Make-over in Phytoplankton Community during Lake Enrichment

The present memoir deals with the upshot of nutrient enrichment on inland waters. Small level functional ecosystems were developed in laboratory by inoculating quantum sufficit of water, soil and planktonic flora. Of some hundred nutrients known to cause eutrophication, five (Ca, Mg, K, N, P) were selected for present study. Different dosages of these nutrients were administered separately and their impact on free floating plant life was assessed, in terms of species diversity, density and relative growth, over a period of one month. Results were suggestive of the fact that algal strains flourished well upto a definite concentration of nutrients (Ca=101.6; Mg=31.0; K=95.0; TKN=49.4; TP= 10.0), beyond which the microcosmal water could not sustain planktonic life except for certain eutrophic taxa viz. Anabaena ornaldii, Microcystis aeruginosa and Oscillatoria amphigranulata. Exposure to nutrients not only checked the development of Chlorophyceae during colonization but also initiated major shifts in the sociology of phytoplankton after a short time. Supply of nutrients upto 5 mg/l concentration did not affect the vegetation significantly, however, further enrichment largely supressed the inland water dominants i.e, Chlorophytes. Conditions, similar to controlled ones, prevailed in treated microcosms too, but for those treated with 10 mg/l and 15 mg/l of nutrients where blue-green forms dominated at the cost of prevailing green algae. In all cases, Crucigenia crucifera, C. rectangularis, Scenedesmus abundans (UL & LL), S. bijugatus, S. dimorphus (UL, LL & SL), Characiopsis longipes, Crucigenia quadricauda and Scenedesmus armatus (SL) registered their presence for most of the period whereas, certain strains viz. Ankistrodesmus falcatus, Scenedesmus obliques, S. parisiensis, S. quadricauda, Amphora ovalis (UL), Eudorina elegans, Oocystis crassa, Staurastrum gracile, S. orbicularae, Tetraedron minimum, Cosmarium granatum (LL), Coelastrum microporum, Pediastrum tetras and Selanastrum gracile (SL) could not withstand the nutritional changes and perished earlier