appendix b final 2008 biological surveys of los angeles and long ...

2.0 Water Quality
The CTD was deployed and recovered from a bow-mounted davit and powered by an electric
winch. The CTD was lowered to a depth of approximately 1 m, where it was allowed to soak
(equilibrate) for a period of approximately 3 to 5 minutes (min). The CTD was then raised to a
shallower depth and lowered to the bottom at a rate of approximately 10 m/min. The CTD was
recovered at approximately the same rate (10 m/min).
After completing the water quality survey, the raw casts (data files) for both the down-casts and
up-casts were copied electronically and saved for post-processing. The data were batch
processed by first converting the raw (.hex) files to scientific units in conjunction with the
updated calibration (.con) file provided during the factory instrument probe
integration/calibration. Data were then processed through a low-pass filter based on the
pressure signal to smooth out high frequency (rapidly changing) data. A loop edit algorithm was
applied to the filtered data to remove data spikes typically caused by waves, ship heave, or
unevenness of the winch motor. The resulting data files were then split into up-cast and downcast
for plotting and bin averaging routines. The up-cast records from each cast were used for
bin averaging, with the exception that the down-cast data were used for Stations LB3 and LB5
due to instrument problems on the up-cast. Each cast was averaged at near-surface (i.e., 1 m)
and at subsequent 1 m intervals to the bottom around whole-meter increments (i.e., +0.5 and -
0.5 meters). The near-surface bin (i.e., 1 m) included measurements between 0.5 to 1.5 m.
The 1 m bin-averaged results were then averaged at standard depth increments (surface [1 m]),
5 m increments, and 1 m above bottom [1 mab]) to provide a basis for inter-station comparisons
that were not skewed by differences among stations in water depths.
2.3 RESULTS
Water quality data for the 29 monitoring stations sampled during the July 2008 survey are
summarized in Table 2.3-1. Water quality profiles for individual stations are provided in
Appendix B. Spatial patterns in the water quality parameters are discussed in Section 2.4 and
comparisons to historical results are discussed in Section 2.5.
Minimum, maximum, and average values for water quality parameters by depth strata (surface,
mid-depth, and bottom) were calculated by averaging surface, mid-water column and bottom
bins over all stations, as summarized in Table 2.3-2. Surface measurements were averaged for
the 1 m depth (e.g., below surface) bins and bottom measurements were averaged at the lowest
bin for each station (i.e., 1 mab). Middle bins were averaged using the mid-water column bins
from Table 2.3-1 that most closely represented the center of the water column based on overall
depth.
2.3.1 Temperature
Water temperatures for surface, mid-depth, and
bottom waters ranged from 19.7 to 22.7 degrees
Celsius (°C), 16.8 to 20.2 °C and 15.2 to 20.4 °C,
respectively (Table 2.3-2). Temperatures were
consistently higher at the surface and decreased
with depth. However, none of the temperature
profiles, with the possible exception of Station LA8,
showed rapid changes in temperature with depth
(i.e., indicating thermoclines). Water temperature at
LA8 (4 m maximum depth) remained around 23.5 °C
to a depth of about 3 m, below which temperatures
decreased sharply to 20.4 °C. The warm water
temperatures at this location probably were
2–2 2008 Biological Surveys of Los Angeles and Long Beach Harbors
April 2010