RELICT GLACIAL LAKEBED ECOSYSTEM Wetlands

While some Relict Lakebed ecosystem wetlands have been mapped to date (2008), more will be mapped in the summer of 2009. These extensive peatlands occur on expansive flat surfaces, which may or may not have been formerly occupied by large early Holocene proglacial lakes. They are composed of bog peat forming on top of fen peat. Initial comparisons with 1960 aerial photography appear to indicate that bogs and fens are in stable equilibrium: neither appears to be expanding or contracting. As more of these wetlands are mapped, more information will be added to this page. They are larger than kettle ecosystem wetlands, which also form on abandoned lakebeds. The centers of these large peatlands are far removed from mineral soil uplands, so surface runoff sources of nutrients appear distant. However they may receive shallow groundwater discharge from below through coarser-textured sediments.

Table 1. Relict Lakebed Ecosystem Wetlands
Peat Depth (n=31)	Water Table (n=36)	Redox features (n=2)	Saturation (n=36)	pH (n= 30)	Specific Conductance (25°C; n=30)	Plant Prevalence Index (n=30)
171 cm	6 cm	99 cm	3 cm	4.5	71.6 µS	1.85

Explanation:

Peat depth is a minimum, because some sites had thicker peat deposits than the length of the auger used (usually 493 cm).

Water table depth is a one time measurement. At sites with seasonally variable water tables this measurement reflects both the conditions that year, and the time of year.

Redox features with low n and deep depths typically indicate deeper peat deposits, which mask redox indicators.

pH and specific conductance measured in surface water or a shallow pit with a YSI 63 meter calibrated each sample.

Plant Prevalence Index calculated based on Alaska indicator status downloaded from the USDA PLANTS database, which may use different values than the 1988 list.

COMMON SOILS

COMMON PLANT COMMUNITIES

HISTOSOLS

Black spruce / Labrador tea

Black spruce / Labrador tea / woodland horsetail

Black spruce / dwarf birch / field horsetail

Round sedge - sphagnum moss

Sweetgale - tufted bulrush

Dwarf birch - tufted bulrush

Explanation:

Soils from 1998 Soil Survey of the Matanuska-SusitnaValley Area, Alaska, available online, follow the link in the table heading.

Plant communities based on Kenai Peninsula wetland mapping and soil survey, or other published accounts, especially Viereck, et.al., 1992.

Tidal-Drainageway Ecosystem Wetland Map Components:

LB1: Open water

LB2: Water table near the surface most of the growing season, often dominated by sedges.

LB3: Bogs, often dominated by sphagnum moss and shrubs. May or may not be forested.

LB4: Dominated by shrubs, especially Labrador tea, leatherleaf and dwarf birch

LB5: Dominated by bluejoint reedgrass, often over relatively shallow peat in areas with large amounts of local groundwater discharge.

LB6: Forested, typically by black spruce.

LBSF: A complex of patterned fen with small high ridges (strangs) alternating with low pools or hollows (flarks) and bog islands which may or may not be forested..