Wetland Classification and Mapping of Seward, Alaska

Seward Map Unit Summary and Naming Conventions

CLASSIFICATION

The goal is to present a classification that can be used to indicate, or model wetland functions.  Wetland functions are valued by society, and society has recognized these values and has created legislation to guide development activity occurring on wetlands.  Wetland functions are diverse, and probably no single map-able classification can be constructed to adequately model all wetland functions.  We could construct a map showing salmon spawning habitat, or floodplains, or sandhill crane foraging areas, all wetland functions that we value, but each of these maps would look different, and contain overlapping areas.  Knowing that we are faced with the essentially impossible task of creating a wetland map that can perfectly predict function, we set out to do just that.

We do know that the three criteria used to indicate jurisdictional wetlands: soils, vegetation, and hydrology, can be used to model wetland function.  Certain soils have a greater moisture holding capacity, thus reflect total groundwater storage, an important flood control function of wetlands, for example.  Local landforms, control the primary wetland indicator, hydrology.  A classification was constructed using local landforms to organize plant and soils occurrences.

The classification names are on three levels.  The broadest level is represented by ecosystems, which describe the common landforms present on the Kenai; the middle level consists of the mapping components, which represent the variation of wetlands found within ecosystems- primarily using water table depth (hydrology); the third level is made up of the typical plant communities that occur within the mapping components.  Ecosystems are subdivided into mapping components which contain typical plant communities.  The plant communities and mapping components are not exclusive: any plant community can potentially occur in any component, and components can (and usually do) contain more than one plant community.

In this project, mapping units are the finest-scale names assigned to wetland polygons.  Map unit names are made up of one or more map components, outlined below.  With a few exceptions, any single map unit is made of components from within only one ecosystem.  A few map unit names are a combination of two ecosystem names.  These represent polygons, often at fuzzy borders between ecosystems, where both systems are present at a scale too fine to delineate.  Plant communities do not nest exclusively into ecosystems or map components; any plant community can potentially occur in any mapping component, or ecosystem.  Strong affinities exist, but many exceptions also.  The map components, and rules for creating map unit names from them, are summarized below.

Mapping Methods

SEWARD MAP UNIT NAMING CONVENTIONS:

• Ecosystems are divided into components, mostly based on hydrology. 

• Map units names are derived from an abbreviation of the name of the ecosystem they occur in, followed by a numerical modifier indicating the components within the ecosystem.  (e.g. 'K1' is in zone one of the Kettle Ecosystem). 

• A map component with standing water or a water table near the surface is usually given a lower number than a component where wetland status is only indicated by redoximorphic features near the surface.  Sedges often indicate a shallower water table; shrubs and trees often indicate a deeper water table. 

• Two ecosystems use a different component naming scheme; in these cases a letter follows the ecosystem abbreviation.  Riparian ecosystem names are modified based on Rosgen's (1996) classification.  Discharge Slope ecosystem map components are based on dominant plant species (e.g. 'SA' is a Discharge Slope dominated by alder).

• To be included in the map unit name, components must each represent at least 10% of the polygon area.  The most abundant component is named first- if each covers an equal area then they are listed in alphanumerically.

• If more than two components, each less than the minimum polygon size, comprise more than about 10% of the cover of a polygon and they are in sequential order, then a code including a dash can be used (e.g. K1-3; indicates a polygon with all the components K1, K2, and K3 present at more than 10% cover). 

Summary of Depression Ecosystem Map Components:

Depressions are wetlands not connected by other wetlands, or streams to Resurrection Bay.

D1- Standing water.  Floating or emergent vegetation.

D2 - Water table at or near the surface.  Sedge and/or sweetgale dominated.  

D3 - Water table does not reach the surface.  Shrubs or bluejoint grass (Calamagrostis canadensis) dominant.

D4 - Redoximorphic features or deep peat the wetland indicator.  Woodland or forest.

Depression map component combinations used so far: D12, D1-3, D21, D23, D31, D32, D34, D43

Summary of Discharge Slope Ecosystem Map Components:

Discharge slopes occur at the bases of slopes where the water table comes to near the surface.

SPS- Sitka Spruce and willow dominated.

SA - Alder (usually thinleaf alder, Alnus incana ssp tenuifolia) dominated.

Summary of Relict Glacial Drainageway Ecosystem Map Components:

Relict Glacial Drainageways were occupied by large braided river systems when glaciers were more extensive.  The now support peatlands, often with small streams flowing through them.

DW3- Deeper water table: hummocky or tussocky micro-topography.  Variety of plants; usually with a shrubby component.

DW5A- Deeper water table.  Peat or redoximorphic features the wetland indicators.  Forested.

Summary of Headwater Fen Map Unit Summaries:

Around Seward all mapped Headwater fens occur on the bedrock bench above Fourth of July Creek, at an elevation of around 800'.  They are peatlands with springs at the headwaters of small streams flowing directly into Ressurection Bay.

H1: A small lake in a headwater basin.

H2: Sedge dominated peatland in a headwater basin; water table at or very near the surface.

H3: Fewflower sedge dominated peatland in a headwater basin; deeper water table.

H4: Woodland/forested peatland in headwater basin.

Headwater Fen Ecosystem Map Component combinations used so far: H1-3, H23, H42, H31, H32, H34, H43

Summary of Kettle Ecosystem Map Components:

Kettle ecosystem wetlands are similar in form to Depression ecosystem wetlands, but they are connected by other wetlands of streams to Resurrection Bay.

K1- Standing water; often a lake.  Submerged, floating and emergent vegetation.

K2- Water table at or near the surface.  Sedge and/or sweetgale (Myrica gale) dominated.

K3- Water table not at the surface.  Usually shrub dominated.  Can contain ombrotrophic bogs.

K4- Deep peats or redoximorphic features near the surface in a mineral soil.  Woodland or forest.  Can include bogs.

Kettle Ecosystem Map Component combinations: K12, K13, K1-3, K1-4, K21, K23, K2-4, K31, K32, K34, K43

Summary of Riparian Ecosystem Map units:

Riparian ecosystem wetlands are associated with streams and rivers.

RB- Higher gradient (>2%); riffle dominated.

RC- Floodplain developed.  Point bars.  Riffle/pool morphology.

RD3C- Braided channels with bed material dominated by cobbles, on glacial deposits.

RD4C- Braided channels with bed material dominated by gravel, on glacial deposits.

RD4SC- Braided river side channels.

RD4T1- Lower terraces of braided rivers.

RD4T2- Upper terraces of braided rivers.

RD4Fx- Floodplain wetlands:

 RD4F1- Floodplain wetlands dominated by open water and floating or emergent plants.

 RD4F2- Floodplain wetlands with water table at or very near the surface; typically dominated by sedges or bluejoint reedgrass.

 RD4F3- Floodplain wetlands with water table near the surface; typically dominated by alder or willow.

 RD4F4- Forested floodplain wetlands.

Floodplain wetland map unit combinations: RD4F12; RD4F1-3; RD4F1-4; RD4F21; RD4F23; RD4F2-4; RD4F32; RD4F34; RD4F43

Tidal Flat Ecosystem Components:

T0- bare mud

T5- Ramensk's sedge (Carex ramenskii) dominates with pools.  Mare's tail (Hippuris), spikerush (Eleocharis spp.), saltmarsh starwort (Stellaria humifusa) 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- Pacific silverweed, largeflower speargrass (Poa eminens) and sometimes circumpolar reedgrass (Calamagrostis deschampsioides) dominate.  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.  On the Kenai, "Riverbank Levees" are typically dominated by beachrye (Leymus mollis ssp. mollis).

Tidal Ecosystem Map Component combinations used so far: T07 T65, T67, T76, T78, T87

Mixture of wetland and upland:

WU- Wetland /Upland complex.  Greater than 25% cover of wetlands of any ecosystem at a scale too small to map, in a larger unit.

Download  Seward shapefile (400k).  Metadata