Aquatic life: selection under extreme conditions

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PLANTS AND LIFE PROCESSES

Alpine streams

In contrast to streams at lower elevations, alpine streams are rather cold. The substratum is predominantly bedrock, boulder and cobble, and the surrounding vegetation is sparse or absent. Therefore, leaf litter which is a major energy source in forested mountain streams is negligible in alpine streams.
The often high altitudinal gradients of alpine headwaters lead to high current velocities and turbulent and well oxygenated water.

1 - Alpine stream types and their major water sources (from Hieber et al. 2002)

There are three primary types of alpine streams which differ in abiotic conditions: kryal streams are fed by glacial meltwater, rhithral headwaters are fed mainly by rain and snowmelt runoff, krenal streams have ground water sources.

2 3 4

Idealized features of alpine stream types (adapted from Ward 1994)
	Kryal	Rhithral	Krenal
Annual degree days	<500	500-1000	>1000
Annual temperature range	0-4 °C	0-10 °C	>0 to <9 °C
Transparency	clear or turbid	clear,except during snowmelt	clear
Flow regime	diel fluctuations	seasonal fluctuations	±constant
Microphytes	sparse diatoms or none	diverse diatoms and algae	diverse diatoms and algae
Macrophytes	Hydrurus foetidus	moss, H. foetidus	moss, H. foetidus
Zoobenthos	stenozonal headwater species	euryzonal mountain fauna at upper altitudinal limits	kryal and rhithral elements
Fish fauna	absent	regionally variable	?

Alpine floodplains often consist of a mixture of different streamtypes, therefore providing various habitats and ecological niches.

29 August 2011 © ALPECOLe 2002-2007