ABSTRACT
An investigation on the water quality and aquatic insect community of an oxbow lake (Phulbari anua) of south Assam, North-East India was carried out during February to April, 2010. Aquatic insect community of the oxbow lake was represented by 9 species belonging to 9 families and 4 orders during the study period. Order Ephemeroptera and Hemiptera were found to be dominant. Record of 5 species and 5 families from the order Hemiptera showed that this is the largest order in terms of aquatic insect diversity of the lake. Computation of dominance status of different species of aquatic insects of the lake based on Engelmann’s Scale revealed that Anisops lundbladiana and Cloeon sp. were eudominant in the system. The Shannon- Weiner’s Diversity Index (H’) and Shannon evenness values (J’) were found to range from 0.3-0.69 and 0.53 -0.97, respectively indicating perturbation of the system. Again in terms of physico-chemical properties of water the lake is in a satisfactory condition where all the parameters are well within the range of IS 10500. The DO values were found to range from 6.8 to14.8 mgl-1. Free CO2 fluctuated from 1 to 4.98 mgl-1 and nitrate in water ranged from 0.4 to 2.1 mgl-1. Margalef’s water quality index values of most of the samplings also indicated clean water condition of the lake. Correlation coefficient analyses of the environmental variables, aquatic insect diversity and density of the lake revealed that aquatic insect diversity of the lake is mainly governed by dissolved oxygen, nitrate, and free carbon dioxide.
ABSTRACT
A study was carried out in Chatla floodplain lake, Barak Valley, Assam, North East India on phytoplankton diversity, density and distribution in different seasons and their correlations with physico-chemical properties of water. A total of 34 phytoplankton taxa belonging to Chlorophyceae, Cyanophyceae, Bacillariophyceae and Euglenophyceae were recorded. Highest number of species was present in pre-monsoon (29) and lowest in winter (23). Members of Chlorophyceae were present in a reasonable number throughout the year while being most abundant in pre-monsoon and monsoon. Bacillariophycae and Cyanophyceae populations did not show much seasonal variation. Percentage composition of Euglenophyceae showed clear seasonal change, being most dominant in post monsoon, moderate in pre- monsoon and winter and nearly absent in monsoon. Total phytoplankton density showed highly significant positive correlation with transparency (p< 0.01) and significant positive correlation with total suspended solids, total hardness and calcium (p < 0.05). Shannon-Wiener diversity index (H/) value (2.66) was found to be the highest during pre-monsoon while the highest evenness (J/) value (0.89) was recorded during winter. Berger-Parker index of dominance (0.45) was highest in post- monsoon. Our study revealed that the growth of phytoplankton is governed by transparency, total suspended solids, calcium and total hardness. These types of studies are prerequisites for evolving fish culture programmes and management of water resources.
ABSTRACT
Red blooms of Euglena sp. in the floodplain wetland ecosystems of Barak Valley, Assam, India, were found to be induced by high concentrations of NH3-N, NO3, Fe, Mg and to some extent, PO4, Cu and Zn in their water. The trace elements were rapidly accumulated by the bloom organisms to high levels, whereby their concentrations in the water declined, leading to a collapse of the bloom, which tended to reappear as decomposition again led to the release of the nutrients. The bloom also harboured fairly high density of certain other algae and zooplankton, thereby acting as a sub-system within the wetland ecosystem. The bloom is non-toxic and is exploited as a fish food by the fish-farmers who artificially induce a bloom for augmenting the growth of surface-feeding species of fishes.