1. Glacial retreat, accompanied by shifts in riparian vegetation and glacier meltwater inputs, alters the energy supply and trophic structure of alpine stream food webs. Our goal in this study was to enhance understanding of dietary niches of macroinvertebrates inhabiting different alpine streams with contrasting glacial and non-glacial (groundwater, precipitation, snowmelt) water inputs in conjunction with seasonal and habitat-specific variation in basal resource availability.  

2. We measured a range of stream physico-chemical attributes as well as carbon and nitrogen isotopes (δ¹³C, δ¹⁵N) of macroinvertebrates and primary food sources at seven sites across seasons within a Swiss glaciated catchment (Val Roseg) undergoing rapid glacial retreat (1-2 km between years 1997–2014). Sampling sites corresponded to streams used in a previous (1997/1998) study within the same alpine catchment.

3. Physico-chemical attributes showed wide variation in environmental conditions across streams and seasons. Significant correlation among physico-chemical proxies of glacier meltwater (P-PO₄^3-, TIC, conductivity, turbidity) and macroinvertebrate δ¹³C, δ¹⁵N and SEA_c (a proxy for feeding niche width) values showed that the extent of glacial water input shapes the energy base among alpine streams. Feeding niche differences among common alpine stream insect taxa (Chironomidae, Baetidae, Heptageniidae) were not significant, indicating that these organisms likely are plastic in feeding behaviour, opportunistically relying on food resources available in a particular stream and season.

4. Seasonal trends in macroinvertebrate δ¹³C largely followed patterns in periphyton δ¹³C values, indicating that autochthonous resources were the main consumer energy source within the stream network, as shown previously. The overall range in macroinvertebrate δ¹³C (-33.5 to -18.4 ‰) and δ¹⁵N (-6.9 to 6.7 ‰) values also corresponded to values measured in the previous study, suggesting that macroinvertebrates altered diets in line with changes in environmental conditions and food resources during a period of rapid glacial retreat. Our results suggest that environmental changes brought on by rapid glacial retreat have not yet caused a profound change in the trophic structure within these fluvial networks.

INVERTS

Excel file showing bulk delta13C and delta15N isotope values from macroinvertebrates collected in different channel types (lake outlet, main channel, proglacial and tributary) within the Val Roseg glacial floodplain (Switzerland), during November 2013 – July 2014. Other columns include taxonomic and functional information about each sample that was analysed for isotopes, and the site name, channel type, sampling date, month and season.

SOURCES

Excel file showing bulk delta13C and delta15N isotope values from food source materials collected in different channel types (lake outlet, main channel, proglacial and tributary) within the Val Roseg glacial floodplain (Switzerland), during November 2013 – July 2014. Other columns include the detailed description of the resource, the classification of the resource in terms of CPOM, FPOM, periphyton and riparian vegetation, and the site name, channel type, sampling date, month and season.