Mangrove wetland ecosystems in Ganges-Brahmaputra delta in ...

446 Shafi Noor ISLAM, Albrecht GNAUCK
Fig. 6 Water salinity after and before Farakka barrage construction in 1975 in India
Ganges flow was 3700 m 3 /s in 1962 whereas it was reduced
to 364 m 3 /s in 2006 (Nishat, 2006) (Fig. 7). As a result, the
high saline sea water has penetrated in the upstream, and
falling water tables occurred. Fig. 7 shows a strong correlation
between Ganges water discharge reduction and
salinity intrusion. The reduced water flow line and
increased salinity line has crossed at a certain point in
1975 (optimum point).
At this cross point the Ganges water flow was almost
1500 m 3 /s. This water level line can be introduced as the
optimal line where both lines crossed at the particular
point and this point can be called as the optimum point
of salinity intrusion. The isohaline salinity map (Fig. 5)
shows the real scenario of salinity intrusion in the
Sundarbans.
To compare the increasing salinity trends of three ecological
zones, the present situation is much more harmful
than that of 30 years before. Considering the value of water
salinity, the eastern zone still has a suitable condition for
mangrove ecosystems; the middle area is rapidly turning
from middle saline zone to high saline zone; and the southwestern
region which carries the highest rate of water salinity
would be more harmful for sensitive mangroves plants
and animals in the Sundarbans (Fig. 4).
6.3 Increased salinity and degraded ecosystems in the
Sundarbans
The reduction of Ganges fresh water in the upstream area is
the main reason for salinity intrusion in the southwestern
Fig. 7 Ganges water flow decreased and salinity increased at Passur-Mongla point