Studies of isotopic hydrology of the basin of Mexico and vicinity: annotated bibliography and interpretation

This study deals exclusively with the behavior of the oxygen-18 and deuterium composition of precipitation, surface water and groundwater within and near the basin of Mexico. It reviews 16 studies from 1974 to 1993, reporting new measurements related to the study area. Location maps and the summary of original conclusions are included. Parts of the documents, whose circulation is restricted, were collected from private files and government libraries. These data, which were not previously available to the scientific community, represent a total of 791 oxygen-18 and 703 deuterium analyses, most of them (d18O, dD)pairs. The discussion is an overview of the whole data set, with interpretation. As inferred from the data, regional precipitation follows the regression dD = 7.97 d18O + 11.03 (n = 85; r2 = 0.97), being slightly different from a local meteoric line previously published; variations in d18O are about -21.7 to -1.3 percent, following a Gaussian distribution: f(d18O)= 0.036 exp[-0.5(d18O + 9.97)/(4.43)]. Groundwater from springs and deep production wells fitted the new regional meteoric line; variations in d18O are about -13.5 to -6.5 percent, and their distribution is also Gaussian: f(d18O)= 0.248 exp[-0.5(d18O + 10.09)/(0.81)]. Shallow piezometer and pore saline waters in the sediments of the former terminal marsh of the study basin showed a trend of isotopic alteration; this feature is interpreted by the corresponding source study as mixing of in situ post-1953 infiltration with older evaporated waters. This mixing trend intersects the regional meteoric line close to d18O= -8.0 percent. Isotope data and our interpretation are consistent with the current concept of a closed groundwater basin associated with the closed surface water basin of Mexico.