Observations on the abundance of Oligochaeta along with some environmental factors in an unmanaged freshwater wetland of West Bengal, India.

Abstract

The present work was undertakedto achievea comprehensive knowledge on theabundance of oligochaeta speciesas well as the results of limnological investigationalong with the ecohydrologycal status of an unmanaged wetland, in the planes of West Bengal, India.For the purpose of thehydrologicalstudy standard methods of American Public Health Association has been followedand the collection of benthic fauna (oligochaeta) was made employing Ekman’s dredge and standardsieve no. 60 having 0.4 mesh size.During study the water temperature varied from 20oC to 30.25oC. 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/litto 11.2 mg/lit.Free CO2 was found to be higher than dissolved oxygen and varied from2.4mg/litto 17 mg/lit. Hardness was always in a lower profile with a minimum of 13 mg/litand a maximum of 20.7 mg/lit. On the other hand Nitrate nitrogen ranged from 0.03 mg/litto 0.08 mg/litwhile dissolved organic matter varied from 0.61 to 4.13 mg/lit.While observingthe biological componentstotal sixspeciesof oligochaetawere identified with a maximum of 3333 ind/m2and a minimum of88 ind/m2. Among thesesix speciesLimnodrilushoffmeisteri was the largest specieswhich varied between 217 ind/m2and 2756 ind/m2with a total 7041 ind/m2,comprised 46.81% of the total oligochaeta.Branchiodrilus sempari,the second largest species formed 22.8%of the total oligochaetawith a variation from44 ind/m2to1820 ind/m2anda total of 3429 ind/m2.Another species Derodigitatavaried between22ind/m2and1267ind/m2and contributed18.96% to thetotal oligochaetawith a total of 2852indm-2.On the other hand,Aulodrilusspcontainedtotal 835 ind/m2andranged from22 ind/m2to222 ind/m2whileAulophorus farcatuscontainedtotal 775 ind/m2and varied between20ind/m2and 378 ind/m2contributed 5.15% and 5.57% oftotal oligochaetarespectively.Branchiura sowerbyi formedonly 2.92% of total populationwith a maximum of 178 ind/m2and a minimum of 44ind/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.