Ecological characteristics of lake outlets in Alpine environments of the Swiss Alps

We examined the physical, chemical, and biological attributes of temporary and permanent lake outlets situated above treeline in the Swiss Alps. Surfa ce now in the temporary outlet streams ceased by mid-September. High discha rge in spring associated with snowmelt was an order of magnitude greater in the temporary outlets than in the permanent outlets. Periphyton biomass at tained 5-9x higher levels in the temporary sites than in the permanent site s by mid-summer. Although macroinvertebrate densities were similar between temporary and permanent sites, taxon richness was 2x greater in the permane nt outlets. Macroinvertebrate groups absent from temporary out lets include d Ephemeroptera, Plecoptera, Trichoptera, and long-lived dipterans such as Limoniidae and Tipulidae. The semi-terrestrial gastropod Galba truncatula c olonized the temporary lake outlets via the lake. Chironomidae, Oligochaeta and Simuliidae also were common and able to complete development in the te mporary lake outlets. Cladocera and Copepoda originating from the lakes att ained high abundances in some outlets regardless of being temporary or perm anent. The harsh Alpine environment in concert with intermittency were stro ng determinants of ecosystem properties in the temporary outlets. Regardles s of flow permanency, the lakes directly affected community dynamics of out lets by influencing physical and chemical properties, and providing colonis ts to outlet streams.