International Journal of Marine Science, 2017, Vol.7, No.12, 102-113
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that of surface water. During the study CO
2
, Alkalinity, HˉCO
3
concentration of surface and subsurface water were
determined. It was observed that their concentration was relatively less in subsurface water than surface water.
2.2 Physico-chemical parameters of bottom soil
The
in situ
soil pH recorded 6.5 to 7.2 (at Sandwip and Barisal respectively) during monsoon and 6.8 to 7.1 (at
Barisal and Sandwip respectively) during post-monsoon. The bottom soil extracted water pH ranged 6.5 to 7.1
(minimum at Hatiya and Chandpur and maximum at Barisal) during monsoon and 6.2 to 6.8 (at Barisal and
Sandwip) during post-monsoon season. It was observed that the
in situ
bottom sediment poured water pH was
more than the soil extracted water pH for both season at all sites (except Hatiya in monsoon). In all sites and
seasons the subsurface water OM concentration were recorded a little more than that of OC. In the present study
the water OC ranged from 0.06 ml/L to 0.83 ml/L (at Sandwip in monsoon and at Chandpur in monsoon
respectively) whereas the OM varied between 0.11 ml/L and 1.43 ml/L (at Sandwip in monsoon and at Chandpur
in monsoon respectively). But in case of bottom soil OM and OC content were more in post monsoon than that of
monsoon (except at Hatiya). During the study OM content ranged from 0.06% to 0.8% (at Chandpur during
monsoon and at Sandwip during monsoon respectively).
Sand-silt–clay percentage of sampling sites were used to calculate soil texture (Table 3). The soil texture of Hatiya,
Bhola and Barisal remain similar during both seasons whereas at Sandwip and Chandpur it showed little change
(Figure 2).
Figure 2 Soil texture in the sampling sites during (A) monsoon and (B) post-monsoon season
2.3 Benthos
A total of 17 major taxa of macrobenthos were identified of which 10 and 15 were recorded during monsoon and
post-monsoon season respectively (Table 4). During monsoon, the highest density of macrobenthos was recorded
at Chandpur (7658.7 Indivs/m
2
) and the lowest (208.1 Indivs/m
2
) at Hatiya. Whereas during post-monsoon the
maximum was 27180.0 Indivs/m
2
at Barisal and the minimum was 1248.7 Indivs/m
2
at Bhola. Polychaetes were
recorded at all sites and seasons (except Hatiya in monsoon). Amphipoda and Nemertea were abundant at
Sandwip and Hatiya in both seasons. Nemertean, Oligochaeta, Polychaeta were the dominating at Chandpur
during the post-monsoon.
2.4 Multivariate analysis
2.4.1 Canonical corresponding analysis (CCA)
The Redundancy Analysis (RDA) triplot is used to explaining the favorite abiotic ecological factors for
distinguishing dominant benthos during monsoon and post-monsoon seasons and also to show the influence of
environmental parameters (Figure 3; Figure 4).
A
B
