Cook Inlet Wetlands
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DISCHARGE SLOPE Wetlands
Discharge Slope wetlands occur over hydric mineral soils where shallow groundwater discharges at or near the surface. This is the most extensive wetland ecosystem on the Kenai Peninsula, and a Discharge Slope dominated by Lutz spruce (Picea X Lutzii) is the most common component. They typically occur at the margin of other wetlands where the upland boundary is indistinct. These wetlands often support only seasonally high water tables, and therefore can be difficult to identify. Shallow groundwater wells in the Mat-Su Valley indicate that sites with late season water tables deeper than 150 cm support growing season hydric conditions sufficient to meet wetland criteria (Clark, 1995).
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| Lutz spruce with Barclay's willow and field horsetail at the margin of a small fen in the Caribou Hills. | A spruce stand with a bluejoint - field horsetail understory on a kame toeslope in the Soldotna Creek watershed. |
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| A thinleaf alder stand on a toeslope near the mouth of the Kenai River. |
Discharge Slope "Hydrologic" components are named after dominant plant species. Broad areas at the toe-slope position of the western margin of the Caribou Hills on the Kenai Peninsula are dominated by Lutz spruce and alder and support near-surface groundwater discharge. 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 augering to depth is sometimes required to accurately delineate these wetlands.
A forested Discharge Slope with an alder understory near Moonlight Lake.
NWI and HGM
Discharge Slope wetlands are primarily classified in the US Fish and Wildlife Service National Wetlands Inventory (NWI) as forested palustrine wetlands (PFO). Forested wetlands were frequently overlooked on the NWI, which was mapped at 1:63,360. Shrub- and herbaceous-dominated Discharge Slopes are classified as PSS and PEM respectively.
The LLWW Hydogeomorphic classification of Tiner (2003) would classify most Discharge Slope wetlands as Terrene Slope groundwater-dominated Throughflow wetlands. If there is no wetland connected upslope, such as along upper terraces or stream valley walls, then they are Terrene Slope Outflow wetlands. A few have Paludified Slope wetland components, although paludification is uncommon over most of the lowlands.
Discharge Slope Geomorphic Components (highlighted in blue) have the deepest, most fluctuating water tables of any component. Although some are temporarily flooded, many sites will exhibit a deep water table by mid-season, as indicated by average values below 30 cm. Specific conductance values and pH are high compared to other Geomorphic Components, indicating the strong groundwater contribution. Discharge Slope components represented: A= Alder; B= Birch; C= Bluejoint reedgrass; G= White spruce; L= Lutz spruce; M= Black spruce; S= Willow. Other ecosystems: D = Depression, K = Kettle; S = Discharge Slope; LB = Lakebed; SF = Spring Fen; RT = VLD Trough; R= Riparian; H = Headwater Fen; DW = Drainageway.
Wetland Indicators
| Table 1. Wetland Indicators in Discharge Slope map components throughout the Cook Inlet Lowlands. | |||||||
Map Component |
Peat Depth (cm) | Water Table (cm) |
Redox features (cm) | Saturation (cm) | pH | Specific Conductance µS/cm | Plant Prevalence Index |
SA |
107 (11) |
34 (10) |
23 (6) |
0 (2) |
6.2(4) |
118.7 (1) |
2.85 (10) |
SB |
83(18) | 56(18) |
29(15) | 45 (17) | 6.5(9) | 191.3 (8) | 3.39 (20) |
SC |
57 (7) | 71(5) | 24 (6) | 7.0(1) | 2.89 (6) | ||
SG |
20 (5) | 52 (5) | 14(4) | 47(4) | 5.7(4) | 74.8(4) | 3.34 (5) |
SL |
31(128) | 38(108) | 26 (82) | 5.4(9) | 48.9 (2) | 2.56 (120) |
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SM |
44(34) | 39 (26) | 33 (14) | 29 (18) | 5.1(9) | 89.6 (6) | 2.52 (28) |
SS |
46 (18) | 30(15) | 26 (8) | 6.4(1) | 86.6 (1) | 2.63(19) | |
SZ |
23 (1) | 1 (1) | 1 (1) | 6.0(1) | 18.4 (1) | 2.35 (1) | |
Explanation:
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.
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.
Soils and Plant Communities
| Table 2. Common soils and plant communities found in Discharge Slope wetlands. | ||
Map Component |
COMMON SOILS | COMMON PLANT COMMUNITIES |
SA |
Typic Cryorthents |
Alnus viridis ssp. sinuata / Equisetum arvense Alnus viridis ssp. sinuata / Equisetum palustre Alnus incana ssp. tenuifolia / Calamagrostis Paper birch - White spruce / Thinleaf alder |
SB |
Paper birch - White spruce / Thinleaf alder |
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SC |
Typic Cryorthents |
|
SG |
HISTOSOLS |
Paper birch - White spruce / Thinleaf alder |
SL |
Picea x lutzii / Salix barclayi / Calamagrostis canadensis Picea x lutzii / Equisetum arvense - Calamagrostis canadensis |
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SM |
HISTOSOLS |
Picea mariana / Equisetum sylvaticum - Ledum palustre ssp. decumbens |
SS |
Salix barclayi / Calamagrostis canadensis - Equisetum arvense |
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SZ |
UNDEFINED | |
| HISTOSOLS are any organic soils greater than 40 cm deep. | ||
Cation Chemistry
Cation chemistry by Geomorphic Component. Discharge Slope wetlands (highlighted in blue) have high cation concentrations compared to other Geomorphic Components. This indicates the strong groundwater discharge influence on porewater chemistry. Although calcium and silicon show the greatest concentrations, magnesium and iron concentrations in our area are high for natural waters. DW = Drainageway, K = Kettle; S = Discharge Slope; LB = Lakebed; SF = Spring Fen; RT = VLD Trough; R= Riparian; H = Headwater Fen; D = Depression.
Samples were collected from a surface pool where possible, otherwise from a separate shallow pit excavated to just below the water table. All samples were filtered through either a 0.2 micron filter using a disposable syringe, or pumped through a 0.45 micron filter using a peristaltic pump. Samples were acidified with ultra-pure nitric acid and kept cool until analysis on a direct current plasma spectrometer to about 5% accuracy (except K, 10-20% accuracy).
Discharge Slope Vegetation 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
NWI: PSS1Bn,g
HGM: Terrene Slope groundwater-dominated Throughflow
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.
NWI: PFO1Bn,g
HGM: Terrene Slope Outflow
SC: Dominate by bluejoint reedgrss (Calamagrostis canadensis).
NWI: PEM1Bn,g
HGM: Terrene Slope groundwater-dominated Throughflow
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).
NWI: PFO4Bn
HGM: Terrene Slope Outflow
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.
NWI: PFO4,5Bn
HGM: Terrene Slope Outflow, if adjacent to upland.
If wetlands above and below: groundwater-dominated Throughflow.
SM: Dominated by black spruce (Picea mariana).
NWI: PFO4Bn,g
HGM: Terrene Slope Outflow
SP: Dominated by Sitka spruce (Picea sitchensis), two wetland polygons in Seward.
NWI: PFO4Bn
HGM: Terrene Slope Outflow
SS: Dominated by willow, usually Barclay willow (Salix barclayi).
NWI: PSS1Bn
HGM: Terrene Slope groundwater-dominated Throughflow,
if wetlands above and below. If wetlands only below, then: Terrene Slope Outflow.
SZ: High elevation moutain meadows of various lush forb assemblages. Mapped only along the upper slopes on Baldy Ridge, above Wasilla.
NWI: PEM1Bn
HGM: Terrene Slope groundwater-dominated Throughflow
| Table 3.Summary of and Cook Inlet Discharge Slope Map Unit occurrence. | ||||
| Map Unit | N | Hectares | % Polygons | % Area |
| SA | 70 | 288 | 0.25 | 0.15 |
| SAB | 1 | 0.3 | 0.00 | 0.00 |
| SAC | 20 | 167 | 0.08 | 0.09 |
| SAG | 3 | 12 | 0.01 | 0.01 |
| SAL | 50 | 604 | 0.21 | 0.32 |
| SAM | 3 | 20 | 0.01 | 0.01 |
| SAS | 9 | 50 | 0.04 | 0.03 |
| SB | 90 | 991 | 0.37 | 0.53 |
| SBA | 4 | 19 | 0.02 | 0.01 |
| SBd | 3 | 7 | 0.01 | 0.00 |
| SBG | 7 | 14 | 0.03 | 0.01 |
| SBM | 10 | 295 | 0.04 | 0.16 |
| SC | 38 | 206 | 0.16 | 0.11 |
| SCA | 20 | 114 | 0.08 | 0.06 |
| SCAd | 5 | 9 | 0.02 | 0.00 |
| SCd | 3 | 0.6 | 0.01 | 0.00 |
| SCG | 2 | 2.7 | 0.01 | 0.00 |
| SCL | 10 | 63 | 0.04 | 0.03 |
| SCLd | 7 | 7.9 | 0.03 | 0.00 |
| SCS | 20 | 107 | 0.08 | 0.06 |
| SCSd | 1 | 24 | 0.00 | 0.01 |
| SG | 59 | 861 | 0.25 | 0.46 |
| SGA | 4 | 84 | 0.02 | 0.04 |
| SGB | 19 | 123 | 0.08 | 0.05 |
| SGC | 3 | 69 | 0.01 | 0.04 |
| SGM | 9 | 105 | 0.04 | 0.05 |
| SGS | 4 | 15 | 0.02 | 0.01 |
| SL | 1463 | 18,715 | 6.08 | 9.97 |
| SLA | 66 | 635 | 0.27 | 0.34 |
| SLC | 7 | 49 | 0.03 | 0.03 |
| SLCd | 2 | 2.1 | 0.01 | 0.00 |
| SLd | 6 | 37 | 0.02 | 0.02 |
| SLM | 58 | 447 | 0.24 | 0.24 |
| SLMd | 2 | 2.9 | 0.01 | 0.00 |
| SLS | 336 | 3164 | 3.18 | 2.53 |
| SLSd | 1 | 0.7 | 0.00 | 0.00 |
| SM | 765 | 4851 | 3.18 | 2.53 |
| SMA | 5 | 34 | 0.02 | 0.02 |
| SMB | 31 | 200 | 0.13 | 0.11 |
| SMC | 1 | 1.7 | 0.00 | 0.00 |
| SMd | 7 | 29 | 0.03 | 0.02 |
| SMG | 24 | 121 | 0.10 | 0.06 |
| SML | 42 | 340 | 0.17 | 0.18 |
| SMLd | 1 | 5.9 | 0.00 | 0.00 |
| SMS | 9 | 55 | 0.04 | 0.03 |
| SPS | 2 | 6.7 | 0.01 | 0.00 |
| SS | 315 | 1580 | 1.31 | 0.00 |
| SSA | 17 | 109 | 0.07 | 0.06 |
| SSC | 29 | 176 | 0.12 | 0.09 |
| SSG | 3 | 15 | 0.01 | 0.01 |
| SSL | 272 | 2149 | 1.13 | 1.14 |
| SSM | 13 | 63 | 0.05 | 0.03 |
| SZ | 20 | 214 | 0.08 | 0.11 |
Contact:
Mike Gracz
PO Box 15301
Fritz Creek, AK 99603
20 February 2012