Hydrogeochemical characterization and isotope investigations of a carbonate aquifer of the northern part of the United Arab Emirates

This paper assesses a carbonate aquifer of the Wadi Al Bih area in the northeastern part of UAE using hydrogeochemical and isotope approaches. Analyses of groundwater samples showed that the TDS and high concentrations of major cations and anions were encountered in the lower segment of the Wadi Al Bih area. Most of the groundwater salinity was noticed downstream of the wadi and this may be attributed to the brines that underlie the groundwater and also to the over-pumping of groundwater with mostly very low recharge. Nitrate concentrations observed in the groundwater of the study area may be ascribed to the nature of the karastic aquifer, which could lead to the dominance of dissolved oxygen that makes NO3- the dominant form of nitrogen. The presence of sulfate in collected groundwater samples is due to the gypsum-bearing mudstone in the lower segment of the Wadi Al Bih carbonate aquifer. Majority of the groundwater samples showed the presence of NaCl, which indicates the possible influence of the underlying brine. The mixing process of brine water and freshwater was noted in the shift from CaHCO3 facies to Ca–Cl facies. The Piper plot showed a Ca-rich to Na-rich water type shift, which could be explained by a cation exchange process.The oxygen and hydrogen isotope compositions in the groundwater samples suggest that the main source of precipitation is the Mediterranean Sea with some possible effects of the Arabian Sea. A trend of increasing chloride concentration with enrichment of hydrogen isotope compositions suggests that groundwater originated from evaporated raindrops or evaporated surface water. The similarity of oxygen and hydrogen isotope compositions between the Eastern Gravel Plain, Ophiolite, and the northern carbonate aquifers indicates the presence of a common source of recharge.