Headwater Fen Ecosystem wetlands are restricted to elevations above about 300 meters in the Kenai Lowlands Project Area.  These are smaller fens located in headwater basins surrounded by tertiary bedrock, or thin, discontinuous till.  Other higher elevation fens, including Depressions, Kettles and Depressions, do not occupy headwater basins.  Kettles occupy landscape dominated by glacial till; Depressions are surrounded by uplands.  Linear features which straddle high divides, and drain to a first-order stream on both sides of the divide, are also considered Headwater Fens, although they sometimes resemble and function similar to Relict Glacial Drainageways.

Headwater fens are found in the Caribou Hills occupying first-order streams basins at elevations above about 300 m.  Below 300 meters, streams originate either outside the project area, or in large Relict Glacial Lakebed or kettle-and-kame complexes.  On older glacial and tertiary surfaces of the Caribou Hills, small peatlands often head short-run streams, particularly the streams that flow southeast into Kachemak Bay, and the Anchor River, Deep and Stariski Creeks.

Headwater fens have most likely formed as small post-glacial tarns filled with peat.  These tarns are almost exclusively found on early or pre-Wisconsin 'Knik' and 'Eklutna' surfaces.  On older, higher elevation 'Eklutna' surfaces, thin, discontinuous till overlies relatively flat Late Snow Plateaus, which surround many Headwater Fens.  On younger 'Knik' surfaces, slopes are steeper, till is thin or absent and Headwater Fens are bordered by steep-sided upland slopes; their only connection to other wetlands is by stream outflow.

NWI and HGM

Headwater Fen Ecosystems fit into the US Fish and Wildlife Service's National Wetland Inventory palustrine category.  They are typically a combination of shrub-scrub and emergent palustrine systems (PSS/EM). 

A Hydro-Geomorphic Model (Tiner, 2003) classification puts most Kenai Lowland Headwater Fens into the Terrene Basin Outflow headwater wetland category.  Where a Late Snow Plateau Ecosystem wetland is adjacent, the headwater fen would be a Terrene Basin groundwater-dominated Throughflow headwater wetland.

A Headwater Fen with a sedge community ringed by a shrub community at the headwaters of Falls Creek, about 20 miles northeast of Homer.

Sedge communities are the most common, and tufted bulrush (Tricophorum caespitosum) is a frequent component of many Headwater Fens (table 1).  Fewflower sedge (Carex pauciflora), and tall cottongrass (Eriophorum angustifolium) are also frequently present.  The most common shrubs are dwarf birch (Betula nana), bog blueberry (Vaccinium uliginosum) and Alaska bog willow (Salix fuscescens).

Many Headwater Fens support high plant species diversity.  In addition to the typical plants found in similar peatlands, subalpine fleabane (Erigeron peregrinus), felwort (Swertia perennis) and Alaska bog willow are also often present.  The widely disjunct rare plant, elephant-head lousewort (Pedicularis groenlandica), is found on many Headwater Fens in the upper Anchor River watershed.   The only location noted for this conspicuous plant in Hulten's Flora of Alaska (1968) is in the extreme southeast corner of the Yukon Territory.  It has only been collected in one other spot in Alaska, near Beluga Lake on the west side of Cook Inlet in 1981 by Steve Maclean.  It is listed as critically imperiled to imperiled in the State of Alaska (S1S2) by the Alaska Natural Heritage Program.

A Headwater Fen with a mixed shrub and sedge diverse plant community, including abundant elephanthead lousewort, in the upper Anchor River.

The typical plant community progression along an open water to woodland gradient is somewhat truncated in Headwater Fens.  Both ends of the gradient, are cut short: open water is rare, and so are woodland and forest communities (although trees appear to be invading ever- higher elevations with increasing climatic amelioration since the middle nineteenth century).  Headwater fens are frequently mixed types, with sedges and shrubs mixed together, without well-developed micro-topography.  However, some Headwater Fens are segregated into centers occupied by sedge and diverse herbaceous plant communities, ringed by a narrow shrubby band.  A few headwater tarns and several headwater woodlands exist.

Function

On the Kenai Peninsula, Headwater Fens, and the fens surrounding the upper reaches of first order streams, in addition to supporting diverse plant communities and the S1S2 plant, elephanthead lousewort, may be particularly important in stream energy cycles.  Eroding peat is an important carbon input.    In some areas, erosion of peat by meandering streams forms a large part of the carbon input to the stream (Peterson, et.al., 1986).  Here on the Kenai Lowlands, headwater basins may play a more dominant role than meander bends.  In Headwater Fens and upper stream reaches, a first order stream will frequently flow beneath the surface of the peat.  Where it emerges, steep headwalls form, which deteriorate into large chunks of peat which fall into the stream.  The carbon in the peat is important to organisms at the core of the stream's food web.  Insects obtain part of their food from carbon processed by micro-organisms.  Larger organisms feed on the insects, and the initial carbon source eventually supports larger organisms, such as anadromous fish (Peterson, et.al., 1986).

Carbon export in a fen at the headwaters of the Anchor River.  This stream re-emerges from a tunnel under the peat.  The headwall and sides of the tunnel have abundant evidence of slumping into the stream.  The carbon from the peatland is an important energy source for the stream ecosystem, including developing anadromous fish.

 Introduction and Key to Plant Communities  

Introduction and Key to Ecosystems

    Kenai Hydric Soils    Map Unit Summary    Methods    Glossary

03 May 2007 18:03