|visit a salt marsh|
Humboldt County's Salt Marshes|
by Andrea Pickart
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. 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). 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.
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!
North Coast Chapter of the California Native Plant Society
Last modified 06/26/01 17:25 EDT