Planktonic scenario of tributaries of the river Ganga in upper stretch

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River Nayar, River Havel and River Balganga are small but important tributaries of river Ganga in its upper stretch. Their water quality and planktonic structure influence biodiversity of river Ganga and may play important roles in biodiversity conservation of valuable fauna and flora of these small rivers. Water of all these tributaries revealed high dissolved oxygen (7.3 - 10 mg L-1), very low BOD (0.4 - 2.4 mg L-1), high current velocity (0.6 - 1.7 m s-1). High silica content of the tributaries was reflected in diatom abundance anddiversity. Plankton population was dominated by diatoms only and no zooplanktonwere recorded. Plankton abundance ranged between 80-1250 u L-1 in Balganga with 15 genera, *140-1290 u L-1 in Havel with 14 genera and 1290-8010 u L-1 in Nayar with 28 genera. In river Nayar plankton population contributed to only three algal groups, viz. Bacillariophyceae, Chlorophyceae and Myxophyceae, which ranged from 45.7 - 97.8%, 1.5 - 54.2% and 0.6 - 2.2 %, respectively. River Havel and river Balganga depicted diatoms as planktonic flora. River Nayar exhibited maximum planktonic diversity followed by river Havel and Balganga. Dominant taxa in summer season were Asterionella, Cymbella, Melosira (diatoms) Spirogyra, Ankistrodesmus, Cosmarium (green algae) andPhormidium (blue green). Dominant taxa in monsoon were Microspora, Pinnularia, Tabellaria and Cymbella. Winter taxa were Tryblionella, Navicula, Melosira, Tabellaria, Denticula, Diatoma and Eunotia. River Nayar may be considered as Hotspot for phytoplankton diversity conservation as physical condition of river is suitable for diatom growth and species richness. River Havel is influenced by tourist activity/ anthropogenic effects, as reflected by higher TDS and specific conductivity but Balganga is havingclear water. Periphytic populations in Balganga, Nayar and Havel were maximum in winter followed by summer and monsoon, and dominated by various species of small diatoms like Eunotia, Cymbella, Navicula and Gomphonema.