RAINWATER CHEMISTRY AT THE EASTERN FLANKS OF THE SIERRA-MADRE ORIENTAL, VERACRUZ, MEXICO

A rainwater chemistry study was carried out at a single site in Xalapa located at the eastern flanks of the Sierra Madre Oriental, Veracruz, Mexico, during the rainy and dry seasons under the influence of diffe rent meteorological conditions. Rain samples were analyzed for the mos t important ions. The statistical results indicated that there were si gnificant differences at the 95% confidence level between the ionic co ncentration measured in Samples collected in both seasons. The lower c oncentration values found during the rainy season could be attributed to dilution processes since in this season 79% of the annual precipita tion occurs, compared to only 21% in the dry season. High and positive ion-pair correlations were found among the most important ions in bot h seasons. Although Xalapa is situated at less than 100 km from the co ast, marine contribution of SO42- and Ca2+ is negligible compared with the nonmarine contribution. In the rainy season, enrichment of SO42-, NH4+, and NO3- is due to upwind medium-and long-distance emission sou rces of Veracruz, as back trajectories of the predominant winds from t he southeast indicate. On the other hand, in the dry season this enric hment is due to emission sources situated in Tampico, Madero, and Poza Rica and south-southeastern Texas, as indicated by the predominant wi nds from the northeast. Finally, wet deposition rates were, as expecte d, higher during the rainy season in spite of the dilution processes.