Abstract
Water bodies are ubiquitous features in Arctic wetlands. Ponds, i.e., waters with a surface area smaller than 104 m2, have been recognized as hotspots of biological activity and greenhouse gas emissions but are not well inventoried. This study aimed to identify common characteristics of three Arctic wetlands including water body size and abundance for different spatial resolutions, and the potential of Landsat-5 TM satellite data to show the subpixel fraction of water cover (SWC) via the surface albedo. Water bodies were mapped using optical and radar satellite data with resolutions of 4mor better, Landsat-5 TM at 30mand the MODIS water mask (MOD44W) at 250m resolution. Study sites showed similar properties regarding water body distributions and scaling issues. Abundance-size distributions showed a curved pattern on a log-log scale with a flattened lower tail and an upper tail that appeared Paretian. Ponds represented 95% of the total water body number. Total number of water bodies decreased with coarser spatial resolutions. However, clusters of small water bodies were merged into single larger water bodies leading to local overestimation of water surface area. To assess the uncertainty of coarse-scale products, both surface water fraction and the water body size distribution should therefore be considered. Using Landsat surface albedo to estimate SWC across different terrain types including polygonal terrain and drained thermokarst basins proved to be a robust approach. However, the albedo–SWC relationship is site specific and needs to be tested in other Arctic regions. These findings present a baseline to better represent small water bodies of Arctic wet tundra environments in regional as well as global ecosystem and climate models.
Highlights
Wetlands cover about 8% (396, 000 km2 ) of the non-glaciated Arctic tundra surface [1]
We investigated the relationship between surface albedo, α, calculated from the Landsat surface reflectance, ρ, and the subpixel water cover (SWC) within each Landsat pixel
Water bodies at all three sites were dominated in number by ponds, i.e., water bodies with a surface area smaller than 104 m2, but dominated in area by a few large lakes (Figures 3 and 4(a))
Summary
Wetlands cover about 8% (396, 000 km2 ) of the non-glaciated Arctic tundra surface [1]. Organic wetland soils store large amounts of carbon [2] and both tundra surfaces and water bodies are a main source of carbon dioxide and methane to the atmosphere [3]. Thawing of permafrost may either increase the number of ponds and lakes when thermokarst depressions fill with water [6,7], or decrease their number when permafrost thaw results in drainage of water bodies [8,9,10]. I.e., water bodies with a surface area smaller than 104 m2 , are by far the dominant water bodies in Arctic wetlands [11,12,13]
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