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Why do wetlands form in some Arctic coastal plains?

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tundra biome — Polar ecosystem Southern limit of Arctic tundra and approximate line of demarcation between Low and High Arctic.

In Arctic coastal plains, wetlands form primarily due to the presence of permafrost, a layer of perennially frozen ground that remains in the soil throughout the year.12

This impermeable layer acts as a barrier that prevents surface water from percolating downward into the ground. Consequently, during the summer thaw, the upper layer of soil—known as the active layer—becomes saturated, as the water has nowhere to drain. This poor drainage creates boggy, waterlogged conditions that are characteristic of Arctic tundra lowlands.1234

Additionally, the flat topography of many coastal plains further contributes to the accumulation of water, as the landscape lacks the steep gradients necessary for rapid drainage. These conditions, combined with the limited evaporation typical of polar climates, sustain extensive wetland ecosystems such as bogs, fens, and peatlands.5214