Aquatic Flora

Abstract

The ecology of alpine streams, in particular glacier-fed systems, has attracted major attention in the past few years (e. g., Brittain & Milner, 2001; Castella et al., 2001; Milner et al., 2001; Milner & Petts, 1994; Robinson et al., 2001; Ward, 1994). There exists, however, surprisingly little information on algal communities in alpine and glacial streams (e. g., Elster & Svoboda, 1996; Hieber et al., 2001; Kawecka, 1980; Kownacki et al., 1997; Vavilova & Lewis, 1999). Alpine streams, especially those fed by glaciers, are harsh environments for aquatic autotrophs. Light availability is reduced by an extended period of snow cover and attenuation by glacial flour; essential nutrients typically occur in low concentrations; low temperatures eliminate all but cold-adapted taxa; suspended sediment and ice action scour surfaces; and dramatic flow fluctuations result in desiccation and unstable substratum. Rooted macrophytes are absent or poorly represented. Allochthonous organic matter input, so important in forested headwaters, is limited in glacial-fed streams (see Chapter 12; Milner & Petts, 1994; Ward, 1994). The major energy base of alpine streams is normally restricted to benthic algae and mosses. Although mosses may be abundant in some alpine streams (Ward, 1994), they were not encountered in the glacial flood plain of the Val Roseg, even in groundwater sources. This chapter therefore, deals exclusively with benthic algae.