WATER RESOURCES RESEARCH, VOL. 41, W01013, doi:10.1029/2004WR003344, 2005 Sources of salinity and boron in the Gaza strip: Natural contaminant flow in the southern Mediterranean coastal aquifer Avner Vengosh,1 Wolfram Kloppmann,2 Amer Marei,3 Yakov Livshitz,4 Alexis Gutierrez,2 Mazen Banna,5 Catherine Guerrot,6 Irena Pankratov,1 and Hadas Raanan1 Received 17 May 2004; revised 26 September 2004; accepted 11 October 2004; published 22 January 2005. [1] Salinization in coastal aquifers is a global phenomenon resulting from the overexploitation of scarce water resources. The Gaza Strip is one of the most severe cases of salinization, as accelerated degradation of the water quality endangers the present and future water supply for over 1 million people. We investigate the chemical and 87 86 11 18 2 34 isotopic ( Sr/ Sr, d B, d O, d H, and d SSO4) compositions of groundwater from the southern Mediterranean coastal aquifer (Israel) and the Gaza Strip in order to elucidate the origin of salinity and boron contamination. The original salinity in the eastern part of the aquifer is derived from discharge of saline groundwater from the adjacent Avedat aquitard (Na/Cl < 1, 87Sr/86Sr 0.7079, and d11B 40%). As the groundwater flows to the central part of the aquifer, a dramatic change in its composition occurs (Na/Cl > 1, 87 86 11 18 2 high B/Cl, SO4/Cl, and HCO3, Sr/ Sr 0.7083; d B 48%), although the d O-d H slope is identical to that of the Avedat aquitard. The geochemical data suggest that dissolution of pedogenic carbonate and gypsum minerals in the overlying loessial sequence generated the Ca-rich solution that triggered base exchange reactions and produced Na- and B-rich groundwater. The geochemical data show that most of the salinization process in the Gaza Strip is derived from the lateral flow of the Na-rich saline groundwater, superimposed with seawater intrusion and anthropogenic nitrate pollution. The methodology of identification of multiple salinity sources can be used to establish a long-term management plan for the Gaza Strip and can also be implemented to understand complex salinization processes in other similarly stressed coastal aquifers. Citation: Vengosh, A., W. Kloppmann, A. Marei, Y. Livshitz, A. Gutierrez, M. Banna, C. Guerrot, I. Pankratov, and H. Raanan (2005), Sources of salinity and boron in the Gaza strip: Natural contaminant flow in the southern Mediterranean coastal aquifer, Water Resour. Res., 41, W01013, doi:10.1029/2004WR003344. 1. Introduction Water quality degradation in the upstream part of these basins often leads to water stress downstream and thus may [2] Salinization of coastal aquifers is a global phenome- non that endangers present and future utilization of ground- lead to regional conflicts. Numerous articles have discussed water resources, particularly in arid and semiarid zones. the political effects of the water shortage in the Middle East, Understanding the effects of salinization is crucial for water especially in the Gaza Strip [e.g., Kelly and Homer-Dixon, management in regions where groundwater is a diminishing 1998; Ohlsson, 1995], which is situated on the southern resource and where future urban, agricultural and, conse- coastal Mediterranean aquifer (Figure 1), because it is quently, economic development depends exclusively on its perhaps the most extreme example where a population of availability and quality. In many basins of the Middle East, over one million is totally dependent on groundwater groundwater resources are shared by more than one state. resources [Moe et al., 2001; Assaf, 2001]. Human pressure on the coastal aquifer in the Gaza Strip has resulted in the overexploitation beyond natural replenishment and in the 1Department of Geological and Environmental Sciences, Ben-Gurion significant drawdown of the water levels and continuous University of the Negev, Be’er Sheva, Israel. degradation of the water quality. For example, the chloride 2 Service EAU, Bureau de Recherches Ge´ologiques et Minie`res (BRGM), and boron contents in the groundwater exceed in most areas Orle´ans, France. 3Faculty of Science and Technology, Al Quds University, Jerusalem, the drinking water limits of 250 mg/L and 1 mg/L, respec- West Bank. tively (i.e., the European Union regulations; Figure 2). 4 Hydrological Service, Jerusalem, Israel. [3] In order to be able to break the vicious cycle of 5 Palestinian Water Authority, Gaza, Gaza Strip. extensive exploitation, hydrological deficit, and contamina- 6Service ANA, Bureau de Recherches Ge´ologiques et Minie`res (BRGM), Orle´ans, France. tion, the sources and flow paths of contaminates in the aquifer must be elucidated. It is essential to identify the Copyright 2005 by the American Geophysical Union. different salinity sources in order to establish in the future a 0043-1397/05/2004WR003344$09.00 reliable water management plan. The most flagrant example W01013 1of19 W01013 VENGOSH ET AL.: SALINITY IN GAZA AND COASTAL AQUIFER W01013 Figure 1. (a) Location map of research wells analyzed in this study on the background of the long-term average values of precipitation isohyet in the region. Dashed line A-B refers to the hydrogeological section (Figure 3). (b) Water level map and groundwater flow directions in the Mediterranean coastal aquifer (fall 1998) and the Avedat aquitard (marked in solid lines). Note the deep hydrological depressions in the northern and southern parts of the Gaza Strip and the general southeast to northwest flow direction. Also note that the eastern margin of the coastal aquifer is located east of the western boundary of the underlying Avedat aquitard, reflecting a direct hydrogeological connection (modified after Livshitz [1999]). of a priori assertions concerning coastal aquifers is to al., 1999, 2002; Penny et al., 2003]. In the fragile hydro- consider seawater intrusion to be the primary salinity political framework within the Gaza Strip, understanding the source. Moreover, it is commonly believed that merely origin of the salinity has many political and economic halting seawater intrusion will solve the aquifer salinity implications (e.g., water sharing with Israel, political stabil- problem [e.g., Jones et al., 1999]. However, many ity, and economic growth) in addition to direct operational studies have shown that other sources of salinity also affect water management. the water quality of groundwater resources in coastal aqui- [4] Tracing the origin of the salinity is not an easy task, fers [Maslia and Prowell, 1990; Izbicki, 1991; Vengosh et particularly in aquifers that may be contaminated from 2of19 W01013 VENGOSH ET AL.: SALINITY IN GAZA AND COASTAL AQUIFER W01013 Figure 2. (a) Distribution of chloride concentrations (mg/L) in the southern Mediterranean coastal aquifer and the Gaza Strip as measured in 2000. Arrows indicate upper limits of drinking-water regulations in Israel and the European Union (EU) and recommended by the World Health Organization (WHO). (b) Distribution boron concentrations (mg/L) in the southern Mediterranean coastal aquifer and the Gaza Strip as measured in 2000. Arrows indicate upper limits of drinking water regulations in Israel and the European Union (EU) and recommended by the World Health Organization (WHO). See color version of this figure at back of this issue. multiple nonpoint saline sources. One of the important compositions of strontium, boron, oxygen, hydrogen, and elements for tracing salinity sources is the assumption that sulfur in groundwater from the southern Mediterranean the chemical compositions of the original saline sources, coastal aquifer that is shared between Israel and the Gaza particularly conservative constituents such as Br/Cl are Strip. Using different geochemical and isotopic tracers preserved during the salinization process [Vengosh, 2003]. provides an efficient diagnostic tool for elucidating the However, additional processes (e.g., water-rock interac- origin of the salinity and boron contamination. We show tions) may hamper the ability to elucidate the original saline that the predominant salinity source in the southern Medi- sources. Here, we investigated the chemical and isotopic terranean coastal aquifer is natural inland saline groundwa- 3of19 W01013 VENGOSH ET AL.: SALINITY IN GAZA AND COASTAL AQUIFER W01013 Figure 3. Schematic general hydrogeological SE-NW cross section of the coastal aquifer along line AB in Figure 1a. The cross section was modified after Tolmach [1991]. ter that flows from the central aquifer in Israel into the Gaza [7] Historic hydrological data [Mercado, 1968; Fink, Strip. 1992; Livshitz,1999;Guttman, 2002] indicate that the natural flow regime was from SE to NW toward the Mediterranean Sea (Figure 1b). This means that part of 2. Hydrogeology the recharge of the Gaza groundwater occurs in the East, on [5] The Coastal Plain aquifer is located along the Med- the territory of Israel. Over the years the amount of pumping iterranean coast of Israel and Gaza Strip. It is composed of in the Gaza Strip has steeply increased (currently 155 Â Pliocene-Pleistocene calcareous sandstone, sands, sandy 106 m3/y) and is not balanced by natural or anthropogenic loam, and clays (Figure 3). The aquifer thickness varies replenishments. The natural recharge of the aquifer is from 200 m in the west near the coast to a few meters at the estimated to be 35 Â 106 m3/y while the human induced eastern margins. Up to a distance of 4 to 6 km from the (agricultural return flow and wastewater) is estimated at coastline, impermeable layers of clays divide the aquifer 52 Â 106 m3/y and lateral inflow from the eastern part of into several confined subaquifers (marked as ‘‘A’’ to ‘‘C’’ in the aquifer is 37 Â 106 m3/y [Moe et al., 2001; Fink, Figure 3), whereas in its central and eastern sections the 1992]. The Gaza Strip is thus facing an overall annual aquifer is undivided and phreatic. The unsaturated zone in deficit of about 30 Â 106 m3/y [Moe et al., 2001].