Spatio-temporal variation in macroinvertebrate assemblages of glacial streams in the Swiss Alps

1. Changes in water chemistry, benthic organic matter (BOM), and macroinvertebrates were examined in four different glacial streams over an annual cycle. The streams experienced strong seasonal changes in water chemistry that reflected temporal changes in the influence from the source glacier, especially in water turbidity, particulate phosphorus and conductivity. 2. Nitrogen concentrations were high (nitrate-N values were 130-274 mug L(-1)), especially during spring snowmelt runoff. Benthic organic matter attained >600 g m(-2) dry mass at certain times, peaks being associated with seasonal blooms of the alga Hydrurus foetidus. 3. Macroinvertebrate taxon richness was two to three times higher (also numbers and biomass) in winter than summer suggesting winter may be a more favourable period for these animals. Benthic densities averaged 1140-3820 ind. m(-2), although peaking as high as 9000 ind. m(-2). Average annual biomass ranged from 102 to 721 Mg m(-2), and reached >2000 mg m(-2) at one site in autumn. 4. Taxa common to all sites included the dipterans Diamesa spp. and Rhypholophus sp., the plecopterans Leuctra spp. and Rhabdiopteryx alpina, and the ephemeropterans Baetis alpinus and Rhithrogena spp. Principal components analysis clearly separated winter assemblages from those found in summer.