visit a salt marsh

Humboldt County's Salt Marshes
by Andrea Pickart

Mad River Slough The majority of salt marshes remaining in Humboldt County are concentrated in Humboldt Bay (approximately 900 acres) with some 20 acres found at the mouth of the Eel River. Both of these estuaries, however, have seen the dramatic destruction of salt marshes since the early 1900s. The conversion of Humboldt Bay's salt marshes to agricultural pasture was hastened by construction of a railroad around the margin of the bay in 1901. Once the railroad berm was completed, the addition of tide gates restricted any further tidal influence over the adjoining 8,000 acres, and these low-lying areas became seasonally saturated freshwater marshes, or "agricultural wetlands," dominated by exotic pasture grasses. Even without the construction of a railroad, the Eel River estuary suffered a similar fate, losing close to 2,500 acres of salt marsh to pasture. ag wetlands Many of these fields are dotted with native soft rush (Juncus effusus) in damper areas. Old tidal sloughs are now freshwater marshes with native wetland plants such as water parsley (Oenanthe sarmentosa) or open water areas that provide breeding sites for ducks. Shorebirds and waterfowl utilize the grazed agricultural wetlands and raptors forage over them. Despite their high wildlife values, they represent a significant alteration of an estuarine to a non-estuarine ecosystem. The high productivity values of the salt marshes, and their unique flora and fauna have been nearly lost.

In addition to the direct displacement of salt marshes by diking, draining, and filling, our area's salt marshes have further suffered from the invasion of non-native dense-flowered cordgrass (Spartina densiflora). <U>Spartina densiflora</U> The Humboldt Bay and Eel River estuaries originally had no cordgrass component, unlike the salt marshes of central and southern California which harbor California cordgrass (Spartina foliosa). Dense-flowered cordgrass was introduced in the mid 1800s, most likely in ship ballast as a result of a lumber trade with Chile. By the time botanists had recognized it as a non-native component of the salt marsh in the mid 1980s, dense-flowered cordgrass was the dominant species of our salt marshes. Cordgrass grows between the tidal elevations of 6.0 and 7.8 MLLW [mean low low-water], but reaches peak cover between 6.25 and 7.5 MLLW. The species is able to reproduce both vegetatively and by seed, although seedling establishment is apparently limited in years of low rainfall. Dense-flowered cordgrass does not go completely dormant in winter months, as the native salt marsh plants do. Year-round growth, along with its relatively tall height and dense growth form give it a competitive advantage over native plants. In Humboldt Bay, cordgrass is least abundant in the high elevation marshes of Mad River Slough. Presumably, these marshes are too high to be preferred habitat. However, cordgrass has been steadily increasing even in these intact marshes. Elsewhere, it is spreading in disturbed areas, including unmanaged restored sites. Efforts are underway by several agencies to collaborate on developing control techniques for this species.

The salt marsh vegetation of Humboldt Bay was classified by Annie Eicher as part of a 1987 study in which she named three marsh types: Salicornia marsh, Spartina marsh, and Mixed marsh. These three types correlated with tidal elevation, with Salicornia marsh occurring below 6.9 ft. MLLW, Spartina marsh between 6.9 and 7.3 ft. MLLW, and Mixed marsh at elevations over 7.3 ft. MLLW.

<U>Salicornia virginica</U>
Salicornia virginica

<U>Grindelia stricta</U>
Grindelia stricta

<U>Castilleja ambigua</U>
Castilleja ambigua

  • Salicornia marsh consists of dense mats of pickleweed (Salicornia virginica), with occasional jaumea (Jaumea carnosa), salt grass (Distichlis spicata), arrow-grass (Triglochin maritima) and dense-flowered cordgrass. This type is common along tidal channels and intertidal flats.
  • Spartina marsh is also low in species diversity, with dense stands of cordgrass in which grows scattered pickleweed. Where openings in the stands occur, other marsh species occur, including salt grass, jaumea, arrow-grass, salt bush (Atriplex patula), sea lavendar (Limonium californicum), gumplant (Grindelia stricta), and hairgrass (Deschmpsia caespitosa).
  • The Mixed marsh type, growing on higher elevation marshes, is the most diverse, with a total of 22 species documented. No single species dominates, resulting in a very diverse vegetation type. In addition to all of the species found in the two other marsh types, mixed marsh supports salt marsh plantain (Plantago maritima var. juncoides), the parasitic dodder (Cuscuta salina), sand spurrey (Spergularia canadensis and S. macrotheca), bulrush (Scirpus cernuus ssp. californicus and S. maritimus), slough sedge (Carex lyngbyei), sea milkwort (Glaux maritima) salt rush (Juncus leseurii), and two rare hemi-parasitic salt marsh annuals: Humboldt Bay owl's clover (Castilleja ambigua ssp. humboldtiensis) and Point Reyes bird's beak (Cordylanthus maritimus ssp. palustris).

The value of the salt marsh to the estuarine ecosystem has been demonstrated in many estuaries on the west coast. Salt marshes are a part of a larger, complex, system which includes brackish marshes at their upland ecotone, mudlfats, subtidal channels, and eelgrass (Zostera marina) beds. Freshwater inputs from creeks bring sediments and nutrients, as do ocean waters that circulate through the bay twice daily during our diurnal tidal cycles. The restoration of salt marshes are a high priority for re-establishing some of the lost ecosystem function. This type of restoration is still in an experimental stage locally, but large scale projects are being carried out San Francisco Bay and elsewhere.

Elk River Slough Wildlife Area offers easy public access to salt marsh. Take the Herrick Road exit on Hwy. 101 immediately south of Eureka, and park in the big paved lot on the west side of the freeway. Walk the short distance to the slough where, you will see a strip of salt marsh on the right. A path leads directly through the high salt marsh. Please stay on the path!
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Last modified  06/26/01 17:25 EDT