The multi-isotope approach for studying groundwater salinization
The problem of ground water salinization is intensified in many coastal basins where increasing human stress affects directly and indirectly water-quality deterioration. Monitoring and identifying the origin of the salinity are crucial for water management and remediation. Yet the variety of the possible salinization sources makes this task extremely difficult. Groundwater salinization can result from both anthropogenic (e.g., agriculture return flows, irrigation with sewage effluent) and natural “geogenic” processes, such as intrusion of sea water or other saline fluids. In Israel the problem of salinization is one of the major water quality problems (Saline Plume,Salinity in Israel). Integration of different geochemical and isotopic tools provides a better assessment of the origin and mechanisms of groundwater salinization. My research has applied the multi-isotope approach to delineate the origin of saline plumes in the Mediterranean coastal aquifer of Israel (Coastal_aquifer_Israel), which led to several other publications on the mechanism of groundwater salinization in Israel and Gaza Strip (Gaza_WRR, Gaza_GW), different basins in Morocco (Souss_massa_Morocco,Tadala basin, Morocco), and the shallow 180-foot aquifer of the Salinas Valley in central California, USA (Paper in WRR). An overview on salinization as a global phenomenon is given in a chapter on Salinization and Saline Environment that was published in the series Treatise of Geochemistry (Salinization).
Joint research projects in the Middle East
Due to mounting pressure on and accelerated degradation of the quality of shared water resources in the Middle East, studying the origin and mechanism of water contamination has many implications for future utilization and stability in the region. I have been involved in establishing several joint scientific projects with Palestinian and Jordanian scientists to enhance cooperation and provide the scientific basis for future negotiations and joint management between Israel and its neighbors. The first study investigated the origin of the salinity in the Eastern Mountain aquifer and shallow groundwater underlying Jericho City in the southern Jordan Valley ( Jericho).
The second project aimed to evaluate the origin of salts that are entering the Jordan River and establish the mechanisms that result in the rise of the salinity in the Jordan River. The project was part of a USAID (Middle East Research Cooperation, MERC) initiative to promote dialogue and collaboration between Israeli and Arab scientists. The use of a large set of isotopic tools enabled us to delineate the source of the salinity and to show that groundwater discharge is the major process that controls the quality of the Jordan River (JordanRiver,Jordan River Management,Jordan Valley Paper,Jordan_management_AG,JR_N). The geochemical study was conducted together with a hydrological investigation that included specific water mass-balance along the river flow (Holtzman_et_al_2005).
The third project was part of the European Union 5th framework research program titled BOREMED that investigated the origin of boron in Mediterranean water resources. A group of Israeli, Palestinian, and French scientists studied the origin of contamination of groundwater in the southern Mediterranean coastal aquifer of Israel and the Gaza Strip. We found that the major source of salinization was the flow of natural saline groundwater from Israel to the Gaza Strip, coupled with nitrate pollution and sea-water intrusion. Here, again we used geochemical and isotopic (boron, strontium, oxygen, deuterium) tracers to delineate the different salinity sources (Gaza_WRR). The geochemical data was used to reconstruct numerical simulation and to establish a possible management scenario to remediate the salinity problem by pumping the saline groundwater along the border and then using it for desalination (Gaza_GW). These management scenarios could facilitate future cooperation between Israel and Palestinians and provide a solution for one of the most severe water-quality crisis in the region.
Boron pollution in Mediterranean water resources: sources and remediation
Results from the European Union Fifth Framework project, entitled BOREMED (Boron contamination of water resources in the Mediterranean region: distribution, sources, social impact and remediation), also showed that boron contamination poses a potential threat to the future use of many groundwater basins along the Mediterranean for the supply of drinking and irrigation water. The new regulation for drinking water in the EU limits boron in drinking water to 1 mg/l due to possible health hazards that can potentially be induced by boron intake. Boron is also a unique micronutrient in which over-dose and under-dose of boron supply cause toxicity and deficiency symptoms in plants, respectively. A survey of the level of boron in water resources in the Mediterranean region shows groundwater from several sites in Italy (Tuscany), Greece (western Chalkidiki), Central Cyprus, Israel (southern coastal aquifer), and the Gaza Strip have high boron levels exceeding the 1 mg/l threshold (Publication 13).
My role in the BOREMED project focused on three aspects. First, I was the coordinator of the geochemistry work project that investigates the sources of boron contamination. By applying geochemical and isotopic (boron, strontium, oxygen, deuterium) techniques, we determined the source of the boron in several sites (Cornia River basin, Italy, western Chalkidiki, Greece, Central Cyprus, and the southern coastal aquifer and Gaza Strip). The geochemical data indicated that the boron contamination was derived primarily from natural (“geogenic”) sources rather than anthropogenic (e.g., sewage effluent) contamination (Publications 10,15).
My second contribution was to develop an alternative methodology for boron removal from water. The high boron level in regional groundwater in some Mediterranean basins requires special treatment in order to meet the EU drinking water regulations. Previous attempts to remove boron employed boron-specific ion-exchange resin and several cycles of RO desalination under high pH conditions. The boron problem is magnified by the only partial (~60%) removal of boron in Reverse Osmosis (RO) desalination due to the poor ionization of boric acid and the accumulation of boron in domestic sewage effluents. Working with my Turkish colleagues in my laboratory, we developed an alternative methodology for boron removal by using coal and fly ash as adsorbents. We conducted a series column and batch experiments that explored the efficiency of boron removal from seawater and desalinated seawater using several types of coal and fly ash materials under controlled conditions. We showed that that coal and fly ash materials could be very effective in removing boron such that the rejection ratio of boron can reach 95% of the initial boron content under certain optimal conditions (Publication 19).
Identification of nitrogen pollution
Nitrate pollution is a major process that causes degradation of the quality of water resources. The use of nitrate isotopes (nitrogen and oxygen) in conjunction with other isotopes, that are used as indirect proxies, provide the tools for identification of the origin of nitrate pollution and evaluating the process associated with nitrogen transformation. I have been involved in two research studies that utilize nitrogen isotopes. The first is a study of the sources and transformations of nitrogen compounds in the Jordan River by applying a combination of geochemical, nitrogen isotopes (both of ammonium and nitrate species) and mathematical analyses. The geochemical and isotopic results suggest that the nitrogen modifications of the Jordan River occur due to both mixing with non-point subsurface groundwater discharge and internal nitrification process (Publication 17).
The second study investigated the origin of nitrate plumes in the Mediterranean coastal aquifer of Israel. High nitrate level in numerous wells from the aquifer exceeds drinking water regulations and consequently more than 50% of the groundwater in this aquifer is unusable for domestic applications. One of my graduate student was involved in studying more than a hundred groundwater samples from the coastal aquifer and analyzed them for chemical and isotopic (nitrogen, oxygen in nitrate, tritium) compositions. The results showed that most of the nitrate pollution in the coastal aquifer is derived from the leaching of nitrogen that has originated from the cultivation of virgin soil. In some areas, we were able to find nitrogen that is derived from sewage pollution with a distinctive nitrogen isotopic composition. We used additional tracers like tritium and boron isotopes to confirm the sewage contribution. Overall, the results indicate that the aquifer has not reached a steady-state condition with respect to nitrate pollution, and nitrogen derived from direct anthropogenic sources like sewage and fertilizers may further contaminate the underlying groundwater. Some results from the Gaza Strip also showed that contamination from sewage effluents is the major mechanism for massive nitrate pollution in the Gaza Strip.
Reconstructing ages and origin of fossil groundwater in the Nubian Sandstone aquifer
The scarcity of water resources in arid zones often requires exploitation of “fossil” groundwater that was recharged into the aquifers during the Late Pleistocene. Future prospects of utilization of the Lower Cretaceous Nubian Sandstone aquifer in many basins in the Middle East are overshadowed by the lack of modern replenishment and groundwater salinity. A study of fossil groundwater from the Negev, Israel included several geochemical and isotopic (B, Sr, O, H, 14C) tracers that enabled us to reconstruct the groundwater recharge regime, delineate possible flow paths, and identify the sources and ages of the dissolved salts (Publication 8). We distinguished between two major recharge sources that originated from two distinctive air masses during the Late Pleistocene, southern humid and northern arid types. Our results contradicted previous models of long groundwater flow from the Sinai Peninsula to the northeastern Negev. Moreover, the common assumption that paleo-waters are always depleted in 18O with low D-excess is not valid for this aquifer, as we obtained high D-excess (16‰) and low 14C values (1-3 pmc). We showed that the groundwater from the Nubian Sandstone aquifer in the Negev is controlled by mixing with groundwater from an underlying aquifer that has interacted with gypsum minerals with distinctive strontium and sulfur isotope compositions (Publication 8).