Conclusion
The rapid retreat of glaciers in mountain catchments (Sommer et
al. , 2020; Hugonnet et al. , 2021) is causing significant changes
in the hydrological and geomorphological characteristics of downstream
rivers (Milner et al. , 2017). Besides the well-studied effects on
invertebrates, especially cold-water specialists, the impacts on primary
producers are only partly understood (e.g., Niedrist et al. ,
2018; Fell et al. , 2018). This study focused on quantifying the
regulation of periphyton biomass and the composition by glacial
contribution, expanding our understanding of glacier loss on primary
production in these rapidly transforming headwaters. We revealed that
reduced glacial influence leads to ameliorated habitat conditions
favoring periphyton growth, with higher biomass content observed in less
glaciated catchments. Thereby, reductions in sediment load have been
identified most beneficial for periphyton growth, whereas summer water
temperature alone may not be the limiting factor for periphyton growth
in these systems. Given the regulatory role of sediment for biota in
glacier-fed rivers, predictions of sediment dynamics are crucial for
understanding future habitat developments in mountain streams. However,
developing such predictive models requires data from diverse glacial
streams with varying topographical characteristics. Therefore, we
recommend a collaborative approach that utilizes existing data from
observed glacial streams to improve the accuracy of predictions.
Additionally, the colonization and establishment of groups previously
underrepresented in highly glaciated catchments, such as cyanobacteria,
are promoted by the reduced glacial influence. This study also
highlights the importance of quantifying periphyton biomass using
ash-free dry mass, even in slightly turbid rivers, since sediments might
blur the estimations using dry mass only. Overall, this research
contributes to our understanding of the complex interactions between
glacier retreat, periphyton communities, and their habitats in mountain
rivers, emphasizing the need for collaborative efforts and further
investigation to predict future habitat developments in the face of
ongoing glacier loss across the globe.