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Stanchi S.,University of Turin | Stanchi S.,Research Center on Natural Risks in Mountain and Hilly Environments | Freppaz M.,University of Turin | Freppaz M.,Research Center on Natural Risks in Mountain and Hilly Environments | And 2 more authors.
Natural Hazards and Earth System Science | Year: 2012

Mountain watersheds are particularly vulnerable to extreme meteorological events, such as high intensity rainfall, and mountain soils often show pronounced fragility and low resilience due to severe environmental conditions. Alpine soil vulnerability is partly intrinsic but in part related to climate change (mainly precipitation regimes), and is enhanced by the abandonment of rural mountain areas that reduced the land maintenance actions traditionally carried out by farmers and local populations in the past. Soil hazards are related to different processes such as water erosion, loss of consistency, surface runoff and sediment transport, often occurring simultaneously and interacting with each other. Therefore, the overall effects on soil are not easy to quantify as they can be evaluated from different soil chemical and physical properties, referring to specific soil loss phenomena such as soil erosion, soil liquefaction, loss of consistency etc. In this study, we focus our attention on a mountain region in the NW Italian Alps (Valle d'Aosta), which suffered from diffuse soil instability phenomena in recent years, as a consequence of extreme rainfall events and general abandonment of the agricultural activities in marginal areas. The main effects were a large number of shallow landislides involving limited soil depths (less than 1 m), affecting considerable surfaces in the lower and middle part of the slopes. These events caused loss of human lives in the year 2000 and therefore raised the attention on land maintenance issues. Surface (topsoil: 0-20 cm) and subsurface (subsoil: 20-70 cm) samples were characterised chemically and physically (pH, carbon and nitrogen contents, cation exchange capacity, texture, aggregate stability, Atterberg limits etc.) and they showed very different soil properties. Topsoils were characterised by better stability, structure, and consistency. The differences between the two depths were potential trigger factors for shallow soil movements involving the upper soil horizons. We assessed a great number of soil properties that are known to be related to vulnerability to the main hazards present in the area. These properties were evaluated at the two depths and a factor analysis was performed to simplify the dataset interpretation, and to hypothesise the most decisive parameters that were potentially related to vulnerability. The factors (soil structure, aggregation, consistency, texture and parent material, cation exchange complex and other chemical properties) were a first step towards identifying soil quality indexes in the studied environment. © 2012 Author(s).

Freppaz M.,University of Turin | Freppaz M.,Research Center on Natural Risks in Mountain and Hilly Environments | Williams M.W.,University of Colorado at Boulder | Seastedt T.,University of Colorado at Boulder | And 2 more authors.
Applied Soil Ecology | Year: 2012

Alpine ecosystems are thought to be particularly sensitive to small environmental changes in climate and other parameters due to the plants and soil organisms being on the edge of environmental tolerances. Snow distribution is critical to microclimate in the alpine, affecting soil temperature, growing season duration, and nutrient cycling. Moreover anthropogenic nitrogen (N) deposition over the past half century has had a detrimental impact on temperate ecosystems, resulting in soil acidification and a reduction in plant biodiversity. Here we used a snowfence experiment combined with an N-fertilization experiment, at the NSF-funded Niwot Ridge (NWT) Long-Term Ecological Research (LTER) site (3528. m ASL), to increase our understanding of how changes in snow properties and N deposition may affect soil processes. The snowfence used in this manipulation resulted in a consistent pattern of snow accumulation, from deep snowpacks near the fence to a shallow snowpack away from the snowfence. As measured after 16 years of the experiment, the amount, timing, and duration of snow cover appears to affect soil properties. Under moderate snow cover and without N addition, the total soil organic carbon (TOC) and total nitrogen (TN) were significantly greater than either under deep or shallow snow. Nitrogen amendments in general worked in the opposite direction of snowpack controls on soil processes. The N addition caused a significant increase under the shallow snow treatments for TOC and TN, while there was a significant decrease of these properties under the moderate snow treatment. In the latter case the N addition did not cause any significant effect on the inorganic N forms but was correlated with a decline of soil pH, and a consequent increase of exchangeable Al and a reduction of exchangeable base cations, which may have influenced soil microbial biomass found in this study. Our results demonstrate how long-term changes in snow properties and N deposition may interact in affecting alpine soil characteristics, with an important response of soil nutrients. © 2012 Elsevier B.V.

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