²¹⁰Pb in Lake Kinneret Waters and Sediments: Residence Times and Fluxes

Abstract

Measurements of ²¹⁰Pb were made of Lake Kinneret waters (Israel), of three sediment cores, of particulate matter collected from sediment traps, and of the particulate load of the inflowing Jordan River. A preliminary balance of the ²¹⁰Pb sources indicates that direct atmospheric input accounts for only about 25% of the ²¹⁰Pb flux to the lake, river load accounts for 55%, and decay of ²²²Rn in the water column accounts for 20%. Ninety percent of the incoming ²¹⁰Pb is lost to the sediments: 0.55 dpm cm⁻² yr⁻¹. The mean residence time of total ²¹⁰Pb in the lake, 0.6 years, is composed of the residence time of dissolved and particulate phases, 1.5 to 2.7 years and 0.1 year, respectively. Sedimentation rates have been calculated in the three sediment cores by applying the correction for Rn diffusion to the porewaters for the vertical ²¹⁰Pb distribution in the sediments; it is shown that only in one of the three cores, where both the sedimentation rate and the ²¹⁰Pb excess/²²⁶Ra ratios were low (less than 0.2 cm yr⁻¹ and less than 1, respectively), was this correction necessary. ²¹⁰Pb fluxes at the sediment-water interface were derived from ²¹⁰Pb activities in the settling material and the respective sedimentation rate; at two sites, out of the three examined, they agree with the lake average ²¹⁰Pb flux to the sediments computed from the ²¹⁰Pb balance of the lake.