Pacific Coast Tidal Marsh

Intertidal salt and brackish marshes are found throughout the Pacific coast, from Kodiak Island and south-central Alaska to the central California coast. They are primarily associated with estuaries or coastal lagoons. Salt marshes are limited to bays and behind sand spits or other locations protected from wave action. Typically these areas form with a mixture of inputs from freshwater sources into coastal saltwater, so they commonly co-occur with brackish marshes. This is a small-patch system, confined to specific environments defined by ranges of salinity, tidal inundation regime, and soil texture. Patches usually occur as zonal mosaics of multiple communities. They vary in location and abundance with daily and seasonal dynamics of freshwater input from inland balanced against evaporation and tidal flooding of saltwater. Summer-dry periods result in decreased freshwater inputs from inland. Hypersaline environments within salt marshes occur in "salt pans" where tidal water collects and evaporates. Characteristic plant species include Distichlis spicata, Limonium californicum, Jaumea carnosa, Salicornia spp., Suaeda spp., and Triglochin spp. Low marshes are located in areas that flood every day and are dominated by a variety of low-growing forbs and low to medium-height graminoids, especially Salicornia depressa, Distichlis spicata, Bolboschoenus maritimus, Schoenoplectus americanus, Carex lyngbyei, and Triglochin maritima. In Alaska, tidal marshes are often dominated by near-monotypic stands of Carex lyngbyei, while the frequently inundated lower salt marshes are often dominated by Eleocharis palustris or Puccinellia spp. Other common species in Alaska include Hippuris tetraphylla, Plantago maritima, Cochlearia groenlandica, Spergularia canadensis, Honckenya peploides, or Glaux maritima. In the Cook Inlet and Alaska Peninsula, Carex ramenskii may be an associated species. High marshes are located in areas that flood infrequently and are dominated by medium-tall graminoids and low forbs, especially Deschampsia cespitosa, Argentina egedii, Juncus arcticus ssp. littoralis, and Symphyotrichum subspicatum, and in Alaska Poa eminens, Argentina egedii, Festuca rubra, and Deschampsia cespitosa. Transition zone (slightly brackish) marshes are often dominated by Typha spp. or Schoenoplectus acutus. Atriplex prostrata, Juncus mexicanus, Phragmites spp., Cordylanthus spp., and Lilaeopsis masonii are important species in California. The invasive weed Lepidium latifolium is a problem in many of these marshes. Rare plant species include Cordylanthus maritimus ssp. maritimus.

Characteristic plant species include Distichlis spicata, Limonium californicum, Jaumea carnosa, Salicornia spp., Suaeda spp., and Triglochin spp. Low marshes are located in areas that flood every day and are dominated by a variety of low-growing forbs and low to medium-height graminoids, especially Salicornia depressa (= Salicornia virginica), Distichlis spicata, Bolboschoenus maritimus (= Scirpus maritimus), Schoenoplectus americanus (= Scirpus americanus), Carex lyngbyei, and Triglochin maritima. In Alaska, tidal marshes are often dominated by near-monotypic stands of Carex lyngbyei, while the frequently inundated lower salt marshes are often dominated by Eleocharis palustris or Puccinellia spp. Other common species in Alaska include Hippuris tetraphylla, Plantago maritima, Cochlearia groenlandica (= Cochlearia officinalis), Spergularia canadensis, Honckenya peploides, or Glaux maritima. In the Cook Inlet and Alaska Peninsula, Carex ramenskii may be an associated species. High marshes are located in areas that flood infrequently and are dominated by medium-tall graminoids and low forbs, especially Deschampsia cespitosa, Argentina egedii, Juncus arcticus ssp. littoralis (= Juncus balticus), and Symphyotrichum subspicatum (= Aster subspicatus), and in Alaska Poa eminens, Argentina egedii, Festuca rubra, and Deschampsia cespitosa. Transition zone (slightly brackish) marshes are often dominated by Typha spp. or Schoenoplectus acutus. Atriplex prostrata (= Atriplex triangularis), Juncus mexicanus, Phragmites spp., Cordylanthus spp., and Lilaeopsis masonii are important species in California. The invasive weed Lepidium latifolium is a problem in many of these marshes. Rare plant species include Cordylanthus maritimus ssp. maritimus.

The frequency of tidal flooding and salinity vary widely. Soils are usually fine-textured and saturated. Tidal marshes have a limited distribution along the Gulf of Alaska and British Columbia coastline due to the topography and geomorphology of the coast, which features steep slopes and deep fjords and offers limited protection from wave action (National Wetlands Working Group 1988).

Tidal marsh zonal mosaics of multiple communities vary in location and abundance with daily and seasonal dynamics of freshwater input from inland balanced against evaporation and tidal flooding of saltwater. Summer-dry periods result in decreased freshwater inputs from inland. Hypersaline environments within salt marshes occur in "salt pans" where tidal water collects and evaporates. High marshes flood infrequently, mid marshes flood usually at higher tides and are usually brackish waters, while low marshes are inundated with saltwater daily.

Conversion of this type has commonly come from coastal development, road building, seawall construction, and cessation of freshwater inputs. Water diversions, ditches, roads, and human land uses in the contributing watershed can also have a substantial impact on the hydrological regime. Channel flow, tidal inundation, and fresh water discharges are disrupted by construction of seawalls, jetties, dikes, and dams. Direct alteration of hydrology (i.e., channeling, draining, damming) or indirect alteration (i.e., road building or removing vegetation on adjacent slopes) results in changes in amount and pattern of herbaceous wetland habitat. Human land uses both within the marshes as well as in adjacent upland areas have reduced connectivity between wetland patches and upland areas. Land uses in the contributing watershed have the potential to contribute excess nutrients into to the system which could lead to the establishment of non-native species and/or dominance of native increasing species. The invasive weeds, such as Spartina spp. are problems in many of these marshes. In general, excessive livestock or native ungulate use leads to a shift in plant species composition. Non-native plants or animals, which can have wide-ranging impacts, also tend to increase with these stressors. Although most wetlands receive regulatory protection at the national, state, and county level, many have been and continued to be filled, drained, grazed, and farmed extensively (Chappell and Christy 2004). Additionally, these regulations only pertain to the filling of these wetlands and do not regulate alterations in ecological conditions of these sites (WNHP 2011).

In the Pacific Northwest Regionally downscaled climate models project increases in annual temperature of, on average, 3.2°F by the 2040s. Projected changes in annual precipitation, averaged over all models, are small (+1 to +2 inches), but some models project wetter autumns and winters and drier summers. Increases in extreme high precipitation (falling as rain) in the western Cascades and reductions in snowpack are key projections from high-resolution regional climate models (Littell et al. 2009). Warmer temperatures will result in more winter precipitation falling as rain rather than snow throughout much of the Pacific Northwest, particularly in mid-elevation basins where average winter temperatures are near freezing. This change will result in: Less winter snow accumulation, Higher winter streamflows, Earlier spring snowmelt, Earlier peak spring streamflow and lower summer streamflows in rivers that depend on snowmelt (most rivers in the Pacific Northwest) (Littell et al. 2009).

Potential climate change effects could include: within San Francisco Bay, sea-level rise may completely obliterate these marshes as coastal development exists where the likely migration of this system would occur (SFBCDC 2011); reduction in freshwater inflows through the further reduction in summer flows (Littell et al. 2009); but models also predict increases in extreme high precipitation over the next half-century, particularly around Puget Sound (Littell et al. 2009), which may provide freshwater pulses that are intermittent, less predictable; drop in groundwater table; increased fire frequency due to warmer temperatures resulting in drier fuels the area burned by fire regionally is projected to double by the 2040s and triple by the 2080s (Littell et al. 2009); and some regional sea-level rise (IUCN 2013a). A recent analysis of sea-level rise for California indicates that by 2035-2064, projected ranges of global sea-level rise are ~6-32 cm above 1990 levels, with no discernable inter-scenario differences (Cayan et al. 2008a, as cited in PRBO Conservation Science 2011). "The combination of severe winter storms with sea-level rise and high tides would result in extreme sea levels that could expose the coast to severe flooding and erosion, damage to coastal structures and real estate, salinity intrusion into delta areas and coastal aquifers, and the degradation of the quality and reliability of freshwater supplies" (PRBO Conservation Science 2011).

This system is found throughout the Pacific coast, from Kodiak Island and south-central Alaska to the California coast.