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Abstract. The study of nitrogen cycling in mountain areas has a long tradition, as it was applied to better understand and describe ecosystem functioning, as well as to quantify long-distance effects of human activities on remote environments. Nonetheless, very few studies, especially in Europe, have considered catchment features controlling nitrogen dynamics above the tree line with focus on running waters.In this study, relationships between some water chemistry descriptors -including nitrogen species and dissolved organic carbon (DOC) -and catchment characteristics were evaluated for a range of sites located above the tree line (1950-2650 m a.s.l.) at Val Masino, in the central Italian Alps. Land cover categories as well as elevation and slope were assessed at each site. Water samples were collected during the 2007 and 2008 snow free periods, with a nearly monthly frequency. In contrast to dissolved organic nitrogen, nitrate concentrations in running waters showed a spatial pattern strictly connected to the fractional extension of tundra and talus in each basin. Exponential models significantly described the relationships between maximum NO 3 and the fraction of vegetated soil cover (negative relation) and talus (positive relation), explaining almost 90 % of nitrate variation in running waters. Similarly to nitrate but with an opposite behavior, DOC was positively correlated with vegetated soil cover and negatively correlated with talus. Therefore, land cover can be considered one of the most important factors affecting water quality in high-elevation catchments with contrasting effects on N and C pools.

Abstract. The role of meteorology, hydrology and atmospheric deposition on the temporal pattern of SO 4 and NO 3 concentrations was investigated for three streams draining alpine catchments in Northern Italy.The study sites lie on a gradient of atmospheric fluxes of SO 4 and NO 3 (from about 50 to 80 meq m −2 y −1 , and from 40 to 90 meq m −2 y −1 , respectively). As a consequence of the increasing N input, the three catchments are also representative of aggrading levels of N saturation. Different methods of statistical analysis were applied to monthly data for the period 1997-2005 to identify which variables (temperature, precipitation, hydrology, SO 4 and NO 3 deposition) were the main predictors of water chemistry and its change in time. Hydrological changes and snow cover proved to be the main confounding factors in the response to atmospheric deposition in the River Masino catchment. Its particular characteristics (small catchment area, rapid flushing during runoff and thin soil cover) meant that this site responded without a significant delay to SO 4 deposition decrease. It also showed a clear seasonal pattern of NO 3 concentration, in response to hydrology and biological uptake in the growing season.The selected driving variables failed to model the water chemistry at the other study sites. Nevertheless, temperature, especially extreme values, turned out to be important in both SO 4 and NO 3 export from the catchments. This result might be largely explained by the effect of warm periods on temperature-dependent processes such as mineralization, nitrification and S desorption.Our findings suggest that surface waters in the alpine area will be extremely sensitive to a climate warming scenario: higher temperatures and increasing frequency of drought could exacerbate the effects of high chronic N deposition.Correspondence to: M. Rogora

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