A diverse Discharge Slope Ecosystem wetland along the valley wall of the South Fork of the Snow River.
The same wetland, outlined in blue, on a satellite image taken in 2003.
Wetland Classification and Mapping of Seward, Alaska
SEWARD WETLAND ECOSYSTEMS
Discharge Slope Ecosystem
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A diverse Discharge Slope Ecosystem wetland along the valley wall of the South Fork of the Snow River. |
The same wetland, outlined in blue, on a satellite image taken in 2003. |
| Discharge
Slope Ecosystem wetlands occur at foot- and toeslope breaks, where shallow
groundwater discharges to near the surface at the base of a slope.
Only three wetlands were named discharge slopes in the Seward area,
all north of Bear Lake. The largest occurs above a beaver pond adjacent to the Snow River. The other two are small
wetlands at foot- and toeslope positions on the bedrock knob between Bear Lake and the
South Fork of the Snow River.
Although only three Discharge Slope ecosystem wetlands were mapped around Seward, there are probably more of them. Others may occur as small pockets around springs at the base of weaker layers in bedrock knobs. These weaker layers serve as groundwater conduits in the same bedrock units around Port Valdez (Reger, pers. comm.). Topography, and the depth of valley fill gravel probably limits expression of Discharge Slopes in the Seward area. Slopes are well drained down to the valley alluvium, which is also well-drained. By contrast, Discharge Slopes are extensive and common on the southern Kenai Lowlands where low relief and dense glacial till, combined with vast adjacent peatlands keeps a water table near the surface. |
Plant Relationships Discharge Slope Ecosystem wetlands are named according to the dominant plants occurring on them. Only three Discharge Slope wetlands were mapped around Seward, two, named SPS, were dominated by Sitka spruce (Picea sitchensis) and willow (Salix spp.); the third, named SA, by Sitka alder (Alnus viridis ssp. sinuata). Sitka willow (S. sitchensis) was the dominant willow at the only spruce - willow Discharge Slope wetland visited (SPS). The wetland was topographically diverse, with some peatland as well as upland inclusions. The alder-dominated discharge slope wetland was also diverse, including small areas of flatter peatlands dominated by Sitka sedge (Carex sitchensis), tall cottongrass (Eriophorum angustifoliun), and fewflower sedge (Carex pauciflora). Devil's club (Oplopanax horridus) was abundant. |
Discharge Slope Ecosystem Plant Communities
Mountain hemlock / rusty menziesia - early blueberry (Tsuga mertensiana / Menziesia ferruginea - Vaccinium ovalifolium)
Bluejoint reedgrass - field horsetail (Calamagrostin canadensis - Equisetum arvense)
Sitka Sedge (Carex sitchensis)
Sitka alder - devil's club (Alnus viridis ssp. sinuata - Oplopanax horridus)
NWI and HGM
US Fish and Wildlife Service National Wetlands Inventory (NWI) would classify most Seward Discharge Slope wetlands as forested palustrine wetlands (PFO). Shrub- and herbaceous-dominated Discharge Slopes are classified as PSS and PEM respectively.
An HydoGeomorphic Model (Tiner, 2003) would classify Seward area Discharge Slope wetlands as Terrene Slope Outflow wetlands. They have small components of Paludified Slope wetland.
Summary of Discharge Slope Ecosystem Map Units:
SPS- Dominated by Sitka spruce and willow
SA- Dominated by Sitka alder
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| 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 |
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