Results of the Austrian-Ceylonese hydrobiological mission 1970 of the 1st Zoological Institute of the University of Vienna (Austria) and the Department of Zoology of the Vidyalankara University of Ceylon, Kelaniya. Pt. 1. Preliminary report: introduction and description of the stations

The Austrian-Ceylonese hydrobiological mission of 1970 investigated and made collections from 36 flowing water systems (brooks, torrents, rivers); of these, 34 water systems were in the mountains regions of south-west and south-east of Sri Lanka. In the crystalline mountain region, the water systems are extremely poor in electrolytes, very soft and slightly acid; these torrential streams have strong falls, high flow velocities and boulder bottoms. The water temperatures increase from the sources and brooks at 2,000 m altitude to the mouths from 15°C to 28°C. The density of animal population (macro and meso-fauna) increases from the river bank regions (and pools) towards the sections with strong current and reaches on the rocks in the cascades a density of 500 to appr. 750 individuals/1/16m².