B. K. Sharmal and Md. Hussain
Abstract
Zooplankton (156 ± 76 n/l) of Samuajan bed, a tropical floodplain lake of the Brahmaputra basin of Assam state, comprised an important component (53.5 ± 12.1 %) of net plankton (253 ± 132 n/l) and depicted trimodal annual pattern. Copepoda (67 ± 44 n/l) > Rotifera (54 ± 33 n/l) > Cladocera (20 ± 19 n/l) > Rhizopoda (14 ± 14 n/l) registered the stated order of quantitative abundance. Copepoda > Rotifera > Cladocera > Rhizopoda and Copepoda > Rotifera contributed to summer zooplankton peak and monsoon maxima respectively while Rotifera mainly resulted in their winter maxima. Further, Zooplankton depicted significant positive correlations with transparency, pH and phytoplankton and an inverse relationship with Chloride. The multiple regression indicated that ten ecological variables namely specific conductivity, pH, dissolved oxygen, transparency, free Carbon dioxide, total alkalinity, hardness, Chloride, net primary production and Potassium together accounted for > 99 % variations of net plankton and zooplankton. This study registered moderate species diversity, lower overall dominance and higher evenness. Remarks are made on abundance of net plankton, zooplankton, their constituent groups and on the relationships between various abiotic and biotic factors.