1. Physico‐chemical conditions and benthic macroinvertebrates were studied in two adjacent alpine streams in the Tyrolean Alps, Austria, for 2 years, and aquatic insect emergence was recorded for 1 year. 2. In the spring‐fed system, maximum discharge and increased concentrations of suspended solids, nitrate and particulate phosphorus occurred during snowmelt in June. In the glacier‐fed stream, high discharge and strong diel fluctuations in flow and concentrations of suspended solids created a harsh and unstable environment during summer. Glacial ablation, variation in groundwater inflow, and water inputs from tributaries draining calcareous rocks caused water chemistry to vary both seasonally and longitudinally in glacier‐fed Rotmoosache. 3. A total of 126 aquatic or semi‐aquatic invertebrate taxa were collected, 94 of which were found in the glacier‐fed stream and 120 in the spring‐fed stream. Chironomid abundance was 2–8 times and taxa richness 2–3 times lower in the glacier‐fed stream than in the spring‐fed stream, as was the number of chironomid taxa (72 versus 93 total). 4. These results broadly support the conceptual model by Milner & Petts (1994) concerning glacier‐fed stream systems. However, single samples and seasonal means showed relatively high invertebrate abundance and richness, especially during winter, indicating a considerable degree of spatial and temporal variability. 5. We suggest that the seasonal shifts from harsh environmental conditions in summer to less severe conditions in autumn and a rather constant environment in winter are an important factor affecting larval development, life‐history patterns and the maintenance of relatively high levels of diversity and productivity in glacier‐fed streams.
1. Alpine streams above the tree line are covered by snow for 6–9 months a year. However, winter dynamics in these streams are poorly known. The annual patterns of macroinvertebrate assemblages were studied in a glacial stream in the Austrian Alps, providing information on conditions under the snow. 2. Snow cover influenced water temperature, the content of benthic organic matter and insect development. Taxa richness and abundance of macroinvertebrates did not show a pronounced seasonal pattern. The duration of the autumn period with stable stream beds was important in determining the abundance and composition of the winter fauna. 3. There were significant differences in species composition between summer and winter. Two potential strategies in larval survival were evident: adaptation to the extreme abiotic conditions in summer (e.g. Diamesa spp.) or avoidance of these conditions and development during winter (e.g. Ephemeroptera and Plecoptera). 4. A comparison of a stream reach with continuous snow cover and a stream reach that remained open throughout winter showed that conditions under snow are suboptimal. At the open stream site, with higher water temperatures and greater food supply (benthic organic matter content), abundance and taxa richness was higher and larval growth was faster. Several taxa were found exclusively at this site. 5. Winter conditions did not provide an entirely homogeneous environment, abiotic conditions changed rapidly, especially at the onset of snowfall and at snowmelt. Continuous monitoring is necessary to recognize spatial and temporal heterogeneity in winter environments and the fauna of alpine streams.
Prevailing water sources and/or regional climate are known to have an important influence on hydromorphology and chemistry of high alpine streams, affecting biology and phenology of aquatic insects considerably. Seven reaches in two different stream types (glacial and non-glacial) in the European Central Alps were investigated along a longitudinal gradient above the tree line to elucidate community structure and emergence patterns of aquatic insects. Aquatic insect emergence was dominated by chironomid taxa in both streams (95.0% in the glacial vs. 90.5% in the spring-fed stream). Emergence rate was much higher in the non-glacial stream, with Chironomidae 638.9 ind. m À2 d À1 and EPT (Ephemeroptera, Plecoptera, Trichoptera) 20.3 ind. m À2 d À1 (annual mean), compared to the glacial stream (Chironomidae 132 ind. m À2 d À1 and EPT 7.0 ind. m À2 d À1 ). Whereas, in the glacial stream a richer and more diverse species composition was found at lower elevations, emergence rate and emerging taxa numbers were higher at higher altitude in the non-glacial stream. Seasonal comparisons also showed a significant difference between the two streams. In the glacial stream maximum emergence was in April/May, whereas, in the nonglacial stream in July. A comparison with similar studies carried out in alpine streams showed that abundance and biomass of emerging insects were relatively low in the glacial stream. The continuous emergence throughout the summer is another example of insect life-cycle adaptation to the harsh environmental conditions in glacial streams: most likely, emergence during the warmer summer months, where the probability of experiencing favourable climate conditions on land is higher than for the rest of the year, was an evolutionary advantage for many glacial stream taxa.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.