STUDY ON SOME PHYSICO-CHEMICAL PARAMETERS WITH SEASONAL VARIATION AND DIVERSITY INDICES OF PLANKTON COMMUNITY OF DHEPA RIVER

Abstract

An experiment was conducted on some physico-chemical parameters with seasonal variation and diversity indices of plankton community of Dhepa river in Dinajpur district from May 2014 to April 2015. The whole experiment duration was divided into four seasons such as summer, autumn, winter and spring. Samples were collected fortnightly from four sampling sites named Vogdoma, Nijpara-1, Nijpara-2 and Itvata. Physicochemical parameters and plankton community were determined both at the field level and departmental laboratory of Fisheries Management, Hajee Mohammad Danesh Science and Technology University, Dinajpur. Significant level of variation (P<0.05) was observed both in physico-chemical factors and plankton community according to the seasons. Depth, dissolved oxygen, pH, PO4-P, hardness and chlorophyll-a were found higher during winter season but reverse result was observed in temperature and transparency. Depth and dissolved oxygen were highest during summer season. Water level of this river was influenced by sluice gate. The plankton community consisted of 74 genera in 4 groups of phytoplankton and 3 groups of zooplankton. The number of genera and density of plankton showed high seasonal variation during winter and summer. Majority of plankton community was shared by phytoplankton. The density of plankton community was higher (32.33×103 cell/L) during winter following phytoplankton and summer due to zooplankton. The density of Chlorophyceae, Bacillariophyceae had the highest density during the early winter and Cyanophyceae during late winter. Rotifera, Cladocera and Copepoda were higher during summer and late autumn to early winter. Plankton community had the highest (3.68) and lowest (2.50) Shannon-Weaver diversity index during winter and summer, respectively. The Shannon-Weaver diversity index remained constant at around 2.78 to 3.44. The maximum Evenness index (1.12) occurred in autumn season, whereas the minimum (0.90) was in spring season. The highest genus richness was observed in the month of November during winter season where as lowest (4.88) in the month of October. Both the highest number of genera and total number of individuals was highest in the month of November. The Shannon-Weaver diversity index value indicates good water quality of the river especially during winter season