Aquatic Biodiversity Unit, Department of Zoology, H. N. B. Garhwal (Central) University, Srinagar 246174, India


*Corresponding author: pn.mahseer@yahoo.com

Abstract

   The river ecosystems from the headwaters to the foothills in the upper mountain reach of the Ganga (Bhagirathi River) were characterized by increasing temperature, pH, total alkalinity, nutrient and BOD and decreasing current velocity, turbidity and DO. The biotic communities included benthos (phytobenthos, zoobenthos) and nekton (fish). The headwaters at Gangotri were heterotrophic and lacked fish (both grazers and predators). Functionally, the detritus and grazing chains operate in headwaters of the upper Ganga. The food chain was short and the web simple. In the middle and lower stretches, the macroinvertebrate assemblages functioned as filtering collectors and scrapers, representing detritus and grazing food chains. The abundance of scrapers indicated transition from heterotrophic to autotrophic state. The food chains and the food web became complex from the middle to lower stretches.