Polycyclic aromatic hydrocarbons and black carbon in sediments of a remote alpine Lake (Lake Planina, northwest Slovenia)

Abstract

Polycyclic aromatic hydrocarbons (PAH) and black carbon (BC) were measured in alpine Lake Planina (Slovenia) sediment. Lake Planina is a remote mountain lake with almost no direct anthropogenic influence. Long-distance atmospheric deposition is a major pathway for the loading of contaminants to the sediment. The PAH were analyzed by gas chromatography coupled to mass spectrometry, whereas the BC was determined by thermal oxidation method. A flux of PAH to surface sediments of approximately 1,100 microg m(-2) year(-1) was obtained and was higher than that in other alpine lakes of the central European Alps. However, surface sediment PAH concentration, normalized to organic carbon content (OC), amounted to 5 microg PAH(pyr)/g OC and showed that Lake Planina is relatively equally exposed to atmospheric pollution compared with other lakes in the region. The BC:OC ratios ranged from 3 to 8% (w/w). In addition, a huge forest fire occurred in 1948 in the lake's surrounding area, which is recorded in the sediment. Both PAH and BC distributions were affected by the fire in 1948 in the lake's watershed, because their concentration increased remarkably. The concentration of retene, a molecular marker of coniferous wood combustion, increased to 1,000 ng/g dry weight sediment at the sediment interval corresponding to approximately the year 1950.