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Papers by Naama Avrahamov

&lt;p&gt;Groundwater recharge of mountain aquifer requires detailed knowledge of ... more &lt;p&gt;Groundwater recharge of mountain aquifer requires detailed knowledge of the hydrologic system and adequate monitoring and modeling methods to determine water amount and water quality evolution. Mountain aquifers are well known of their highly complex lithologic structure and surface morphology. These become more significant in dry climate regions (&lt;300 mm rainfall/year) which are characterized by erratic rain pattern and extreme deep thickness unsaturated zone.&lt;/p&gt;&lt;p&gt;In this study we monitor the isotopic and geo-chemical evolution affecting the composition of the unsaturated porewater during deep infiltration, from surface to depth that is not affected from evaporation. The geo-chemical processes were characterized related to land surface morphology and climate conditions.&lt;/p&gt;&lt;p&gt;The research setup includes instrumentation of first-order stream which is characterized by two main typical geomorphologic setting: rocky terrain and deep soil along the stream channel. Each plot was instrumented with a monitoring setup that include a meteorological station and Vadose Zone Monitoring System (VMS) that enables continuous water content measurement and collection of unsaturated porewater from the vadose zone.&lt;/p&gt;&lt;p&gt;Fast increases in water content and arrival of depleted &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O (VSMOW) reveal quick and deep infiltration of rainwater during storm events, while enriched &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O arrival indicates slower infiltration of water that is exposed to evaporation. In addition, the geo-chemical processes exhibited depletion in &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C (PDB) of rainwater during the infiltration (-19 to -11 &amp;#8240;) which indicates on dominant of biogenic activities and relatively low rock-water interactions. Major elements correlation network expresses the contribution of dust and rain to the rock evolution across the water flow path.&lt;/p&gt;&lt;p&gt;The study results clearly exhibited different infiltration rates in each site. Fast infiltration at the rocky terrain due to rock outcrops on the surface create funnels for collecting the local runoff and delivering it into high permeability fractured zones where the water penetrates directly to the deep sections. In contrast, the bare soil areas such as hilltops or man-made terraces in streams with highly developed soil cross-section, reveal limited infiltration. Also, the annual rainfall pattern impacts the geochemical process and finally impacts the groundwater quantity and quality.&lt;/p&gt;

ABSTRACT. Due to its possible role in solid/water carbon isotope exchange, the effect of salinity... more ABSTRACT. Due to its possible role in solid/water carbon isotope exchange, the effect of salinity on radiocarbon dating of groundwater was examined by batch interaction of alluvial sediment and calcite powder with freshwater (Cl – = 100 mg L–1) and Dead Sea (DS) brine (Cl – = 225 g L–1). These 2 water types were spiked with H13CO3 – tracer and kept under constant agi-tation for about 1 yr. Several bottles were respiked twice with the tracer. The uptake of the 13C by calcite was monitored through repeated isotopic measurements of the aqueous solutions, and the effect on 14C groundwater dating was evaluated using a simple transport reaction model. The results indicate that the kinetics of water/calcite isotope exchange start with a very fast initial step followed by a slower one, which was used here to simulate the long-term water/solid exchange in “real” aquifers. The exchange model that best fits the data was homogeneous recrystallization that formed just a very thin layer of newly ...

Springer Hydrogeology, 2020

The geochemistry of groundwater surrounding the Dead Sea reflects mixing between different water ... more The geochemistry of groundwater surrounding the Dead Sea reflects mixing between different water bodies that occupied the Dead Sea basin and fresh groundwater flowing from the highlands to the basin. The distribution of various geochemical parameters is affected by changes in the lake level, including natural fluctuations and the present lake level drop. This chapter deals with different aspects of groundwater flow mechanisms in the coastal aquifer of the Dead Sea and their relationship with the groundwater geochemistry. Dead Sea water circulation in the coastal aquifer occurs during a steady-state lake level but also persists during lake level drop. This interaction between the Dead Sea water and the sediments removes Ba, U, and 226Ra and contributes Fe, Mn, and short-lived Ra isotopes to the Dead Sea. 14C and tritium values in the Dead Sea groundwaters are affected by mixing with fresh water and between brines that occupied the Dead Sea Rift during different times. In addition to ...

Journal of Hydrology, 2021

Geochimica et Cosmochimica Acta, 2018

Groundwater age in a carbonate karstic aquifer was assessed using a multiple tracer method that e... more Groundwater age in a carbonate karstic aquifer was assessed using a multiple tracer method that enables identification of modern groundwater (recharged after 1955; using 3 H-3 He, 85 Kr CFCs, SF 6 ,), older components (39 Ar, 14 C) and quantification of the mixing between them. Twelve wells were sampled in the Eastern Mountain Aquifer (EMA) of Israel along two trajectories, from the recharge area in the mountains, to the natural outlets in the Dead Sea area. The concentration of the dissolved 39 Ar in the groundwater decreased from 96 to 12% along the trajectories, indicating recent recharge upstream, and groundwater aged more than 800y downstream. Other tracers present a similar general trend of decreasing concentrations with distance from the recharge area at two distinct rates, suggesting two different groundwater flow velocities in the two different groundwater flow paths. In most of the wells, pronounced mixing was observed according to the presence of young (after 1955) and older water components. The fraction of the young water was quantified by tritium (3 H) and by the combination of 3 H and 85 Kr measurements and found to be between 1 to 67%. The wide age distribution is likely caused by the karstic nature of the aquifer with pronounced dispersion and exchange between highly permeable flow channels and stagnant water stored in the rock matrix. Another mixing mechanism is vertical leakage from the upper to the lower sub-aquifer and vice versa according to the groundwater head differences between the two sub-aquifers. Mixing, diffusive exchange and water rock interaction lead to a reduction of 14 C in DIC, resulting in an apparent half-life of ~900y instead of 5,730y for radioactive decay only. This is concluded from the comparison of 14 C and 39 Ar ages.

Earth and Planetary Science Letters, 2019

Radioactive noble-gas isotopes tracers 81 Kr and 39 Ar are used for the first time to measure the... more Radioactive noble-gas isotopes tracers 81 Kr and 39 Ar are used for the first time to measure the residence times of deep (~1000 m) saline coastal groundwater, and to determine its connection mode with the sea. The average rate of seawater intrusion into the deep aquifer in Israel, located near the Mediterranean Sea, is estimated. 81 Kr-ages of the saline water samples, found to be younger than 40 ka, contradict previously estimated ages of up to several million years based on hydrogeological considerations. The new results imply a stronger and more recent connection between the aquifer and the sea, and indicate that the intrusion occurred during the sea-level rise that began about 20 ka ago. These coastal aquifers need to be managed with caution because lowering of the adjacent fresh water level due to over pumping could accelerate seawater intrusion in a relatively short time. This study demonstrates the suitability of these two noble-gas tracers for the examination of hydrogeological systems in general and for the study of seawater intrusion in particular.

Radiocarbon, 2010

This work presents an attempt to date brines and determine flow rates of hypersaline groundwater ... more This work presents an attempt to date brines and determine flow rates of hypersaline groundwater in the extremely dynamic system of the Dead Sea (DS), whose level has dropped in the last 30 yr by ∼20 m. The processes that affect the carbon species and isotopes of the groundwater in the DS area were quantified in order to estimate their flow rate based on radiocarbon and tritium methods. In contrast to the conservative behavior of most ions in the groundwater, the carbon system parameters indicate additional processes. The dissolved inorganic carbon (DIC) content of most saline groundwater is close to that of the DS, but its stable isotopic composition (δ13CDIC) is much lower. The chemical composition and carbon isotope mass balance suggest that the low δ13CDIC of the saline groundwater is a result of anaerobic organic matter oxidation by bacterial sulfate reduction (BSR) and methane oxidation. The radiocarbon content (14CDIC) of the saline groundwater ranged from 86 pMC (greater tha...

Chemical Geology, 2015

ABSTRACT The concentrations and isotopic compositions of methane, higher alkanes, dissolved inorg... more ABSTRACT The concentrations and isotopic compositions of methane, higher alkanes, dissolved inorganic carbon (DIC) and CO2 were studied in fresh groundwater, brines and springs along the Dead Sea Transform (DST), from the Hula Valley in the north to the Dead Sea (DS) basin in the south. Although the occurrence of methane along the DST was documented before, this is the first time that comprehensive research was conducted on the methane provenance and the post-genetic reactions involved. The methane stable carbon isotopic composition (δ13CCH4) shows a distinct geographic pattern. In the northern part of the DST studied, in the Hula valley and Lake Kinneret, where recent marshy and lacustrine environments exist, the methane source seems to be related to intense shallow depth methanogenesis. This microbial methane shows low 13C values in the range of δ13CCH4 between − 58‰ and − 72‰ and high alkane ratios (C1/C2 + C3) between 100 and 1000. The isotope fractionation α CO2-CH4 of 1.065‰ suggests the domination of hydrogenotrophic methanogenesis rather than acetoclastic methanogenesis. In the waters of Hammat Gader and Tiberias hot spring, whose source is the Cretaceous aquifer, δ13CCH4 has high values of − 28‰ and − 56‰, respectively, with low alkane ratios of ~ 40 in both sites. The high δ2HCH4 values of Hammat Gader, in addition to the isotopic composition of the DIC and the difference between CO2 and CH4, reject the possibility of local microbially produced methane and suggest a sub-surface thermogenic source of an initial stage of thermal degradation of bituminous chalk of Senonian age. Similarly, methane in groundwater from the DS basin is also interpreted to be of thermogenic origin. In accordance with the local geology context in the DS basin of buried asphalt, and due to the low geothermal gradient in the region, it is speculated that methane is produced from slight heating of the asphalts. In general, it seems that there is a thermogenic methane contribution along the entire DST, which is locally masked by high microbial activity in shallow organic-rich environments, such as Lake Kinneret and the Hula basin.

Radiocarbon, 2013

Due to its possible role in solid/water carbon isotope exchange, the effect of salinity on radioc... more Due to its possible role in solid/water carbon isotope exchange, the effect of salinity on radiocarbon dating of groundwater was examined by batch interaction of alluvial sediment and calcite powder with freshwater (Cl– = 100 mg L–1) and Dead Sea (DS) brine (Cl– = 225 g L–1). These 2 water types were spiked with H13CO3– tracer and kept under constant agitation for about 1 yr. Several bottles were respiked twice with the tracer. The uptake of the 13C by calcite was monitored through repeated isotopic measurements of the aqueous solutions, and the effect on 14C groundwater dating was evaluated using a simple transport reaction model. The results indicate that the kinetics of water/calcite isotope exchange start with a very fast initial step followed by a slower one, which was used here to simulate the long-term water/solid exchange in “real” aquifers. The exchange model that best fits the data was homogeneous recrystallization that formed just a very thin layer of newly formed calcite...

Geochemical and microbial evidence points to anaerobic oxidation of methane (AOM) likely coupled ... more 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 d 13 C DIC 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 AE 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.