Wetland Classification and Mapping of Seward, Alaska
SEWARD WETLAND ECOSYSTEMS
Relict Glacial Drainageway Ecosystem Wetlands
A Sitka sedge and Sitka alder-dominated opening in the large Relict Glacial Drainageway Ecosystem Wetland complex between Glacier Creek and Sawmill Creek.
The same wetland, outlined in blue, on a 1:25,000 scale satellite image taken in 2003.
Glacial Drainageway Ecosystem wetlands are peatlands occupying former
glacial meltwater channels. They could be considered spring fens.
Here shallow groundwater is in relatively close contact with a mineral
substrate, producing a richer (in groundwater mineral composition), fen
One, 166 acre, Relict Glacial Drainageway complex was mapped in the Seward area. The large complex contains three named wetlands. A large forested wetland forms the matrix, with one wetland opening within it, and another at its wet southern margin.
It occupies a unique landscape position behind the large rock drumlin northeast of town, between Glacier and Sawmill Creeks. Alluvium from both Glacier Creek and a creek draining an unnamed glacier south of the Bear Lake Glacier isolates the northern edge of the wetland from Glacier Creek.
However, groundwater from the unnamed creek probably feeds the large Relict Glacial Drainageway wetland complex through the alluvium. The complex probably also receives some groundwater from Glacier Creek, the rock drumlin, and the mountain slopes to the east. It overlies fine-grained sediments deposited at the bottom of an ancient glacial lake, or in a slow moving meltwater channel. The fine sediments impede downward drainage, perching the water table that facilitates peatland development. A stream connects the complex southward to Sawmill Creek.
The forested matrix of the complex is dominated by a Sitka spruce / Sitka alder (Picea sitchensis / Alnus viridis ssp. sinuata) forest, with early blueberry (Vaccinium ovalifolium) and field horsetail (Equisetum arvense).
The wetter openings are dominated by Barclay and Sitka willow (Salix barclayi and S. sitchensis), Sitka, Lyngbye, and silvery sedge (Carex sitchensis, lyngbyei and C. canescens), bluejoint reedgrass (Calamagrosits canadensis), and more alder (A. viridis ssp. sinuata). Some small fewflower sedge (Carex pauciflora) and tall cottongrass (Eripohorum angustifolim) openings are encountered.
Relict Glacial Drainageway Ecosystem Plant Communities
Sitka alder / bluejoint reedgrass (Alnus viridis ssp sinuata / Calamagrostis canadensis)
Barclay willow / Sitka sedge (Salix barclayi / Carex sitchensis)
Sitka Sedge (Carex sitchensis)
Barclay willow / bluejoint reedgrass (Salix barclayi / Calamagrostis canadensis)
NWI and HGM
Relict Glacial Drainageways are palustrine wetlands in the US Fish and Wildlife Service's National Wetlands Inventory classification. They contain a variety of plant dominants from herbaceous emergents (PEM) to shrubs (PSS) and forest (PFO), with a saturated hydrologic regime (e.g. PSSB).
In the Hydro-Geomorphic Model the Seward area Drainageway is a Flat Terrene groundwater-dominated throughflow headwater wetland (Tiner, 2003).
Summary of Relict Glacial Drainageway Ecosystem Map Units:
DW3- Sedge and shrub dominated openings
DW5A- Forested, but still with a shallow water table
|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 15:28