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International Journal of Marine Science 2013, Vol.3, No.2, 4
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6
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6
generally low (0.6 m) in KAE particularly during
monsoon season and it was negatively correlated with
BOD values at 5% level (r =-0.688, p<0.05). In fact,
high turbidity values were observed in the KAE with an
average of 9.8 NTU with a peak concentration was
recorded during south west monsoon season (20.2
NTU). Highest mean turbidity value was observed at
mouth of the estuary (EMZ) represented by Station 1
(13.1 NTU).
The discernible spatio-temporal variation was also
observed in the pH values and it was generally on an
alkaline side (7.4). However the peak monsoon was
marked by heavy rain, pH values tended to fall in all
the stations of KAE (6.9). Higher pH values were
observed in stations EMZ (station 1; 7.5) when
compared to the station in EUZ (Station 7; 7.2).
Relatively high alkalinity was observed during
pre-monsoon period (43.7 mg/L), when compared to
the monsoon (24.4 mg/L) and post monsoon (36.9 mg/L)
seasons. Highest mean alkalinity value was recorded at
station 1 (40.3 mg/L). The ANOVA of alkalinity
showed the variation between months were significant
at 1% level (F=22.490). Average salinity of estuary
showed mesohaline nature. The maximum average
salinity was recorded at mouth region (Station1; 18.9 psu)
and minimum at EUZ (Station 7; 10.2 ± 8.6 psu). Clear
vertical stratification and seasonality were observed in
salinity pattern. The salinity values showed a definite
trend, where it decreased from estuarine mouth to head.
During the monsoon period (June to September)
salinity values were comparatively low (5.4 psu);
however, salinity enormously increased (21.6 psu)
during post monsoon period (October to January). But,
salinity tends to decrease (16.1 psu) during
pre-monsoon period (February-May), as a result of
commencement of south west monsoon. The ANOVA
of salinity showed that the variation between months
were significant (F=33.433, p<0.01). Tides in the KAE
are semidiurnal, with amplitude of 1m during spring
tide and 60 cm during neap tides and average rain fall
in the area was 310 cm (Revichandran and Abraham,
1998). During the present study average
macronutrient concentration observed in the KAE
were (15.0±12.1) µmol/L for dissolved inorganic
nitrogen (DIN), 49.1 ± 28.7 µmol/L for dissolved
inorganic silicate (DISi), and 1 ± 1.3 µmol/L for
dissolved inorganic phosphate (DIP). Among the three
major macronutrients, DIP concentrations were
comparatively low in the KAE. The average nitrate-
nitrogen (NO
3
-N) of KAE water was 10.2 µmol/L. The
average NO
3
-N values ranged from 7.9 ± 9.9 µmol/L in
Station 2 (EMZ) to 13.6 µmol/L in Station 7 (EUZ).
Comparatively high NO
3
-N was observed during
monsoon period (19.1 ± 19.4 µmol/L), whereas
relatively low NO
3
-N content was observed in post
monsoon (7.4 ± 3.6 µmol/L) and pre monsoon periods
(3.8 ± 3.3 µmol/L). The ANOVA of macronutrient
showed monthly variations significant at 1% level;
(nitrate-nitrogen, F=50.537; silicate-silicon, F=38.965;
phosphate-phosphorus, F=10.897). The average Chl
-a
for the seven stations of KAE was 6.42 mg/m
3
and
varied from 5.07 mg/m
3
in Station 2 (EMZ) to 7.80 mg/m
3
in Station V. Peak value of Chl-
a
was observed during
pre-monsoon period (10.89 mg/m
3
) and decreased to an
average of 5.16 mg/m
3
during the monsoon season. The
ANOVA of Chl-
a
showed the variation between
months were significant at 1% level (F=14.295). The
GPP showed an average of 1580 mg C m
-3
d
-1
and NPP
was 790 mg C m
-3
d
-1
during the study period. Highest GPP
was observed during pre-monsoon (1785 mg C m
-3
d
-1
)
followed by post monsoon (1589 mg C m
-3
d
-1
) and
monsoon (1 517 mg C m
-3
d
-1
). Generally increased
GPP was noticed in the stations of EMZ (Station 1;
1625 mg C m
-3
d
-1
, Station 2; 1750 mg C m
-3
d
-1
and Station
3, 1750 mg C m
-3
d
-1
). Highest NPP was observed during
post monsoon (1035 mg C m
-3
d
-1
) followed by
monsoon (828 mg C m
-3
d
-1
) and pre monsoon (585 mg
C m
-3
d
-1
) respectively. Relatively high mean NPP
values were observed in Station 3 (921 mg C m
-3
d
-1
)
but Station 6 showed comparatively low average NPP
values (588 mg C m
-3
d
-1
).
2.2 Fish abundance, species richness, and diversity
A total of 144 tows (EMZ, 72; EUZ, 72) data were
collected representing 63 fin fishes belonging to 37
families
(Table 1). Six species of penaeid shrimps, one
species of palemonid prawns, two species of crabs, four
species of clams and two species of edible oysters were
observed. The average fish production in the KAE was