METODOLOGÍA OPERACIONAL DE TRANSPORTE POR POLIDUCTOS

Within this work, several approaches to estimate the initial 14C activities of the spring waters were applied. Results are given in Table 34, Table 35 and Table 36. CARMI et al. (1985) in

their study accounted for the exchange of CO2 between river water and the atmosphere and concluded that the 14C level in the Mount Hermon aquifer baseflow and the 14C level in the atmospheric CO2 is at a constant ratio of approximately 0.44.

Assuming that carbonate dissolution alone causes the dilution of the initial 14C activity, BAJJALI et al. (1994, 1997, 2006) suggested that the dilution factor q can be calculated by:

atmosphere e rech e rech C C q 14 arg 14 arg =

where 14Crecharge and 14Catmosphere are average values of 14C measured in the recharge area and the atmosphere respectively. In this study, the 14C content of atmospheric CO2 is considered to be about 103 pmc (see above). Hence, the dilution factor for the Hermon springs is about 0.56, while for the Golan springs it averages to about 0.68. CLARK and FRITZ (1997) quote

dilution factors of 0.65-0.75 for karst systems. Within this study, we did not correct for geochemical reactions along the flowpath (And), which is left to future studies and more extensive investigations of carbon chemistry in the study area.

An additional precondition for the determination of corrected radiocarbon ages was the assignment of δ13_{C values in soil CO}

2 as input parameter for some of the correction models. Literature values of 13C content in soil CO2 dependent on the type of vegetation are given in Table 32. At present, C3-plants dominate vegetation in the Eastern Mediterranean region, hence soil CO2 generally ranges between -27 to -24 ‰ V-PDB (CERLING et al., 1991; CERLING and QUADE, 1993). Accounting for diffusive fractionation of soil CO2 by microbial activity of about 4 ‰ (CERLING et al., 1991), δ13C of soil CO2 in most C3 landscapes is generally about -23 ‰ V-PDB (CLARK and Fritz, 1997). This value was thus assigned to soil

CO2 in the Golan region and for the intake area of the Senir stream.

In the Hermon region however, soil covers are thin or absent and soil waters in other karst regions have been shown to have higher δ13_{C values of about -14.7 ‰ V-PDB (L}

EE and

KROTHE, 2001). BAR-MATTHEWS et al. (1996) investigated carbon isotopes in a close-by

Mediterranean karst area. Assuming that fast infiltrating seepage waters have dissolved both soil CO2 derived from the C3-type vegetation and marine carbonate host rock and given that the 12C/13C fractionation between bicarbonate ion and C3-type organic matter is -7.5 ‰ at T ≅ 20°C (HENDY, 1971), the isotopic composition of DIC in equilibrium with C3 organic matter is around -19.5 to -16.5 ‰ V-PDB (BAR-MATTHEWs et al., 1996). Therefore, a value

of -19.5 ‰ V-PDB was assumed for soil CO2 in the Hermon area.

The results of the isotopic and geochemical calculations of the initial activities A0 and the corrected water ages according to the different models and assumptions are summarized in Table 34, Table 35 and Table 36. Groundwater mean residence times derived from the original data, the Mass Balance model, the Vogel model and the dilution factor of CLARK and

FRITZ (1997) for karst systems vary widely and are unrealistic. The Mook model did not

apply to the data. However, there is some consistency for the remaining models (Tamers, Ingerson and Pearson, Fontes and Garnier, Eichinger) and assumptions (CARMI et al., 1985;

BAJJALI et al., 1994, 1997) indicating the dominance of recent water in the Hermon

springs which agrees with groundwater residence times derived on tritium analyses and earlier investigations in the study area (CARMI et al., 1985). However, Kezinim water seems

to have significantly larger mean residence times than the other spring waters which is reasonable considering that this spring is dominated by matrix flow and shows little variations in discharge over time (GUR et al., 2003). Starting with the highest groundwater mean

residence time, Hermon springs can be ranked in the following order: Kezinim > Banias > Dan > Leshem > Barid.

In the Golan area, the situation seems to be more complex. The calculated A0 values and the derived groundwater mean residence times vary broadly and a consistency between the models such as for the Hermon springs was not observed, except for the Dupheila spring which seems to be dominated by recent water. Refering to the Bajjali model most of the spring waters seem to have mean residence times below 1000 years.

A significant drawback of the conducted radiocarbon based age estimations is that in situ 13C concentrations of soil CO2 and the initial atmospheric 14C activity could not be determined. Parameter uncertainty was shown to lead to age uncertainties of up to several thousand years, especially where δ13_{C values of groundwater are less negative than -12 ‰ (P}

EARSON, 1992).

Subsequent studies should thus include the measurement of soil CO2 for carbon isotopes in the respective recharge zones. Additionally, the determination of the carbon isotope composition at epikarstic outlets in the Hermon area could provide NETPATH input data (“initial well”) that allow to account for geochemical reactions along the flow path as well. In the Golan area, an extensive network of boreholes exist that should be included in future studies.

ƒ the overestimation of the 14C-age due to transport delays of 14C without significant

δ13_{C changes (M}

ALOSZEWSKI & ZUBER, 1991)

ƒ the influence of isotope exchange (AESCHBACH-HERTIG, et al., 2002)

ƒ the diffusive exchange of 14C into the matrix (between aquifer and aquitards) resulting in the overestimation of 14C-age (SUDICKY and FRIND, 1981)

ƒ sulphate reduction (BAJJALI et al., 1997; KATTAN, 2002)

ƒ the incorporation of geogenic CO2 (BARNES et al., 1978; GASPARINI et al., 1990; KATTAN, 2002) or

ƒ methanogenesis.

Table 34: Corrected initial 14_{C activities and subsequently calculated groundwater mean residence times of the sampled Hermon springs. The}

measured in situ activities are given as ‘Original data’.

Kezinim Banias Dan Leshem Barid Senir

A0 Age A0 Age A0 Age A0 Age A0 Age A0 Age

pmc year pmc year pmc year pmc year pmc year pmc year

NETPATH model

Original Data 46.6 6130 55.9 4675 56.7 4560 60.6 4030 62.0 3835 75.1 2300

Mass Balance 62.2 2388 60.6 675 63.1 879 62.6 269 63.5 199 57.2 Recent

Vogel 85.0 4967 85.0 3469 85.0 3348 85.0 2803 85.0 2604 85.0 1025

Tamers 55.5 1443 55.0 Recent 54.7 Recent 53.9 Recent 53.9 Recent 54.3 Recent

Ingerson and Pearson 38.1 Recent 56.1 34 53.0 Recent 43.4 Recent 49.2 Recent 69.0 Recent

Mook 110.2 3174

Fontes and Garnier 37.5 Recent 57.1 174 52.9 Recent 43.2 Recent 49.1 Recent 78.2 337

Eichinger 33.3 Recent 52.9 Recent 49.7 Recent 39.9 Recent 45.9 Recent 67.0 Recent

Other

Clark and Fritz (1997) 67.0 2994 67.0 1496 67.0 1375 67.0 829 67.0 631 67.0 Recent

Carmi et al. (1985) 45.3 Recent 45.3 Recent 45.3 Recent 45.3 Recent 45.3 Recent 45.3 Recent

Table 35: Corrected initial 14_{C activities and subsequently calculated groundwater mean residence times of the sampled Golan springs (I). The}

measured in situ activities are given as ‘Original data’.

Dupheila Divsha Bet HaMekhes Elmin Jedida Gonen

A0 Age A0 Age A0 Age A0 Age A0 Age

pmc yr pmc yr pmc yr pmc yr pmc yr

NETPATH model

Original Data 54.6 4865 64.3 3550 73.7 2445 81.6 1635 67.1 3205

Mass Balance 61.8 1031 62.4 Recent 71.1 Recent 64.7 Recent 62.7 Recent

Vogel 85.0 3665 85.0 2310 85.0 1175 85.0 337 85.0 1955

Tamers 53.1 Recent 52.3 Recent 52.2 Recent 53.7 Recent 52.1 Recent

Ingerson and Pearson 51.3 Recent 65.9 208 76.7 326 76.2 Recent 60.7 Recent

Mook 33.9 Recent 101.7 3793 145.9 5643 139.2 4413 80.1 1467

Fontes and Garnier 51.2 Recent 74.1 1180 91.2 1760 89.6 777 65.9 Recent

Eichinger 48.6 Recent 63.7 Recent 74.9 125 74.6 Recent 58.4 Recent

Other

Table 36: Corrected initial 14_{C activities and subsequently calculated groundwater mean}

residence times of the sampled Golan springs (II). The measured in situ activities are given as ‘Original data’.

Hamroniya Jalabina Notera

A0 Age A0 Age A0 Age

pmc yr pmc yr pmc yr

NETPATH model

Original Data 67.6 3150 66.5 3275 67.2 3190 Mass Balance 67.0 Recent 71.9 645 66.1 Recent

Vogel 85.0 1898 85.0 2029 85.0 1938

Tamers 53.5 Recent 51.9 Recent 51.9 Recent Ingerson and Pearson 42.2 Recent 79.4 1460 75.1 914

Mook 162.3 7378 146.7 6450

Fontes and Garnier 41.9 Recent 95.9 3025 89.3 2344

Eichinger 39.1 Recent 77.4 1254 73.0 677

Other

7.

Runoff generation in the main tributaries of the Upper Jordan River