or mineral) or biological in nature, potentially enabling the reconstruction of variations such as hydrology, erosion, weathering, pollution, biogeochemical cycles or ecosystem health. Further research projects could then be set up.
Prospective observation of the critical zone in the French Southern and Antarctic Lands (Sébastien Gogo et al., ECOBIO Rennes)
Observation of the critical zone in the Antarctic and sub-Antarctic regions is still patchy. What’s more, Antarctica and the sub-Antarctic islands will undergo major changes (e.g. greening, loss of glacier mass, impacts of cap dynamics, changes in atmospheric and oceanic currents) that need to be documented and understood. With the Terres Australes et Antarctiques Françaises (TAAF), we have a suitable open-air laboratory for developing an integrated approach to the critical zone in polar and/or sub-polar environments.
The objectives of this transverse action (4 workshops over 2022 and 2023) are 1) to create a space for discussion and reflection around long-term observation of the critical zone in the sub-Antarctic and/or Antarctic zone, 2) to take stock of what exists, 3) based on what exists, to define the gaps and propose actions, 4) to discuss and analyze, with the various stakeholders, the feasibility of these potential actions.
Participatory science in the OZCAR RI (Jules Kouadio et al., LEE, Nantes)
One of the first actions of this theme aims to see how to amplify knowledge on the Critical Zone using scientific and citizen data of varying quality? More specifically, the aim is to structure participatory research within RI OZCAR; to propose a methodology that will serve as a working basis for participatory research initiatives within the OZCAR community; to develop reflections on the issue of the citizen sensor (“citizen sentinel of the environment”) and low-cost transverse sensors to be proposed to observatories; to strengthen links with SHS. The first phase of the project will involve a survey of existing participatory science initiatives in the OZCAR IR.
Preservation tests for water samples (Jonathan Prunier et al., GET Toulouse)
The aim of this theme is to promote a standardized approach to the treatment and preservation of continental surface water samples collected within the OZCAR observation networks, and to study the evolution of their chemical (and if possible isotopic) compositions in the short and long term as a function of water type. It is proposed to focus on short-term storage and to compare, for each type of water (rich or not in Dissolved Organic Carbon, white or black water, acidic or basic, etc.), the impact of the following parameters on major, trace and isotopic element contents: the material of the filtration unit used for sample treatment; the type of conditioning (acidic or not) up to analysis and for preservation; storage conditions: at room temperature or in a cold room at 4°C.
Controlling O2 and CO2 fluxes in the critical zone (Camille Bouchez et al., Géosciences Rennes)
This cross-disciplinary theme aims to answer the following question: What are the dynamics (transport and reactivity) of O2 and CO2 in the subsurface, and what factors explain the distributions of O2 and CO2 with depth? What are the fluxes of O2 and CO2 at the interface between deep and surface environments?
To answer these questions, it is proposed to jointly characterize water fluxes and concentrations in the subsurface environment and in rivers, based on existing knowledge and measurements. Residence time data, which are good descriptors of water storage/recharge in basins, will provide a framework for interpreting O2 and CO2 fluxes. Comparing results between different sites within OZCAR will enable us to investigate the factors forcing these dynamics: lithology, topography, climate.
Cross-cutting themes 2023
Atmospheric precipitation (Brice Boudevillain, IGE Grenoble and Marie-Claire Pierret, ITES Strasbourg)
The monitoring of atmospheric precipitation is present in all (or almost all) observatories in the critical zone, as it is essential for the study of several physical processes (infiltration, runoff, mechanical erosion, leaching), chemical (weathering, atmospheric deposits, acidity of rainfall), and biological processes (vegetation growth or dieback, microbial and bacteriological development), as well as for the study of interactions with humans (water resource quality and quantity, hydrometeorological hazards such as floods and severe low-water periods). However, there has been little exchange on the subject of precipitation within the OZCAR community, whether on technical aspects such as instrumentation, measurement and sampling protocols, processing of acquired measurements and their criticism, or on more scientific aspects such as the study of processes linked to atmospheric precipitation in the critical zone. The challenge is therefore firstly to initiate exchanges and discussions and thus unite teams of technicians, engineers and researchers around practical issues ranging from the acquisition of rain and snow measurements to the banking of data and products, and secondly to initiate collective research actions.
Isotopic characterization of chlorides transferred downstream in watersheds (Pierre Agrinier, IPGP Paris and Jérôme Gaillardet, IPGP Paris)
This cross-disciplinary theme proposes to use the OZCAR RI observatories to access water samples from suitably selected watersheds and measure chlorine isotopes. Why should we do this? Chlorine (in the form of the highly soluble chloride ion) is a popular element with hydrologists and geochemists, as it has a reputation for being conservative. A tracer of water masses, rather than of biophysical-chemical processes. This cross-disciplinary theme aims to revisit the hypothesis of chlorine’s conservativity and work on identifying its sources.
Can we work on the notion of planetary limit in the OZCAR RI observatories? (Jérôme Gaillardet, IPGP Paris)
The notion of planetary limit has become one of the key concepts in the Anthropocene narrative. It is associated with the risk of collapse or of the planet becoming uninhabitable, in both the physical and political senses. This cross-disciplinary theme proposes to reflect on the application of this notion of planetary limit to more situated, territorialized and local contexts, drawing on the RI OZCAR observatories.
Cross-cutting themes 2024
Micro-lives in the critical zone (Alexandra Arènes, IPGP)
In this cross-disciplinary theme, the proposed work focuses on a cross-disciplinary theme that is still not very widespread: micro-lives in the critical zone; and what sensors and cartographic reference systems are capable of understanding and visualizing them. This is a unifying theme between the natural and social sciences, addressed through an art science project. We’ll be building on ongoing research into TERRA FORMA sensors for detecting bacteria in underground environments. Bacteria are all too often observed off-site (in the lab, off the field). But the critical zone, with its observatories, offers opportunities to meet and understand them in situ. The maps produced will aim to see bacteria from this new angle: in their environment, constitutive of the environment, following Margulis and his understanding of Gaia as the set of bacteria producing the world’s biogeochemical conditions.
LASSO: Liens d’Attachment Spécifiques des Scientifiques des Observatoires (Noémie Vanier and Laure Boissel, SciencesPo)
This theme aims to explore the following question: Are there specific links between the scientific teams of the Critical Zone Observatories and their terrain, and how can they be represented? The research hypothesis is as follows: “The laboratory teams of the Critical Zone Observatories have a strong and specific bond of attachment to their terrain”. To explore this hypothesis, we propose to extend the work initiated as part of Sciences Po Paris’ Master in Political Arts (SPEAP), supervised by Jérôme Gaillardet and Marie-Claire Pierret with the OHGE team in Aubure. This master’s program helped define a method for studying this issue. Our aim was to describe these links appropriately. This led to a focus on gestures that can be collected in the laboratory and in the field. In studies carried out in other disciplines, a gesture is defined as any physical interaction involving contact between two agents, at least one of whom addresses his action to the other (human-human/human-non-human). These gestures are analyzed using video material. Following initial work on the OHGE, the project presented here proposes to carry out a multicentric observational study of these links in several observatories of the OZCAR IR.
Completed or reconfigured projects
Role of the root zone within the critical zone (Yves Godderis, GET Toulouse). Project 2019
This theme aims to understand the role of deep roots in the water cycle and water-rock reactions in OZCAR RI observatories. The multi-disciplinary and multi-observatory workshop held in June 2019 in Toulouse led to the submission of an ANR project accepted in 2020. This is the project “NUTRILIFT, deep roots versus pumps: comparison of deep nutrient withdrawals in dry tropical eco and agrosystems” led by Jean Riotte.
“Calcite bags” (Stéphane Binet, ISTO Orléans). Project 2019
This research project aims to install bags containing easily soluble calcite crystals to deduce acidity conditions in the soils of RI OZCAR observatories. This project is inspired by the worldwide tea-bag experiment (carried out in ILTER) to study the degradation of organic matter along climatic gradients. By simple weighing, this experiment will enable an indirect determination of the rate of calcite dissolution and therefore of the partial pressure of carbon dioxide in the soil of RI OZCAR observatories. The project aims to explore the diversity of climatic, geological and land-use conditions enabled by the OZCAR network, and to understand the factors affecting soil acidity. This project has been completed.
Gaz-Ex: dissolved gases in OZCAR observatory waters (Thierry Labasque, Géosciences Rennes). Project 2019
“Gaz-ex” is a workshop-project to take stock of the measurement of dissolved gases in the various OZCAR RI observatories. The aim is also to make the most of the analytical equipment acquired by CRITEX (MIMS spectro) for measuring dissolved gases. The project proposes to compare measurement protocols and launch long-term tests and campaigns to try and estimate the CO2 degassing coefficient in OZCAR RI rivers, for example. This cross-cutting theme is taken up in WP3 activities and the implementation of dissolved gas measurements in various settings.
“DEDMOS”: Ecological determinants and dynamics of organic matter in OZCAR observatory soils (Priscia Oliva, GET Toulouse). Project 2020
This project is the result of the merger of three proposed and complementary projects, and aims to develop a cross-disciplinary “SOLS” action within the OZCAR IR. This project combines geochemistry, pedology and hydrology in contrasting climatic contexts. The aim is to organize a workshop to take stock of knowledge and databases on OZCAR’s soils. It aims to develop a monitoring system for carbon stock and dynamics analyses in RI OZCAR observatories, and to constrain the relationships between organic and mineral fractions, soil biodiversity and environmental parameters. This project has led to the proposal of a soil characterization protocol, which can be consulted here.
IR OZCAR river metabolism (Sophie Guillon, MINES Paris Tech Fontainebleau). Project 2020
The project aims to understand and quantify the metabolism of small rivers by integrating high-frequency dissolved oxygen data from RI OZCAR observatories. It relies on the use of data acquired in operating Riverlabs to understand the biogeochemical functioning of the hyporheic zone in particular, and CO2 degassing fluxes. A master’s internship is being funded in 2021 to integrate high-frequency data from two agricultural catchments. Project completed. This project has been integrated with the intermittent rivers project.
The response of the water-soil-plant system to global change (Damien Lemarchand, Lhyges). Project 2021.
This project aims to develop diagnostic tools to study the response of forest ecosystems to global changes in their nutrient stock management strategy. In particular, it aims to use boron isotopes to determine the balance between lithogenic and biogenic fluxes and the relationship between this balance and environmental conditions. This approach has the potential to be extended to other non-traditional stable isotopes, including macronutrients such as Mg, Si and Ca, and to be transposable to all forest and agricultural ecosystems. This project takes advantage of the wide range of hydrogeochemical conditions at sites in the OZCAR network. It is also intended as a starting point for a medium-term structuring approach within the OZCAR network to develop and standardize isotopic tools on a watershed scale. This project is part of the ANR NUTRIBOR (Dynamique nutritionnelle des écosystèmes forestiers: le point de vue des isotopes du boron) project, led by J. Gaillardet, which began in 2024.
Nanoparticles in the critical zone (Marc Benedetti, IPGP Paris). Project 2022
Over the past twenty years, the emergence of a new potential pollutant – nanoparticles between 1 and 100 nm in size – has led to widespread concern about their impact on human health and the natural environment. Nanoparticles can be of natural origin or man-made. It is necessary to quantify the concentrations and flows of nanoparticles in the environment in order to study their life cycles and potential ecotoxicological impacts. It is proposed to focus on small river basins, where the two main hypotheses to be tested will be: 1/ Land use will influence NP concentrations and fluxes measured in watercourses; 2/ Hydrological and biogeochemical parameters such as flow rate, conductivity or organic matter concentration changing over the course of a year will be key process parameters governing the concentration and fate of nanoparticles newly injected into the river ecosystem.
The first step will be to detect natural, accidental and/or manufactured nanoparticles in surface waters over several years in a number of pilot basins, before going on to identify control processes. Project completed.
Fluorine mobilization during major flood events and impact on surface waters in mountainous areas (Erica Erlanger, GFZ, Potsdam, Germany). Project 2023
Fluorine is essential to life on Earth and fundamental to human health. On a global scale, rivers transport around 15.8 x 1012 g of dissolved and particulate fluoride per year to the oceans. Around 60% of this flow comes from natural chemical and physical erosion, and up to 30% is attributed to anthropogenic sources of fluorine, making it one of the most human-disturbed cycles within the critical zone. Fluorine is unique in its behavior during weathering. As the source areas for much of the sediment, dissolved elements and organic matter in rivers, mountain watersheds are key areas for understanding how flooding affects weathering-related cycles. The hypothesis is that, during a flood, fluorine peaks in river water correspond to a loss of fluorine by leaching from potential solid sources. To constrain where the fluorine released by weathering comes from, we need to characterize the sources present in the study catchment, and quantify their contribution. We propose to do this by combining fluorine levels in water with an estimate of the sources of dissolved load, and even of the fluxes of silicate and carbonate weathering, organic matter export and fertilizer contribution (where applicable). The OZCAR infrastructure is ideal for this comparative approach to studying the fluorine cycle in instrumented catchments. This project could not be completed.