Distributions of polycyclic aromatic hydrocarbons in a sediment core from the north basin of Lake Biwa, Japan

We analyzed the vertical distributions of 19 polycyclic aromatic hydrocarbons (PAHs), total organic carbon (TOC), total nitrogen (TN) and stable carbon isotope ratio (δ13C) in a 27 cm sediment core from the north basin of Lake Biwa in order to elucidate changes in PAH sources and events possibly affecting the lake over the last few decades. Both TOC and TN increased gradually from the deepest layer (TOC, 1.2 wt.%; TN, 0.14 wt.%) to the uppermost layer (TOC, 4.0 wt.%; TN, 0.45 wt.%). The TOC/TN ratio, a useful indicator for distinguishing between aquatic and terrestrial plant sources, increased remarkably at 11-13 cm (10.3-11.1 vs. 8.5-9.7 at other depths), indicating that large amounts of terrestrial material entered the lake when that layer was deposited. All PAHs except perylene gradually increased from the deepest layer, but not as clearly as TOC and TN. At 11-13 cm, all PAHs except perylene transiently decreased and perylene transiently increased. Since the PAH ratios used for the elucidation of sources did not change greatly throughout the core, we consider that the major source of PAHs in the lake has not changed during the last few decades. The brief decrease in PAHs at 11-13 cm could be the result of dilution by a large input of terrestrial material, which brought in perylene.