2008 Annual Monitoring Report (pdf 10.9MB) - Bolsa Chica ...

Bolsa Chica Lowlands Restoration Monitoring
2008 Annual Report
from July 1-16 and generally ranged between 5 and 20 NTU. Dissolved oxygen data at Station 1 were
unacceptable, but deployment, mid-deployment, and retrieval readings taken with a separate
instrument recorded DO levels ranging between 5.6 and 7.6 mg/L. Dissolved oxygen at Station 2 for
the 30-day period ranged from 4.1 to 9.4 mg/L, with a mean of 7.2 mg/L.
Additional spot water quality readings taken at the same stations during concurrent fisheries
monitoring were presented in the fisheries monitoring section of this report.
Discussion
The water quality conditions observed in the FTB during the last three quarters of Year 2 monitoring
show the tidal marine influence that exists in the basin, reflecting the daily and monthly tidal
fluctuations seen in the open ocean. All parameters were well within acceptable ranges to support the
developing fish, invertebrate, and vegetation communities, and are indicative of a well-flushed marine
environment. On-going physical monitoring of the condition of the inlet and the flood shoal is
important to ensure proper circulation of the basin and maintenance of good water quality.
The lack of usable paired temperature data at both stations makes comparisons difficult, but reviewing
the limited data available in conjunction with water quality measurements taken at the time of the
fisheries monitoring allows for some assessment. In the April and July months, there was a south to
north gradient of increasing water temperature. During warmer months the slow-circulating waters in
at the northern end of the basin tended to have higher temperatures because of increased solar heating.
The better circulated waters of the southern portion of the basin were more influenced by cooler
oceanic water, maintaining lower temperatures during the warmer months. Very little difference in
temperature was seen between the two stations during the January sampling.
Monthly average sea surface temperature data were obtained from the Coastal Data Information
Program (CDIP) (http://cdip.ucsd.edu/) for the closest station: 092 San Pedro (offshore of LA/LB
Harbors, 10 kilometers south of Point Fermin). The mean monthly sea surface temperature in January
2008 was 13.7 °C, while it was an average of 13.4 °C at both Station 1 and 2 in the FTB. In April
2008 the sea surface was 14.3°C (compared to 16.1°C at Station 2). In July 2008 the sea surface was
20.2°C (compared to 24.0°C at Station 1 and 20.8°C at Station 2). The FTB appears to closely match
the ocean temperature in the winter, with higher temperatures than the ocean in the summer months, a
condition typically seen in other coastal embayments in the region.
Dissolved oxygen levels measured at Bolsa Chica were within the expected range and reflected the
strong influence of diurnal tidal flow, with DO levels rising and falling with tides as water masses with
differing physical and biotic conditions were exchanged. Dissolved oxygen concentrations in water
are determined by a number of factors including: production through photosynthesis, atmospheric gas
exchange, oxygen consumption through biochemical oxygen demand and chemical oxygen demand,
and saturation capacity as dictated by temperature, salinity, and barometric pressure. The condition of
the FTB inlet remained suitable to provide enough tidal circulation throughout the basin to maintain
DO levels generally well above 5.5 mg/L, with daily tidal peaks in the 7.5 to 8.5 mg/L range, even
during the warm July month when unhealthy drops in DO can be observed in poorly circulated
systems.
The salinity data available reflected the absence of significant freshwater input into the FTB, with
salinities similar to typical oceanic salinities.
Merkel & Associates, Inc. 71