1.1 MB pdf - Bolsa Chica Lowlands Restoration Project

SECTION 3: ANALYSIS
2. For Dry Samples
• Seawater was used to hydrate the sediments during the sediment compositing
process. After an equilibration period of at least ten days, pore water was extracted
and its salinity measured.
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If pore water salinity was within range, sediments and pore waters were used as
test media with no adjustment.
If pore water salinity was out of range, sediments and pore waters were adjusted
as described for wet samples.
Sediments
Bolsa Chica sediment samples were evaluated for acute toxicity to the marine amphipod,
E. estuarius, using the procedures outlined in ASTM (1990) guidelines. The tests were
conducted by ToxScan, Inc., of Watsonville, California. Test and control sediments were
sieved, and the salinity, pH, dissolved sulfide, and total ammonia were measured on the
sediment sample pore water to ensure that ammonia and sulfide concentrations were below
threshold limits for E. estuarius. This species was chosen as the test organism for this bioassay
because of its euryhaline characteristics, its relative insensitivity to grain size, and its ability
to perform well in a full range of salinities (2 to 34 ppt). It was anticipated that many
sediments tested would be best served if salinity adjustments could be avoided. It should be
noted that several sediments either required hydration (by addition of seawater) or showed
porewater salinities outside the tolerance limits of Eohaustorius. In such cases, salinity
adjustments were performed prior to testing, using ASTM recommendations for guidance.
Five replicates were randomly assigned to 1-liter glass test jars with enough sediment to
form a 2- to 3-centimeter layer on the bottom of each jar. The sediments were aerated using
a pasteur pipet after settling and then covered with water of appropriate salinity. The test
was started by randomly assigning 20 amphipods to each jar.
The test was conducted for 10 days under static conditions with constant illumination and
aeration in a chamber with a static 15° C ambient temperature. Daily measurements of
temperature, pH, and dissolved oxygen were made in each test jar. At the end of the 10-day
exposure period, the contents of each jar were poured through a sieve, and the surviving
amphipods were counted. Survivors were then placed on a clean (home) sediment overlain
by seawater at 15° C, and the number of amphipods that buried themselves within a 2-hour
period was recorded. Pore water ammonia and dissolved sulfide concentrations were
measured in one replicate of each test sediment at test initiation and at test termination.
Reference toxicant bioassays were performed using cadmium chloride with each batch of
test animals to verify the health and relative sensitivity of that test organism population.
The results of the amphipod bioassay testing, summarized in Table 3-14, show that survival
of the E. estuarius test organisms ranged from 0 percent to 98 percent. Among the test
exposures with surviving organisms, the percent reburial ranged from 22 percent to
100 percent. Survival rates were significantly different from controls in 30 out of 51 samples,
whereas the reburial rates differed significantly in only 3 out of 51 tests. However, 5 tests
had no survivors and thus no test organisms to rebury. Further analysis of these bioassay
data is provided in Section 3.2.1.3.
SAC/143368(003.DOC) 3-27 ERA REPORT
7/31/02