Meteoric isotopic gradient on the windward side of theSierra Madre Oriental area, Veracruz - Mexico

The isotopic composition (delta O-18, delta D parts per thousand) of precipitation in the windward side of the Sierra Madre Oriental on the eastern flank of the Mexican Volcanic Belt was characterized along a 90 km transect from sea level up to an altitude of 4220 meters. Rain samples were collected during the rainy season (May through October) from 2007 through 2012. The Local Meteoric Water Line (LMWL), determined with linear regression of isotope results, is delta D = 7.44 delta O-18 + 7.4, R-2 = 0.99. This line departs from the Global Meteoric Water Line (GMWL) for precipitation at altitudes greater than 3000 masl due to deuterium enrichment processes. The results obtained in this research were compared with isotopic data of the Global Network of Isotopes Precipitation (GNIP) data base from the port of Veracruz. The altitude (Z) gradient of delta O-18 was also determined by the linear regression of precipitation data, resulting in the relation delta O-18 = -2.1Z - 5.56, R-2 = 0.86, where Z is altitude in kilometers. This implies a delta O-18 vertical gradient of -0.21 parts per thousand/ 100 m, which falls within the normal range described in the literature for tropical areas. Finally, the isotopic record of meteoric waters during the years of observation shows anomalous enrichment in delta O-18 and delta D at an altitude of about 1400 m, probably influenced by the local topography and/or an isotope effect related to tropical storms typical of this latitude. This characterization will increase the understanding of important hydrological processes and will provide a foundation for future hydrological research.