Depression Ecosystem wetlands are surrounded by uplands. They are common as peatlands on the glacial outwash deposits around Palmer, and moraines south of Big Lake. Depressions peatlands typically support lower pH and specific conductance, indicating bog, rather than fen conditions. A high water table is supported by a silt or clay confining layer.  Steep sides limit sunlught penetration, resulting in a micro-climate with low evapotranspirational losses. Steep-sided depressions, such as those found in the Cravasse Moraine area, south of Palmer, can support permafrost. At least 30 cm of hard ice was encountered 27 cm below the surface under a black spruce canopy in one Depression in the Crevasse Moraine area late in the season, on 21 August 2007.

Spring Fen Ecosystem wetlands are similar to Depression Ecosystem wetlands in that they are surrounded by uplands. However, Spring Fens are fed by groundwater discharge, thus have correspondingly higher pH and specific conductance indicating a direct connection to shallow groundwater.

Kettle Ecosystem wetlands occur on similar landforms as Depression Ecosystem wetlands, but have a wetland or surface water connection to a navigable waterbody. Geomorphologically, Depression Ecosystem wetlands are kettles (as are Spring Fens), but the naming distinctions were developed to distinguish kettle features. This distinction is required because of differences in wetland jurisdiction and ecosystem services between wetlands occurring in a similar eco-hydrogeologic setting.

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.

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.

Depression Ecosystem Wetland Map Components:

D1: Ponds in Depressions.

D2: Depressions with water table near the surface most of the growing season. Often dominated by sedges, dwarf birch and/or sweetgale.

D3: Depressions with fluctuating water table, often dominated by shrubs.

D4: Depressions with deeper, fluctuating water table, forested.

Map Units currently in use: D1, D1-3, D1-3c, D1-4, D12, D13, D14, D1c, D1d, D2, D2-4, D21, D21c, D23, D23d, D24, D2d, D3, D31, D32, D32c, D34, D34d, D3d, D4, D42, D43, D43d, D4d

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2 April, 2009