Wetland Classification and Mapping of Seward, Alaska



Map Unit Descriptions


Ecosystem: Tidal


Map Units: T78; T87


Seward Area Extent:

T78: 1 wetland polygon; 11.8 acres

T87: 2 wetland polygons; 3.1 acres

Beachrye with a more diverse plant community, including yarrow (T8).

Wetland Indicators

Type: Tidal

Depth to water table: Varies with tidal stage

Organic layer thickness: not measured

Depth to redoximorphic features: not measured

Common Soils: probably Oxyaquic Cryofluvents and Typic Cryaquents

Common Plant communities:

Beachrye (Leymus mollis ssp. mollis)

Beachrye - Yarrow (Leymus mollis ssp. mollis - Achillea borealis ssp. millefolium)


Only a few wetlands were named with T8 components.  T8 is at the upper reaches of the tidally influenced zone, where beachrye thins, forming a more diverse plant community, with abundant yarrow.  T78 and T87 are a mix of nearly pure beachrye (Leymus mollis ssp. mollis) stands (T7) with a more diverse Beachrye and yarrow (Achillea borealis ssp. millefolium) type (T8).  When beachrye dominates, the wetland in named T78, and when a more diverse plant assemblage of beachrye with yarrow is dominant, T87.


T7 wetlands are found on coastal storm berms and higher riverbank levees.  Vince and Snow (1984) describe 'Riverbank Levees' dominated by other grasses, and that "Still higher levees featured [Beachrye] and large forbs..."  Their lower elevation riverbank levees flood an average of 1 time per summer; probably higher T7 beachrye berms or levees flood only when storms correspond with the highest spring tides.  Around Seward, T7 seems to occupy wetter areas than around Cook Inlet.


T8 corresponds to Vince and Snow's (1984) 'Riverbank Levees zone 6'.  Vince and Snow estimate that Riverbank Levees are inundated an average of once per summer (range 0-2 times for a duration of 2-3 hours) by the highest spring tides.



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12 February 2007 15:31