Source Assessment and Sedimentary Record of Pyrolytic Polycyclic Aromatic Hydrocarbons in Lake Bled (NW Slovenia)

Polycyclic aromatic hydrocarbons (PAH) were determined in two sediment cores in urban Lake Bled (NW Slovenia). In surface sediments of the deep western basin, the total PAH concentration was 1150 ng g–1 dry weight (dw), whereas in shallower, nearshore Zaka Bay the PAH concentration was 1900 ng g–1 dw. Four- to six-ring PAH were the most abundant compounds, suggesting that most PAH in Lake Bled sediments are pyrogenic, probably of coal combustion origin as inferred by several PAH ratios. Uniform compositions for pyrogenic PAH were observed downcore in both cores. The highest concentrations of PAH in Lake Bled sediments occurred in sediments deposited in mid 20th Century (ca. 1945), leading to organic carbon (OC) normalized concentrations of 120 μg PAH g–1 OC, compared to contemporary concentrations of 21 and 30 μg g–1 OC in the western basin and Zaka Bay, respectively. Using PAH concentrations and sedimentation rates, we estimate that present-day PAH fluxes are 630 and 1800 μg m–2 yr–1, respectively. These contemporary PAH fluxes to Lake Bled were still 3–4 fold higher than in nearby but remote alpine Lake Planina, confirming elevated PAH contamination in the urban setting.