Nutuvukti Lake and Fen: A Patterned Wetland in Gates of the Arctic

Nutuvukti Lake, in the Kobuk Preserve portion of Gates of the Arctic National Park and Preserve, is one of the largest lakes in northern Alaska. It lies in a trough between two mountain ridges covered with dwarf subarctic spruce forest and alpine tundra. At six miles long it is smaller than its more famous neighbor, Walker Lake, and it is home to lake trout, arctic grayling, arctic char, northern pike and whitefish.

Nutuvukti Lake (image from NPS's page).

Nutuvukti Lake is in the southern part of the park. North of the lake lie the fen, a glacial moraine and a proposed road (image from NPS's page).

What a fen is

A fen is a wetland where the ground is peat, partly decomposed plants. The spongy peat is saturated with water, and the vegetation is mostly grass-like sedges, usually with some moss and low shrubs. Fen water is not strongly acidic, because it comes from groundwater carrying dissolved mineral nutrients. It seeps slowly downhill in a wide sheet, which is why the Florida Everglades, the most famous fen, is sometimes called a "River of Grass."

Looking west from the middle of Nutuvukti Fen. Sedges dominate, with mosses and low shrubs in the saturated peat (image from NPS's page).

Nutuvukti Lake gets its water as runoff from the nearby mountain slopes and from the fen on its northern shore. The fen is one of the few, and perhaps the largest, patterned fens in all of interior Alaska. "Patterned" means it is covered with an intricate pattern of low ridges and pools.

The western side of the fen from the air. The green wavy lines, the vegetated ridges, are about 10-15 feet wide (image from NPS's page).

Permafrost decides where the water goes

Most of the landscape around the lake sits on permafrost, ground that stays frozen all year. Only the top foot or two thaws each summer, so water from snowmelt and summer rain runs quickly downslope over the permafrost and never soaks in deeply. As it runs, it concentrates into "water tracks," visible as green lines of vegetation. The permafrost holds bodies of ice, and where it thaws the ground subsides into pits and ponds.

A pond formed by melting ice in the ground at the edge of the fen (image from NPS's page).

Water runs over permafrost to Nutuvukti Lake (at the bottom). The tracks appear as green stripes of dense vegetation about 50 feet wide (image from NPS's page).

Just north of the fen is a low, rocky area of hills called a glacial moraine, which marks the end of a glacier in the last ice age. It is one of the few places in this landscape without permafrost, so water there soaks deep into the ground and moves underground into the fen and on to the lake.

The Nutuvukti moraine north of the lake and fen (image from NPS's page).

A road nearby

The law that established the park and preserve provides for a transportation corridor to the Ambler Mining District. The State of Alaska is considering a road route that passes near the lake, and the National Park Service page notes that a supplemental environmental impact statement with recommendations for the road was nearing completion.

Sources

• National Park Service, Gates of the Arctic National Park and Preserve, Nutuvukti Lake and Fen; rewritten in hubnx's own words.