The information system of the French Peatland Observation Service: Service National d'Observation Tourbières – A valuable tool to assess the impact of global changes on the hydrology and biogeochemistry of temperate peatlands through long term monitoring

Mitigating and adapting to global changes requires a better understanding of the response of the Biosphere to these environmental variations. Human disturbances and their effects act in the long term (decades to centuries) and consequently, a similar time frame is needed to fully understand the hydrological and biogeochemical functioning of a natural system. To this end, the ‘Centre National de la Recherche Scientifique’ (CNRS) promotes and certifies long‐term monitoring tools called national observation services or ‘Service National d'Observation’ (SNO) in a large range of hydrological and biogeochemical systems (e.g., cryosphere, catchments, aquifers). The SNO investigating peatlands, the SNO ‘Tourbières’, was certified in 2011 (https://www.sno-tourbieres.cnrs.fr/). Peatlands are mostly found in the high latitudes of the northern hemisphere and French peatlands are located in the southern part of this area. Thus, they are located in environmental conditions that will occur in northern peatlands in coming decades or centuries and can be considered as sentinels. The SNO Tourbières is composed of four peatlands: La Guette (lowland central France), Landemarais (lowland oceanic western France), Frasne (upland continental eastern France) and Bernadouze (upland southern France). Thirty target variables are monitored to study the hydrological and biogeochemical functioning of the sites. They are grouped into four datasets: hydrology, fluvial export of organic matter, greenhouse gas fluxes and meteorology/soil physics. The data from all sites follow a common processing chain from the sensors to the public repository. The raw data are stored on an FTP server. After operator or automatic processing, data are stored in a database, from which a web application extracts the data to make them available (https://data-snot.cnrs.fr/data-access/). Each year at least, an archive of each dataset is stored in Zenodo, with a digital object identifier (DOI) attribution (https://zenodo.org/communities/sno_tourbieres_data/).

range of hydrological and biogeochemical systems (e.g., cryosphere, catchments, aquifers). The SNO investigating peatlands, the SNO 'Tourbières', was certified in 2011 (https://www.sno-tourbieres.cnrs.fr/). Peatlands are mostly found in the high latitudes of the northern hemisphere and French peatlands are located in the southern part of this area. Thus, they are located in environmental conditions that will occur in northern peatlands in coming decades or centuries and can be considered as sentinels. The SNO Tourbières is composed of four peatlands: La Guette (lowland central France), Landemarais (lowland oceanic western France), Frasne (upland continental eastern France) and Bernadouze (upland southern France). Thirty target variables are monitored to study the hydrological and biogeochemical functioning of the sites.
They are grouped into four datasets: hydrology, fluvial export of organic matter, greenhouse gas fluxes and meteorology/soil physics. The data from all sites follow a common processing chain from the sensors to the public repository. The raw data are stored on an FTP server. After operator or automatic processing, data are stored in a database, from which a web application extracts the data to make them available (https://data-snot.cnrs.fr/data-access/). Each year at least, an archive of each dataset is stored in Zenodo, with a digital object identifier (DOI) attribution (https://zenodo. org/communities/sno_tourbieres_data/).

| INTRODUCTION
There is a need for long-term observation to document and understand ecosystem responses to climate change and to stimulate synergies between observation and models. Responses of the water and the carbon (C) cycles of ecosystems to anthropogenic disturbances have to be addressed in a long-term time frame. However, long-term observation data are still scarce for many ecosystems. Peatlands are wetlands that cover only 3% of continental surfaces, but that contain between 17 and 27% of the world soil C stock (Jackson et al., 2017;Yu et al., 2010).
Although peatlands function as a global C sink, they have switched locally to source systems . This can have dramatic effects on climate change as a large amount of greenhouse gases (GHG) can be released into the atmosphere, thereby generating a positive feedback on temperature increase. Furthermore, the occurrence of peatlands within a catchment area influences the water fluxes and the export of organic carbon (OC) downstream, impacting the water quality (Fenner et al., 2011). Hence, long-term monitoring of water and C cycles in catchment areas containing such sentinel ecosystems is required. This is the rationale for the construction of the 'Service The same sensor is also used to assess the streamflow at the outlet of the catchment containing the peatlands. The outflow intensity is proportional to the water height. At low frequency, water outflow is measured using salt dilution and the water column height is simultaneously recorded. A calibration curve relating outflow and water height is established. This curve is used to produce a high frequency outflow time series (1 recording every 30 min).
Fluorescence of the dissolved organic matter (fDOM) is used as a proxy to assess the DOC concentration (Rosset, 2019a). A fraction of the total DOM flouresces. It is assumed that the total DOC is proportional to the fraction of fluorescent DOM (Rosset, 2019a). A fluorimeter (EXO fDOM) is connected to the multiparameter station (EXO2,

| INVOLVEMENT OF THE SI SNO TOURBIÈRES IN NATIONAL AND INTERNATIONAL RESEARCH INFRASTRUCTURES
At the national level, the SNO Tourbières is part of OZCAR, the French research infrastructure (RI) on the critical zone (https://www. ozcar-ri.org/, Gaillardet et al., 2018), and is registered in the OZCAR information system, THEIA-OZCAR (https://in-situ.theia-land.fr/; Braud et al., 2020). Attributing a DOI to a dataset ensures its correct citation and long lasting archiving. Each DOI is associated to a landing page that has to remain accessible in the long term. The strategy in the SNO Tourbières is to assign a fixed DOI to a dataset and apply a versioning to avoid too many landing pages. To do so, the chosen application is Zenodo (Figure 2), an open access data, research and software repository that generates a DOI and manages versioning. With the versioning, as soon as we have a new dataset, a new DOI is created with its associated metadata. This process makes the system flexible, traceable and manageable. The data are updated between one and three times per year. A SNO Tourbières data repository has been created: https://zenodo.org/communities/sno_tourbieres_data/. This application allows contribution from and to other data managing structures. An article can be written with a subset of data. These data can be deposited in another data repository with the reference to the article. The SNO Tourbières dataset will mention if it contains this particular sub-dataset: 'HasPart' (e.g., Rosset, 2019b;. Furthermore, datasets of the SNO Tourbières can be contained in a larger data set (e.g., Fluxnet, ICOS, OZCAR) and will mention it as: 'IsPartOf'.

DATA AVAILABILITY STATEMENT
The data belong to the French State and as such can be used by anybody as long as the data are properly cited (either by acknowledging the SNO Tourbières and/or by citing their digital object identifier -DOI -when available).Unless otherwise stated, data from SNO-Tourbières are licensed under Creative Commons CC BY-SA 4.0.