GLACIAL RIVERS - PHYSICAL HABITAT AND ECOLOGY

1. This review examines the physical habitat and ecology of glacial ri vers which have been relatively unstudied compared with rivers origina ting from other sources. 2. Typical glacial rivers have summer tempera tures below 10 degrees C, a single seasonal peak in discharge, which i n the Northern Hemisphere typically occurs in July, a diel fluctuation in flow which usually peaks in late afternoon, and turbidity levels i n summer that exceed 30 NTU. These variables contrast with those in sn owmelt/rainfall streams, particularly in summer, and make conditions m ore extreme for the biota. 3. Where maximum temperatures are less than or equal to 2 degrees C benthic invertebrate communities are dominate d by Diamesa (Chironomidae). Downstream, temperatures increase, channe ls become more stable and valley floors become older. Orthocladiinae ( Chironomidae), Simuliidae, Baetidae, Nemouridae and Chloroperlidae bec ome characteristic members of the invertebrate community. 4. Fauna may be displaced, or at least colonization delayed, by channel instabilit y; the variable age structure of the valley floor will influence the f aunal gradient, which may also be reset by the effects of tributaries, lakes and valley confinement. 5. We propose a qualitative model that outlines zoobenthic community gradients determined by two principal va riables, water temperature and channel stability, as a function of dis tance downstream, or time since deglaciation.