Lead concentrations and isotopic ratios in the sediments of the Sea of Galilee

The isotopic composition and concentrations of Pb in the sediments of the S ea of Galilee (Lake Kinneret) were measured. The studied sediments have bee n deposited in the lake since the early 1900s (ca. 1920), hence Pb data rec ord the transition from a period when the lake vicinity was sparsely popula ted to the present (approximately 100 000 people living in the area around the lake). In general, there is either a constant or a relatively slow incr ease in Pb concentrations from 40 cm depth (3.5-4.4 mug/g; ca. 1920) to 17 +/- 2 cm below the sediment-water interface (3.7-7.2 mug/g;), which was dep osited in the mid-1960s. From 17 +/- 2 cm below the surface, there is a muc h faster increase up to 7 +/- 2 cm below the surface (from 6.5 to 11.5 mug/ g; 1982-1983), and from 7 +/- 2 cm there is a gradual decrease in Pb concen trations toward the sediment water interface. At station G, near the outlet of the Jordan River, Pb concentrations drop between 29 and 25 cm below the surface, probably reflecting changes in the particulate load of the Jordan River due to the drying out of the Hula Swamp in the early 1950s. Pb-206/P b-207 values in all the stations record most of the shifts displayed by Pb concentrations in the sediment. The estimated value of total Pb deposited a nnually in the lake sediment in the early 1990s is very close to the value obtained from measurements of Pb fluxes to the lake from eolian and fluvial sources. On the basis of the linear relationship between Pb-206/Pb-207 (or Pb-208/(207P)b) and 1/[Pb], we argue that two end-members contribute most of the Pb to the lake sediments. Sources of Pb to the lake include (i) the weathering of basalt from the eastern Galilee and the Golan Heights contrib uting 2.6 +/- 0.5 mug/g Pb to the sediment and (ii) anthropogenic Pb that i s affecting both surface and deep (from 30 to 40 cm) lake sediments. At sta tion S, a third source, Pb released from soils developed on carbonates, sho uld be considered as well.