Abstract
1. The organic content of lake deposits has been determined for 53 Japanese lakes.
2. Loss on ignition: In the fresh water lakes of harmonic type, the pereentage of loss on ignition ranges from a minimum. of 8.4% in Lake Kutarako (Oligotrohpic type) to a maximum of 21.0% in Lake Toroko (Eutrophic type) with a mean of 14.5%. The dystrophic pons have the highest, as would be expected, from 336.2% to 60.8%.
3. Carbon and Nitrogen: As we detected in general a negligible amount of carbonate-carbon in common lake deposits of Japan, it is probable that the carbon constitutes essentially organic matter. Excluding the dystrophic lakes, the amount of carbon varies from a minimum of 1.5% in Lake Shinjiko (Eu. Brackish) to a maximum of 8.6% in Lake Toroko. The amount of nitrogen falls between 0.15% in Lake Shinjiko (Eu. Brackish) and 1.04% in Lake Haruna (Meso) and shows a good parallelism with that of _??_ the mean ratio of Nitrogen to Carbon being 0.116.
4. Ether extract ranges from 0.28% to 1.50%.
5. The lakes have been divided from the standpoint of biological produc-tivity, and have been further divided on the basis of transparency and. salinity. So far as we have determined, it seems that there is no marked difference in the organic cotent of deposits in the lakes.
The assumption that the eutrophic lake deposits may contain much organic matter is not always true. The typical oligotrophic lake-deposits certainly have a smaller amount of carbon and nitrogen, but the content of organic matter in some eutrophic lake deposits are as small as in the oligotrophic lake deposits.
