Kettle Ecosystem wetlands are typically present on a kettle and kame landscape.  Landscapes with kettle and kame topography are created at the margins of retreating glaciers under zones of stagnant melting ice.  Supra-glacial streams transport material which is deposited in ice surface depressions.  When the ice melts, the stream-deposited material is left behind as a hill of moderately stratified sands and gravels, forming an upland kame.  Kames are deposited on a flat (wetland) surface of fine materials (Price, 1973), leaving a distinctive reticulate pattern on the landscape.  The fine materials are predominantly silts, which were formerly trapped in the glacial ice, but now are left behind, perching a water table.  Kettles are peatlands that form on the flat silts, which perch a water table. The perched water table combined with local climate creates conditions conducive to peat formation.

On the Kenai Lowlands, there are at least five distinct kettle-and-kame landscapes. One is located between Homer and Anchor Point along the Old Sterling Highway.  The largest covers the extensive series of  moraines north of Soldotna, re-worked by glaciers from the Tordrillo Mountains during the late-Wisconsin maximum (Moosehorn) (Reger, et al., 1996).  A third lies in a band at about 350 meters elevation along the north shore of Kachemak Bay, between Caribou Lake and McNeil Canyon, behind the Moosehorn maximum of glaciers from across Kachemak Bay.  While the previous three kettle-and-kame landscapes all occupy a position behind Moosehorn moraines, the fourth area of kettles and kame-like features lies in front of the Moosehorn maximum of the Tustumena Glacier, in a heterogeneous band from Clam Gulch to Soldotna.  This area was probably created by Tustumena Glacier ice meeting ice originating in the Aleutian Range, across Cook Inlet.  The final, and smallest, kettle-and-kame landscape wraps around the west end of diamond Ridge, above the Old Sterling Highway Kettles, including the hills and peatlands near the Homer Landfill and Demonstration Forest.  This fifth area probably lies behind the early Wisconsin maximum (Knik) of the same glacier that created the Old Sterling Highway kettle-and-kame country.

Not all Kettle Ecosystem Wetlands occur on a kettle-and-kame landscape.  Many small Kettles lie on the upper terrace tread of the west slope of the Caribou Hills, especially on the northwest slope of Ptarmigan Head.  These Kettle Ecosystem wetlands  are often adjacent to Riparian, Discharge Slope, or Relict Glacial Drainageway Ecosystem wetlands that connect to streams.

Kettle Ecosystems are connected to each other by streams, adjacent kettles, or by peatlands which have formed in the Relict Glacial Drainageway Ecosystem wetlands that sometimes occur between larger kettles. 

Kettle Ecosystem wetlands can be difficult to discern from Depressions.  Depressions are hydrologically isolated from other wetlands, but connections between wetlands can be difficult to detect without aerial photography or a thorough ground search.  Connections between kettles and other wetlands are occasionally too small to map at a scale of 1:25,000.  However, if a connection was discernable using stereo-paired aerial photographs, or was discovered on the ground, the wetland was mapped as a Kettle.

Both Kettles and Depressions were formed by similar processes, namely deposition at the margins of ablating glaciers.  While Depression Ecosystem wetlands form atop the terminal moraine after a glacier has retreated, Kettles form behind the moraine, between it and Relict Glacial Lakebed Ecosystem wetlands, if a pro-glacial lake was present.  Other Lakebed wetlands formed on a large lake or lakes created when Cook Inlet was dammed  by ice.  Some Kettle wetlands formed as Depressions, but due to rising sea level and shoreline erosion they are now connected to Cook Inlet.

At the other end of the landform size continuum, Kettle Ecosystems could be confused with Relict Glacial Lakebed Ecosystems, as they are, in fact, small relict glacial lakebeds.  In this project, Relict Lakebed Ecosystem wetlands describe the extensive flat pro-glacial lakes or the vast flats created when Cook Inlet was dammed by ice (Karlstrom, 1964).  In a few areas, especially near Caribou Lake and along the Old Sterling Highway southwest of Anchor Point, Kettle wetlands gradually grade into Relict Lakebed wetlands.  In these areas, Kettles are found just behind a moraine, between it and more extensive lakebed sediments.  In this environment, where kettles gradually transition to a lakebed as kames become less distinct, the dividing line between a Kettle Ecosystem Wetland and a Relict Glacial Lakebed Ecosystem wetland becomes somewhat subjective.

Since kettles are frequently connected by relict drainageways, drawing a line between where a Kettle Ecosystem ends and a Relict Glacial Drainageway Ecosystem begins can be a judgment call.  The Relict Drainageway category describes long linear features that were occupied by large volumes of meltwater at the end of Wisconsin time, but now contain no channelized flow.  Kettles are poor fens, or even bogs, with sluggish near-surface groundwater movement.  Drainageways are spring fens, occupied by surface or near-surface water flowing at a discernable rate (although not in a channel), and often occupied by tall shrubby plant communities or plants that prefer richer groundwater, especially water sedge (Carex aquatilis) (Sjors, 1963; Kenkel, 1987; Glaser, et.al., 1990).

Soils

Soils in Kettle Ecosystems are typically peats, and open water is frequently present.  Doroshin and Starichkof Series Histosols are the most common. 

NWI and HGM

Kettle Ecosystems fit into the US Fish and Wildlife Service's National Wetland Inventory palustrine category.  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). 

The Hydro-Geomorphic Model (Tiner, 2003) would classify most Kenai Lowland Kettle Ecosystems as Terrene Basin groundwater-dominated throughflow wetlands.  When the kettle is occupied by a central lake, greater than 20 acres and deeper than 6.6 feet, it would be named a Lentic Fringe throughflow wetland.  Some may also form the headwaters to small streams, in which case the modifier "headwater" is appended.

Plant relationships

Plant communities in the Kettle Ecosystem follow similar patterns as those in Depression and Relict Glacial Lakebed Ecosystems.  Frequently, a pool with floating pond lily (Nuphar polysepala) and pondweed (Potamogeton spp.) occupies the center; while the edges of the pool supports water horsetail (Equisetum fluviatle), along with emergent sedges, often beaked (C. utriculata) and livid sedge (C. livida). 

Towards the upland, a progression of dominant plants follows.  Completely terrestrial sedges are found next, especially fewflower (C. pauciflora), manyflower (C. pluriflora), water (C. aquatilis), tufted bulrush (Trichophorum caespitosum), and tall cottongrass (Eriophorum angustifolium).  The dwarf shrubs sweetgale (Myrica gale) and dwarf birch (Betula nana) are found among the sedges, followed by Labrador tea (Ledum palustre ssp. decumbens) and crowberry (Empetrum nigrum), which occur above most sedges.  At the highest positions, a peatland black spruce (Picea mariana) forest (rarely white, P. glauca) with an ericaceous shrub or willow understory, respectively grades to upland. 

South of Clam Gulch, Lutz spruce (Picea X lutzii) woodland or forest, with a Barclay's willow (Salix baclayi) understory is more common.  Sometimes a sphagnum moss-dominated community (typically with round sedge, C. rotundata) occurs between the shrub-dominated communities and the black spruce forest. 

If toe-slope groundwater discharge is high, the sphagnum community can be replaced by bluejoint grass (Calamagrostis canadensis).  Many Kettle Ecosystems are occupied by only one or two plant communities, most commonly ericaceous shrubs and black spruce forest, lacking the full range from open water to forest.

A kettle with a full range of plant communities from open water and pond lily to black spruce forest, near Mackey Lake.

A large kettle filled by a sphagnum moss – ericaceous shrub peatland near Mackey Lakes.

 Introduction and Key to Plant Communities  

Introduction and Key to Ecosystems

    Kenai Hydric Soils    Map Unit Summary    Methods    Glossary