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"Man-made" or unconventional freshwater, like desalinated seawater or reclaimed effluents, is increasingly introduced into regional water cycles in arid or semi-arid countries. We show that the breakthrough of reverse osmosis-derived freshwater in the largely engineered water cycle of the greater Tel Aviv region (Dan Region) has profoundly changed previous isotope fingerprints. This new component can be traced throughout the system, from the drinking water supply, through sewage, treated effluents, and artificially recharged groundwater at the largest Soil-Aquifer Treatment system in the Middle East (Shafdan) collecting all the Dan region sewage. The arrival of the new water type (desalinated seawater) in 2007 and its predominance since 2010 constitutes an unplanned, large-scale, long-term tracer test and the monitoring of the breakthrough of desalination-specific fingerprints in the aquifer system of Shafdan allowed to get new insights on the water and solute flow and behavior in engineered groundwater systems. Our approach provides an investigation tool for the urban water cycle, allowing estimating the contribution of diverse freshwater sources, and an environmental tracing method for better constraining the long-term behavior and confinement of aquifer systems with managed recharge.

The response of hypersaline terminal lakes to negative water balance was investigated by studying brines evaporating to extreme salinities in sinkholes along the western coast of the Dead Sea and during on-site evaporation experiments of the Dead Sea brine. Density and temperature were determined in the field and all samples were analyzed for their major and a few minor solutes. The activity of H 2 O ( a H2O ) in the brines was calculated, and the degree of evaporation (DE) was established using Sr 2+ as a conservative solute. The relations between density and water activity were obtained by polynomial regression, and the relation between the lake’s volume and level was established using Hall’s (1996) hypsographic model for the Dead Sea basin. Relating the results to the modern, long-term relative humidity (RH) over the basin shows that (a) The lowermost attainable level of a terminal lake undergoing evaporation with no inflow is dictated by the median RH; this level represents equilibrium between the brine's a H2O and RH; (b) Small, saline water bodies with high surface to volume ratios (A/V), such as the hypersaline brines in the sinkholes, are very sensitive to short term changes in RH; in these, the brines' a H2O closely follows the seasonal changes; (c) the level decline of the Dead Sea due to evaporation under present climatic conditions and assuming no inflow to the lake may continue down to 516–537 m below mean sea level (bmsl), corresponding to a water activity range of 0.46–0.39 in its brine, in equilibrium with the overlying relative air humidity; this suggests that the lake level cannot drop more than ∼100 m from its present level; and (d) The maximum RH values that existed over the precursor lake of the Dead Sea (Lake Lisan) during geologically reconstructed minima levels can be similarly calculated.

An ancient, brackish, anoxic, and relatively hot water body exists within the Yarqon-Tanninim Aquifer in southern Israel. A hydrogeological-geochemical conceptual model is presented, whereby the low water quality is the outcome of three conditions that are met simultaneously: (1) Presence of an organic-rich unit with low permeability that overlies and confines the aquifer; the confining unit contains perched horizons with relatively saline water. (2) Local phreatic/roofed conditions within the aquifer that enable seepage of the organic-rich brackish water from above. The oxidation of the dissolved organic matter in the seeping water consumes the dissolved oxygen and continues through bacterial sulfate reduction, with H2S as a product. These exothermic reactions result in some heating. (3) The seeping water comprises a relatively large portion of the water volume. In the presented case study, the latter condition first developed in the Late Pleistocene following climate change, which led to a dramatic decline in recharge. Consequently, water flow in the local basin has nearly ceased, as evident by old water ages, specific isotopic composition, and nearly equipotential water levels. The continuous seepage from above into the almost stagnant water body has resulted in degraded water quality. Seepages of organic-rich brackish water exist at other sites throughout the aquifer but have limited impact on the salinity and redox conditions due to the dynamic water flow, which flushes the seeping water, that is, the third condition is not met. The coexistence of the above three conditions may explain the development of anoxic and saline groundwater in other aquifers worldwide.

The freshwater of the Judea Group aquifer that recharges on the crest of the Judea and Samria Mountain ridge flows east and west, defining two groundwater basins. At the foothills of both basins the freshwater encounters ancient saline or brackish water. The mode of interaction between the two water bodies within each basin is different, although both eventually discharge as brackish spring system. We describe these systems and identify the source of the higher salinity end members.

We document and analyze the rapid development of a real-time karst system within the subsurface salt layers of the Ze'elim Fan, Dead Sea, Israel by a multidisciplinary study that combines interferometric synthetic aperture radar and light detection and ranging measurements, sinkhole mapping, time-lapse camera monitoring, groundwater level measurements and chemical and isotopic analyses of surface runoff and groundwater. The >1 m/yr drop of Dead Sea water level and the subsequent change in the adjacent groundwater system since the 1960s resulted in flushing of the coastal aquifer by fresh groundwater, subsurface salt dissolution, gradual land subsidence and formation of sinkholes. Since 2010 this process accelerated dramatically as flash floods at the Ze'elim Fan were drained by newly formed sinkholes. During and immediately after these flood events the dissolution rates of the subsurface salt layer increased dramatically, the overlying ground surface subsided, a large number of sinkholes developed over short time periods (hours to days), and salt-saturated water resurged downstream. Groundwater flow velocities increased by more than 2 orders of magnitudes compared to previously measured velocities along the Dead Sea. The process is self-accelerating as salt dissolution enhances subsidence and sinkhole formation, which in turn increase the ponding areas of flood water and generate additional draining conduits to the subsurface. The rapid terrain response is predominantly due to the highly soluble salt. It is enhanced by the shallow depth of the salt layer, the low competence of the newly exposed unconsolidated overburden and the moderate topographic gradients of the Ze'elim Fan.

Nitrate contamination of shallow aquifers poses a major challenge in the development of sustainable agriculture, particularly in (semi-)arid regions, where groundwater is also used as potable water. In this study we estimate the relative contribution of the various nitrate sources contaminating the shallow aquifers underlying agricultural fields in the extremely arid region of the Central Arava Valley (CAV), southern Israel. The estimates are based on a chemical and isotopic mixing-reaction model describing the evolution of the δ18ONO3 and δ15NNO3 isotopic compositions from the sources to the aquifer. The model indicates that all fertilizers used in the agricultural fields: synthetic NO 3 − , synthetic NH 4 + and manure, contaminate the CAV groundwater with nitrate. In most of CAV groundwaters, the contribution of each fertilizer to the groundwater contamination is relative to its proportion in the fertilization scheme of the cultivated fields. Two exceptions of this general observation were found: 1. One field showed a direct nitrate contamination from a “leaking” sewage reservoir, as indicated by its exceptionally high δ15NNO3 value that reached 9.2‰; and 2. A very shallow alluvial aquifer, recharged by winter floods and not by the irrigation water, showed no nitrate isotopic “fingerprint” of manure, which is applied to the cultivated fields only during summer. Groundwater nitrate contamination is actuated by infiltration of irrigation water, which in addition underwent salinization as a result of evapo-transpiration in the cultivated fields. Based on the relatively uniform and depleted groundwater δ18OH2O compositions and the depleted δ18ONO3 values, within the possible range of fertilizers-derived nitrate as deduced by the model, the water-loss in the cultivated fields is transpiration-controlled. The isotope mixing-reaction model used here to identify the major nitrate contamination sources maybe used to help design a sustainable cultivation management strategy in similar arid regions. It can also be used to assess the fertilization efficiency and the relative impact of each fertilizer type. Such models may be particularly useful in evaluating highly heterogeneous and complicated aquifer systems, for which the formulation of absolute water and nitrate mass balances are impossible.

Manganese enrichment is common in various sedimentary environments, e.g. deep ocean floor, shallow sedimentary environments where the overlying water column is oxic and phreatic aquifers, in which the Mn aquatic geochemistry is controlled by redox conditions. In many cases, aquifers recharged by organic-rich waters contain high amounts of dissolved Mn 2+ that was mobilized from sedimentary Mn-oxides during microbial oxidation of the organic matter under low-oxygen conditions. Thus, the identification and quantification of the processes controlling Mn mobilization and speciation is of great practical importance as a geochemical tool for sustainable management of aquifers. This study uses column experiments to quantify the role of adsorption and precipitation in retarding Mn 2+ mobilization in sandy aquifers under low-oxygen conditions. Flow-through columns were packed with pristine sandy sediment and were recharged by low-oxygen artificial solutions containing different Mn 2+ concentrations. Outflow solutions from the column experiments were analyzed and simulated using a Mn 2+ transport-reaction model. The results were used to demonstrate the importance of adsorption on Mn mobilization in three different aquifers. The experimental data showed that adsorption of Mn 2+ on the column solids was the main control on the Mn 2+ breakthrough behavior. Nevertheless, up to 20% of the Mn that entered the experimental columns was precipitated as MnCO 3 . The rate of MnCO 3 precipitation ( k p = 0.04 h −1 ) was found to be ∼3 orders of magnitude slower than the rate of Mn 2+ adsorption ( k a = 10–200 h −1 ). Given the slow mineral-precipitation kinetics, the water flow rate is critical in determining the potential of MnCO 3 precipitation in immobilizing Mn within an aquifer. A scale-up of the Mn retardation time found in the column experiments to natural aquifer conditions, suggests that adsorption is responsible for the prolonged retardation of Mn 2+ observed in three different sandy aquifers. An important practical conclusion of this study is that the environmental response to perturbation in the hydro-geochemical regime of an aquifer might be delayed for several decades.

Summary This research describes a field study and laboratory simulations of the geochemical evolution of groundwater following a recharge of effluent into aquifers. The study was conducted in the soil aquifer treatment (SAT) system of the Shafdan sewage reclamation plant, Israel. The SAT system recharges secondary effluent into the calcareous sandstone sediments of the Israeli Coastal Aquifer as a tertiary treatment. The reclaimed effluent is recovered ca. 500 m off the recharge basin and is used for unlimited irrigation. The laboratory simulations in which effluent was pumped through experimental columns packed with pristine Shafdan sediment showed that the chemical composition of the outflowing water was controlled mainly by cation exchange and CaCO3 dissolution. Na+, K+ and Mg2+ were adsorbed and Ca2+ was desorbed during the initial stage of recharge. The equilibrium distribution of the adsorbed cations was: Ca2+ ∼ 60%, Mg2+ ∼ 20%, and Na+ and K+ ∼ 10% each. The Ca2+ in the Shafdan production wells and in the experimental columns outflow (∼5 meq L−1) was always higher than the Ca2+ in the recharged effluent (∼3.5 meq L−1), indicating continuous CaCO3 dissolution. This study demonstrates that besides mixing, a suite of geochemical processes should be considered when assessing groundwater quality following artificial recharge of aquifers.

The chemical composition of groundwater in the Jordan Valley, along the section between the Sea of Galilee and the Dead Sea, is investigated in order to evaluate the origin of the groundwater resources and, in particular, to elucidate the role of deep brines on the chemical composition of the regional groundwater resources in the Jordan Valley. Samples were collected from shallow groundwater in research boreholes on two sites in the northern and southern parts of the Jordan Valley, adjacent to the Jordan River. Data is also compiled from previous published studies. Geochemical data (e.g., Br/Cl, Na/Cl and SO4/Cl ratios) and B, O, Sr and S isotopic compositions are used to define groundwater groups, to map their distribution in the Jordan valley, and to evaluate their origin. The combined geochemical tools enabled the delineation of three major sources of solutes that differentially affect the quality of groundwater in the Jordan Valley: (1) flow and mixing with hypersaline brines with high Br/Cl (>2 × 10−3) and low Na/Cl (

Recent geochemical and hydrological findings show that the water quality of the base flow of the Lower Jordan River, between the Sea of Galilee and the Dead Sea, is dependent upon the ratio between surface water flow and groundwater discharge. Using water quality data, mass-balance calculations, and actual flow-rate measurements, possible management scenarios for the Lower Jordan River and their potential affects on its salinity are investigated. The predicted scenarios reveal that implementation of some elements of the Israel–Jordan peace treaty will have negative effects on the Jordan River water salinity. It is predicted that removal of sewage effluents dumped into the river (∼13 MCM/a) will significantly reduce the river water’s flow and increase the relative proportion of the saline groundwater flux into the river. Under this scenario, the Cl content of the river at its southern point (Abdalla Bridge) will rise to almost 7000 mg/L during the summer. In contrast, removal of all the saline water (16.5 MCM/a) that is artificially discharged into the Lower Jordan River will significantly reduce its Cl concentration, to levels of 650–2600 and 3000–3500 mg/L in the northern and southern areas of the Lower Jordan River, respectively. However, because the removal of either the sewage effluents or the saline water will decrease the river’s discharge to a level that could potentially cause river desiccation during the summer months, other water sources must be allocated to preserve in-stream flow needs and hence the river’s ecosystem.

Sediment and groundwater profiles were compared in two villages of Bangladesh to understand the geochemical and hydrogeological factors that regulate dissolved As concentrations in groundwater. In both villages, fine-grained sediment layers separate shallow aquifers (28 m) high in As from deeper aquifers (40 -90 m) containing 10 g/L As. In one village (Dari), radiocarbon dating indicates deposition of the deeper aquifer sediments 50 ka ago and a residence time of groundwater of thousands of years. In the other village (Bay), the sediment is 20 ka old down to 90 m and the deeper aquifer groundwater is younger, with a residence time of hundreds of years. The shallow aquifers in both villages that are high in As contain bomb- 3 H and bomb- 14 C, indicating recent recharge. The major and minor ion compositions of the shallow and deeper aquifers also differ significantly. Deeper aquifer water is of the Na-HCO3 type, with relatively little dissolved NH4 (76 192 mol/L), Fe (27 43 mol/L) and Mn (3 2 mol/L). In contrast, shallow aquifer water is of the Ca-Mg-HCO3 type, with elevated concentrations of dissolved NH4 (306 355 mol/L), Fe (191 73 mol/L), and Mn (27 43 mol/L). In both villages, the quantity of As extractable from deeper aquifer sands with a 1 mol/L phosphate solution (0.2 0.3 mg/kg, n 12; 0.1 0.1 mg/kg, n 5) is 1 order of magnitude lower than P-extractable As from shallow deposits (1.7 1.2 mg/kg, n 9; 1.4 2.0 mg/kg, n 11). The differences suggest that the concentration of P-extractable As in the sediment is a factor controlling the concentration of As in groundwater. Low P-extractable As levels are observed in both deeper aquifers that are low in As, even though there is a large difference in the time of deposition of these aquifers in the two villages. The geochemical data and hydrographs presented in this study suggest that both Holocene and Pleistocene deeper aquifers that are low in As should be a viable source of drinking water as long as withdrawals do not exceed recharge rates of 1 cm/yr. Copyright © 2005 Elsevier Ltd

The Dead Sea is a severely disturbed ecosystem, greatly damaged by anthropogenic intervention in its water balance. During the 20th century, the Dead Sea level dropped by more than 25 meters, and presently (2003) it is at about 416 meters below mean sea level. This negative water balance is mainly due to the diversion of water from the catchment area of the lake by Israel, Jordan and Syria. During the 2002 World Summit on Sustainable Development Israel and Jordan jointly announced their interest in saving the Dead Sea by constructing the “Peace Conduit” that will pipe water from the Red Sea to the Dead Sea. The inflow of seawater (or reject brine after desalinization) into the Dead Sea will have a major impact on its limnology, geochemistry and biology. During the filling stage, relatively diluted surface water will form and the rate of evaporation will therefore increase. Dilution of the surface water will most likely result in microbial blooming whose duration is not known, while the lower water layer is likely to develop reducing conditions, including bacterial sulfate reduction and presence of hydrogen sulfide (H2S). Mixing between the calcium-rich Dead Sea brine and the sulfate-rich seawater will result in gypsum precipitation (CaSO4⋅ 2H2O). Once the target level is reached, inflow will be outbalanced by evaporation and salinity of the surface water will increase due to accumulation of seawater-salts. The water column will re-mix when the density of the surface water will equal that of the lower water column. In spite of its large volume and high salinity relative to that of the inflowing water, over the long run the composition of this unique lake will change. Before a decision is made on the planning and construction of the Conduit, it is essential that the long term evolution and characteristics of the “renewed” Dead Sea be known and anticipated changes examined. Once decided upon, the planning and construction of the Conduit should be conducted so as to minimize possible negative impacts of seawater introduction on the Dead Sea. This can only be achieved through a thorough understanding of the expected changes in the limnological physical/chemical characteristics of the Dead Sea and its unique brine.

Differences in the impact of irrigation with freshwater versus wastewater on the underlying shallow groundwater quality were investigated in the Coastal Aquifer of Israel. Seven research boreholes were drilled to the top-most 3–5 m of the saturated zone (the water table region-WTR) in the agricultural fields. The unsaturated zone and the WTR below the irrigated fields consist mainly of clayey sands, while the main aquifer comprises mainly of calcareous sandstones and sands. We show that the salinity and composition of the groundwater at the WTR are highly variable over a distance of less than 1 km and are controlled by the irrigating water and the processes in the overlying unsaturated zone. Tritium data in this groundwater (4.6 tritium units (TU)) support that these water are modern recharge. The water at the WTR is more saline and has a different chemical composition relative to the overlying irrigation water. High SAR values (sodium adsorption ratio) in wastewater irrigation lead to absorption of Na C onto the clay and release of Ca 2C into the recharging water, resulting in low Na/Cl (0.4 compared to 1.2 in the wastewater) and high Ca/Cl ratios. In contrast, in the freshwater-irrigated field the irrigation water pumped from the aquifer (Na/ClZ0.9; SARZ0.6) is modified into Na-rich groundwater (Na/ClZ2.0) due to reverse base-exchange reactions. The high NO3 concentration (>100 mg/l) in the WTR below both fields is derived from the agricultural activities. In the freshwater field, the source of NO3 is fertilizer leachates, whereas in the wastewater field, where less fertilizers are applied, nitrate is probably derived from nitrification of the NH4 in the wastewater. Some of the original inorganic nitrogen in the wastewater is consumed by the agricultural plants, resulting in a lower inorganic-N/Cl ratio in the WTR as compared to that in the wastewater. This study demonstrates the important role of the composition of irrigation water, combined with lithology and land use, in determining the quality of the water that recharge the aquifer below agricultural fields. q 2004 Elsevier B.V. All rights reserved.

tions from small springs and rare flood events. Currently, the only two water sources at the starting point The Lower Jordan River is located in the semiarid area of the of the Lower Jordan River are the effluent of the Bitania Jordan Valley, along the border between Israel and Jordan. The implementation of the water sections of the peace treaty between wastewater treatment plant and the Saline Water CarIsrael and Jordan and the countries’ commitment to improve the rier (Sites 1 and 2 in Fig. 1). The Bitania source includes ecological sustainability of the river system require a better under- poorly treated human and animal waste effluents. The standing of the riverine environment. This paper investigates the Saline Water Carrier contains a mixture of saline spring sources and transformations of nitrogen compounds in the Lower water diverted from the Sea of Galilee and urban sewage Jordan River by applying a combination of physical, chemical, isoto- effluent. As a result of the degradation of water quantity pic, and mathematical techniques. The source waters of the Lower and quality, the Lower Jordan River has become brackJordan River contain sewage, which contributes high ammonium loads

The chemical and isotopic ( 87 Sr/ 86 Sr, 11 B, 34 Ssulfate, 18 Owater, 15 Nnitrate) compositions of water from the Lower Jordan River and its major tributaries between the Sea of Galilee and the Dead Sea were determined in order to reveal the origin of the salinity of the Jordan River. We identified three separate hydrological zones along the flow of the river: (1) A northern section (20 km downstream of its source) where the base flow composed of diverted saline and wastewaters is modified due to discharge of shallow sulfate-rich groundwater, characterized by low 87 Sr/ 86 Sr (0.7072), 34 Ssulfate (2‰), high 11 B( 36‰), 15 Nnitrate (15‰) and high 18 Owater (2 to-3‰) values. The shallow groundwater is derived from agricultural drainage water mixed with natural saline groundwater and discharges to both the Jordan and Yarmouk rivers. The contribution of the groundwater component in the Jordan River flow, deduced from mixing relationships of solutes and strontium isotopes, varies from 20 to 50% of the total flow. (2) A central zone (20 -50 km downstream from its source) where salt variations are minimal and the rise of 87 Sr/ 86 Sr and SO4/Cl ratios reflects predominance of eastern surface water flows. (3) A southern section (50 -100 km downstream of its source) where the total dissolved solids of the Jordan River increase, particularly during the spring (70 - 80 km) and summer (80 -100 km) to values as high as 11.1 g/L. Variations in the chemical and isotopic compositions of river water along the southern section suggest that the Zarqa River ( 87 Sr/ 86 Sr0.70865; 11 B25‰) has a negligible affect on the Jordan River. Instead, the river quality is influenced primarily by groundwater discharge composed of sulfate-rich saline groundwater (Cl - 31-180 mM; SO4/Cl0.2- 0.5; Br/Cl2-310 -3 ; 87 Sr/ 86 Sr0.70805; 11 B30‰; 15 Nnitrate 17‰, 34 Ssulfate4 -10‰), and Ca-chloride Rift valley brines (Cl - 846 -1500 mM; Br/Cl 6-8 10 -3 ; 87 Sr/ 86 Sr0.7080; 11 B40‰; 34 Ssulfate4 -10‰). Mixing calculations indicate that the groundwater discharged to the river is composed of varying proportions of brines and sulfate-rich saline groundwater. Solute mass balance calculations point to a 10% contribution of saline groundwater (Cl282 to 564 mM) to the river. A high nitrate level (up to 2.5 mM) in the groundwater suggests that drainage of wastewater derived irrigation water is an important source for the groundwater. This irrigation water appears to leach Pleistocene sediments of the Jordan Valley resulting in elevated sulfate contents and altered strontium and boron isotopic compo- sitions of the groundwater that in turn impacts the water quality of the lower Jordan River. Copyright © 2004 Elsevier Ltd

Detailed hydrochemical measurements, δ34SSO4 and 3H analyses were performed on 37 groundwater samples collected during February 1999, January and March 2000 from 6 locations in eastern and southeastern Bangladesh to examine redox processes that lead to As mobilization in groundwater. The study sites were chosen based on available nation-wide As surveys to span the entire spectrum of As concentrations in Bangladesh groundwater, and to represent 3 of 5 major geological units of the Ganges-Brahmaputra Delta: uplifted Pleistocene terrace, fluvial flood plain and delta plain. Arsenic was found to be mobilized under Fe-reducing conditions in shallow aquifers ( 50 μg/l; or > 0.7 μM ) were always accompanied by high dissolved [HCO3−] (> 4 mM), and were close to saturation with respect to calcite. Groundwater enriched in As (200–800 μg/l; or 2.7–10.7 μM) and phosphate (30–100 μM) but relatively low in dissolved Fe (5–40 μM) probably resulted from re-oxidation of reducing, As and Fe enriched water. This history was deduced from isotopic signatures of δ34SSO4 and 3H2O (3H) to delineate the nature of redox changes for some of the reducing groundwaters. In contrast, As is not mobilized in presumed Pleistocene aquifers, both shallow (30–60 m) and deep (150–270 m), because conditions were not reducing enough due to lack of sufficient O2 demand.

An increase in salinity and change from oxic to anoxic conditions are observed in the Upper subaquifer of the Judea Group in the Kefar Uriyya pumping field at the western foothills of the Judea Mountains, Israel. Hydrogeological data indicate that the change, which occurs over a distance of only a few kilometers, coincides with a transition from confined to phreatic conditions in the aquifer. The deterioration in the water quality is explained as a result of seepage of more saline, organic-rich water from above, into the phreatic "roofed" part of the aquifer. The latter is derived from the bituminous chalky rocks of the Mount Scopus Group, which confine the aquifer in its southeastern part. In this confined part, water in perched horizons within the Mount Scopus Group cannot leak down and flow westward while leaching organic matter and accumulating salts. However, upon reaching the transition area from confined to phreatic conditions, seepage to the Judea Upper subaquifer is possible, thereby allowing it to be defined as a leaky aquifer. The incoming organic matter consumes the dissolved oxygen and allows bacterial sulfate reduction. The latter accounts for the H2S in the aquifer, as indicated by sulfur isotopic analyses of coexisting sulfate and sulfide. Thus, from an aquifer management point of view, in order to maintain the high quality of the water in the confined southeastern part of the Kefar Uriyya field, care should be taken not to draw the confined-roofed transition area further east by over pumping.

International audience; Soil aquifer treatment (SAT) systems utilize infiltration basins for recharging pre-treated effluent into the aquifer for water quality improvement. The present research focuses on the diurnal and seasonal variations of oxygen, carbon and nitrogen species in the infiltration basins and in the uppermost vadose zone for determining the impact of different environmental conditions on the composition of the infiltrating effluent. The study was conducted in one of the infiltration basins of the Dan Region Sewage Reclamation Project (Shafdan), Israel. Solar radiation and aeration were recognized to be the two main factors controlling the chemical composition of the effluent within the basin and the uppermost vadose zone. The effluent entering the basin show initial enrichment with dissolved oxygen (DO) due to gas exchange caused by "injection'' through the inlet fountain and turbulence during basin filling. The DO, pH and dissolved inorganic carbon (DIC) fluctuate diurnally as a result of intense in-basin daylight photosynthesis and nighttime respiration. DO and pH increase during day and decrease during night and the DIC shows an opposite behavior. The daylight net primary production was similar to 240 mu mol L-1 d(-1) and the diurnal respiration rate was similar to 430 mu mol L-1 d(-1) (assuming that the nighttime respiration rate is constant over a whole diurnal cycle). The gross primary production during daylight was similar to 450 mu mol L-1 d(-1). Dissolved organic carbon (DOC) and inorganic nitrogen species (NH4+ + NO3) varied significantly in the uppermost vadose zone, however, neither the vadose zone nor the basin showed diurnal fluctuations. It appears that chemical variations between three sampling campaigns conducted in different seasons stemmed mainly from the efficiency of basin aeration that resulted from changes in basin's operation regime and local environmental conditions. The results of this study lead to the following basin management recommendations: (1) keeping short flooding and drying cycles and allowing complete basin desiccation before the next flooding; and (2) flooding the basin during daytime, starting at dawn to maximize oxygen production and minimize infiltration during nighttime. Following these routines would result in higher redox potential of the infiltrating effluent.

Geochemical and microbial evidence points to anaerobic oxidation of methane (AOM) likely coupled with bacterial sulfate reduction in the hypersaline groundwater of the Dead Sea (DS) alluvial aquifer. Groundwater was sampled from nine boreholes drilled along the Arugot alluvial fan next to the DS. The groundwater samples were highly saline (up to 6300 mm chlorine), anoxic, and contained methane. A mass balance calculation demonstrates that the very low δ(13) CDIC in this groundwater is due to anaerobic methane oxidation. Sulfate depletion coincident with isotope enrichment of sulfur and oxygen isotopes in the sulfate suggests that sulfate reduction is associated with this AOM. DNA extraction and 16S amplicon sequencing were used to explore the microbial community present and were found to be microbial composition indicative of bacterial sulfate reducers associated with anaerobic methanotrophic archaea (ANME) driving AOM. The net sulfate reduction seems to be primarily controlled by the salinity and the available methane and is substantially lower as salinity increases (2.5 mm sulfate removal at 3000 mm chlorine but only 0.5 mm sulfate removal at 6300 mm chlorine). Low overall sulfur isotope fractionation observed ((34) e = 17 ± 3.5‰) hints at high rates of sulfate reduction, as has been previously suggested for sulfate reduction coupled with methane oxidation. The new results demonstrate the presence of sulfate-driven AOM in terrestrial hypersaline systems and expand our understanding of how microbial life is sustained under the challenging conditions of an extremely hypersaline environment.

[1] This paper examines, for the first time, the unique situation of a groundwater system adjacent to a long-term stratified (meromictic) lake. Using conceptual and numerical models, the configuration of groundwater interfaces between the three different water bodies (regional groundwater and upper and lower lake waters) and the flow patterns were quantitatively evaluated assuming a homogenous aquifer. A complex flow system, controlled by density difference, is created near the lake, where three circulation cells are developed. These results are different from the classic circulation cell that is found adjacent to nonstratified water bodies (lakes or oceans). Sensitivity analyses reveal that the results are sensitive to changes in thickness and density of the upper water mass of the lake. The Dead Sea, under its possible future meromictic conditions, serves as an ideal example of such a system. Thus, the model's results can be used as a preliminary assessment for groundwater behavior adjacent to the lake, if and when stratification will develop.

[1] The high-degree of spatial variability of dissolved As levels in shallow aquifers of the Bengal Basin has been well documented but the underlying mechanisms remain poorly understood. We compare here As concentrations measured in groundwater pumped from 4700 wells

The Dead Sea is a severely disturbed ecosystem, greatly damaged by anthropogenic intervention in its water balance. Since the beginning of the 20th century, the Dead Sea level have dropped by more than 20 meters, and presently (2006) it is about 419 meters below mean sea level. The rate of water level drop over the last 10 years is about 1.0 m/yr, representing an annual water deficit of about 650 million cubic meters. The sharp level drop reflects the annual interception by riparian countries of over 1000 million cubic meters of freshwater which in the past drained to the Dead Sea. In addition to the water interception upstream, the Israeli and Jordanian mineral industries contribute to this deficit by artificially maintaining extensive evaporation surfaces in the otherwise now dried southern Dead Sea basin.

The composition of groundwater reclaimed from tertiary soil aquifer treatment systems reflects the dynamic processes taking place in the subsurface, between the infiltration basin and the production wells. At the end of year 2000, following more than a decade of operation, high Mn concentrations (2 micromol L(-1)or = Mnor = 40 micromol L(-1)) appeared in the reclaimed effluents of the Dan Region Sewage Reclamation Project (Shafdan), Israel. A mass balance indicates that the high Mn excess originated from the aquifer rocks, most likely following reduction of sedimentary Mn-oxides under suboxic conditions. The subsequent adsorption of the Mn2+ results in a slow Mn2+ front that advances in the direction of groundwater flow only when all the Mn2+ exchangeable sites are saturated. A retardation factor obtained from two independent estimates based on a simple reduction-adsorption-advection model yields a value of about 10. This explains the delayed appearance of the high Mn concentrations at a distance of only -500 m from the infiltration basin.

[1] The Dead Sea is a hypersaline terminal lake experiencing a water level drop of about 1 m/yr over the last decade. The existing estimations for the water balance of the lake are widely variable, reflecting the unknown subsurface water inflow, the rate of evaporation, and the rate of salt accumulation at the lake bottom. To estimate these we calculate the energy and mass balances for the Dead Sea utilizing measured meteorological and hydrographical data from 1996 to 2001, taking into account the impact of lowered surface water activity on the evaporation rate. Salt precipitation during this period was about 0.1 m/yr. The average annual inflow is 265–325 × 106 m3/yr, corresponding to an evaporation rate of 1.1–1.2 m/yr. Higher inflows, suggested in previous studies, call for increased evaporation rate and are therefore not in line with the energy balance.

1 , which is about 40 times lower than the historical flow by ground water contribution (including agricultural re- rates. Our measurements and calculations indicate that ground water turn flows) and that surface inputs alone cannot account input was 20 to 80% of the river water flow, and 20 to 50% of its for the overall chemical changes. In the present study, solute mass flow. This study independently identifies the composition we quantify the ground water contribution by an integra- of possible end-members. These end-members contain high sulfate tionofflowratemeasurements withthechemicalchanges concentration and have similar chemical characteristics as were found that were observed along the Lower Jordan River. in agricultural drains and in the "saline" Yarmouk River. Future regional development plans that include the river flow rate and chem- istry should consider the interactions between the river and its shallow MATERIALS AND METHODS ground water system. Wepresentresultsofflow-ratemeasurements,chemicalanal- yses, and mass-balance calculations along the upper (northern) 20km ofthe LowerJordan River.The resultswere obtainedin W ater resourcesin arid and semiarid regions are collaboration between Jordanian, Israeli, and Palestinian re- often overexploited. Many rivers in these regions searchers between 1999 and 2001. The rainfall during these become saline and polluted, and their low flow rates years was limited (approximately 75% of the annual average) further endanger their future sustainability (Pillsburry, and thus the reported results represent base flows under 1981; Williams, 2001). The Lower Jordan River is an ex- drought conditions. treme example of such a river, where the combination of excessive water needs and lack of environmental at- The Study Area

The Lower Jordan River received in the past a large volume of freshwater from Lake Tiberias, the Yarmouk River, and local runoffs. Currently, a much smaller flow-rate of mostly poor-quality fluids enters the river. The severe reduction of inflow and the poor-quality flows have led directly to the degradation of the water quality along the river. According to the regional peace agreements, both sewage and saline waters will be treated and used. Carrying out these agreements will result in a dramatic reduction of input flow-rates into the river. Under these circumstances, the almost sole available source will be drainage and groundwater. The objective of this study is to evaluate the different components that presently control the quality of water in the Lower Jordan River. In particular, the study is looking for ways to assess the role played by the subsurface contributions. We present here preliminary results of an ongoing research, which involves researchers from Israel, Jordan, and the Palestinian Authority. By means of water sampling, chemical analysis, isotope analysis, flow-rate measurements, and mass balance calculations, the study improves our understanding of the hydrology and hydrochemistry of the river system.

The level of the Dead Sea (the lowest surface on Earth) is currently declining at a rate of 0.8 m/yr, and has dropped about 20 m since the beginning of the twentieth century; it reached −410 m in 1997. We address the question of whether the level of the Dead Sea will continue to decline. A numerical model, developed in this study to determine the water balance, accounts for the increase in salinity and the concomitant decrease in the rate of evaporation that accompanies reduction in the activity of the water. Simulations based on ranges of water withdrawal scenarios suggest that the Dead Sea will not “die”; rather, a new equilibrium is likely to be reached in about 400 yr after a water-level decrease of 100 to 150 m.