STUDY THE AVAILABILITY OF PLANKTON, BENTHOS AND RELEVANT WATER QUALITY PARAMETERS IN THE BARRAGE REGION OF TEESTA RIVER

Abstract

This study was conducted from July 2018 to April 2019 (10 months) to monitor the present status of productivity and overall health status of Teesta river ecosystem closest to Teesta barrage situated in the Lalmonirhat district of Bangladesh. Water and sediment samples were collected twice in a month during the study period from six different sampling sites selected from the upstream and downstream poles of the barrage. Plankton analysis and identification were done in the laboratory of Fisheries Biology and Genetics department of Hajee Mohammad Danesh Science and Technology University, Dinajpur. The findings of this study disclosed the planktonic flora of 27 genera and fauna of 9 genera of Teesta river closest to Teesta barrage which revealed that comparative higher density of plankton (n >11500 per liter) as well as more number of planktonic flora (>18 nos.) and fauna (>7 nos.) were available in the early monsoon and monsoon season (April-September). On the other hand, comparative lower density (n<10000 per liter) and less number of phytoplankton (<12 nos.) and zooplankton (<4 nos.) were found in the pre-monsoon season (January February). The Teesta riverine ecosystem near to barrage were contained 16 species of macro-benthos from different groups. Monitored minimum temperature (20ºC) was recorded in January and it was maximum (33ºC) in July. Gradual increase of temperature was recorded from March to July (early monsoon) indicates that water temperature is normally uplifted according to the seasonal change. The observed dissolve oxygen level in the Teesta river showed that relatively lower (6.0 mg/l) DO level was remained in July and comparatively higher (8.5 mg/l) DO level was found in January. Average temperature and DO were significantly (p < 0.05) varied among different sampling months. We were found positive relationship between water temperature and plankton abundance while inverse relationship has revealed between river water temperature and DO. It is important to note that downstream region of barrage had slightly higher DO level than the upstream region which might be the impact of barrage water flow. The recorded available pH values were revealed that slightly alkaline pH level were remained in the Teesta River all the year round where the range varied from 6.8 to 8. Besides, both NO3-N and PO4-P levels in the study area were observed little higher in the late monsoon season at upstream and downstream region of the barrage. The findings of this study suggested that productivity indicators (availability of planktonic flora and fauna) were better in the early monsoon and monsoon season than the pre-monsoon and late monsoon. Similarly, better ecosystem health (temperature, pH and abundance of plankton) was also observed in early monsoon season. Last of all, it can be said that today is the high time to take all effective necessary actions to conserve the ichthyo-biodiversity of Teesta River particularly to protect and conserve all the commonly available endangered and critically endangered fishes. At the same time, river associated people and other relevant authorities should be aware enough to prohibit all manmade interventions that destroying riverine ecosystem health