Major element chemistry in inner alpine snowpacks (Aosta Valley Region, NW Italy)

Abstract

Major element chemistry of the snow cover was investigated at 15 sampling sites at about 2000 m a.s.l. in the Aosta Valley Region (North Western Italy), an inner alpine region characterized by a continental climate, during late winter 2005–2006. Snowfall in winter 2005–2006 was primarily due to westerly, Atlantic air flows, while southerly flows were not a significant source of precipitation. These two factors (i.e. the inner alpine topography and the peculiar air flow patterns) determined a unique ion distribution compared to rest of the Alps. Calcium and magnesium concentrations in snowpacks were low, consistent with the absence of Saharan dust events and local geological sources. Sodium and chloride concentrations were higher than the average for the Alps, supporting the influence of the Atlantic air masses on the ionic composition of snowfall. Sulfate concentrations were in the range of background concentrations reported for high altitude and latitude sites, indicating that industrial emissions were not a main source of chemicals in Aosta Valley snowpacks for winter 2005–2006. Ammonium and nitrate values were comparable to concentrations found in other sites of the Alps for low-emission winters. We estimated dissolved inorganic nitrogen stored in snow to range between 0.25 and 0.75 kg N ha− 1, corresponding to about 2–6% of the over-winter-N mineralization in Alpine soils in the Western Alps. In the Aosta Valley, local biogenic pollution rather than long-range transport may contribute substantially to the ionic load in the snowpack when westerly air masses are the main source of precipitation. Although conducted over only one winter season, this study suggests a peculiar and previously unreported pattern of snowpack chemistry, that may be representative of the inner alpine, continental valleys in the absence of strong anthropogenic pollution or dust deposition. Due to the fact that inner alpine valleys cover a non-negligible surface of the Alps, we suggest these patterns to be taken into account while modeling ion depositions at a global scale.