Impact of Water Salinity into the Local Plant Diversity of the Bakkhali River, Cox’s Bazar

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.