THESIS APPROVAL

prevents the diffusion of atmospheric air into the overlying water. Living pattern of
the worms was observed half an hour later. The second microcosm was set by placing
a group of 50 worms into a petri dish filled with spring water and small decaying
materials such as plant debris or lump of soft sediment. Clumping behavior of these
worms was observed using stereo microscope. A part of the worms was separated to
another dish and then a portion of same sediment was added to make food supply.
Feeding and excretory behaviors were observed under stereo microscope.
3. Estimation on the Specific Growth and Biological Activities
3.1 Preparation of Sediment and Test Organism
The day before the experiment starts, sieved sediment was taken off the
refrigerator and then manually mixed in cleaned plastic tub. Fresh oligochaetes
acclimated for 1 d in the plastic container were used in this test. The worms were
isolated by sieving sediment through a 0.5 mm mesh sieve and the content on the
sieve was then placed in an enamel tray with tap water. Individual worm was gently
picked and transferred with fine forceps. They were first clean with tap water and
then placed in a petri dish containing distilled water to excrete their fecal pellets.
Non-sexually mature individuals of approximately similar size (length ≈ 2.0-2.5 cm)
were used in the majority of experiment. Weight of each 100 individuals from a total
of 5,400 test organisms were estimated at the start of the experiment to determine
population sizes by the method of Lundkvist (1978). Each group of these animals
was placed in another dish containing distilled water prior to being return to the
experimental vessels.
3.2 Experimental Design
There were two experimental treatments and two control sediments
prepared for this study (Table 8) consisting of worms placed to the sediment added
low level of food (E-WL), worms added to the sediment enriched with high level of
food (E-WH), worms added to the sediment without the supplement of food (E-WN)
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