Glacier Retreat Effects On Ecosystem Development And Carbon Dynamics

Abstract

One of the clearest indicators of global warming is the retreat of Alpine glaciers. Organisms rapidly colonize bare ground free from ice, and in less than a century complex ecosystems can develop in a process of primary succession, where community changes as terrain age increases and interactions within species change over time. When glaciers retreat the resulting ice-free soil is exposed to new forms of chemical and biological weathering, with initiating soil formation as an important driver of evolving ecosystems. Soils play an important role in the global carbon (C) cycle, serving as the largest reservoir of carbon. CO2 is removed from the atmosphere by plant photosynthesis, then stored in biomass and soils, and released again to the atmosphere via plant and soil respiration. Soil respiration includes CO2 production by heterotrophic soil organisms (e.g., bacteria, fungi, invertebrates) that metabolize plant litter and soil organic matter, and autotrophs (e.g. plant roots). However, little is known about the development of soils, their physico-chemical changes, and their influence on plant diversity and soil carbon emission (CO2) after glacier retreat. This study aims to investigate how the retreat of the Mont Mine and Ferpecle glaciers (Valais Alps, Switzerland) influences soil functioning and vegetation development. For this purpose, we carried out soil analyses and vegetation surveys on 5 ice-free stages deglaciated between 1864 and 2023. Soil physico-chemical properties (pH, soil organic matter, organic carbon and nitrogen, granulometry, available elements, total elements), soil CO2 respiration fluxes, and plant communities (composition, diversity, richness, biomass) were studied in 20 plots along the glacier forefield. Our results show that vegetation develops according to the principles of primary succession, going further from glacier front: from pioneer vegetation 7 years after glacier retreat, progressing through early vegetation at 20 years, then to intermediate vegetation, and ultimately culminating in a climax coniferous forest, 140 years after glacier retreat. Over 140 years, the increase in vegetation productivity results in a greater transfer of organic matter (SOM) to the soil, which increases organic carbon, nitrogen, and nutrient levels, and decreases pH values as it releases organic acids. Aboveground plant biomass (i.e. carbon storage) increases over the succession, however, plant diversity and richness peak at the intermediate stages and then level off due to the dominance of few species in the late stages. At the intermediate stage, there is also a peak observed in soil respiration (CO2 flux), which in turn promotes plant colonization and diversity. Thus, the soil, along with its development stages and properties, plays a critical role in carbon accumulation, leading to an increased potential for carbon release as organic matter storage increases. This project aims to contribute to the understanding of the consequences of global warming on recently deglaciated ecosystems, which remain still poorly overlooked.