Stable isotopes of lakes and precipitation along an altitudinal gradient in the Eastern Alps

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Altitude encompasses broad environmental gradients that influence the isotopic composition of lake water. We selected 55 lakes in the Eastern Alps along an altitudinal gradient [214–2,532 m above sea level (a.s.l.)] to model the isotopic signal of surface water dependent on intrinsic (lake geomorphometry) and extrinsic (air temperature, precipitation) factors. Ordinary and generalised least squared regression were used for statistical analysis. The isotope signal of lake water was lower in spring than in summer and decreased with altitude (−0.21 δ18O ‰/100 m; −1.5 δ2H ‰/100 m). This pattern largely depended on temperature and a pseudo-latitude effect. The isotopic signal in monthly precipitation (12 stations; altitudinal gradient 90–2,730 m a.s.l.) generally showed the expected pattern of less enriched values with altitude; however, unusual values were related to weather anomalies. The local meteoric water line was similar to the global meteoric water line as shown by overlapping confidence intervals. By discriminating different elevational bands, we could show that high elevation lakes (>1,500 m a.s.l.) experience different patterns of evaporation with respect to low elevation lakes (<1,500 m a.s.l.). Our study showed that lakes have a unique isotopic fingerprint along an altitudinal gradient, potentially useful for tracing ecological processes and for paleoclimatic studies.