Arctic Wetlands Fens Research

Wetlands are considered to be one of the most productive ecosystems on Earth. Wetlands provide important habitats and perform ecological functions that are vital to the health and sustainability of landscapes. Wetlands are regulators of water; they capture and retain surface and ground water and slowly release it into the landscape. Wetlands also restore groundwater, regulate local humidity, and ensure that the base flow of small and large streams is maintained. Natural mechanical and biological filters found in wetlands remove sediments, minerals, nutrients, and other chemicals from inflow by settling and decomposition, resulting in cleaner water being discharged into the landscape.

Broadly defined, a wetland is an area of land where the water table is at or above the level of the mineral soil for the entire year. A fen is one of five types of wetlands and is defined as a lowland covered wholly or partly with shallow water with water-loving vegetation that decays to form peat. Fens are one of two types of organic wetlands (the other being bogs) that are also referred to as peatlands, and are areas with accumulations of more than 40 cm of peat above the mineral soil. Fens are often regarded as a transitional stage from a marsh to a bog, particularly in northern climates.

Peatlands are the most common form of wetland in wet, cool climates at northerly latitudes and at higher elevation midlatitude zones. Peatlands typically form in poorly drained, waterlogged depressions. Due to wet, cool conditions, dead plant material accumulates faster than it decomposes, resulting in a buildup of organic material called peat. Peatlands are dominated by thick mats of moisture-loving mosses and sedges, and often support a sparse growth of shrubs and stunted spruce trees. The term muskeg is often used in North America to refer to peatlands characterized by a large expanse of Sphagnum moss and sparse shrub and black spruce woodland.

In contrast to a bog, where the pH of the organic soil is very acidic, the soil in a fen is alkaline, neutral, or only slightly acid. Fens are influenced by inflows of surface and groundwater, resulting in a more nutrient-rich and less acidic environment, which is in contrast to bogs, which receive the majority of their water supply through precipitation. In this less harsh environment, sphagnum moss is not as common, while sedges typically thrive. A wide variety of aquatic plants, grasses, shrubs, and sparse scattering trees find suitable growing conditions in fens.

Fens are further classified into 17 different forms, which are dependent upon the surface morphology of the wetland (flat, raised, sloping), presence of patterns (ridges, nets, palsa mounds, polygons), position in the landscape (valley, delta, basin), tidal effects, and proximity to water bodies. The forms reflect the differences caused by environmental factors, including the origin of the water (rainwater, groundwater flow, and water bodies), differential peat development, and permafrost (palsas and polygons). Two of the more common forms of fens are raised and ribbed fens. Raised fens form in old glacial lake basins or in shallow plains where the water table meets the surface of the land. Vegetation overlaying accumulated peat grows upward, resulting in a raised appearance. Ribbed or patterned fens have parallel peat ridges with pools of water oriented perpendicular to the direction of slope and drainage.

Fens are most commonly found in the Subarctic. The High Arctic is a polar desert and has few wetlands, while the Mid- and Low Arctic regions have more snow, more meltwater, and more wetlands. The main climatic factors influencing wetland development in the Arctic are cold temperatures and low precipitation. Permafrost plays an important role in wetland development by prohibiting internal drainage and concentrating available water at the surface. Arctic wetlands are subject to frost cracking, which leads to the development of ice-wedge polygons (when ice-filled cracks meet in a geometric pattern to enclose a low or high central area). Many Arctic wetlands are located in depressions caused by glacial scour and filled with water from snowmelt. Wetlands in the Subarctic tend to be distinctive due to the presence of discontinuous permafrost, and include types such as collapse scar fens.

Wetlands are among the most threatened ecosystems on earth. Climate, hydrology, natural disturbances, and human activity all influence the function and condition of wetlands and the plants and wildlife that are dependent on these habitats. In particular, fens are fragile environments and walking across one may leave footprints that can last for several decades.

Aynslie Ogden

See also Marshes; Peatlands and Bogs; Sedge Meadows

Further Reading

Delesalle, Bruno, Understanding Wetlands: A Wetland

Handbook for British Columbia's Interior, Kamloops,

Canada: Ducks Unlimited Canada, 1998

Discover Canada's Wetland Habitats, University of Guelph, Guelph, Ontario, Canada. Available on-line at National Wetlands Working Group, The Canadian Wetland Classification System, Land Environment Canada, Ecological Land Classification Series No. 21, 1987 Nicholson, B.J., L.D. Gignac, S.E. Bayley & D.H. Vitt, "Vegetation Response to Global Warming: Interactions between Boreal Forest, Wetlands and Regional Hydrology." In Mackenzie Basin Impact Study Final Report, 1997, edited by Stewart Cohen, Environment Canada, 1997, pp. 125-145 Research Report 554, Michigan Agricultural Experiment Station Michigan State University, 1997. Available on-line at Roulet, N.T. & M.K. Woo, "Low arctic wetland hydrology."

Canadian Water Resources Journal, 11(1) (1986): 69-75 Rubec, Clayton et al., "Guidelines for developing and implementing National Wetland Policies." In People and Wetlands: The Vital Link, Seventh Meeting of the Conference of the Contracting Parties to the Convention on Wetlands, San José, Costa Rica, 1999 US Fish and Wildlife Service et al, Classification of Wetlands and Deepwater Habitats of the United States, Washington, District of Columbia: Fish and Wildlife Service, US Dept. of the Interior, 1979 Woo, M.-k. & K.L. Young, "Characteristics of patchy wetlands in a polar desert environment, Arctic Canada." In Proceedings Permafrost: Seventh International Conference, June 23-27, 1998, Yellowknife, edited by Antoni G. Lewkowicz & Michel Allard, Collection Nordicana, No. 57, 1998, pp. 1141-1146

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