Chapters 1 - U.S. Fish and Wildlife Service

Chapter 4
salinity, and alternately expose mudflats and adjacent shorelines. Tidal flushing is an important
factor in dispersing pollutants, maintaining water quality, and moderating water temperature.
In an unaltered salt marsh system, salinity in the marsh can vary significantly depending upon the
amount of freshwater that flows into the marsh during storm events. As discussed above, the
system has been disturbed to the point that freshwater flows into this marsh are extremely low,
which can affect the quality of some vegetation. Salinity, temperature, dissolved oxygen, and
turbidity data were first collected and recorded in Anaheim Bay in 1969 when monthly sampling
occurred at one station within the marsh (Chan and Lane in California Department of Fish and
Game 1975). This site was located to the south of Bolsa Avenue and the west of the Oil Island
access road. In January 1970, three additional stations were added within the north, central, and
south sections of the middle tidal channel that extends north/south through the main marsh
complex. By December 1970, a total of 15 sampling stations were established to include the west,
middle, and east tidal channels, as well as areas of cordgrass-dominated salt marsh (Chan and
Lane in California Department of Fish and Game 1975).
Sampling results indicate considerable daily and seasonal fluctuations in water temperature within
the marsh complex, due in large part to average channel depths of approximately two to three
meters at high tide. During this study, the maximum and minimum monthly mean water
temperatures in the marsh were 23.7 Celsius (74.7 Fahrenheit) in the summer and 12.4 Celsius
(54.3 Fahrenheit) in the winter (California Department of Fish and Game 1975). A fluctuation in
water temperature due to tidal influx was also observed, with temperature fluctuations of 1 to 3
Celsius (1.8 to 5.4 Fahrenheit) often observed. In general, water temperatures in the higher
elevations of the marsh were cooler in the winter and warmer in the summer than in the lower
elevations of the marsh (California Department of Fish and Game 1975).
In addition to changes in temperature over time, water temperature also varies within the water
column. This is most notable in the summer, when surface temperatures are approximately 0.5
Celsius (0.9 Fahrenheit) warmer than the temperatures at the bottom of the water column (U.S.
Navy 2011). These seasonal temperature fluctuations are greater in the higher marsh elevations
where water levels are generally very shallow.
Data collected in the 1970s indicated an average salinity in the marsh between May and October of
between 34.2 and 34.5 parts per thousand (ppt), slightly higher than the salinities recorded in the
outer harbor of Anaheim Bay, which ranged from 33.5 to 34 ppt. Once the rainy season began
surface water salinity levels dropped and were often recorded at less than 30 ppt (California
Department of Fish and Game 1975); however, high salinity levels were recorded below the
surface. Salinity data were also collected between 1990 and 1992 as part of the monitoring effort
for the Port of Long Beach mitigation project. Thirteen tidal wetlands at the four mitigation sites
and one reference site (located within the main marsh complex, between NASA Island and Hog
Island) were sampled between June and November 1990 and then bimonthly through July 1992.
Salinity of surface water ranged from 22.2 to 34.3 ppt, and bottom water salinity levels ranged from
29.11 to 34.22 ppt (MEC 1995, Navy 2011).
Dissolved oxygen data collected during the 1970s study included a uniform vertical oxygen
distribution in the marsh’s tidal channels. Seasonal variation was small, with dissolved oxygen
levels at about 6 to 8 milligrams per liter (mg/l) in the summer months and 7 to 11 mg/l in the
winter months (California Department of Fish and Game 1975). Dissolved oxygen values
recorded between 1990 and 1992 for the Port of Long Beach reference site ranged from 10.2 mg/l
in the winter of 1990-1991 to a low of 3.7 mg/l the following May. On average, the dissolved oxygen
concentration exceeded 5 mg/l throughout the water column during each survey (MEC 1995).
4-22 Seal Beach National Wildlife Refuge