Geochemical and boron, strontium, and oxygen isotopic constraints on the origin of the salinity in groundwater from the Mediterranean coast of Israel

In order to identify the origin of the salinity and formation of saline plumes in the central part of the Mediterranean coastal aquifer of Israel, we determined the elemental and boron, strontium, and oxygen isotopic compositions of fresh and brackish groundwater (Cl up to 1500 mg/L). We distinguish between two key anthropogenic sources: (1) sewage effluents used for irrigation with high Na/Cl, SO4/Cl, and B/Cl ratios and low Br/Cl ratios relative to seawater ratios, low delta(11)B values (0-10 parts per thousand) and high delta(18)O values (>-4 parts per thousand); and (2) imported water from the Sea of Galilee that is artificially recharged to the aquifer with high Br/Cl (3 x 10(-3)) and delta(18)O values (-1 parts per thousand) and a low Sr-87/Sr-86 ratio of 0.70753. The brackish groundwater from the saline plumes have relatively low Na/Cl ratios (0.5-0.8) and high Ca/Mg, Mg/Cl, and Ca/(SO4 + HCO3) (>1) ratios relative to seawater ratios; marine SO4/Cl and Br/Cl ratios; delta(11)B values of 24.8-49.9 parts per thousand; delta(18)O Of -2.95 parts per thousand to -4.73 parts per thousand; and Sr-87/Sr-86 ratios of 0.708275-0.708532, The composition of most of the investigated groundwater from the saline plumes differs from those of the anthropogenic sources, imported water, fresh uncontaminated groundwater (Sr-87/Sr-86 of 0.70866, delta(11)B of 20-30 parts per thousand), and saline water from the adjacent Eocene aquitard. Only in areas of artificial recharge does local groundwater have high Br/Cl and delta(18)O values that are typical to the Sea of Galilee. The linear relationships between chloride and most of the ions, including B and Sr, the relatively high delta(11)B (>30 parts per thousand) and low delta(18)O (<-4 parts per thousand) values, and the chemical signature of the saline plumes (e.g., marine Br/Cl and SO4/Cl ratios), suggest that (1) mixing processes control the chemical composition of the brackish water within the aquifer, and (2) the saline postulated end-member has a chemical composition that resembles modified seawater with a marine and higher delta(11)B values, and a Sr-87/Sr-86 ratio of <0.7083. We propose that most of the salinization phenomena and the formation of saline plumes in the inner parts of the coastal aquifer are derived from upconing of underlying natural saline water bodies and enhanced by overexploitation and draw-down of the overlying fresh groundwater.