Alpine glacier-fed river hydrology, chemistry, and biology can vary significantly in space and over diurnal to interannual time scales as a function of dynamic inputs of water from snow, ice, and ground water. The sensitivity of biota to these water-source dynamics potentially makes them susceptible to hydrological changes induced by anthropogenic activities, such as flow regulation, but most alpine studies have been focused on intact rivers during summer only. We examined the spatiotemporal dynamics of physicochemical habitat and macroinvertebrate assemblages in a high-altitude (> 2000 m) floodplain in the European Alps over an 18-mo period. We present a novel insight into the river system and macroinvertebrate assemblage responses to natural glacier-melt-driven expansion-contraction of unregulated river sites and to intermittent flow pulses caused by hydropower regulation. Mainstem glacier-fed sites had cyclical seasonal dynamics in macroinvertebrate assemblage composition that shifted to be partly reminiscent of groundwater tributaries in winter then back to melt water in the following spring. Significant unimodal relationships were found between glacial influence and macroinvertebrate assemblage density, richness, Simpson's diversity, evenness, and beta diversity. These relationships suggest that glacial influence can positively affect biodiversity where glacier melt water mixes with nonglacial water and habitat diversity is maximized. Regulation-induced flow pulses led to inconsistent responses among macroinvertebrates, with no significant effects in summer 2008 but increased density and decreased taxonomic richness in 2009. Assemblage composition was unaffected by reservoir releases despite significant increases in water temperature and discharge at these times. The effects of alpine river management for hydropower production on macroinvertebrate assemblages in this river system appear to be relatively minor, but further studies should be undertaken in other alpine locations to assess the generality of this finding.

Quantification of contemporary geomorphological activity is a fundamental prerequisite for predicting the effects of future earth surface process and landscape development changes. However, there is a lack of high-resolution spatial and temporal data on geomorphological activity within alpine catchments, which are especially sensitive to climate change, human impacts and which are amongst the most dynamic landscapes on Earth. This study used data from repeated laser scanning to identify and quantify the distribution of contemporary sediment sources and the intensity of geomorphological activity within the lower part of a glaciated alpine catchment; Ödenwinkelkees, central Austria. Spatially, geomorphological activity was discriminated by substrate class. Activity decreased in both areal extent and intensity with distance from the glacier, becoming progressively more restricted to the fluvially-dominated valley floor. Temporally, geomorphological activity was identified on annual, seasonal, weekly and daily timescales. Activity became more extensive with increasing study duration but more intense over shorter timescales, thereby demonstrating the importance of temporary storage of sediment within the catchment. The mean volume of material moved within the proglacial zone was 4400 m3.yr− 1, which suggests a net surface lowering of 34 mm.yr− 1 in this part of the catchment. We extrapolate a minimum of 4.8 mm.yr− 1 net surface lowering across the whole catchment. These surface lowering values are approximately twice those calculated elsewhere from contemporary measurements of suspended sediment flux, and of rates calculated from the geological record, perhaps because we measure total geomorphological activity within the catchment rather than overall efflux of material. Repeated geomorphological surveying therefore appears to mitigate the problems of hydrological studies underestimating sediment fluxes on decadal–annual time-scales. Further development of the approach outlined in this study will enable the quantification of geomorphological activity, alpine terrain stability and persistence of landforms.

Impacts of anthropogenic flow regulation on the thermal regimes of alpine river systems are poorly understood. This is surprising given the importance of water temperature for river ecosystems and the widespread regulation of mountain rivers across the world. This study examined water temperature dynamics year-round between July 2008 and September 2009 in the Eisboden river system, central Austrian Alps. Water temperature data were examined alongside hydroclimatological data to infer the key processes driving thermal variability from diurnal to inter-annual scales. As expected, interactions between meteorology and water source controlled year-round thermal heterogeneity. However, water entering the proglacial river from a hydropower storage reservoir caused significant increases in water temperature during both late summer and early winter, resulting in a marked longitudinal thermal discontinuity. The timing and duration of flows discharged from reservoirs, and thus effects on river thermal regimes, differed considerably from previous studies of subalpine hydropeaking. Furthermore, thermal responses to flow regulation extended laterally to some groundwater tributaries even where there was no upstream surface connectivity, suggesting significant hyporheic flow or conduction of heat through coarse alluvium. River water temperature continued to be altered even after reservoir releases had ceased due to the removal of winter snow cover and recharged groundwater sources. Together, these insights into the thermal variability have broad implications for conservation and management of alpine river systems because water temperature is a key variable influencing aquatic ecosystems, and because anthropogenic pressures on alpine environments are expected to grow in the future.