Ecology

The lower Salinas River ecological environment is composed of four major systems: salt marsh, freshwater marsh, riparian woodland, and river/lagoon. In the past, various water resource development activities have been responsible for significant degradation or loss of these once abundant systems throughout central California and elsewhere in the West. Because of the magnitude of past losses and the inherent biological values of these systems, they are now the focus of attention in ecological circles.

Salt Marsh

About 25 ha. (63 ac.), or seven percent of the study area, is salt marsh intermixed with mudflats and salt pans. The salt marsh system is located in the lower river sections near the confluence of the coast and lagoon environments. High concentrations of soil salts restrict the diversity of plants that can exist in the salt marsh. California coastal salt marshes are dominated by pickleweed and salt grass and receive only irregular salt water flooding. Pickleweed comprised about 90% of the salt marsh vegetation. Additional plant species appeared in localized areas along the lagoon/marsh interface where more frequent flooding reduces soil salinity.

The mixture of shallow water, mudflats, and vegetation in the salt marsh constitute an important wildlife area, especially for birds. The dense stands of pickleweed were heavily utilized by both resident and migrant waterfowl. Bird abundance and species diversity in the salt marsh and adjacent lagoon area were the highest in the study area. Over 127 species, both resident and migrant, have been observed in the general area. Major bird groups included gulls, terns, shorebirds, wading birds, and waterfowl. Figure 3 shows the lagoon and bordering salt marshes.

Figure 3.
Salinas River Lagoon, with salt marsh area in the foreground and sand dunes separating the
lagoon from Monterey Bay in the background. Note the utilization of the lagoon by birds.

Inputs of soil moisture in the salt marsh come from both freshwater and saltwater sources. Saltwater comes directly from nearby Monterey Bay as salt spray or storm surges. High winds and tides send water around or over the dunes and onto low-lying marsh areas. Freshwater inputs are supplied primarily by rainfall. However during flood conditions, overbank flooding from the Salinas River is an additional source.

Land elevation has very important effects on salt marsh soil moisture and standing water dynamics. Elevation of the salt marshes isolates them and prevents their regular inundation by either saltwater from the bay or freshwater from the Salinas River. The salt marshes are perched

above the normal river channel and receive water from the river only during extremely high flow conditions. During normal flow conditions, water of the lower Salinas River Lagoon is channeled away from the salt marshes by high streambanks and therefore plays no significant role in the salt marshes' short-term hydroperiod. The water and salinity regime of the Salinas salt marshes are instead controlled by rainfall and by oceanic and evaporative processes not linked to normal river flows.

Freshwater Marsh

The freshwater marsh system is very limited in size and distribution; this system totals less than 0.8 ha. (2 ac.), less than 0.5% of the study area. Freshwater marshes occur as isolated, small stands rather than large, contiguous units. The dominant emergent plant was broad-leafed cattail. Small stands were scattered throughout the channel; they were most abundant below the Blanco Drain outfall, where water was constantly available.

The limited distribution and small size of this system precludes the development of any uniquely associated wildlife assemblage. Wildlife species present in freshwater marsh areas were also found in adjacent riparian woodlands.

The presence of standing water is the crucial parameter in this system. The depth of water and duration of submergence determine vegetative composition, zonation, and succession.

Riparian Woodland

Riparian woodland dominates the terrestrial areas, comprising approximately 93% of the upland portion of the study area. Riparian woodland extended almost continuously from the Highway 68 bridge to just east of the Highway 1 bridge. It formed an extremely narrow corridor, being confined to the Salinas River channel and occasional scattered waste places along the banks and floodplain that have not been converted to agricultural uses. Cottonwood and willow species were the important plant dominants. The relative abundance of these plants varied considerably along the river. Land elevation, local depth to groundwater, and, most importantly, the local land management techniques employed in adjacent areas determine the vigor, stature, and relative abundance of these species in the corridor.

The open floodplain bordering the Salinas River channel is frequently flooded by the natural rising of the river. Species growing in this habitat are adapted to flooding and constantly moist soil. Groundwater is continually recharged by overbank flows and subsurface seepage from nearby surface flows (Keller 1977; Johnson etal . 1976; Crouch 1979). Most species are low-growing annual or perennial herbs and grasses.

Wherever unstable soils accumulate to form slightly elevated gravelbars, dense stands of shrubs up to 7 m. (24 ft.) tall have developed. The dominant shrub, sandbar willow, is the first species to colonize the gravelbars. Other dominant shrubs include arroyo willow and mule fat. Herbs usually grow towards the edge of the gravelbars. In time, the elevation of the gravelbar becomes higher and the gravelbar more distant from the river due to continual soil deposition. As a result, flood frequency decreases.

These new conditions favored the establishment of riparian forest, characterized by tall trees crowded and tangled with vines (Sands 1979). There were several vegetation layers within the forest along the Salinas River. Overstory trees attained heights up to 23 m. (75 ft.). The dominant overstory species was Fremont cottonwood. A subcanopy layer 4.6–13.7 m. (15–45 ft.) high was formed by red willow, black cottonwood, and box elder. Understory species consisted primarily of tall herbs and tangling vines.

This riparian forest or woodland corridor provides refuge for a large number of wildlife species unable to exist in adjacent agricultural areas. Bird population levels and species diversity were high. Common mammals included raccoon, deer, and cottontail rabbit. Coyote, grey fox, and bobcat were occasionally present.

River/Lagoon

For analytical and descriptive purposes, the river and brackish lagoon environments were combined into one functional ecosystem. This was done because of the intricate interdependencies, the absence of any distinct boundary between the two systems, and the functional similarity of the driving forces of the two systems.

The freshwater riverine zone extends roughly from the Alisal wastewater treatment plant outfall downstream approximately to the California Highway 1 bridge. At the bridge, a gradual transition from fresh to slightly brackish water occurs as the river merges imperceptibly into the lagoon itself. The position of the interface betwen these two zones shifts continually. Water salinity in the lagoon and upstream transitional zone fluctuates seasonally depending on river discharges, rainfall, and periodic saltwater influxes from Monterey Bay.

A larger sandbar forms across the river mouth during the summer and fall months, effectively sealing off the lower river from Monterey Bay and restricting regular tidal exchanges with bay waters. Sandbar development and maintenance are predominantly controlled by alongshore forces. Normal river discharges are too weak during the summer to counterbalance sandbar development. A water-control weir diverts summer streamflow from the lagoon to Monterey Bay through the old Salinas River channel which discharges through Moss Landing Harbor about 1.5 km. (1 mi.) to the north. The sandbar essentially excludes saltwater influences, making upstream freshwater discharges the system's sole driving

force and the source of system energetics. Consequently, the hydrodynamics of the lower stream and lagoon areas during the summer and fall seasons are unlike classic river-influenced bays in which saltwater influxes and river discharges are physical forces of approximately equal importance regulating plant and wildlife populations.

Formerly, the Salinas River and Lagoon supported large populations of fish. Today, however, the populations have been significantly altered by major hydrologic changes in the watershed. Three groups of fish currently occur in the Salinas River: native, introduced, and marine visitors. Over the years, 23 fish species have been reported in the Salinas River; five are introduced, 16 are native, and two are anadromous. Among the native fish, populations of eight species have declined significantly in recent years. The other eight species have remained stable. Benthic invertebrates are also basic components of the Salinas River and Lagoon food chains.