2.4. Experimental design
100 g dry weight (DW) of air dried sediment
was added to 15 × 12 × 5 cm plastic containers and
artifi cially fl ooded with 500 ml distilled water with
three levels of constant salinity from fresh to saline.
Salinity treatments included 300 mg dm-3, 5000 mg
dm-3 and 15 000 mg dm-3. These concentration were
justifi e considering 300 mg dm-3 as the freshwater
salinity level, 5000 mg dm-3 refers to saline to freshwater
threshold based on Australian standard and
15 000 mg dm-3 considered as high salinity level.
Salinity of 300 mg dm-3 was established simply
by adding reverse osmosis (RO) water to the sediment.
For sediment with actual salinity level above
300 mg dm-3, dilution was needed to establish salinity
level of 300 mg dm-3. This was done by fi ltering the
water through a 35 μm zooplankton net and replacing
the water with RO water. The procedure was
repeated until the desired salinity was obtained. Three
replicates were assigned for each treatment using
a composited sample. All samples were incubated
in a temperature controlled culture room at 20°C
with day and night cycle using artifi cial light of
12 hours day and 12 hours night for 21 days. The
salinity level was measured daily for one week and
weekly for the rest of incubation period.For each
treatment, salinity levels were maintained either by
adding synthetic sea salt (Instant Ocean by Aquarium
System) to increase salinity or by adding tap water
as necessary.
Zooplankton was collected on day 7, 14 and 21
from the treatment containers. On each collection
day, a volume of the overlaying water from each
container was decanted and fi ltered through a 35μm
mesh net before being preserved in 70% ethanol
prior for identifi cation and counting. Filtered water
was returned to the microcosm.