Wetland Classification and Mapping of the Kenai Lowland, Alaska
FLOATING ISLANDS ECOSYSTEM
Extent: 5 wetland polygons; 13.5 hectares; 0.01% of wetland area, 0.03% of wetland polygons.
Floating islands are rare human-generated ecosystems on Kenai Lowlands lakes. They are literally islands floating on lakes. The floating islands depicted on the aerial photograph above were formed when the outlet of a peatland was dammed by road construction. The peatland flooded, forming Suneva Lake, and leaving several vegetation mats floating on its surface. These islands are about a hectare (2.47 acres) in size, and one was observed drifting 1 kilometer over the course of three hours with a breeze of less than 5 mph.
A few floating islands, described in field notes, are dominated by water horsetail (Equisetum fluviatle) with western water hemlock (Cicuta douglasii) sometimes fringed with Sitka sedge (Carez aquatilis var. dives), and lesser amounts of beaked (C. utriculata), owlfruit (C. stipata) and smoothstem sedges (C. laeviculmis). The introduced weed, nodding beggartick (Bidens cernua), was encountered on one mat.
On Beluga Lake in Homer, another lake dammed by human activity, occasional small mats of bluejoint are broken off from floating mats along the lake margin during high water events. These 25 square meter 'islands' float quickly with the wind, eventually lodging against the causeway which created the lake (Lake Street), where they are removed.
Soils are not described, but are entirely organic. Based on a couple of nearby measurements, the mats are probably up to about 3 meters thick.
NWI and HGM
NWI would classify Kenai Lowlands floating islands as L1AB4Hh (permanently flooded diked or impounded Lacustrine Limnetic floating aquatic bed) while the island was floating over deeper lake water, or L2AB4Hh (permanently flooded diked or impounded Lacustrine Littoral floating aquatic bed) when the island was against the shore, or over water shallower than about 2 meters (6.6 feet).
In HGM Floating Islands are classified as Lentic Island Floating mat throughflow wetland. Throughflow, because both Suneva and Beluga Lake have inlets and outlets.
Bluejoint floating mat is the only type documented for this ecosystem and is represented by a single plot:
| Summary of plant frequency and average cover for plants occurring
on the single plot measured |
|||||
| Wetland Indicator Status | |||||
| TAXON |
f |
% Cover |
Alaska |
National |
|
| Calamagrostis canadensis | 1.0 | 75.0 | FAC | FAC, OBL |
|
| Comarum palustre | 1.0 | 3.0 | OBL | OBL | |
| Carex laeviculmis | 1.0 | 1.0 | FACU* | UPL, FACU | |
| Carex magellanica | 1.0 | 1.0 | OBL | OBL | |
| Epilobium palustre | 1.0 | 0.5 | OBL | OBL | |
| Andromeda polifolia | 1.0 | 0.5 | OBL | OBL | |
| Menyanthes trifoliata | 1.0 | 0.5 | OBL | OBL | |
| Chamaedaphne calyculata | 1.0 | 0.5 | FAC | FAC | |
|
|
Introduction and Key to Plant Communities |
| Contact: Mike Gracz Kenai Watershed Forum PO Box 15301 Fritz Creek, AK 99603 907-235-2218 |
03 May 2007 18:03 |
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