Tidal ecosystem wetlands occur where tidewater contacts the land over a broad protected gradient, such as behind the berm of a large stream mouth, or in a lagoon.  Due to the extremely high tidal energy of Cook Inlet, deltas do not aggrade.  Stream- and river-deposited sediments are pushed along shore by the prevailing tidal energy, forming a berm between Cook Inlet and the river channel.  Behind the berm, tidal marshes occupy estuaries with tidal and fluvial forces maintaining a gradual gradient.  These marshes exist as small, localized ecosystems on the Kenai Lowlands.

The berms that form at the mouths of the major streams empting into Cook Inlet support small Estuarine fringe marshes behind them, particularly at the mouths of the Kenai, Kasilof and Anchor Rivers.  Smaller marshes occupy the mouths of Deep, Bishop and Starisky Creeks, and the Swanson and Ninilchik Rivers.  See als the Tidal river (Rt) map unit description.

Lagoons can form behind the berms of larger stream, and a small one exists at the mouth of the Anchor River.  Larger lagoons occur in a only a few places.  On the Kenai lowlands larger lagoons occur on the west side of the base of the Homer Spit (Mariner Lagoon), and north of Nikiski, where, following 1964 earthquake subsidence, the tide breached a narrow coastal divide, burying a peatland in silt.

The area behind the base of the Homer spit, Mud Bay, is a lagoon-like feature supporting a narrow band of salt marsh vegetation near the intersection of the Homer Spit Road and Kachemak Drive.  In addition to the vegetation typically found in salt marshes, the rare plant  Kamchatka spikerush (Eleocharis kamtschatica) (G4, S2) occurs in abundance there. 

Mud Bay is protected first by the Homer Spit, and also by a berm system at its entrance that is submerged by the highest tides.  The Homer Spit was initiated by glacial moraines, and is kept supplied by sediments eroding from the bluffs to the northwest, and along–shore currents (and rip-rap).

The lagoon north of Nikiski is formed over a peatland.  Fifty centimeters or more of silt overlies the peat in the zone dominated by the seaside arrowgrass-goosetongue community; the silt is deeper in the barren tidal flat central portion of the lagoon.  The deposition occurred after saltwater breached the divide (which subsided during the1964 earthquake) between the former peatland and Cook Inlet.  One lobe of the peatland maintains freshwater fen conditions.

NWI and HGM

NWI classifies most Kenai Tidal Ecosystem wetlands as E2EM1, Intertidal Emergent Persistent Estuaries.  The few complexes with non-tidal wetland ecosystems (T9SA, T9K3 and T9, LB3), and some T9 map components fall into E2SS1, Intertidal Shrub-scrub Broad-leaved Deciduous Estuaries.

In an HGM classification (Tiner, 2003) the Tidal wetlands not found in estuaries are classified as Macrotidal Bidirectional Barrier Beach Fringe wetlands.  However, 'Tcs' is a Macrotidal Bidirectional Bay Fringe wetland when immediately adjacent to Cook Inlet or Kachemak Bay. 

Estuaries are variously classified.  The wetlands in the lagoon north of Nikiski are Macrotidal Bidirectional Fault-formed Tectonic Estuarine fringe wetlands.  The wetlands in Beluga Slough and behind clearwater rivers and creeks are Macrotidal Bidirectional Bar-Built Estuarine Fringe wetlands.  Finally, the estuaries behind the Kasilof and Kenai Rivers are most likely Macrotidal Bidirectional River channel Drowned River Valley Estuarine fringe wetlands.

Plant Relationships

Plants are subject to various tidal inundation regimes.  Some zones are covered daily, others monthly, while others are covered less frequently, or only during storms occurring in conjunction with extreme spring tides.  Where the gradient is sufficiently gentle and homogeneous, the ecological preferences of individual plants are easily observed . 

Saltpannes, barren of vegetation, form at the topographically lowest places, where high tides leave behind slowly evaporating pools.  Just above saltpannes, stickystem pearlwort (Sagina maxima) is the first plant to colonize the most saline tide flats.  Glasswort (Salicornia maritima), occurs just above the pearlwort.  Seaside arrowgrass (Triglochin maritimum), often in association with the slightly higher goosetongue (Plantago maritima), both occur just above pearlwort.  Arrowgrass and goosetongue commonly occupy a zone flooded 6-13 times per summer (Vince and Snow, 1984).

In the zone above these plants, lies an alkaligrass (Puccinellia spp.) zone, with creeping alkaligrass (P. phryganodes) occupying the zone slightly below Hulten’s and Nootka alkaligrass. This zone floods anywhere from 10-46 times per summer (Vince and Snow, 1984).  Above the alkaligrass zone, a typically abrupt transition to a sedge zone occurs.  Ramensk’s sedge (Carex ramenskii) is encountered first, followed by a transition into a Lyngbye’s sedge (Carex lyngbyei) zone.  In the sedge zone, pools can form that will frequently support fourleaf mare’s-tail (Hipparus tetraphylla), saltmarsh starwort (Stellaria humifusa), and Kamchatka spikerush (Eleocharis kamtschatica).  This zone floods an average of 0-5 times per summer (Vince and Snow, 1984).  

Above the pools and sedge zone, a transition to upland plants affected by storms and the highest tides begins.  Pacific silverweed (Argentina egedii), then largeflower spikegrass (Poa eminens) and big-head sedge (Carex macrocephala), beachrye (Leymus mollis spp. mollis) and beach lovage (Ligusticum scoticum) typify this zone, which floods from 0-2 times per summer (Vince and Snow, 1984). 

A discharge slope often occurs next, just below uplands. Sitka alder (Alnus viridis ssp. sinuata) usually with an understory of bluejoint (Calamagrostis canadensis) and field horsetail (Equisetum arvense) occupies this discharge zone.  This zone may only be affected by saltwater during the largest storms on extreme spring tides. 

 Introduction and Key to Plant Communities  

Introduction and Key to Ecosystems

    Kenai Hydric Soils    Map Unit Summary    Methods    Glossary

03 May 2007 18:04