Matanuska-Susitna Wetland Mapping

Cook Inlet Wetlands

RELICT GLACIAL LAKEBED ECOSYSTEM Wetlands

A patterened Relict Glacial Lakebed Ecosystem wetland north of Beaver Lakes. The patterning consists of low-lying pools and mud-bottoms with intervening shrubby strings and tree islands.

These extensive peatlands occur on expansive flat surfaces, which were formerly occupied by large proglacial lakes. Peatlands develop on these surfaces through a process known as "primary peat formation". In contrast to lake infilling, the classical model of peatland formation, typical of ice-block depressions (Kettle, Depression and Spring Fen Ecocsystem wetlands), primary peat formation is the process responsible for most of the peatlands on Earth. Primary peat formation is where a wide, shallow, marshy area gradually fills with peat. The third peat-forming process is paludification, where accumulating sphagnum peat invades upland surfaces.

Relict Lakebed peatlands are mostly fens, often with patterning. The patterns consist of low-lying pools, which can dry up seasonally to form mud-bottoms (flarks), and intervening strangs (low shrubby ridges). Tree islands often form. The tree islands are areas where bog peat is forming on top of the 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. This could be because relict lakebeds support a drainage network sufficient to prevent bog mounds from forming. Mound formation is limited by distance to streams, and mounds typically develop on broad interfluves.

Relict Glacial Lakebed Ecosystem peatlands are larger than Kettle Ecosystem wetlands, which also form on abandoned lakebeds. The centers of large Lakebed peatlands are far removed from uplands, so surface water runoff originating from mineral sources appears distant. However, remember that the mineral soil is never more than several meters away, beneath the peatland. Many fens receive shallow groundwater discharge from beneath through sandy underlying sediments.

Explanation:

All data from wetlands throughout the Cook Inlet Lowlands, not just from the Matanuska-Susitna Valley.

Numbers in paraentheses indicate number of samples.

Peat depth is a minimum, because some sites had thicker peat deposits than the length of the auger used (between 160 - 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. If no water table was encountered, no value was recorded; use number of samples to aid interpretation. Deeper average water tables idicate higher variability.

Redox features with deep depths typically indicate deeper peat deposits, which mask redox indicators so the depth corresponds to the peat thickness.

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.

Relict Glacial Lakebed Ecosystem Wetland Map Components:

Map unit names are made of combinations of map components. A suffix 'c' idicates a created wetland, and a 'd' indicates a highly disturbed wetland.

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..