Relict Glacial Drainageway Ecosystem wetlands all contain significant shallow groundwater flow, but segregate into a diverse array of five major types.  These types all basically function as spring fens, areas where groundwater discharge supports a rich peatland.  The five types are: abandoned features, which can be either 1) wide or 2) narrow; 3) stream fringes, features adjacent to modern streams; 4) spring fens, which are areas of relatively strong groundwater discharge; or 5) surface water fens, where a stream originating on the slopes above empties onto a peatland terrace.  With the exception of most spring and surface water fens,  Relict Glacial Drainageway Ecosystem wetlands occupy broad linear features that transported meltwater from ancient glaciers.

Most drainageways function as spring fens, although other characters define them.  In this classification, map components typically stratify along a depth to water table gradient.  However, the water table is near the surface in many Relict Drainageway wetlands regardless of whether sedge, shrub, or spruce plant communities are dominant.  At spring fens, groundwater composition probably determines the type of vegetation.  Dissolved oxygen, mineral content and flow rate are probably all important (Glaser, et.al., 1990).

Abandoned Drainageways segregate into the first two types of drainageways: wide and narrow features.  They vary in gradient (both perpendicular and parallel to flow) and wetness.  Wider abandoned drainageways tend to be occupied by perennial surface flow (figure 1), while narrower abandoned drainageways tend to support shallow, subsurface flow, or seasonal flow (figure 2), or may be drying due to a wide combination of factors from climatic warming to drainage or groundwater depletion.

Some wide abandoned drainageways gradually grade in and out of Relict Glacial Lakebed Ecosystems characterized by strang-flark features, creating a confusing combination of ecosystem elements.  Some narrow Relict Drainageways occur as short run connections between Kettle Ecosystem wetlands, especially where kettles are larger.

Stream fringe Relict Glacial Drainageway Ecosystems lie along the margins of modern underfit streams. Underfit stream valleys formerly carried large volumes of meltwater from glaciers. These modern streams are too small to have carved the valley they now occupy; they flow across deposits laid down by larger, glaciofluvial processes.  A few poorly-integrated drainageways, associated with the interlobate moraine, between the Moose River and Cook Inlet, may be the result of catastrophic flooding when Glacial Lake Cook emptied around the end of Eklutna time (Karlstrom, 1964). 

At stream fringe drainageways. stream flow and probably groundwater discharge seems to support a high water table in an underfit valley. The fringes are different from the well-developed floodplains of larger streams. Underfit stream valleys were carved by larger, ancient glacial meltwater, and the modern underfit stream only floods its oversized valley because the slope is nearly flat.  Point bars and cut banks are absent.

Not all Relict Glacial Drainageway Ecosystem wetlands are linear features.  A striking example of the fourth type of Relict Glacial Drainageway, the spring fen, lies at the edge of the project area between two moraines northwest of Tustumena Lake.  A wet wooded peatland is supported by a broad area of groundwater discharge from beneath the moraine closer to Tustumena Lake.  The peatland forms a headwater divide between Slikok Creek, which flows northward to the Kenai River, and Coal Creek, which flows west into the Kasilof River.  So, water originating in Tustumena lake makes it way outside the Kasilof River watershed into the Kenai River.

At some spring fens groundwater discharges to the surface of the peat.  A few of these fens are found in the same landscape position as the headwater divide, described above, but further south, east of Clam Gulch. 

At surface water fens, modern streams spread across the surface of a peatland from the slopes above.  a very wet sedge fen grows where the stream enters the peatland.  Most spread out widely.  At a few locales the streams re-form, eroding through the peat down to the till.  At one locale east of Anchor Point the stream form a small waterfall over a peatland headwall.

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 hydrologic regimes ranging from saturated through permanently, semi-permanently, and seasonally flooded (PSSB, PEMH, PEMF and PEMC, respectively).   

In the Hydro-Geomorphic Model they fall into two major types; those along streams are Lotic Stream Slope/Flat throughflow headwater wetlands and separate features are mostly Terrene Slope/Flat groundwater-dominated throughflow headwater wetlands (Tiner, 2003), with slopes often close to or a little more than 2%.

Plant Relationships

In abandoned Relict Drainageways, uniform plant communities are often segregated linearly, parallel to flow, while in Drainageways adjacent to modern stream courses, plant communities are frequently mixed together.

Plants are similar to those found in communities on Relict Glacial Lakebed Ecosystems, however, a few species typify Relict Drainageways.  Abundant species include water and creeping sedge (Carex aquatilis and C. chordorrhiza), marsh fivefinger (Comarum palustre), and marsh horsetail (Equisetum palustre).  Shrubs are often robust, and either sweetgale (Myrica gale) or thinleaf alder (Alnus incana ssp. tenuifolia) can be abundant.  Typically absent are pond lily (Nuphar polysepala), bladderwort (Utricularia spp.) and moor rush (Juncus stygius).  Occasionally, if spahgnum is abundant, leatherleaf (Chamaedaphne calyculata) is present just above creeping sedge, and below sweetgale (figure 1). 

Although plant relationships to depth to water table are often confusing in drainageways, they generally follow a similar pattern as in other ecosystems.   Plant relationships for the five basic types of drainageways are described below.All have somewhat different plant relationships.

On the first type, wide abandoned Relict Glacial Drainageways, a wet linear center, usually dominated by creeping sedge, is bordered by a well-developed hummocky ericaceous peatland margin and a forested toeslope.  At the toeslope, the area of near surface groundwater discharge is confined to a relatively narrow central core.  The center is often covered with open water, with creeping sedge, marsh fivefinger and water horsetail emergent.  The margin is often a shrubby peatland, characterized by Labrador tea (Ledum palustre ssp. decumbens), bog blueberry (Vaccinium uliginosum) with dwarf birch (Betula nana) and/or crowberry (Empetrum nigrum) or a nearly ombrotrophic bog with sphagnum moss and round sedge, (Carex rotundata).   A hummocky transition zone lies between the shrubby peat or bog-like margin and the creeping sedge center.  Sweetgale, water sedge and leatherleaf typically occupy hummock tops above creeping sedge, marsh fivefinger and water horsetail  (figure 1) in the transition zone.  

On narrow (and often more seasonal) abandoned Relict Glacial Drainageways, the center is typically occupied by livid sedge (Carex livida), which seems tolerant of later season drought.  Towards the upland, a shrubby community, often dominated by sweetgale, borders the livid sedge.  Further upslope, bluejoint grass (Calamagrostis canadensis) frequently associates with sweetgale.  Bluejoint also occurs with sweetgale at the edges of incipient channels if they are relatively steep banked.  Bluejoint will continue growing on its own, above the sweetgale zone, usually where the drainageway margins are relatively steep, shallow to mineral soil, and contain significant groundwater discharge (figure 2). 

Plant communities segregate poorly in stream fringes.  Frequently a spruce forest with bluejoint grass openings occurs, often with  thinleaf alder (Alnus incana ssp. tenuifolia) mixed with a hummocky sweetgale - dwarf birch - water horsetail plant community in the understory; water sedge is also common.

The fourth type of drainageway, spring fens, contain nearly identical, poorly segregated forest and woodland communities as stream fringes.

One spring that bubbles to the peat surface east of Clam Gulch supports the widely disjunct Alaska Natural Heritage Program S1S2 rare grass, Catabrosa aquatica.  C. aquatica has only been collected in Alaska from a few locales near Shelikof Strait (in a similar environment), otherwise its range has a gap between the Rocky Mountain crest, and Central Siberia (Hultén, 1968).

The final Relict Glacial Drainageway Ecosystem wetland type is a surface water fen.  Surface water fens are created when a stream, originating on the slopes above, empties onto a large, flat peatland. This happens in several locations on the fluted moraines fronting the west slope of the Caribou Hills.  Typically, a wet hummocky sweetgale - dwarf birch - water horsetail plant community occupies surface water fens.

Soils

Soils are typically histosols, the most common are Starichkof Series Dystic fluvaquentic borohemists, if the peat is thick (the Dystic fluvaquentic criteria are usually met by aeolian tephra deposits), and Doroshin terric cryohemists, if the peat is thinner than 1.3 m.

Bluejoint at the margin of a narrow, seasonally dry drainageway near Kenai airport.

Livid sedge in the center of the same drainageway, with sweetgale occupying slightly higher topographic positions.

% Cover

29.1

24.9

47.7

42.7

27.8

23.3

37.7

54.1

51.4

12.1

29.1

21.0

28.0

12.7

62.5

25.0

15.4

56.3

27.5

10.0

3.0

 Introduction and Key to Plant Communities  

Introduction and Key to Ecosystems

    Kenai Hydric Soils    Map Unit Summary    Methods    Glossary

03 May 2007 18:03