Glacier melt-down changes habitat characteristics and unique microbial community composition and physiology in alpine...

Glacial melt-down alters hydrological and physico-chemical conditions in downstream aquatic habitats. In this study, we tested if sediment-associated microbial communities respond to the decrease of glaciers and associated meltwater flows in high-alpine lakes. We analyzed 16 lakes in forefield catchments of three glaciers in the Eastern Swiss Alps on physico-chemical and biological parameters. We compared lakes fed by glacier meltwater with hydrologically disconnected lakes, as well as "mixed" lakes that received water from both other lake types. Glacier-fed lakes had a higher turbidity (94 NTU) and conductivity (47 µS/cm), but were up to 5.2°C colder than disconnected lakes (1.5 NTU, 26 µS/cm). Nutrient concentration was low in all lakes (TN < 0.05 mg/l, TP < 0.02 mg/l). Bacterial diversity in the sediments decreased significantly with altitude. Bacterial community composition correlated with turbidity, temperature, conductivity, nitrate, and lake age and was distinctly different between glacier-fed compared to disconnected and mixed water lakes, but not between catchments. Chemoheterotrophic processes were more abundant in glacier-fed compared to disconnected and mixed water lakes where photoautotrophic processes dominated. Our study suggests that the loss of glaciers will change sediment bacterial community composition and physiology that are unique for glacier-fed lakes in mountain and polar regions.