Abstract:
Bangladesh is a deltaic land with hundreds of rivers. Many of them flow through and
fall into the Bay of Bengal (BoB). Changing climate lead 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 Bakkhali river of Cox’s Bazar. We
also tried to observe the impact of water salinity on local plant diversity of the Bakkhali
river. In order to meet with the objectives, we directly measured the water salinity in
the sampling locations, we collect 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
the sampling location to measure the level of TDS and EC of the river water. A dam is
situated in the middle of our study area. Due to that, we conducted our data collection
process in two-phase, one is in the downstream zone (from the dam to Maheshkhali
Channel) and another one is in the upstream zone (from the dam to Shikolghat,
Rajarkul) of the river. In the downstream zone, highest salinity (250 ppt) was found in
Maheshkhali Channel (transition point of Bakkhali river with the BoB). In the
downstream zone, as salinity gradually increases (10 ppt to 250 ppt), the downward
distance of sampling locations from the dam to Maheshkhali Channel also increase
gradually. We observed almost zero salinity level in the river water of the upstream
zone. Salinity level remains the same throughout the upstream zone. In the downstream
zone, plant diversity value of both indexes decreases with the increase of downward
distance from the dam to Maheshkhali Channel. The range of plant diversity value in
downstream zone are, D = 1.808 to 3.311 and H = 0.635 to 1.552. In the upstream zone,
any significant changes in plant diversity not observed at all. All values of plant
diversity are almost the same and close to each other. Highest plant diversity also
estimated in this zone (in Muktarkul, D = 5.848 and H = 1.767). The range of plant
diversity value in the upstream zone is, D = 4.608 to 5.848 and H = 1.564 to 1.767.
From the statistical analysis between all the findings above, we reach into a conclusion
that in the downstream zone, as salinity increases, plant diversity tends to decrease
towards the BoB from the dam. In the upstream zone, various anthropogenic factors
lead to very slight changes in plant diversity rather than the salinity.
