Estimating groundwater mixing and origin in an overexploited aquifer in Guanajuato, Mexico, using stable isotopes (strontium-87, carbon-13, deuterium and oxygen-18).
Stable Isotopes (strontium-87, deuterium and oxygen-18, carbon-13) have been used to reveal different sources of groundwater and mixing processes in the aquifer of the Silao-Romita Valley in the state of Guanajuato, Mexico. Calcite dissolution appeared to be the main process of strontium release leading to relatively equal (87)Sr/(86)Sr ratios of 0.7042-0.7062 throughout the study area which could be confirmed by samples of carbonate rocks having similar Sr ratios (0.7041-0.7073). delta(13)C values (-11.91- -6.87 per thousand VPDB) of groundwaters confirmed the solution of carbonates but indicated furthermore influences of soil-CO(2). Deuterium and (18)O contents showed a relatively narrow range of-80.1- -70.0 per thousand VSMOW and -10.2- -8.8 per thousand, VSMOW, respectively but are affected by evaporation and mixing processes. The use of delta(13)C together with (87)Sr/(86)Sr revealed three possible sources: (i) carbonate-controlled waters showing generally higher Sr-concentrations, (ii) fissure waters with low-strontium contents and (iii) infiltrating water which is characterized by low delta(13)C and (87)Sr/(86)Sr ratios. The third component is affected by evaporation processes taking place before and during infiltration which might be increased by extraction and reinfiltration (irrigation return flow).
Horst
Axel
A
Centro de Estudios del Agua, Tecnológico de Monterrey, Monterrey, N.L., Mexico. axelhorst@itesm.mx
Mahlknecht
Jürgen
J
Merkel
Broder J
BJ
D002247:Carbon Isotopes / Q000032:analysis; D003903:Deuterium / Q000032:analysis; D004784:Environmental Monitoring / Q000379:methods*; D005618:Fresh Water / Q000032:analysis / Q000737:chemistry; D055593:Geological Phenomena; D005844:Geology; D007554:Isotopes / Q000032:analysis*; D008800:Mexico; D010103:Oxygen Isotopes / Q000032:analysis; D013325:Strontium Isotopes / Q000032:analysis; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014881:Water Supply / Q000032:analysis / Q000592:standards
D002247:Carbon Isotopes; D007554:Isotopes; D010103:Oxygen Isotopes; D013325:Strontium Isotopes; D014874:Water Pollutants, Chemical; D003903:Deuterium