2011 Volume 27 Pages 117-127
Short sediment cores were taken from four lakes in Nagano Prefecture, Japan. They are Nishina Three Lakes (Aoki, Nakatsuna and Kizaki) situated at the east foot of the Japan Northern Alps, and Nojiri located to the northeast, about 20km apart from Nagano City. Sediments were analyzed for anthropogenic polynuclear aromatic hydrocarbons (PAHs). Vertical distribution and their accumulations in individual lake sediments were determined since their concentration apparently increased. Despite scarce population and absence of considerable emission sources around the Nishina Three Lakes, PAHs in the sediment cores show significantly high concentration, maximizing in the mid-depth of the cores, which are in the order Kizaki>Nakatsuna>Aoki and evidently higher than that of Nojiri. Particularly high concentration was observed in Kizaki, where it amounted to 3.5μg/g dry sediment. Accumulation of PAHs in the Nishina Three Lake sediments was in the range of 4-8μg/cm2, whereas it remained around 1.5μg/cm2 in the Nojiri sediments. The Nishina Three Lakes are surrounded by mountains as high as 1,300-1,600m, from which surface water may flow down into the lakes. On the contrary, the catchments of Nojiri are narrow compared with the surface area of the lake basin. Thus an explanation may be possible that PAHs once deposited on the catchments may contribute much to those in the lake sediments.
