WATER QUALITY PARAMETERS AND PLANKTONIC COMMUNITY OF THE TANGAN RIVER IN THAKURGAON DISTRICT OF BANGLADESH

Abstract

An investigation was carried out on physico-chemical parameters and planktonic community of the Tangan river in Thakurgaon district to know the baseline information for a period of one year from April 2016 to March 2017. Samples were collected fortnightly from four sampling sites namely Senihary village, Saguni village, Rubber dam or Saguni Bridge and Rail Bridge. Physico-chemical parameters and plankton community were determined both at field level and Department laboratory of Fisheries Management, Hajee Mohammad Danesh Science and Technology University, Dinajpur. During the study period the mean range of values of physico-chemical parameters namely water temperature, water level, pH, DO and total alkalinity of four sampling sites were 26.89 to 28.28 0C, 1.08 to 1.25 m, 7.73 to 7.84, 6.66 to 6.99 mg/l and 11.94 to 12.14 mg/l respectively. A total of 66 genera of plankton were identified with 24 belongs to Chlorophyceae, 13 to Bacillariophyceae, 9 to Cyanophyceae and 3 to Euglenophyceae. Out of identified 66 genus of plankton, 17 were zooplankton with 8 belongs to Rotifera, 6 to Cladocera, 2 to Copepoda and Crustacean larvae also identified. During the present study a distinct fluctuation of plankton population in different months was observed. The range of total plankton was from 4.90×103 to 20.14×103 cells/l with mean value 9.37×103 to 9.83×103 cells/l. During the whole study period phytoplankton was dominant in plankton community and percentage composition of phytoplankton was 82.92% and 17.08% was zooplankton. During the study period the phytoplankton number and percentage was high in Chlorophyceae group (39.42%) followed by Bacillariophyceae (34.22%), Cyanophyceae (7.74%) and Euglenophyceae (1.93%). In zooplankton community the dominant group was Rotifera (7.68%) followed by Crustacean larvae (4.05%), Copepoda (2.78%) and Cladocera (2.57%). Statistically, a negative correlation was found between phytoplankton and temperature; positive relationships were found between phytoplankton with DO, pH, transparency and total alkalinity. On the contrary, positive correlation was found zooplankton with temperature and the negative correlation with dissolved oxygen. The present study revealed that the water quality of the Tangan river was fairly good for the growth and survival of plankton