Abstract:
Bangladesh is a deltaic land with hundreds of rivers. Many of them flow through and
fall into the Bay of Bengal. Changing climate leads to the SLR and rising sea level
causes the salinity in river water. The increasing salinity of river water directly affects
the local ecosystem and plant diversity. In this study, we tried to assess the status of
water salinity and existing plant diversity of the Sangu river of Chattogram. We also
tried to observe the impact of water salinity on the local plant diversity of the Sangu
river. In order to meet with the objectives, we directly measured the water salinity in
eleven (11) sampling locations, we collected plant diversity information from all
sampling locations and estimated the status of plant diversity using both Simpson (D)
and Shannon (H) Diversity Index Formula. Then statistically we observed the impact
of salinity on the plant diversity on the riverside. We also collected water samples from
sampling locations to measure the level of TDS and EC of the river water. We
conducted our data from Kodom Rosul to Rasulabad of the Sangu river. In the study
area, the highest salinity (10 ppt) was found in Kodom Rosul (transition point of Sangu
river with the Bay of Bengal). In the upstream zone, salinity gradually decreases (10
ppt to 1 ppt) from Kodom Rosul to Majhir-ghat. We observed almost zero salinity level
in the river water of the upstream zone. The salinity level remains the same throughout
the upstream zone. In the study area, the plant diversity value of both indexes increases
with the increase of distance from the Kodom Rosul to Rasulabad. The range of plant
diversity value is D = 3.906 to 9.434 and H = 1.467 to 2.309. All values of plant
diversity are almost the same and close to each other. The highest plant diversity was
also estimated in Rasulabad, D = 9.434 and H = 2.309. From the statistical analysis of
all the findings above, we reach into a conclusion that in the downstream zone, as
salinity increases, plant diversity tends to decrease towards the Bay of Bengal.
