Biogéochimie

Résumé

vignette|Biogeochimie La biogéochimie est l'étude du processus cyclique de transfert des éléments chimiques de l'environnement à partir des milieux abiotiques vers les organismes qui à leur tour retransmettent ses constituants à l'environnement. (Traduction française de l'article d'Odum, 1971) Cette notion a été « inventée » par le savant russe Vladimir Vernadski. Différentes analyses moléculaires permettent de qualifier le caractère biogéochimique de la matière organique comme l'analyse des sucres, des lipides, des phénols de la lignine. La quantification de ces molécules permet d'apprécier l'activité biologique dans différents milieux géologiques (tourbes, sédiments, sols forestiers, eaux de nappe, de lacs...). Exemples en archéologie La concentration dans le sol en espèces chimiques issues de l'urine a ainsi été utilisée pour la première fois en 2019 pour étudier le site préhistorique d'Aşıklı Höyük, et plus particulièrement le nombre d'individus et de têtes de bétail

Source officielle

https://fr.wikipedia.org/wiki/Biog%C3%A9ochimie

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Surface-groundwater interactions in intermittent rivers and ephemeral streams (IRES), waterways which do not flow year-round, are spatially and temporally dynamic because of alternations between flowing, non-flowing and dry hydrological states. Interactions between surface and groundwater often create mixing zones with distinct redox gradients, potentially driving high rates of carbon and nutrient cycling. Yet a complete understanding of how underlying biogeochemical processes across surface-groundwater flowpaths in IRES differ among various hydrological states remains elusive. Here, we present a conceptual framework relating spatial and temporal hydrological variability in surface water-groundwater interactions to biogeochemical processing hotspots in IRES. We combine a review of theIRES biogeochemistry literature with concepts of IRES hydrogeomorphology to: (i) outline common distinctions among hydrological states in IRES; (ii) use these distinctions, together with considerations of carbon, nitrogen, and phosphorus cycles within IRES, to predict the relative potential for biogeochemical processing across different reach-scale processing zones (flowing water, fragmented pools, hyporheic zones, groundwater, and emerged sediments); and (iii) explore the potential spatial and temporal variability of carbon and nutrient biogeochemical processing across entire IRES networks. Our approach estimates the greatest reach-scale potential for biogeochemical processing when IRES reaches are fragmented into isolated surface water pools, and highlights the potential of relatively understudied processing zones, such as emerged sediments. Furthermore, biogeochemical processing in fluvial networks dominated by IRES is likely more temporally than spatially variable. We conclude that biogeochemical research in IRES would benefit from focusing on interactions between different nutrient cycles, surface-groundwater interactions in non-flowing states, and consideration of fluvial network architecture. Our conceptual framework outlines opportunities to advance studies and expand understanding of biogeochemistry in IRES.

2021

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Snow cover manipulation effects on microbial community structure and soil chemistry in a mountain bog

Luca Bragazza, Alexandre Buttler, Vincent Eric Jules Jassey, Bjorn Jozef Maria Robroek

Alterations in snow cover driven by climate change may impact ecosystem functioning, including biogeochemistry and soil (microbial) processes. We elucidated the effects of snow cover manipulation (SCM) on above-and belowground processes in a temperate peatland. In a Swiss mountain-peatland we manipulated snow cover (addition, removal and control), and assessed the effects on Andromeda polifolia root enzyme activity, soil microbial community structure, and leaf tissue and soil biogeochemistry. Reduced snow cover produced warmer soils in our experiment while increased snow cover kept soil temperatures close-to-freezing. SCM had a major influence on the microbial community, and prolonged 'close-to-freezing' temperatures caused a shift in microbial communities toward fungal dominance. Soil temperature largely explained soil microbial structure, while other descriptors such as root enzyme activity and pore-water chemistry interacted less with the soil microbial communities. We envisage that SCM-driven changes in the microbial community composition could lead to substantial changes in trophic fluxes and associated ecosystem processes. Hence, we need to improve our understanding on the impact of frost and freeze-thaw cycles on the microbial food web and its implications for peatland ecosystem processes in a changing climate; in particular for the fate of the sequestered carbon.

Springer Netherlands2013

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Wetlands occupy the transitional zone between aquatic and terrestrial systems. Hydrological conditions have significant influence on wetland plant communities and soil biogeochemistry. However, our knowledge about plant-soil interactions in wetlands along hydrological gradients is still limited, although it is crucial to guide wetland management decisions and to adapt, whenever possible, hydrological conditions to the different plant communities. To this aim, we related vegetation composition, plant functional traits, soil physicochemical properties, soil microbial biomass, and soil enzymatic activities in wetlands on the southeastern shore of Neuchatel lake, Switzerland, a lake whose level is partly regulated. Aboveground and belowground plant biomass and correspondent C, N and P concentrations remained constant or decreased moving from the vegetation community subjected to more frequent flooding events to the community with almost no flooding. The soil organic layer exhibited always higher nutrient concentrations and greater enzymatic activities than the organo-mineral and mineral layers. The chemical and biological characteristics of the soil organic layer showed decreasing values for most of the parameters along the hydrological gradient from lakeshore to upland wetland communities. On the basis of nutrient stoichiometiy, plant-soil system in the plant community with most flooding events had no-nutrient limitation, while there was a N limitation in the transitional community. In the upland plant community where there was no flooding effect, the plant-soil system was characterized by N and P co-limitation. These findings are important because they provide a threshold for flooding regime by the lake in the context of optimization of lake level regulation under various stakeholders needs. (C) 2020 Elsevier B.V. All rights reserved.

ELSEVIER2020

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2021