Horizontal distribution of carbon and nitrogen and their isotopic compositions in the surface sediment of Lake Biwa |
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Authors: | J Murase M Sakamoto |
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Institution: | (1) School of Environmental Science, University of Shiga Prefecture, 2500 Hassaka, Hikone, Shiga 522-8533, Japan Tel. +81-749-28-8310; Fax +81-749-28-8463 e-mail: murase@ses.usp.ac.jp, JP |
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Abstract: | The horizontal distribution of the abundance and isotopic composition of carbon and nitrogen was studied on surface sediment
samples (0–15 cm) collected from the entire area of Lake Biwa, the largest freshwater lake in Japan. As water depth increased,
a marked increase in organic matter content was observed at the sampling sites, especially in the western North Basin, characterized
by a steep slope. In the northwestern North Basin, which has no major inflowing streams, the sediments contained large amounts
of organic matter, suggesting the possibility of lateral transportation of sedimented matter from other places by lake currents.
The total amounts of carbon and nitrogen in the top-2 cm of sediment of the entire area of Lake Biwa were estimated to be
9.2 × 104 tC and 1.0 × 104 tN. The δ15N values in the littoral sediment were low and close to those in the inflowing river sediment, suggesting selective sedimentation
of allochthonous organic matter onto the littoral area. In the North Basin, vertical profiles of organic matter content and
δ13C values of the sediments in the littoral area showed a smaller downward decrease than in the profundal area, whereas δ15N values decreased with sediment depth in both areas. It was suggested that the littoral sediments contained abundant amounts
of allochthonous and relatively refractory organic matter. Further, it was suggested that the autochthonous organic matter
originated from primary production deposited mainly on the profundal zone and was easily decomposed in early diagenesis after
sedimentation.
Received: July 30, 1999 / Accepted: December 10, 1999 |
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Keywords: | Sediment Carbon Nitrogen Stable isotope Lake Biwa |
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