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Classification and Mapping of the Kenai Lowland, Alaska
Map Unit Descriptions Ecosystem: Depression Map Unit: D2-4; D24; D42
Extent: D2-4: 74 wetland polygons; 114.0 ha; 0.08% of wetland area; 0.45% of wetland polygons. D42: 3 wetland polygons; 6.1 ha; 0.00% of wetland area; 0.02% of wetland polygons. D24: 1 wetland polygon; 4.8 ha; 0.00% of wetland area; 0.01% of wetland polygons. |
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 A segregated, concentric D2-4 depression, with a central sedge area, then shrub plant communities, and then black spruce forest near Sterling (polygon 861). |
Wetland Indicators Type: Peat with mineral soil margins Average depth to water table: D2: 6.8 cm; n=5 D3: 10.0 cm n=1 D4: 55.5cm, n=11 Organic layer thickness: D2: 6.8 cm; n=5 D3: 10.0 cm n=1 D4: 85.8cm; n=17 Average depth to redoximorphic features: D2-3: n/a D4: 24.3 cm; n=3 Common Soils: STARICHKOF, TRUULI, SPENARD, NIKOLAI, DOROSHIN Common Plant communities: D2 component: Tall cottongrass - Livid sedge Beaked sedge – Water horsetail D3 component: D4 component: Black spruce / Woodland horsetail - Labrador tea |
| Accuracy assessment: 7 polygons interpreted as D2-4 on aerial photographs were field checked. 3 remained D2-4, 1 each was revised to: D23, D34, K34 and upland. The single polygon visited that was interpreted as D24 on aerial photographs was revised to upland. No D42 units were visited. | |
D2-4 units are relatively common, but small depressions, too small to be visible on the range map above. They are a combination of all the Depression map components except the open water emergent component (D1). A sedge community (D2) transitions through a shrub community (D3) to a forest or woodland (D4). The components are almost always arranged in concentric rings, with the sedge component in the center, then the shrub (or bluejoint), then forested component, then the upland. Often, the forested transition from the edge of the depression to upland is rapid and steep, thus too small to map at 1:25,000. The even rarer D42 and the unique D24 depressions occur as a forest ringing a sedge dominated center. If the sedge (often with the shrubs sweetgale (Myrica gale) and dwarf birch (Betula nana)) center is larger than the forest the name is D24.
Depressions are most common on younger glacial surfaces, such as the moraine between Nikiski and Sterling, and also east of Sterling.
