HESS Hydrology and Earth System Sciences HESS Hydrol. Earth Syst. Sci. 1607-7938 Copernicus Publications Göttingen, Germany 10.5194/hess-17-409-2013 Impact of elevation and weather patterns on the isotopic composition of precipitation in a tropical montane rainforest Windhorst D. 1 Waltz T. 1 Timbe E. 2 Frede H.-G. 1 Breuer L. https://orcid.org/0000-0001-9720-1076 1 Institute for Landscape Ecology and Resources Management (ILR), Research Centre for BioSystems, Land Use and Nutrition (IFZ), Justus-Liebig-Universität Gießen, Gießen, Germany Grupo de Ciencias de la Tierra y del Ambiente, DIUC, Universidad de Cuenca, Cuenca, Ecuador 31 01 2013 17 1 409 419 Copyright: © 2013 D. Windhorst et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://hess.copernicus.org/articles/17/409/2013/hess-17-409-2013.html The full text article is available as a PDF file from https://hess.copernicus.org/articles/17/409/2013/hess-17-409-2013.pdf

This study presents the spatial and temporal variability of &delta;<sup>18</sup>O and &delta;<sup>2</sup>H isotope signatures in precipitation of a south Ecuadorian montane cloud forest catchment (San Francisco catchment). From 2 September to 25 December 2010, event sampling of open rainfall was conducted along an altitudinal transect (1800 to 2800 m a.s.l.) to investigate possible effects of altitude and weather conditions on the isotope signature. <br><br> The spatial variability is mainly affected by the altitude effect. The event based &delta;<sup>18</sup>O altitude effect for the study area averages −0.22&permil; × 100 m<sup>−1</sup> (&delta;<sup>2</sup>H: −1.12&permil; × 100 m<sup>−1</sup>). The temporal variability is mostly controlled by prevailing air masses. Precipitation during the times of prevailing southeasterly trade winds is significantly enriched in heavy isotopes compared to precipitation during other weather conditions. In the study area, weather during austral winter is commonly controlled by southeasterly trade winds. Since the Amazon Basin contributes large amounts of recycled moisture to these air masses, trade wind-related precipitation is enriched in heavy isotopes. We used deuterium excess to further evaluate the contribution of recycled moisture to precipitation. Analogously to the &delta;<sup>18</sup>O and &delta;<sup>2</sup>H values, deuterium excess is significantly higher in trade wind-related precipitation. Consequently, it is assumed that evaporated moisture is responsible for high concentrations of heavy isotopes during austral winter.

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