Matanuska-Susitna Wetland Mapping

Cook Inlet Wetlands

DISCHARGE SLOPE  ECOSYSTEM Wetlands

A 2004 satellite photo showing Discharge Slope wetlands (outlined in blue) between Wasilla and Knk Arm. These wetlands frequently lie along toesloes at the base of valley walls.

Discharge Slope wetlands occur over hydric mineral soils where shallow groundwater discharges at or near the surface. These wetlands often support only seasonally high water tables, and therefore can be difficult to identify. Shallow groundwater wells indicate that sites with late season water tables deeper than 100 cm support growing season hydric conditions sufficient to meet wetland criteria (Clark, 1995).

Wetlands in this ecosystem are named after dominant plant species. In the area between Palmer and Houston, Discharge Slopes are frequently forested with paper birch (Betula papyrifera) and/or white spruce (Picea glauca) with an understory of field horsetail (Equisetum arvense). Both of the trees are listed as facultative upland plants, as is the horsetail on the 1988 list of plant indicator status, further complicating wetland determinations. Good local knowledge, consideration of the surrounding landscape and redox features, and auguring to depth is sometimes required.

A forested Discharge Slope with an alder understory near Moonlight Lake.

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.

Discharge Slope 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.

SA: Dominated by alder, usually Alnus incana ssp. tenuifolia

SB: Dominated by birch. Taxonomy of local birches is problematic; tree biches in this project have been designated Betula payrifera, realizing that B. Kenaica is widespread, and other taxa are porbably present.

SC: Dominate by bluejoint reedgrss (Calamagrostis canadensis).

SG: Dominated by white spruce (Picea glauca); occurs primarily in the Matanuska Susitna Valley. Much of the spruce that is not black spruce (P. mariana) is Lutz spruce (Picea X Lutzii), a hybrid between the more continental white spruce and coastal Sitka spruce (P. sitchensis).

SL: Dominated by Lutz spruce (Picea X Lutzii), a hybrid between the more continental white spruce (P. glauca) and coastal Sitka spruce (P. sitchensis). Most common on the Kenai Peninsula, especially closer to maritime influence.

SM: Dominated by black spruce (Picea mariana).

SZ: High elevation moutain meadows of various lush forb assembladges. Mapped only along the upper slopes on Baldy Ridge, above Wasilla.