Observations On The Abundance Of Oligochaeta Along With Some Environmental Factors In An Unmanaged Freshwater Wetland Of West Bengal, India. Observations on the abundance of Oligochaeta along with some environmental factors.

Abstract

ABSTRACT

        The present work was undertaked to achieve a comprehensive knowledge on the abundance of oligochaeta species as well as the results of limnological investigation along with the ecohydrologycal status of an unmanaged wetland, in the planes of West Bengal, India. For the purpose of the hydrological study standard methods of American Public Health Association has been followed and the collection of benthic fauna (oligochaeta) was made employing Ekman’s dredge and standard sieve no. 60 having 0.4 mesh size.

        During study the water temperature varied from 20^oC to 30.25^oC. Transparency was higher     (88 cm) in winter and lower (21.15 cm) in post monsoon. pH was found to vary between alkaline (6.67) to acidic (8) in nature. Dissolved oxygen showed maximum fluctuation from 1.2 mg/lit to 11.2 mg/lit. Free CO₂ was found to be higher than dissolved oxygen and varied from   2.4 mg/lit to 17 mg/lit. Hardness was always in a lower profile with a minimum of 13 mg/lit and a maximum of 20.7 mg/lit. On the other hand Nitrate nitrogen ranged from 0.03 mg/lit to 0.08 mg/lit while dissolved organic matter varied from 0.61 to 4.13 mg/lit.

       While observing the biological components total six species of oligochaeta were identified with a maximum of 3333 ind/m² and a minimum of 88 ind/m². Among these six species Limnodrilus hoffmeisteri was the largest species which varied between 217 ind/m²and 2756 ind/m² with a total 7041 ind/m², comprised 46.81% of the total oligochaeta.  Branchiodrilus sempari, the second largest species formed 22.8% of the total oligochaeta with a variation from 44 ind/m² to 1820 ind/m² and a total of 3429 ind/m². Another species Dero digitata varied between 22 ind/m² and 1267 ind/m² and contributed 18.96% to the total oligochaeta with a total of 2852  ind m^-2. On the other hand, Aulodrilus sp contained total 835 ind/m² and ranged from 22 ind/m² to 222 ind/m² while Aulophorus farcatus contained total 775 ind/m² and varied between 20    ind/m² and 378 ind/m² contributed 5.15% and 5.57% of total oligochaeta respectively. Branchiura sowerbyi formed only 2.92% of total population with a maximum of 178 ind/m² and a minimum of 44    ind/m². During community study it was found that the index of dominance varied from 0.345 to 0.902 and index of dominance from 0.098 to 0.655.

Key Words: Abiotic factors, Abundance, Freshwater, Oligochaeta, Unmanaged, Wetland.