Wetland Classification and Mapping of Seward, Alaska
SEWARD WETLAND ECOSYSTEMS
Tidal Ecosystem Wetlands
|A Tidal Ecosystem wetland at the former mouth of Fourth of July Creek, near the City Campground on the east side of Resurrection Bay.||The same wetland, outlined in blue, on a satellite image taken in 2003.|
Ecosystem wetlands are influenced by twice daily tidal fluctuations.
They form where some protection from storm waves has developed; usually
behind spits and berms, and in lagoons at the mouths of rivers and
streams. A few small Tidal Ecosystem wetlands are found behind berms
along the margins of the Fourth of July and Spruce Creek alluvial fans.
The largest Tidal Ecosystem wetlands form behind beach berms at the mouth of
the Resurrection River.
Vince and Snow (1984) describe many zones at the Susitna River Estuary. Zones are dominated by different plants and characterized by different tidal inundation regimes. Some are inundated frequently during the growing season, but retain water for only hours, while others are inundated only once or twice, but can retain water for nearly a week. These zones are repeated at other Cook Inlet lagoons, and estuaries.
Many of Vince and Snow's zones are absent at the Resurrection River estuary, however. Here only the zones inundated the least frequently and which retain water the longest are expressed: beach berms dominated by beachrye grass, and extensive marshes dominated by open pools and Lyngbye sedge. Absent are bare mud, creeping alkaligrass, arrowgrass, goosetongue, Nootka and HultÚn's alkaligrass and Ramenski's sedge.
These common tidal zones are probably absent because the tidal range of Resurrection Bay is much less than that of Cook Inlet. Other factors, such as braided river aggradation, earthquake effects, and exposure to higher storm waves, probably also contribute to estuarine zonal attenuation at the head of Resurrection Bay.
Cook Inlet tides can exceed 40 feet, and wave action is rarely large. Resurrection Bay tides are almost always less than 15 feet. The few braided river systems feeding Cook Inlet lack the high aggradation rates of the Resurrection system.Comparison of 1950 and 1997 aerial photographs reveals that the Resurrection River delta has expanded substantially, although the area subsided following the 1964 earthquake.
Open beach fronts support bare ground (gravel) and scattered seaside sandplant (Honckneya peploides) and tundra alkaligrass (Puccinellia tenella). Beach berms support Beachrye (Leymus mollis ssp. mollis) often with yarrow (Achillea millefolium). Marshes behind the berms are almost wholly composed of Lyngbye sedge (Carex lyngbyei). A diverse plant community dominated by Beachrye and yarrow occupies a drier, infrequently inundated zone sometimes encountered above the marsh.
Common Tidal Ecosystem Wetland Plant Communities:
Lyngbye sedge (Carex lyngbyei)
Beachrye (Leymus mollis ssp. mollis)
Beachrye - yarrow (Leymus mollis ssp. mollis - Achillea millefolium)
NWI and HGM
NWI classifies Seward are Tidal Ecosystem wetlands as E2EM1, Intertidal Emergent Persistent Estuaries.
In an HGM classification (Tiner, 2003) the Tidal wetlands not found in estuaries are classified as Macrotidal Bidirectional Barrier Beach Fringe wetlands.
The Tidal Ecosystem wetlands behind the Resurrection river are Macrotidal Bidirectional Bar-Built Estuarine Fringe wetlands.
Summary of Tidal Ecosystem Map Components:
T0 - Bare ground, gravel.
T5- Open water pools, sometimes with Ramensk's sedge (Carex ramenskii). Sparse mare's tail (Hippuris vulgairs) and saltmarsh starwort (Stellaria humifusa) sometimes found in and around the pools. Vince and Snow's (1984) "Outer Sedge Marsh zone 3". Inundated 0-5 times per summer (mean=3).
T6- Lyngbye's sedge (Carex lyngbyei) cover nearly continuous. Vince and Snow's (1984) "Outer Inner Sedge Masrh zone 7". Inundated 0-4 times per summer (mean=2).
T7- Beachrye (Leymus mollis ssp. mollis) diverse plant community on storm berms. Probably in the same position as Vince and Snow's (1984) "Riverbank Levee zone 6", which is innundated 0-2 times per summer (mean=1). Vince and Snow did not include beachrye in their Susitna Flats plant zonation work, except to mention that it becomes more abundant above about 12 cm "relative altitude" ("...relative to about 10 m above mean low water of spring tides").
T8- Beachrye and yarrow dominate sometimes with Pacific silverweed (Argentina egedii), and largeflower speargrass (Poa eminens). A combination of Vince and Snow's (1984) "Riverbank Levee zone 6" and "Inner Mudflats zone 4". Inundated 0-2 (mean=1), and 8-13 (mean - 11) times per summer, respectively.
Tidal map component combinations used around Seward: T07, T65, T67, T76, T78, T87
|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 15:27