Cook Inlet Wetlands

 
Wetland Permitting General Information

Wetland Classification

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KETTLE Wetlands

Idealized cross section showing Kettle hydrologic componentsRange map of kettles

Left: An idealized cross-section of a Kettle wetland showing hydrologic componets and typical plants. Drawing by Conrad Field. Right: Range of wetlands mapped as Kettles.

Kettle wetlands are peatlands occupying depressions created when ice-blocks entrained in glacial till melted at the end of the last glacial advance (ice-block depressions). Kettles have a wetland or stream connection to Cook Inlet, unlike Depression and Spring Fen wetlands, which also formed in ice-block depressions. Depressions and Spring Fens are surrounded by uplands.

Photo of a kettle south of Big Lake

A Kettle south of Big Lake.

Table 1. Wetland Indicators of Kettle Geomorphic 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

K1

        6.6 (34) 70.4 (34)  

K2

172(59)

6 (69)

  1 (35) 5.5(32) 82.1 (25) 1.59 (47)

K3

138 (82) 21 (87)   5.2 (30) 4.8 (30) 77.1 (21) 2.20 (72)

K4

104 (64) 32 (66) 36 (21) 25 (27) 5.2(13) 69.6 (10) 2.46 (57)

NWI and HGM

Kettles fit into the US Fish and Wildlife Service's National Wetland Inventory palustrine category.  They contain a variety of plant dominants from herbaceous emergents (PEM) to shrubs (PSS) and forest (PFO), with hydrologic regimes ranging from saturated through permanently, semi-permanently, and seasonally flooded (PSSB, PEMH, PEMF and PEMC, respectively). 

The LLWW Hydrogeomorphic classification (Tiner, 2003) would classify most Kettles as Terrene Basin groundwater-dominated throughflow wetlands.  When the kettle is occupied by a central lake, greater than 20 acres and deeper than 6.6 feet, it would be named a Lentic Fringe throughflow wetland.  Some may also form the headwaters to small streams, in which case the modifier "headwater" is appended.


Graph showing water table fluctuations, pH and specific conductance of wetland ecosystems with kettle ecosystem map components highlighted

Kettle Ecosystem wetlands (highlighted in blue) have deeply fluctuating water tables, and K2 and K3 can be flooded at the surface. Much late season water storage becomes available in these wetlands as the water table draws down during the summer dry period. Specific conductance values are relatively high compared to other wetland map components, indicating significant groundwater contributions. 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 Kettle 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

K1

        6.6 (34) 70.4 (34)  

K2

172(59)

6 (69)

  1 (35) 5.5(32) 82.1 (25) 1.59 (47)

K3

138 (82) 21 (87)   5.2 (30) 4.8 (30) 77.1 (21) 2.20 (72)

K4

104 (64) 32 (66) 36 (21) 25 (27) 5.2(13) 69.6 (10) 2.46 (57)

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 Kettle wetlands.

Map Component

COMMON SOILS COMMON PLANT COMMUNITIES

K2

STARICHKOF

DOROSHIN

HISTOSOLS

Trichophorum caespitosum - Trichophorum alpinum

Trichophorum caespitosum - Carex pauciflora

Trichophorum caespitosum - Betula nana

Sphagnum spp. - Carex chordorrhiza

K3

STARICHKOF

DOROSHIN

HISTOSOLS

Sphagnum spp. - Ericaceae

Carex pauciflora - Betula nana

Sphagnum spp. - Carex rotundata

Empetrum nigrum - Ledum palustre ssp. decumbens

K4

STARICHKOF

DOROSHIN

HISTOSOLS

Picea mariana / Ledum palustre ssp. decumbens

Picea mariana / Equisetum sylvaticum - Ledum palustre

HISTOSOLS are any organic soils greater than 40 cm deep.

Cation Chemistry

Stacked bar graphs showing total major cation chemistry and percent composition for wetland ecosystems, with kettle ecosystem values highlighted

Cation chemistry by Geomorphic Component. Kettle wetlands (highlighted in blue) have the third highest cation concentrations compared to other Geomorphic Components, indicating a strong groundwater influence on porewater chemistry. Kettles have the highest cation concentrations of any of the ice-block depression wetlands. The other ice-block depression wetlands (Spring Fens and Depressions) are isolated. 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).


Kettle Wetland Hydrologic Components:

K1: Kettle pond. If larger than 20 acres, the kettle is classified as a Lake.

K2: Water table at or very near the surface, often sedge-dominated.

K3: Deeper, more variable water table, often shrub dominated.

K4: Seasonally high water table, forested.

Table 3. Summary of Cook Inlet Kettle Map Unit occurrence.
Map Unit N Hectares % Polygons % Area
K1 428 977 1.78 0.52
K12 59 330 0.25 0.18
K12c 1 8 0.00 0.00
K13 21 101 0.09 0.05
K1-3 219 1395 0.91 0.74
K14 1 0.5 0.00 0.00
K1-4 36 257 0.15 0.14
K14d 1 3.6 0.00 0.00
K1c 16 85 0.07 0.05
K1d 3 18 0.01 0.01
K2 390 1257 1.62 0.67
K21 111 602 0.46 0.32
K21c 1 0.5 0.00 0.00
K21d 1 5.4 0.00 0.00
K23 475 2155 1.97 1.15
K23c 1 1.11 0.00 0.00
K23d 4 16 0.02 0.01
K24 25 69 0.10 0.04
K2-4 194 1058 0.81 0.56
K2-4c 1 2 0.00 0.00
K2-4d 2 4.0 0.01 0.00
K2c 2 11 0.01 0.01
K3 900 2031 3.74 1.08
K31 17 58 0.07 0.03
K31d 1 1 0.00 0.00
K32 402 1460 1.67 0.78
K32d 1 1.2 0.00 0.00
K34 654 2730 2.72 1.45
K34d 2 4.8 0.01 0.00
K3d 7 3.0 0.03 0.00
K4 1141 5813 4.74 3.10
K41 2 0.8 0.01 0.00
K42 25 119 0.10 0.06
K43 589 3164 2.45 1.69
K43d 2 9.3 0.01 0.00
K4d 22 77 0.09 0.04

Contact:

Mike Gracz

PO Box 15301

Fritz Creek, AK 99603

mike@kenaiwatershed.org

19 October, 2011