Groundwater-Discharge Wetlands in the Tanana Flats, Interior Alaska
1991
Racine, Charles H. | Walters, James C.
In the northwest corner of the Tanana Flats, a lowland basin just south of Fairbanks in interior Alaska, there is a vast network of floating-mat wetlands or fens that appears to be unique in terms of their origin, large areal extent, and absence of sphagnum moss and associated peat. During the summers of 1989 and 1990 a study of the impacts of airboats on these wetlands included aerial and ground reconnaissance of 20 sites to characterize the vegetation, hydrology and subsurface conditions. These wetlands consist of a floating vegetation mat up to 1 m thick, forming an almost complete cover over deeper water bodies. The mats consist of a tall, dense and productive network of emergent vascular plants, including buckbean (menyanthes trifoliata), swamp horsetail(Equisetum fluviatile), sedges (Carexaquatilis), marshfivefinger(potentilla palustris),water hemlock (Cicuta mackenzieana) and bladderwort (Utricularia sp.). Evidence that these wetlands are formed by groundwater discharge includes (a) the apparent absence of permafrost under these wetlands but its presence on the adjacent forested uplands, (b) nearby winter icings resulting from artesian springs, (c) the relatively high pH, conductivity, calcium and magnesium concentrations of the water, (d) the vascular plant species composition and in particular the absence of Sphagnum moss, and (e) the flow of water and the geological history of the area. Expansion of these fens in several places is suggested by dead and dying white birch along the upland-fen margin, were permafrost thaw and subsidence (thermokarst) is taking place.
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