Use of phosphate oxygen isotopes for identifying atmospheric-P sources: a case study at Lake Kinneret.

The input of phosphorus (P) through atmospheric deposition can be a major source of P to fresh water bodies and may strongly affect their biogeochemistry. In Lake Kinneret (LK), northern Israel, dust deposition provides a significant fraction of the bioavailable P input. Here, we demonstrate that the oxygen isotopic composition of resin-extractable inorganic phosphate (δ(18)OP) in dust particles can be used to identify the phosphate source. Samples of soils with both natural vegetation and agricultural cover were collected upwind of LK and found to have distinct δ(18)OP value ranges (17.4-18.2‰ and 19.3-22.1‰, respectively). The δ(18)OP values for dust, collected continuously over LK during June 2011 to March 2012, were in the same range as agricultural soils. The dust concentration in the air decreased from the dry to the wet season and was correlated with a decrease in P concentration in air, yet no correlation was found between these parameters and dust δ(18)OP. Dust deposited during short-term desert dust events was characterized by a combination of high δ(18)OP values ranging from 22.2‰ to 22.7‰ and high concentrations of dust in the air. The data we present demonstrates a new application of δ(18)OP measurements for direct estimation of dust-P sources to lakes, as well as the potential for tracing dust-P on larger scales.