MACROBENTHOS OF DHEPA RIVER IN DINAJPUR DISTRICT: SEASONAL VARIATION AND BIODIVERSITY ASPECTS

Abstract

An experiment was conducted in Dhepa River of Dinajpur district in order to study the qualitative and quantitative abundance of macrobenthos with their seasonal variation. The study also focused on the biodiversity index of benthos community. Two sampling sites from Dhepa River in Dinajpur district were selected for research purpose. The whole experiment duration was divided into three seasons such as summer, winter and spring. Sampling was conducted at two sampling sites in Dhepa River from February 2016 to July 2016 and from November 2016 to January 2017. Physico-chemical parameters of water and abundance of benthic community were determined. The abundance of macrobenthos showed significant variation among the seasons and sites. A total of 12 individuals representing three phylla such as mollusca, arthropoda and annelida were identified. Of these 12 were mollusca represents 4, 5 individuals belonged to arthropoda and 3 individuals belonged to annelida. Among the 5 genera of arthropoda, chironomus was dominant. The abundance of total benthos found higher during summer period (2398±639 individuals m-2) followed by winter (2266±631 individuals m-2) and spring (1624±343 individuals m-2). Comparatively higher abundance of mollusca was observed during winter season (1198±424 individual m-2) than other two seasons. Similar observation was also recorded in case of arthropoda group (743±232 individuals m -2). Temperature showed positive relation with Chironomus, Gyrinus, Pheretima, Pila and Melanoides sp. Transparency has negative significant relation with the abundance of Forcipomyia sp. The abundance of Chironomous sp. and Tubifex sp. was decreased with increase in water level. Similarly, total abundance of annelida was found higher during summer (359±248 individuals m-2). Study sites from Dhepa river might be considered as moderately polluted areas according to the results obtained from Shannon-Weaver index of species diversity (1.64 to 2.30 respectively) and Margalef’s species richness (2.33 to 3.04 respectively). The evenness index of species diversity ranged from 0.59 to 0.98. However, maximum biodiversity was recorded in muddy bottom and minimum was recorded in sand bottom during the study period. This study would serve as baseline data for water quality and abundance of macrobenthos population in a diverse riverine system. Long term monitoring and improvement strategies are recommended to improve macroinvertebrate population and quality of water.