Wetland Classification and Mapping of Seward, Alaska
SEWARD WETLAND ECOSYSTEMS
Headwater Fen Ecosystem
A sloping Headwater Fen peatland on the glacier-scoured bedrock bench above Fourth of July Creek.
The same peatland, outlined in blue, on a satellite image taken in 2003.
Headwater Fens are peatlands occupying the upper reaches of first order streams. The only features named Headwater Fens in the Seward area are located on the 800' bench north of Fourth of July Creek, above the correctional facility. These peatlands are unique on the entire area mapped, both around Seward and on the Western Kenai Lowlands.
Peatlands often occupy flat terrain, but the Headwater Fens around Seward are sloping, as much as 10% or more. They seem transitional between the flat peatlands on the western Kenai Lowlands, and the steep sloping fens in Prince William Sound.
A wet, humid climate is required for peat to accumulate on slopes. In Scotland "blanket mires" occur on slopes up to 28% (Moore and Bellamy, 1974). Some can slide catastrophically in so-called "bog bursts". Probably, the sloping fens above Fourth of July Creek are not so inclined.
They do exhibit small headwater spring features, where steep peat headwalls surround the headwaters of a stream. These sites are important sources of stream carbon.
Carbon erodes from the headwalls as chunks of peat. The carbon forms the base of energy for the stream food web, from micro-organisms to anadromous fish (Peterson, et.al., 1986).
A stream emerging from eroding peat in a Headwater Fen in the Upper Anchor River.
As in Kenai Lowland Headwater Fens sedge communities are dominant. In the sloping fens above Fourth of July Creek fewflower sedge (Carex pauciflora) is by far the dominant plant. Some diversity is encountered, but thick uniform stands of fewflower sedge make up most Headwater Fens around Seward. Tufted bulrush (Tricophorum caespitosum), star gentian (Swertia perennis) and calthaleaf avens (Geum calthifolium) commonly occur with the sedge.
A few pools and ponds are found, some with floating pond lily. Others support emergent water horsetail and buckbean, one had a dense cover of Carex saxatalis. Some flarks are encountered, occupied by tall cottongrass.
Forests are found at fen edges, along streams and in one low-lying area connecting two open fens. The forests are dominated by stunted mountain hemlock (Tsuga mertensiana), with early blueberry (Vaccinium ovalifolium), rusty menziesia (Menziesia ferruginea) and sometimes Sitka alder (Alnus viridis ssp. sinuata).
Considerable evidence of old tree-cutting activity was seen all around the Headwater Fens. An old collapsed cabin was also encountered.
An old 55 gallon drum (left) and collapsed cabin (right) in the largest Headwater Fen.
Common Headwater Fen Plant Communities:
Fewflower sedge (Carex pauciflora)
Fewflower sedge - tall cottongrass (Carex pauciflora - Eriophorum angustifolium)
Tall cottongrass (Eriophorum angustifolium)
Mountain hemlock / early blueberry (Tsuga mertensiana / Vaccinium ovalifolium)
Mountain hemlock / early blueberry - rusty menziesia (Tsuga mertensiana / Vaccinium ovalifolium - Menziesia ferruginea)
NWI and HGM
The US Fish and Wildlife Service's National Wetlands Inventory classifies this ecosystem into its palustrine category. Palustrine wetlands are further divided based on dominant plants and hydrologic regime. Seward area Headwater Fens support a variety of plant dominants from herbaceous emergents (PEM) to shrubs (PSS) and forest (PFO), with hydrologic regimes ranging from saturated to permanently, semi-permanently, and seasonally flooded (PSSB, PEMH, PEMF and PEMC, respectively).
The Hydro-Geomorphic Model (Tiner, 2003) would classify most Seward area Headwater Fen Ecosystem wetlands as Terrene Basin groundwater-dominated throughflow headwater wetlands.
Summary of Headwater Fen Ecosystem Map Components:
H1- Open water. Floating or emergent vegetation.
H2 - Water table at or near the surface. Sedges and/or dwarf birch dominated.
H3 - Water table does not reach the surface. Shrubs or bluejoint grass (Calamagrostis canadensis) dominant.
H4 - Redoximorphic features or deep peat the wetland indicator. Woodland or forest.
Headwater Fen map component combinations used around Seward: H1-3, H23, H31, H32, H34, H42, H43
|Contact: Mike Gracz Kenai Watershed Forum Homer Field Office Old Town Professional Center 3430 Main Street Suite B1 Homer, AK 99603 907-235-2218||
11 December 2006 17:55