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Glacier loss and vegetation expansion alters organic and inorganic carbon dynamics in alpine streams

Tom Ian Battin, Nicola Deluigi, Andrew Lean Robison, Camille Aude Rolland

High-mountain ecosystems are experiencing acute effects of climate change, most visibly through glacier recession and the ‘greening’ of the terrestrial environment. The streams draining these landscapes are affected by these shifts, integrating hydrologic, geologic, and biological signals across the watershed. We examined the organic and inorganic carbon dynamics of streams in four Alpine watersheds in Switzerland to assess how glacier loss and vegetation expansion are affecting the carbon cycle of these high mountain ecosystems. We find that organic carbon concentration and fluorescence properties associated with humic-like compounds increase with vegetation cover within a catchment, demonstrating the increasing importance of allochthonous carbon sources following glacier retreat. Meanwhile, streams transitioned from carbon dioxide sinks to sources with decreasing glacier coverage and increasing vegetation coverage, where the relative importance of chemical weathering and soil respiration likely determine the balance. Periods of sink behavior were also observed in non-glaciated streams, possibly indicating carbon dioxide uptake as a result of chemical weathering could be more common in high-mountain, minimally vegetated environments than previously known. Together, these results demonstrate the dramatic shift in carbon dynamics of alpine streams following glacier retreat, with significant changes to both the organic and inorganic carbon cycles. The clear link between the terrestrial and aquatic zones further emphasizes the coupled dynamics with which all hydrologic and biogeochemical changes in these ecosystems should be considered.

2022

Leveraging species distribution models to predict the impact of climate change on glacier-fed stream biofilms

Tom Ian Battin, Massimo Bourquin, Susheel Bhanu Busi, Leïla Ezzat, Stylianos Fodelianakis, Tyler Joe Kohler, Grégoire Marie Octave Edouard Michoud, Hannes Markus Peter, Andrew Lean Robison

Owing to climate changes, glaciers and ice sheets are rapidly shrinking worldwide, altering the geophysical properties of many ecosystems. In this context, glacier-fed streams are expected to undergo major physical and chemical modifications in the future. Lying at the glacier forefront, glacier-fed streams host a diverse, yet poorly characterised, microbial diversity. Bacteria form biofilms, along with eukaryotic algae, that develop on the streambed during the melting season and represent a major component of life in this ecosystem, even driving biogeochemical fluxes of global relevance. However, little is known about the microbes that form these biofilms, and how climate changes will impact them. The Vanishing Glaciers Project aims at unravelling the microbial life inhabiting glacier-fed streams at a global scale, coupling amplicon sequencing and metagenomics with measurements of glaciological and biogeochemical parameters. To predict the impact of climate change on the glacier-fed stream microbiome, we will use a species distribution modelling approach. First, we will use the parameters measured in this project along with climatic and geographical data to model the abundance of key bacterial taxa. Subsequently, we will use climatic and glaciological parameters to model biogeochemical parameters, and applying predictions of future scenarios of climate change, we will understand how the glacier-fed stream ecosystem will be altered by glacier retreat. Finally, we will use the distribution models and project them onto to these future scenarios, enabling us to understand how the distribution of the main bacterial taxa forming glacier-fed stream biofilms will be impacted by climate changes.

2022

Predicting the impact of climate change on the glacier-fed streams microbiome

Tom Ian Battin, Massimo Bourquin, Susheel Bhanu Busi, Leïla Ezzat, Stylianos Fodelianakis, Tyler Joe Kohler, Grégoire Marie Octave Edouard Michoud, Hannes Markus Peter, Andrew Lean Robison

Glacier shrinkage is among the most conspicuous impacts of climate change with numerous effects on downstream ecosystems. Lying at the glacier forefront, glacier-fed streams represent important headwaters in high-mountain regions across the world. Owing to climate change, the latter are predicted to undergo major physical and chemical modifications as the glaciers recede, potentially inducing important ecological shifts. In the glacier-fed streams ecosystem, bacteria play a key role, forming biofilms along with eukaryotic algae in the sediments, and driving biogeochemical fluxes of global relevance. However, little is known about the glacier-fed stream microbiome and how climate change will impact it. To unravel and understand the glacier-fed stream ecosystem, the Vanishing Glaciers Project aims at characterising its global microbiome by sequencing metagenomes, coupled with glaciological and biogeochemical parameters measurements. To predict the impact of climate change on the glacier-fed streams microbiome, we will characterise the geophysical parameters affecting the distribution of bacterial amplicon sequence variants using a species distribution modelling approach. Using climatic, glaciological and biogeochemical parameters, we will model the abundance of the most prevalent amplicon sequence variants at a global scale. We will then leverage glaciological and climatic future scenarios of climate change to model the evolution of biogeochemical parameters and how they will be impacted. Importantly, this approach will allow us to project the species distribution models onto these future scenarios to predict how key bacterial taxa and lineages will be affected by climate change.

2022