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Wetland Classification and Mapping of the Kenai Lowland, Alaska
Map Unit Descriptions Ecosystem: Any Map Unit: DISTURB
Extent: 130 wetland polygons; 520.8 ha; 0.37% of wetland area; 0.79% of wetland polygons. |
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 A unit disturbed by logging activity near Anchor Point (polygon 3).
A DISTURB unit in the City of Kenai, created by impeded drainage due to poor culvert design (polygon 872).
A DISTURB unit created by shooting range activity near Mackey Lakes (polygon 625). |
Wetland Indicators Type: Mineral or Peat Average depth to water table: 71.5 cm; n=2 sites Organic layer thickness: 85.6 cm; n=5 sites Average depth to redoximorphic features: 90 cm at the single site measured. Common Soils: DOROSHIN STARICHKOF, NIKOLAI Common Plant communities: Sphagnum moss - Red cottongrass Lutz spruce / Field horsetail – Bluejoint
The disturbed portion of an identifiable unit (LB6) near Anchor Point. Many more wetland polygons contain areas of disturbance than are mapped as DISTURB, but their proper ecosystem and map component are otherwise recognizable (polygon 266). |
A wetland is classified as DISTURB when its character can not be discerned from the present landscape or the landscape recorded on 1996 aerial photography. Many units that might have been mapped as disturbed may have been missed due to the inherent difficulty of mapping wetlands in developed areas from 1:25,000 aerial photography. Many wetlands have substantial disturbance, but their pre-disturbance character can be discerned so they are mapped accordingly. Therefore, a user should be careful about drawing conclusions about the portion of disturbed wetlands in the project area from the area mapped as DISTURB. DISTURB only indicates those units that are disturbed beyond recognition of their pre-human disturbance character. DISTURB units can be created by a variety of human activities; the most common activities in the project area are road building, logging and gravel extraction.
One of the goals of this project is to capture as much information as possible about Kenai wetlands in their relatively undeveloped state. Information about "Reference Standard Condition" is lacking in other areas of the United States, where it would be especially useful to guide restoration projects where managers are largely guessing at what sort of pre-development wetland exited on a site. The classification and mapping of Kenai Lowland wetlands is, in part, a legacy project, providing baseline reference standard conditions for the future.
Alaska in general, and the Kenai Peninsula in particular, is uniquely fortunate in having little of its wetland area affected by human activity. Overall, most development on the Kenai has occurred on uplands, where it is easiest to build. Although disturbed wetlands account for less than one percent of the wetland area mapped to date on the Kenai, that figure misrepresents current human effects on local wetland functions. In some localized watersheds, the percentage of wetland disturbance is much higher. Wetland disturbance affects habitat, water quality and flood control capacity, among other functions. Wetlands serve society in a variety of ways which is why dredge and fill activities in wetlands are regulated under section 404 of the Clean Water Act.
Magnitude and effects of wetland disturbance are often qualitatively described, but can be quantified. In an Anchorage study, watersheds with greater than only 4.4-5.8% impervious surface cover (including uplands), had impairment to riparian and in-stream habitat, macro-invertebrate populations, and water and sediment chemistry (Ourso and Franzel, 2003). Not much wetland loss in a small watershed can cause measurable damage. Restoration is costly, as are the losses of wetland functions such as flood control and water quality.
In the city of Homer, a more detailed mapping project was funded, and wetlands were mapped at a finer scale and with more attention to historic conditions. Old aerial photography and more detailed soil surveys allowed for accurate mapping of wetlands that would have been mapped simply as DISTURB in the wider project area. In Homer, the suffix 'd' appended to any map unit indicates a disturbed wetland where we were able to discern the wetland's original condition.
