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).
Centro de Estudios del Agua, Tecnológico de Monterrey, Monterrey, N.L., Mexico. axelhorst@itesm.mx
Axel
A
Horst
Jürgen
J
Mahlknecht
Broder J
BJ
Merkel
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