Peatlands are wetlands with at least 30-40 cm of accumulated peat [1]. They cover 3% the Earth's surface and store ~25% of the global soil carbon derived from atmospheric CO₂ [2]. But, because of predominantly anaerobic conditions they are also important sources of methane (CH₄) to the atmosphere. In Europe it is estimated there is nearly 600,000 km² to 1,000,000 km² of peatlands [3]. In Canada there is over 1,000,000 km², covering ~12% of the national territory [4]. Their ecological, hydrological and biogeochemical functions are coupled to climate [5], but the full impact of climate change on these ecosystems is not fully understood [6]. Simulation models have shown that northern peatlands could undergo significant changes to their carbon cycling where they become either reduced sinks or may become sources of carbon to the atmosphere [7].

In Canada there are four types of peatlands: bogs, fens, marshes and swamps. Bogs cover the largest surface area. Ombrotrophic bogs receive water and nutrient inputs via precipitation or deposition. They are characterized by acidic, low nutrient content peat, which has slower decomposition than accumulation rates. The ground cover is mostly comprised of Sphagnum spp. mosses with varying density of tree cover and vascular shrubs. Assessment of their structure (e.g., microtopography), biogeochemistry (e.g., pigment content), hydrology and function (e.g., net ecosystem exchange) are important aspects in determining their continued ability to uptake and store carbon. Recent insights from peatland biogeochemical research have shown a bimodal diel pattern in ecosystem respiration (ER) [8], a shift in plant community composition from mosses to vascular plants following long-term Nitrogen deposition [9], a vegetation species and scale dependence of water table depth [10], and the importance of soil temperature on ER [11]. Recent research has also shown that CH₄ emission increases following nutrient addition [12], a strong spatial association of plant species with CH₄ emission [13] and a non-monotonic relationship between water table depth and CH₄ emission [14].

Peatlands are fundamentally important for global climate change mitigation and many ecosystem services. Yet they are poorly resolved in global and regional land cover maps, and continue to be omitted from the main Earth system models used for future climate change projections. See Leifeld and Menichetti (2018) for a discussion on the importance of peatlands to global climate change mitigation strategies and Loisel et al. 2021 on the vulnerability of the global peatland carbon sink.

Mer Bleue is a protected ombrotrophic bog with a hummock-hollow-lawn microtopography. It is located at the eastern boundary of the City of Ottawa, Ontario, Canada and is part of the National Capital Greenbelt and is managed by the National Capital Commission. Mer Bleue is recognized as a Wetland of International Importance under the Ramsar Convention on Wetlands, a Provincially (Ontario) significant Wetland, and a Provincially (Ontario) Significant Life and Earth Science Area of Natural and Scientific Interest.

Its long axis in the east–west orientation is dissected by two longitudinal sections of fluvial sand/gravel separating three distinct arms of the peatland [15]. The climate is cool continental temperate with a 30-year (1971–2000) mean annual air temperature of 6.0 °C. The mean annual precipitation is 943 mm, of which 235 mm falls as snow generally between December and March. During the period of January to August 2016, the mean monthly air temperature ranged from -8.1°C in February to 22 °C in August, with minimum (26.2 mm) and maximum (91.6 mm) precipitation in May and August respectively. The bog is slightly domed, with a peat depth greater than 5-6 m across most of the area. In the northern arm, this decreases to 30 cm towards the edge where narrow beaver ponds are inundated year-round [15].

Mer Bleue is the northern peatland with the longest continuous Eddy Covariance measurements - photos above show the tower set up and starting measurements in May 1998.

For additional information on the long term data acquisition, baseline background or to learn more about Mer Bleue's establishment as an LPVE supersite, see the individual researcher links below. For a comprehensive list of those having conducted research at the site check out the publications page.

Two decades ago users of Earth observation data were interested in raw data and they wanted to understand and process satellite imagery themselves. This required a high-level understanding of the sensors, data products and overall remote sensing theory. Today, the largest user community of satellite imagery prefers data products as input for decision making. They are not necessarily remote sensing specialists interested in all aspects of the processing chain. As a result, there are substantial ongoing efforts to generate widely accessible, comparable and reliable Earth observation data. This requires:

• New algorithms for processing and quality assurance
• New protocols to generate standardized data products
• Methods to quantify the accuracy of data products through calibration and validation exercises
• Data harmonization across sensors

Currently Mer Bleue is the only peatland designated as a CEOS Land Product Validation 'supersite'. These ground reference sites are characterized using well established protocols to acquire data for the validation of at least three satellite land products. They are also active long-term sites supported by infrastructure and airborne LiDAR and/or hyperspectral imagery.

The current Quality Assurance Framework for Earth Observation (QA4EO) project builds upon the successful completion of the Mer Bleue Arctic Surrogate Simulation Site (MBASSS) Sentinel-2 and Landsat 8 Validation Project. MBASSS was performed as part of the Cal/Val Activities and In-Situ Field Campaigns activity within the Sensor Performance, Products and Algorithms (SPPA) element of the European Space Agency (ESA) Earth observation ground segment. The project was led by the National Research Council of Canada’s Flight Research Laboratory (NRC-FRL) in collaboration with the Applied Remote Sensing Laboratory (ARSL), the Canada Centre for Remote Sensing (CCRS) and LOOKNorth.

Check out the MBASSS StoryMap for more information.

One of the primary objectives of MBASSS was to compare data products (surface reflectance and vegetation indices) for Sentinel-2 imagery, hyperspectral imagery and satellite simulations for four time periods capturing phenological changes at the landscape level at Mer Bleue. This was done through a multi-scale approach, including field spectroscopy, UAV photogrammetry and airborne hyperspectral imagery. The results are described in:

Arroyo-Mora J.P., Kalacska M., Soffer R., Ifimov G., Leblanc G., Schaaf E.S., Lucanus O. 2018. Evaluation of phenospectral dynamics with Sentinel-2A using a bottom-up approach in a northern ombrotrophic peatland Remote Sensing of Environment 216:544-560.

The diagram below illustrates the multi-scale integrated approach. To learn more about the airborne remote sensing component check out the National Research Council of Canada's - Flight Research Lab and the Canada Center for Mapping and Earth Observation for information about the satellite simulations.

This worked was financially supported by the European Space Agency through the IDEAS-QA4EO program as implemented within the NRC Integrated Aerial Mobility Program. The research at Mer Bleue has been supported by the National Capital Commission, Ottawa, for which the researchers are grateful. We also thank the Natural Sciences and Engineering Research Council of Canada, the National Science Foundation USA, the Canadian Foundation for Innovation, the Fonds de recherche du Québec – Nature et technologies, the German Ministry of Science and Education, the Academy of Finland, the Ontario Ministry of Environment and Climate Change, Fluxnet Canada, the Canada Carbon Project and BIOCAP Canada.

[1] National Wetlands Working Group. Wetlands of Canada, in Canada Committee on Ecological Land Classification, Environment Canada, Ecological Land Classification Series No 24. (1988).
[2] Yu et al. Global peatland dynamics since the Last Glacial Maximum. Geoph Res Let 37, (2010).
[3] Tanneberger et al. The peatland map of Europe. Mires and Peat 19, 22 (2017).
[4] Tarnocai et al. Peatlands of Canada. 2011, Geological Survey of Canada, Open File 6561. (2011).
[5] Wu, Response of peatland development and carbon cycling to climate change: a dynamic system modeling approach. Env Earth Sci 65, (2011).
[6] Lees et al. Potential for using remote sensing to estimate carbon fluxes across northern peatlands - A review. Sci Total Environ 615, (2018).
[7] Helbig et al. Increasing contribution of peatlands to boreal evapotranspiration in a warming climate. Nat Clim Change 10, (2020).
[8] Jarveoja et al. Bimodal diel pattern in peatland ecosystem respiration rebuts uniform temperature response. Nat Commun 11, (2020).
[9] Moore & Bubier Pland and soil Nitrogen in an ombrotropic peatland, Southern Canada. Ecosystems 23, (2020).
[10] Malhotra et al. Ecohydrological feedbacks in peatlands: an empirical test of the relationship among vegetation, microtopography and water table. Ecohydrology 9, (2016).
[11] Lafleur et al. Ecosystem Respiration in a Cool Temperate Bog Depends on Peat Temperature But Not Water Table. Ecosystems 8, (2005).
[12] Juutinen et al. Long-term nutrient addition increased CH4 emission from a bog through direct and indirect effects. Sci Rep 8, (2018).
[13] Lai et al. Spatial and temporal variations of methane flux measured by autochambers in a temperate ombrotrophic peatland. J. Geo Res: Biogeosciences 119, (2014).
[14] Brown et al. Evidence for a nonmonotonic relationship between ecosystem-scale peatland methane emissions and water table depth. J. Geo Res: Biogeosciences 119, (2014).
[15] Roulet et al. Contemporary carbon balance and late Holocene carbon accumulation in a northern peatland. Global Change Biology 13(2), (2007).