Compilation and review of 87Sr/86Sr and stable isotopes from groundwater, calcite fracture fillings, mineral, and whole-rock sampling at Äspö, Sweden.

Integrated isotopic and hydrochemical studies of groundwater at Äspö, Sweden, support mixing models involving deep saline water, low-solute infiltration, and Baltic Sea water. Carbon, oxygen, and strontium isotope analyses of calcite fracture fillings indicate that paleohydrologic conditions were different than those of today in terms of the isotopic composition of water flowing through fractures. Sr isotopes of whole-rock and mineral (plagioclase, microcline, biotite, and epidote) samples are used to assess the effects of water-rock interaction. Biotite is a major reactant in the early stages of water-rock interaction. Strontium isotope systematics of groundwater from deep in the Hard Rock Laboratory, and underground research facility, and from low conductivity zones revealed a first order mixing line defined by a high-chloride saline component with 66 mg/L Sr and an ancient sea water component with approximately 4.5 mg/L. Dilution with low salinity recharge has produced groundwater with variable Sr contents and 87Sr/86Sr values between 0.7186 and 0.7160. Differences between Äspö and Laxemar groundwater are shown by trends in Sr concentrations plotted against 87Sr/86Sr. The Äspö trend shows increasing 87Sr/86Sr values with increasing concentrations of Sr, whereas the Laxemar groundwater trend shows little variability in 87Sr/86Sr with increasing Sr concentrations. These trends are controlled by the differences in 87Sr/86Sr composition of the saline end members in the two areas.

Isotope methods for management of shared aquifers in northern Africa.

Access to fresh water is one of the major issues of northern and sub-Saharan Africa. The majority of the fresh water used for drinking and irrigation is obtained from large ground water basins where there is minor contemporary recharge and the aquifers cross national borders. These aquifers include the Nubian Aquifer System shared by Chad, Egypt, Libya, and Sudan; the Iullemeden Aquifer System, extending over Niger, Nigeria, Mali, Benin, and Algeria; and the Northwest Sahara Aquifer System shared by Algeria, Libya, and Tunisia. These resources are subject to increased exploitation and may be severely stressed if not managed properly as witnessed already by declining water levels. In order to make appropriate decisions for the sustainable management of these shared water resources, planners and managers in different countries need an improved knowledge base of hydrological information. Three technical cooperation projects related to aquifer systems will be implemented by the International Atomic Energy Agency, in collaboration with the United Nations Educational, Scientific and Cultural Organization and United Nations Development Programme/Global Environmental Facility. These projects focus on isotope hydrology studies to better quantify ground water recharge and dynamics. The multiple isotope approach combining commonly used isotopes 18O and 2H together with more recently developed techniques (chlorofluorocarbons, 36Cl, noble gases) will be applied to improve the conceptual model to study stratification and ground water flows. Moreover, the isotopes will be an important indicator of changes in the aquifer due to water abstraction, and therefore they will assist in the effort to establish a sustainable ground water management.