Nicola Deluigi | EPFL Graph Search

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

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

Glacier shrinkage will accelerate downstream decomposition of organic matter and alters microbiome structure and function

Tom Ian Battin, Massimo Bourquin, Jade Brandani, Susheel Bhanu Busi, Vincent Henri De Staercke, Nicola Deluigi, Leïla Ezzat, Stylianos Fodelianakis, Tyler Joe Kohler, Grégoire Marie Octave Edouard Michoud, Hannes Markus Peter, Paraskevi Pramateftaki, Martina Andrea Schön, Michail Styllas, Matteo Tolosano

The shrinking of glaciers is among the most iconic consequences of climate change. Despite this, the downstream consequences for ecosystem processes and related microbiome structure and function remain poorly understood. Here, using a space-for-time substitution approach across 101 glacier-fed streams (GFSs) from six major regions worldwide, we investigated how glacier shrinkage is likely to impact the organic matter (OM) decomposition rates of benthic biofilms. To do this, we measured the activities of five common extracellular enzymes and estimated decomposition rates by using enzyme allocation equations based on stoichiometry. We found decomposition rates to average 0.0129 (% d−1), and that decreases in glacier influence (estimated by percent glacier catchment coverage, turbidity, and a glacier index) accelerates decomposition rates. To explore mechanisms behind these relationships, we further compared decomposition rates with biofilm and stream water characteristics. We found that chlorophyll-a, temperature, and stream water N:P together explained 61% of the variability in decomposition. Algal biomass, which is also increasing with glacier shrinkage, showed a particularly strong relationship with decomposition, likely indicating their importance in contributing labile organic compounds to these carbon-poor habitats. We also found high relative abundances of chytrid fungi in GFS sediments, which putatively parasitize these algae, promoting decomposition through a fungal shunt. Exploring the biofilm microbiome, we then sought to identify bacterial phylogenetic clades significantly associated with decomposition, and found numerous positively (e.g., Saprospiraceae) and negatively (e.g., Nitrospira) related clades. Lastly, using metagenomics, we found evidence of different bacterial classes possessing different proportions of EEA-encoding genes, potentially informing some of the microbial associations with decomposition rates. Our results, therefore, present new mechanistic insights into OM decomposition in GFSs by demonstrating that an algal-based “green food web” is likely to increase in importance in the future and will promote important biogeochemical shifts in these streams as glaciers vanish.

Wiley2022

Response of alpine stream biofilms to climate change induced stressors

Tom Ian Battin, Nicola Deluigi, Grégoire Marie Octave Edouard Michoud, Hannes Markus Peter, Paraskevi Pramateftaki

Alpine streams are expected to face an intensification of environmental stressors due to climate change. At the vanishing cryosphere interface, alpine streams are particularly susceptible to increasing temperatures and to changing hydrology. As biofilms are the dominant form of microbial life in alpine streams, monitoring their microbial composition changes due to environmental stressors would inform on how alpine streams respond to climate change. In this study, we designed a flume set-up using water from an alpine stream to directly grow biofilms under hydrological and temperature stressors. Biofilms were grown on clay coupons in flumes under four different flow regimes and two temperatures, as follow: a natural flow reproducing the natural flow events of the alpine stream, a constant flow, a purely stochastic flow, and an intermittent flow with zero-flow days and peak flows, all at the in situ stream temperature or at 2ºC warmer. This represented eight different flow/temperature conditions, each in triplicate. This setup was repeated over to summers, where biofilms were harvested from the coupons for DNA extraction, for bacterial abundance and chlorophyll A quantification, to evaluate the community composition of each flow/temperature conditions over time. Preliminary results suggest that time is the main driver of changes in the microbial community, and is responsible for an increase in bacterial abundance, chlorophyll A concentration and alpha diversity. However, the intermittent flow regime had a significant impact on the microbial composition, while the other flows did not induce changes: drought decreased the bacterial and algal abundance and the alpha diversity, promoted the colonization by members of the Hymenobacter and Massilia genus, while decreased the representation of the Luteolibacter genus. Further analyses will be used to identify the sentinel taxa, ie. taxa driving the phylogenetic turnover in communities, using the “community assembly” and the “phyloscore analysis” frameworks.

2022