Active layer characteristics across a latitudinal gradient in Victoria Land (Continental Antarctica) as indicator of functional processes in permafrost environments and ecosystems

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Cannone, N. , Guglielmin, M. , Wagner, D. and Hubberten, H. W. (2004): Active layer characteristics across a latitudinal gradient in Victoria Land (Continental Antarctica) as indicator of functional processes in permafrost environments and ecosystems , XXVIII SCAR Meeting, Bremen, GermanyJuly 2004. .
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Soil analyses have been carried out in permafrost environment in Victoria Land, Continental Antarctica, in 9 sites, located along a latitudinal and geographical transect, covering 5 degrees (77° - 72°S). The samples have been collected in correspondence of long term monitoring sites within the network of the sensitive system permafrost-vegetation established for the assessment of climate change effects (Cannone and Guglielmin, 2003). Within each site the samples have been collected in different ecological and environmental conditions concerning active layer thickness, vegetation type and coverage, substrata, occurrence of glacial and periglacial features. In each site the vertical profile of the ground have been described and the samples have been collected within the active layer representing all the layers with visible differences regarding texture, structure and color.Organic C and N show specific patterns allowing to discriminate: a) vegetated vs unvegetated sites; b) among the unvegetated sites, ground with and without disturbance processes, mainly represented by frost heave and salt concrections. The barren grounds with frost heave and/or salt efflorescences show highest values of organic C and N. The highest value of organic C is associated to a buried gley horizon, and is compatible with the low rate of organic matter mineralization associated to the anaerobic environment producing this kind of layers. The vertical distribution of the measured parameters show regular patterns, with lower values at the surface, the maximum value at intermediate depth, and a decrease in the deeper parts of the profile. These depths are consistent with the values of active layer thickness characterizing the different sites.In the vegetated sites, organic C and N show different patterns related to the vegetation type and to their ecological requirements in terms of nutrient regime. The higher values are associated in particular with moss communities and with ground colonized by nitrophytic epilithic lichens. On inundated grounds the content of both organic C and N show an increase respect to sites located in the close nearby and with a similar vegetation occurring. This fact indicates the lower speed of mineralization processes of the organic substances and a tendency to peat production and accumulation. The vertical distribution of both organic C and N show two different patterns: a) the same pattern characterising the unvegetated sites, with the maximum values occurring at intermediate depth; b) a different accumulation rate, with the highest values associated to the more surficial layers and a progressive decrease with depth. The former one is typical of vegetation composed by lichens, indipendently from their growth form. The latter pattern is typical of moss communities developing directly on the ground and indicates that the greatest part of the organic substances is strictly associated to these living organisms. These patterns, as well as those associated to disturbance processes in the unvegetated sites, are highly susceptible of significant variations in response to climate change effects. Therefore, it is essential to include their analysis within the monitoring activities planned for the network of the sensitive system permafrost-vegetation as indicators of functional processes occurring in the physical environment and in the associated ecosystems. Furthermore, it is planed to study CO2 fluxes and the involved microbial community along the transect for understanding the carbon dynamic under changing environmental conditions.

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