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Pedro Freitas


Ph.D. student

Department of Biology, Université Laval

Alexandre-Vachon Building
1045 avenue de la Médecine
Université Laval
Quebec, Canada
G1V 0A6

418.656.5644 extension 405644




Projet de recherche

Dynamics and spatial variability of Arctic and sub-Arctic thermokarst ponds and their biogeochemical properties


The Arctic and Subarctic are changing rapidly, with warming and changes in precipitation leading to permafrost degradation and the formation of thermokarst lakes and ponds. These act as biogeochemical hotspots for the mobilization of soil organic carbon through microbial and photochemical transformations and are a form of abrupt permafrost thaw, contributing to an increase of the global CH4 and CO2 emissions. They exhibit diverse optical properties, reflecting their biogeochemical and limnological characteristics, contributing differentially to greenhouse gas production, and are considered a positive feedback mechanism to global warming. However, due to their small size, these small lakes and ponds are not adequately represented in global climate and Earth System models.


Identifying the biogeochemical variables of thermokarst lakes (e.g. Total Suspended Solids, Dissolved Organic Matter, Colored Dissolved Organic Matter, Chlorophyll a) that can be characterized using UAV and satellite imagery, allowing the development of classification algorithms. Identifying local factors (lithological, climatic, vegetation) that control the biogeochemical and spectral properties of thermokarst lakes. Developing methodologies for upscaling observations from local to the regional scales, considering problems related to shadows, wind and reflected radiation from the surrounding environment, currently not considered in regional remote sensing analysis. Characterizing and analyzing the spectral variability of thermokarst lakes along two regional transects in Northern Canada, from the isolated to continuous permafrost zones, and identify the main conditioning factors at the seasonal and interannual levels.

Study sites

Two regional transects will be analyzed: Transect 1- The transect in eastern Hudson Bay, will be between 55° and 58°N, allowing analysis of the tundra-boreal forest transition zone, in an area where permafrost degradation (ice-rich permafrost mounds degradation forming thermokarst lakes) is advanced and shrubification processes are evolving very rapidly. Fieldwork will take place in detailed areas near the CEN stations at Kuujjuarapik-Whapmagoostui and Umiujaq. Transect 2 - The Mackenzie river transect, will be between Eagle Plains and Tuktoyaktuk from 66° to 69°N, with several detailed study sites along the Dempster and Tuktoyaktuk roads. In this transect larger lakes will also be analyzed.

Material and methods

Unmanned Aerial Vehicles equipped with optical and multispectral cameras will be used to spectrally characterize the thermokarst lakes, classify the vegetation, calculate indices, characterize the geomorphology and structure of the vegetation, and perform biomass calculations. A multiparameter probe will be used for the physical-chemical characterization of parameters associated to the optical properties of the lakes (DOC, TSS, etc.). Water samples will be collected and analyzed in the laboratory. These data will be used to calibrate satellite images through linear and non-linear regressions. Chemical and particle size analysis of lake basin soils will be made, highlighting organic carbon and nutrient content. Point sampling (DGPS) of ground truth with different landcover types will be used for training and validation of satellite image classifiers.


Walter Anthony, K., Deimling, T. S., Nitze, I., Frolking, S., Emond, A., Daanen, R. Anthony, P., Lindgren, P., Jones, B., Grosse, G. (2018). 21st-century modeled permafrost carbon emissions accelerated by abrupt thaw beneath lakes. Nature Communications, 9:3262. DOI: 10.1038/s41467-018-05738-9. Bouchard, F., MacDonald, L., Turner, K., Thienpont, J., Medeiros, A., Biskaborn, B., Korosi, J., Hall, R., Pienitz, R., Wolfe, B. (2016). Paleolimnology of thermokarst lakes: a window into permafrost landscape evolution. Arctic Science, Vol. 3, 91-117. DOI: 10.1139/as-2016-0022. Schuur, E. A. G., McGuire, A. D., Schadel, C., Grosse, G., Harden, J. W., Hayes, D. J., Hugelius, G., Koven, C. D., Kuhry, P., Lawrence, D. M., Natali, S. M., Olefeldt, D., Romanovsky, V. E., Schaefer, K., Turetsky, M. R., Treat, C. C., Vonk, J. E. (2015). Climate change and the permafrost carbon feedback. Nature, Vol. 520, 171 - 179. DOI:10.1038/nature14338.

Location of the research sites

Scientific communications

Folhas, D., Duarte, A.C., Pilote, M., Vincent, W.F., Freitas, P., Vieira, G., Silva, A.M.S., Duarte, R.M.B.O., Canário, J., 2020. Structural characterization of dissolved organic matter in permafrost peatland lakes. Water, 12(11), 3059. DOI: 10.3390/w12113059 .

Freitas, P., Vieira, G., Canário, J., Folhas, D., Vincent, W.F., 2019. Identification of a threshold minimum area for reflectance retrieval from thermokarst lakes and ponds using full-pixel data from Sentinel-2. Remote Sensing, 11(6): 657. DOI: 10.3390/rs11060657.

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