Productivity of Backwaters and Estuaries
147
5. Oxygen
The dissolved O2 shows little change at different depths during the premonsoon
season. With the start of the monsoon rains, the O2 values at the surface increase, but at
deeper layers a decrease in the dissolved O2 is noticed (Fig. 7). The vertical gradient
normally continues until marine conditions in the backwater are restored.
6.0
E
a,i3.0
g:
x
01 .5
Fig. 7. Average monthly values of dissolved oxygen at 3 different depths of the backwater. Symbols
as in Fig. 5
6. Hydrogen Ion Concentration
The pH showed seasonal fluctuation at all depths. The values remain high when
conditions are marine and fall progressively as the system becomes freshwater-dominated
(Fig. 8).
8.t.
8.0
7.6
I
a.
72
6.8
D
Fig. 8. Average monthly values of pH at 3 different depths of the backwater. Symbols as in Fig. 5
7. Alkalinity
Fig. 9 shows the va nation in alkalinity. Like salinity, the alkalinity of the water
showed small changes during the premonsoon period and large changes during the
monsoon months.