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The study was conducted to investigate the concentrations, distributions, sources and potential ecological risk of heavy metals in surface sediments from the Old Brahmaputra River. Sediment samples were collected from ve sampling stations and analyzed with inductively coupled plasma mass spectrometer (ICP-MS). The results showed that mean concentrations (mg/kg) of heavy metals were in order of Ni (58.82) Cr (32.45) Pb (21.04) Cu (14.24) Cd (3.81) As (2.02). In terms of spatial variation, sedimentary metals differed substantially, and the bulk of metal distribution and abundance can be traced back to man. Element-speci c environmental indices exposed that the ecological risks trailed the downward direction as Cd Ni Pb As Cu Cr. The contamination factor (CF), enrichment factor (EF) and geoaccumulation index (Igeo) exposed all cases a modest level of contamination except Cd, which has a signi cant level of contamination. Only, Ni and Cd were found high ecological risk for aquatic life, based on the sediment quality guidelines.Low to moderate ecological risk was suggested by the prospective ecological risk factor and potential ecological risk. The river sediments were mostly uncontaminated to mildly contaminated, posing a minimal ecological risk. The study concluded that the Old Brahmaputra River is subjected to anthropogenic disturbances for the aquatic environment. In this regards, proper management initiatives and regular monitoring should be carried out immediately by Department of Environment (DoE) to maintain sound and healthy aquatic environment of the River.

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This study was conducted to investigate the seasonal variation of water qualities for drinking and conservation of aquatic organisms from river, lake and waterfalls in Chattogram Hill Tracts of Bangladesh during pre-monsoon, monsoon and post-monsoon seasons from the period of March 2021 to February 2022. Water samples were collected from four sampling locations and analysed in the research laboratory of the Department of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University. Results were recorded on the parameters like temperature, EC, TDS, DO, BOD, pH, total alkalinity and total hardness in Kaptai Lake, Chengi River, and Shuvolong and Risang Waterfalls. The study revealed that the temperature, EC, TDS, BOD and pH were higher in pre-monsoon than monsoon followed by post-monsoon seasons. On the other hand, total alkalinity and total hardness were higher in post-monsoon than monsoon followed by pre-monsoon seasons. In the waterfalls, DO was higher in monsoon season when compared to pre-monsoon and post-monsoon seasons. The study provides baseline data on physiochemical water qualities in lake, river and waterfalls at the Chattogram Hill Tracts, which contributes to the long-term conservation of those aquatic ecosystems for human consumption and fisheries management.