L - Cochin University of Science and Technology

analysed after acidification by titration against standard sodium thiosulphate using
starch as indicator. The concentration of oxygen in the sample was calculated as,
Dissolved oxygen (mill) = 5.6*N*(S-Bm)* VI V-l)*lOOOIA
Where.
N = Normality of thiosulphate in solution
S = Titre value for sample
Bm = Mean titre value for blank
V = Volume of the sample bottle
2.2.2 Sediment and benthic samples
A = Volume of sample titrated (50 ml)
Sampling was done for the estimation of sediment parameters like texture and
organic matter and for macro and meiobenthos from all the stations. A total of 48
grab samples (23 from post-monsoon season and 25 from pre-monsoon season
cruises) were collected for the present work. Modified Smith Mc lntyre Grab was
used for collecting sediment samples (Plate 3). It traps a substantial volume of
sample, as its open mouth covers a surface area of 0.lm2. During the sampling. the
vessel was maintained stationary and the wire was kept as vertical as possible to
ensure vertical set down and lift-up of the grab at right angles to the hottom. As
recommended (ICES, 1994). the final 5 m of descent was maintained at a rate < 0.5
m.s- I
to minimize the shock bow wave disturbances. The sample showed a
distinguishable undisturbed surface layer. often including loose flocculent deposits
and no sign of sediment leakage, such as from incompletely closed buckets.
Approximately 150 gm of wet sediment sample from each station was taken and
dried onboard the ship at 70° C in an oven and stored in the polythene bags for the
study of sediment characteristics. The dried samples were taken to the laboratory for
further analysis.
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