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Title (Primary) Saisonale chemische Variationen des See Genezareth, seiner Zuflüsse und deren Ursachen
Author Siebert, C.;
Journal PhD Dissertation
Year 2006
Department HDG;
Volume 1/2006
Language deutsch;
UFZ inventory Leipzig, Bibliothek, Reportsammlung, 00159746, 06-0439 F/E
Abstract


The aim of the study was to detect, to characterise and to quantify groundwater-inflows into the Lake Kinneret (Sea of Galilee, Lake Tiberias or See Genezareth). To detect those inflows, it was necessary to chemically acquire all ground- and surface waters, which are involved in this process by using a combination of advanced hydrochemical methods: major and minor elements, trace elements (REE+Y), radiogenic (3H) and stable isotopes (δ 18O, δ 2H, δ 13C, δ34S).

Seasonal hydrochemical variations clarify the hydraulic connection of groundwaters to (i) specific aquifers, (ii) different thermo-saline groundwaters, and (iii) to recharge waters, which are chemically dependent on the lithology of their recharge areas.

In the Beq’at Kinarot, 5 types of groundwater are outlined on the base of spiderpatterns and ionic ratios. That grouping gives information about the lithology of the aquifers of discharge and the mixing with thermo-saline groundwaters.

- Type B1 represents waters from Judea-limestones, where only small amounts of halite and gypsum occur. With exception of well D 906 no other groundwater of this type is influenced by thermo-saline waters.

- Type B2 comprises waters mainly from Eocene Avedat- and only minor from Judealimestones, which also contain some gypsum and halite. Based on ionic ratios this type is subdivided in type B2a (Tabgha group) and type B2b (Hammat Gader group). Waters of type B2a is compositionally altered by ascending Na-Ca-Mg-Cl-brines, whereas type B2b is influenced by weathering solutions of basalts.

- Type B3 represents thermo-saline waters. They are solely from Lower Aquifer of the western graben shoulder showing Mg/Ca molar ratios <1. Cl/Br- and B/Cl ratios in Fuliya and Tabgha (KIN 8) indicate high contributions of ablation brines of still undiscovered evaporate bodies (halite, gypsum). However, in Tiberias mixing with Na-Ca-Mg-Cl-brines dominates.

- Type C represents water from oxidative weathering of basalts. High contents of nitrate document a strongly anthropogenic influence by agriculture.

- Type D with high Mg/Ca molar ratios >1 and with elevated to high salinities is solely observable along the eastern graben shoulder and south of Tiberias. Ionic ratios of groundwater from Ha’On 1 indicate the presence of a primary evaporation brine of the Sdom Sea. The recharge area of Gofra spring is rich in glauconitic minerals, which may explain the high contents of B in this type of water.

In Beq’at Kinarot, all groundwaters with elevated mineralisation show molar 2Na/ (Ca+Mg)>1, which indicates intensive leaching of evaporate bodies such as that of in Zemah borehole.

In Tiberias, the saline end-member is a mixture of residual evaporation brine chemically modified by albitisation and dolomitisation and a Na dominated ablation brine. As part of the saline end-member, the modified brine is only observable in and north of Tiberias. However, the mixture ratios locally strongly differ. Modification of primary evaporation brine is the result of their migration through alkali-olivine-basalts, gabbros and limestones as they occur in the graben sensu stricto and in the western graben flank. The former Mg/Ca molar ratio >1 is turned <1, because of chloritisation and albitisation of plagioclase and the dolomitisation of the limestones. Waters from Tiberias show strong analogies (Cl/Br, Na/Cl) to those in Ha’On 1. In Tiberias, these refer to a saline end-member which is similar to the primary brine in Ha’On.

In well developed flow systems rare earth elements including yttrium (REY) cover the aquifer walls with the initial signature of the water. In contrast to the major elements, water maintains the REY-signature of the lithology in the area of infiltration. Using REY-patterns, waters have been classified.

- Type REY-A1 corresponds to waters from the carbonaceous and sometimes marly Judeagroup. The patterns show a distinct flat course with a slight decline from light towards the heavy rare earths.

- Type REY-A2 occurs only in the Tabgha area and is characterised by low contents of REY and well developed negative Ce-, positive Gd- and Y-anomalies. These waters represent the oxygen rich karstified system of the Eocene limestone aquifers.

- Type REY-A3 represents thermo-saline waters from Tiberias. With flat patterns and well developed Y-anomalies. They are similar to type REY-A1 but are in contact with hydrothermally altered limestones of the Lower Aquifer.

- Type REY-A4 is characterised by predominantly steep decline of the light REE (La to Sm). Groundwater of this type is also of thermo-saline origin, form instance, contact zones of limestones and intruded igneous basic rocks.

- Type REY-B is present solely along the eastern graben shoulder and in Ein Porih. Patterns with variable Ce-, Gd- and Y-anomalies refer to solutes from weathering of the Golan- and Cover Basalts, where precipitation of FeOOH occurred.

Stable isotopes δ18O and δ2Η in groundwaters are the results of mixing of (i) isotopically light recharge and (ii) isotopically heavy, ascending thermo-saline groundwaters. δ18O and δ2H in Tabgha waters establish an inflow of isotopically very light groundwater from the north into the Beq’at Kinarot.

The distribution of major-, minor- and trace elements as well as of isotopes in the water of Lake Kinneret was investigated in 12 lake-water profiles. With the exception of profiles “Barbutim”, “Tabgha” and “G” were hydrochemistry and isotopes clearly indicate the inlet of groundwater, in all other locations constant inflow of groundwater into the lake water was only provable by the systematic change of Ce-anomalies and marginal changes in REYpatterns at the sediment/water interface.

On the base of data from Mekorot Comp. Ltd., the amount of inflowing groundwater at the lake bottom and the contents of Cl and Br were balanced for the hydrological year 2002/03. The results are inflow of 84×106 m3/a, Cl and Br equal 66×106 and 0.54×106 kg/a, respectively. However, the uncertainties of the monthly in- and outflows of the lake fully cover the estimated inflow.

Combination of (i) areal information on specific electric resistivities in pore-waters and (ii) chemical analyses of pore fluids, lead to a yearly minimum input of 22×106 kg chloride by diffusion/advection. Weighting the Cl input by areas of similar specific resistivities describes the reality much better than a lump-sum view of the basal area of the lake.

From the systematic changes of the Ce-anomalies at the sediment/water interface a net-stream of minimal 44×106 m3 pore water into the lake was derived. From the assumption in the upper 0.3m of the sediment chloride is about 350 mg/l a net-inflow of >17×106 kg Cl per year is derived. The inflow of chloride through the lake bottom as calculated by diffusion/advection and by the changing Ce-anomalies are definitely more than 20×106 kg/a, without knowing the upper limit.

ID 3038
Persistent UFZ Identifier https://www.ufz.de/index.php?en=20939&ufzPublicationIdentifier=3038
Siebert, C. (2006):
Saisonale chemische Variationen des See Genezareth, seiner Zuflüsse und deren Ursachen
Dissertation, Freie Universität Berlin
PhD Dissertation 1/2006
Helmholtz-Zentrum für Umweltforschung - UFZ, Leipzig, 180 S.