150
S. Z. QASIM:
-2.5
"0 20
,
Ol
3-1.5
fii
Ol
~ 1.0
Fig. 13. Average monthly values of nitrite-nitrogen at 3 different depths of the backwater. Symbols
as in Fig. 5
12. Silicate-Silicon
The silicon values in the backwater were closely related to the silt-loaded freshwater
discharge, thus making the values very high during the monsoon months (Fig. 14).
=-50
"040 ,
Ol
330
c
o
,g 20
iJi
~ 10
o u
~ O~~~~~~~~L,~~~~
Fig. 14. Average monthly values of silicate-silicon at 3 different depths of the backwater. Symbols
as in Fig. 5
II. Rate of Primary Production
The rate of photosynthesis was measured by the light and dark bottle O2 technique
and the 14C method of STEEMANN NIELSEN (1952). The former method gave a measure of
gross production and the latter of net production. The factor for converting the O2
changes to C assimilation was 0.375/PQ, where the value of PQ was taken as 1.2
(STRICKLAND, 1960). Experiments with light and dark bottle and 14C were conducted in
situ, using a float throughout the year, at the site shown in Fig. 1.
The primary production in relation to depths is given in Fig. 15. The data for different
months have been pooled according to the 3 seasons. It is clear from the figure that about
90% of the total production is confined to the topmost layer. Maximum production
occurs either at the surface or slightly below. This is because highly turbid conditions