Remote sensing evaluation of High Arctic wetland depletion following permafrost disturbance by thermo-erosion gullying processes

Abstract

Northern wetlands and their productive tundra vegetation are of prime importance for Arctic wildlife by providing high-quality forage and breeding habitats. However, many wetlands are becoming drier as a function of climate-induced permafrost degradation. This phenomenon is notably the case in cold, ice-rich permafrost regions such as Bylot Island, Nunavut, where degradation of ice wedges and thermo-erosion gullying have already occurred throughout the polygon-patterned landscape resulting in a progressive shift from wet to mesic tundra vegetation within a decade. This study reports on the application of the normalized difference vegetation index to determine the extent of permafrost ecosystem disturbance on wetlands adjacent to thermo-erosion gullies. The analysis of a GeoEye-1 image of the Qarlikturvik valley, yielding a classification with five classes and 62% accuracy, resulted in directly identifying affected areas when compared to undisturbed baseline of wet and mesic plant communities. The total wetland area lost by drainage around the three studied gullies approximated to 95 430 m 2 , which already represents 0.5% of the total wetland area of the valley. This is worrisome considering that 36 gullies have been documented in a single valley since 1999 and that permafrost degradation by thermal erosion gullying is significantly altering landscape morphology, modifying wetland hydrology, and generating new fluxes of nutrients, sediments, and carbon in the watershed. This study demonstrates that remote sensing provides an effective means for monitoring spatially and temporally the impact of permafrost disturbance on Arctic wetland stability.Key words: Arctic wetlands, thermo-erosion gullies, permafrost disturbance, remote sensing, normalized difference vegetation index (NDVI).Résumé : Les terres humides du Nord ainsi que leur végétation de toundra fertile sont d'une grande importance pour la faune arctique en procurant un fourrage de grande qualité et des habitats de reproduction. Cependant, beaucoup de terres humides deviennent plus sèches en fonction de la dégradation du pergélisol d'origine climatique. Ce phénomène est notamment le cas dans les régions de pergélisol froides, riches en glace comme l'île Bylot, Nunavut, où les phénomènes de fonte de coins de glace et de ravinement par érosion For personal use only.thermique se sont déjà produits partout dans le paysage de polygones en plan, entraînant un changement progressif de la végétation de toundra humide à mésique en une décennie. Cette étude fait état de l'application d'indice de végétation par différence normalisée afin de déterminer l'ampleur de la perturbation des écosystèmes du pergélisol affectant les terres humides adjacentes aux ravins d'érosion thermique. L'analyse d'une image de GeoEye-1 de la vallée Qarlikturvik, rapportant une classification à cinq classes avec une exactitude de 62%, a permis de directement identifier les zones touchées lorsque comparées à la référence, soit les communautés intactes de plantes humides et mésiques...

Effects of changing permafrost and snow conditions on tundra wildlife: critical places and times

“…This resulted in a fivefold decrease in the aboveground biomass of grasses and sedges that are the preferred foraging plants of snow geese (Chen caerulescens) in the area. Perreault et al (2017) found that gullies created by thermal erosion led to 55 m 2 of disturbed area per metre of gullying, leading to a significant loss of wetlands in a major brood-rearing area used by snow geese on Bylot Island. Climate warming has a strong potential to enhance and accelerate these processes, which could have far-reaching consequences for the habitat of geese and possibly other wildlife species of the tundra.…”

Pathways for Ecological Change in Canadian High Arctic Wetlands Under Rapid Twentieth Century Warming

“…Across Arctic wetlands, warming has been linked to greater plant biomass (Hill & Henry, ), vegetation composition changes and desiccation (Woo & Young, , ; Zhang, Piilo, et al, ). Ice wedge polygon mires specifically are complex and dynamic systems (de Klerk et al, ; Fritz et al, ), and degradation in response to recent warming has led to changes in vegetation and drainage (Fraser et al, ; Jorgenson et al, ; Liljedahl et al, ; Perreault et al, ). Similarly, vegetation in some sub‐Arctic and Arctic coastal wetlands has been altered by increasing bird grazing pressures in recent decades (Jefferies & Rockwell, ; Peterson et al, ).…”

Deep Convolutional Neural Networks for Automated Characterization of Arctic Ice-Wedge Polygons in Very High Spatial Resolution Aerial Imagery

“…LCP polygons are commonly observed within relatively young terrain units (e.g., young drained-lake basins, floodplains) with actively growing ice wedges and are usually are of a larger diameter than HCP polygons, which prevail primarily within older terrain units (e.g., yedoma, old drained-lake basins) [36]. The microtopography associated with the IWPs governs many aspects of permafrost [34,35,37,38], vegetation [22,25,39,40] and hydrologic dynamics [27,41,42], and Arctic ecosystem in general [30,32,35,38] at plot-to-local scales (1-100 m), landscape (100 m-10 km), and regional scales (10-1000 km), mainly due to the role of polygon type on the flow and storage of water [27,41].Through satellite imagery, aerial photos, and ground observations, large-scale ice-wedge degradation was observed across the Arctic, and in many places, this degradation has resulted in transformation of LCP polygons into HCP polygons in less than a decade [27,29,37,38,[43][44][45][46][47][48][49][50][51][52][53][54][55][56]. In most cases, ice-wedge degradation, which is extremely hazardous for both environment and infrastructure, has been triggered by climatic fluctuations [27,38], wildfires [57], human activities [48], or any other factors that lead to increase in the active-layer thickness.…”

“…Lara et al [29]conducted polygonal tundra geomorphic classification in the Barrow Peninsula, Alaska with an overall accuracy of 0.75 using hybrid procedures (pixel-based classification, object-based image analysis, and threshold method) in conjunction with images from Landsat-7 (30 m resolution) and Quickbird (0.6 m resolution). Based on high-resolution GeoEye-1 satellite imagery, Perreault et al [55] assessed the extent of high Arctic wetlands combining normalized difference vegetation index and a threshold-based classification method. Remote sensing-based ice-wedge polygon mapping effort to date follow manual or semi-automated approaches, which quickly constrain the geographical extent of the application.Due to IWPs' varying spectral and morphometric characteristics (e.g., irregular shape and trough spacing) [73], visual inspection and manual digitization has so far been the most widely adopted and promising method to delineate polygons from LiDAR or VHSR imagery [13,26,56,65,69,70,74].…”

“…Through satellite imagery, aerial photos, and ground observations, large-scale ice-wedge degradation was observed across the Arctic, and in many places, this degradation has resulted in transformation of LCP polygons into HCP polygons in less than a decade [27,29,37,38,[43][44][45][46][47][48][49][50][51][52][53][54][55][56]. In most cases, ice-wedge degradation, which is extremely hazardous for both environment and infrastructure, has been triggered by climatic fluctuations [27,38], wildfires [57], human activities [48], or any other factors that lead to increase in the active-layer thickness.…”