Tadashiro Koyama

The occurrence of stanols in various living organisms and the behavior of sterols in contemporary sediments

Abstract Unsaturated sterols (stenols) and saturated sterols (stanols) in phytoplankton and Zooplankton from Lake Suwa and from higher plants around the lake were analyzed by combined GLC and MS. In all the organisms investigated, 5α-cholestanol, 24-methylcholestan-3β-ol and 24-ethyl-5α-cholestanol were found, although in low concentrations, together with large quantities of stenols. This strongly suggests the contribution of stanols from living organisms to recent sediments. Findings from incubation experiments of cholesterol and 5α-cholestanol in the surface sediment from Lake Suwa extending through 450 days suggest the following: (1) stanols are slowly degraded and tend to survive unaltered in sediments in comparison with stenols, (2) in a relatively oxidative depositional environment such as Lake Suwa, the greater part of the stanols in the surface sediment originates from living organisms, (3) the reduction zone in which the degradation of sterols is suppressed and the rapid hydrogenation of stenols takes place may be in the microbiologically active sediment from 1 cm to about 10 cm in Lake Suwa, and (4) the increase in the ratio of stanols to stenols with depth below the zone may be caused by the simultaneous progress of preferential degradation and slow hydrogenation of stenols during long-term preservation in sediments.

Early diagenesis of fatty acids in lacustrine sediments-I. Identification and distribution of fatty acids in recent sediment from a freshwater lake

Abstract Fatty acids have been isolated and quantitatively determined from a 1.5 m sediment core of Lake Suwa, a eutrophic lake in the central districts of Japan. The fatty acids identified by combined gas chromatography-mass spectrometry were straight-chain saturated (C 12 to C 34 ), monounsaturated with even carbon number (C 16 to C 24 ) and branched-chain ( iso, anteiso , 10-methyloctadecanoic) acids. The concentrations of the higher molecular weight (⩾ C 20 ) saturated fatty acids remained nearly constant throughout the core, suggesting a high degree of preservation of those acids, whereas the monounsaturated and the lower molecular weight saturated fatty acids indicated a great decrease in concentration with depth to an approximately 20cm level. It is suggested that the microbial activity in sediments causes a significant reconstruction of the fatty acid distribution during early diagenesis.

Microbial metabolism in reduction process of paddy soils (Part 1)

Abstract In contrast to upland crops, rice plant is usually cultivated in the waterlogged condition. On waterlogging, the arable soil changes from an oxidizing to a reducing condition because of the oxygen consumption, and the accumulation of reduced materials as a result of the decomposition of soil organic matter under limited oxygen supply from the surface water. A waterlogged soil may be defined as one which is essentially reductive in character.

Stenols and stanols in lake sediments and diatoms

Abstract 5α-cholestan-3β-ol (cholestanol), 24β-methyl-5α-cholestan-3β-ol (ergostanol) and 24α-ethyl-5α-cholestan-3β-ol (stigmastanol) were identified by combined gas-liquid chromatography (GLC) and mass spectrometry (MS), from core sediments of Lake Suwa, which is one of the eutrophic lakes in Japan. The same stanols as those found in the sediments were also determined in the diatom, Melosira granulata , collected from this lake. This suggests that a certain portion of the stanols in the sediments originates from diatoms, although reduction processes of stenols to stanols may also take place in the core sediments as reported by several workers. It was found that the ratio of stanols to stenols in the lake sediments tended to increase from the surface of the sediment to a depth of 1.5 m. Also absolute amounts decrease sharply with depth.

Early diagenesis of fatty acids in lacustrine sediments—II. A statistical approach to changes in fatty acid composition from recent sediments and some source materials

Abstract The percentage composition and total amounts of fatty acids from plankton, live and dead plants (waterweeds and higher plants) and a forest soil, considered as possible origins of autochthonous and allochthonous organic materials in lacustrine sediments, have been determined by gas-liquid chromatography. Statistical analyses were carried out by computing distance index of the fatty acid composition between these source materials and the uppermost sediment from Lake Suwa, and the composition diversity index (CDI) of fatty acids in the recent sediments from Lake Suwa. The distance index indicated that the fatty acid composition in the uppermost sediment is similar to those in diatoms, Zooplankton and forest soil, and the values for dead leaves were smaller than for live ones. It suggests that the autolysis and/or decomposition processes prior to deposition onto the top sediment makes the fatty acid composition of organic debris similar to the uppermost sediment. The CPI in recent sediments varied irregularly, whereas the CDI increased during early diagenesis to yield a value comparable to ancient sediments.

Positional isomer composition of monounsaturated fatty acids from a lacustrine sediment

Abstract From the surface sediment of a eutrophic lake (Japan), the double bond position in the monounsaturated fatty acids (C 15 -C 26 ) has been determined by combined gas chromatography-mass spectrometry of the methoxylated derivatives. The relative abundance of 11-octadecenoic acid, suggested to be of bacterial origin, is higher in the chloroform-methanol extract than the extract by saponification.

MICROBIAL METABOLISM IN REDUCTION PROCESS OF PADDY SOILS (PART 2) : Effect of Iron and Organic Matter on the Reduction Process (1)

Abstract The previous experiences1-3) with incubation experiments of the soils under submargd condition indicated that the disappearance of molecular oxygen and nitrates occurred shortly after sub-emerging, and then the reduction of ferric iron proceeded, being followed by the reduction of sulfates and the formation of methane which nre caused by the activities of strict anaerobes. It was suggested from the above fact that the reduction process in the submarged soils was affected mainly by two factors: namely, the amount of reducible ferric iron and the soil organic matters which are avaiable as substrate for microbial metabolism.

Inhibitors of methane production in paddy soils

Abstract Global warming is now attracting the world attention. Methane is an important greenhouse gas next to CO2. Prather et al. (1995) estimated that rice paddy fields account for 14% of all biogenic atmospheric methane. It is considered that methane production from rice paddy fields is increasing along with the increase of the population. Therefore, the development of rice cultivation techniques for reducing methane production is essential, in order to preserve the global environment.

Early diagenesis of organic matter in lacustrine sediments in terms of methane fermentation

The amounts of organic compounds such as amino acids (proteinaceous substances), fatty acids, and sterols in lacustrine sediments were found to decrease greatly from the mud‐water interface to depths of 20 cm and less at greater core depths. The amounts of methane produced by microbial activity in subsamples incubated for 40 days at 27°C were also found to decrease with core depth, apparently limited by the exhaustion of organic substrates subject to methane fermentation. Decomposition rates of certain organic compounds added to sediment samples were determined by incubation experiments at different temperatures for 40 to 450 days. Experimental results with mixed cultures of microorganisms in lacustrine sediments indicated the following: (a) The marked decomposition of organic compounds such as amino acids, fatty acids, and sterols in the lacustrine sediments resulted mainly in the formation of methane, (b) Unsaturated compounds were more readily decomposed with the ultimate formation of methane than satu...

INFLUENCE OF SEA SALTS ON THE SOIL METABOLISM. : I.On the Behaviour of Iron, Manganese, Ammonium, and Carbohydrates in Waterlogged Soils

Abstract Microbial metabolism in reduction process of waterlogged paddy soils has been studied by Takai, Koyama, and Kamura (1, 2, 3, 4, 5, 6), Koyama (7, 8, 9, 10, 11, 12), and others. The results indicated that microbial metabolism in waterlogged soils takes place according to the following steps: (1) In the early stage of the incubation period, dissolved O2, is consumed and the redox potential drops rapidly. (2) NO2− and NO2− are reduced to N2. (3) Mn4+ is reduced to Mn2+. (4) Fe3+ is reduced to Fe2+. (5) SO4 2− is reduced to S2−. (6) H2 and CH4 are produced. Takai and Chiang (13) reported that NH4+ and PO4 3+ in waterlogged paddy soils increase with the incubation period. Chiang and Takai (14) indicated that carbohydrates in the soil solutions almost remain constant throughout the incubation period, however, organic acids change similarly to those reported previously (5, 6).