Hiroshi Mizutani

The use of stable isotopes for food web analysis

General aspects in isotope biogeochemistry was summarized with emphasis on delta 15N and delta 13C contents in plants and animals in natural ecosystems. In the estuary, the variation of isotope ratios were principally governed by the mixing of land-derived organic matter, marine phytoplankton, and seagrasses. A clear cut linear relationship between animal delta 15N and its trophic level was obtained in the Antarctic food chain system. Several current efforts to use the stable isotopes for food web analysis were demonstrated for some terrestrial and marine systems as well as human food web.

Biogeochemical studies on the transport of organic matter along the Otsuchi River watershed, Japan

The distributions and stable isotope ratios of biogenic nitrogen and carbon were investigated in detail along a small watershed in order to establish a biogeochemical framework for assessing the fate of organic matter. Forest ecosystems supply soluble and particulate materials to river systems which are depleted in 15N and 13C. The number of suspended particles and the concentrations of δ15N and δ13C in the river sediments increased along the watershed, indicating a change from river to marine ecosystems. Dramatic variation of δ15N and δ13C were observed in the intertidal sediments, where the progress of denitrification, discharge of domestic sewage, and the accumulation and the decomposition of macroalgae and seagrasses took place. n nThe contribution of land-derived organic matter to estuarine sediments has been estimated from δ13C and from δ15N data. The contribution the landderived organo-silty-clay mineral was 70–100% in the inner bay sediments and 34–42% at the open bay. Possible factors that influence the variation of stable isotope ratios along the watershed are discussed. The relationship between the sizes of particles and isotope ratios clearly demonstrated that organo-silty-clay minerals with diameter smaller than 64 μm were the major source of land-derived refractory organics.

High nitrogen isotope ratio for soils of seabird rookeries

Soils from rookeries of penguin, of gull, and of albatross were examined for their nitrogen isotope ratio. The ratio was far higher than any so far reported for soils. Furthermore, there was an apparent dependence of the ratio on the latitude of rookery locations. The high ratio seemed to have had resulted from a relatively high ratio for incoming nitrogen to the rookeries, and from the large fractionation factor during the ammonia volatilization from the rookeries. The isotope ratio for ammonium nitrogen of the penguin rookery soils averaged 45 per mil, while that of the gull rookery soils gave the mean of 27 per mil during the breeding season of the birds. Soils of gull rookeries and of albatross rookery gave, on the average, a similar ratio of 17 per mil for Kjeldahl nitrogen, though its content of soils of gull rookeries was nearly two orders of magnitude higher than that of albatross rookery. Soils from penguin rookery showed the ratio of 32 per mil for Kjeldahl nitrogen, the enrichment of15N being two and a half times as large as that for soils of other rookeries.

Effect of high atmospheric CO2 concentration on δ13 of algae

Precambrian reduced carbon is more depleted in13C than what would be expected from the carbon isotopic composition of modern marine algae and algal mats. Since the photosynthetic carbon fixation by algae is the most likely source of the reduced carbon, the depletion has been considered an anomaly.We examined factors that might have contributed to the carbon isotope fractionation from inorganic sources through algae to organic matter in a sedimentary rock, and related laboratory obtainable data to those from Precambrian rocks. Laboratory culture experiments were then performed with nine strains of algae at various concentrations of carbon dioxide, and the result was interpreted according to the relationship.It indicated that the depletion could be understood in terms of a combined effect of fractionation factors, most depletion occurring at the fractionation during the photosynthetic carbon fixation. It also suggested that all but one algal strain incorporated bicarbonate as the source of carbon for its growth. The exception was a thermophilic, acidophilic alga, which must have used carbon dioxide as the carbon source.The present study suggests that Precambrian atmosphere was enriched in carbon dioxide roughly two orders of magnitude more than its present atmospheric level.

Carbon isotope composition of CH4 from rice paddies in Japan

Carbon isotope ratios (δ13C) for bubble CH4 in a submerged paddy soil were studied in Yokohama, Japan, throughout a growing period, and its variation was found. Bubble CH4 collected from other 33 paddy fields in Japan was also measured for its δ13C and the results agreed with Yokohama. Furthermore, the variation occurred irrespective of the amount and the type of supplied organic substances to the fields (whole rice straw, rice stubble, or compost). The δ13C value (average value of -55.9 ± 4.24‰) from these paddy fields was higher than those of the CH4 emitted from African and North American paddies. The higher value was little affected by their difference in the supplied organic substances. CH4 oxidation likely occurs for bubble CH4 in the shallow paddy fields. A rough estimate of the total CH4 production, using isotope mass balance, showed that 17 to 22% of organic carbon supplied to Japanese paddies transforms to CH4.

Combustion of organic samples by infrared furnace for carbon isotope analysis.

An apparatus for converting organic samples to carbon dioxide is described. It is especially designed to determine stable carbon isotope ratio of field samples. Unlike previous apparatus of similar configuration, a Craig-line, it is free from the deposition of charred carbon on the line that results from an incomplete conversion. It includes an infrared furnace that heats both a CuO column and a sample tube. A removable, stainless-steel tube is present around the heated area, and this particular configuration makes it possible to begin every combustion procedure from room temperature, and consequently, to achieve a complete evacuation of air from the line even for heat-labile samples. The apparatus also includes a column that eliminates contaminating oxides such as nitrous oxide. The time necessary to process a sample is less than 30 min, and the precision of the carbon isotope measurement is comparable with that of Craig-line. The coefficient of variation of carbon content determinations was no more than a few percents for most samples examined. An incidental finding was made that an isotopic fractionation of uric acid occurred during its preparation from penguin excreta by a high-performance liquid chromatography.

High-performance liquid chromatographic isolation of uric acid from soil for isotopic determination

Abstract Uric acid was extracted from soil into potassium phosphate solution and isolated from other components by high-performance liquid chromatography, then the isolated fraction was subjected to nitrogen isotope analysis. Studies of the adsorption of uric acid on clay indicated no significant isotope fractionation during the exchange reaction; hence the isotope ratio found in the extract was the same as that in the soil. An increase in soil ammonia content followed the decomposition of uric acid. No uric acid isotopic preference by uric acid bacteria during the decomposition was found. The fractionation at the time of ammonia evaporation was mainly responsible for the high nitrogen isotope ratio in bird rookeries. An extremely high ratio for soil ammonia was found in a simulation experiment. This phenomenon may be mimicked in nature.

Linear correlation netween latitude and soil15N enrichment at seabird rookeries

Mesure du rapport isotopique de lazote dans lobjectif de determiner si letude de la volatilisation ammoniacale est relative a une mesure globale

High-performance liquid chromatographic determination of uric acid in soil

Abstract The large deposits of organic nitrogen in sea-bird rookeries may be responsible for an establishment of an ornithocoprophilous plant community. Uric acid, a major end-product of avian nitrogen metabolism, must play an important role in making this unique ecosystem. The acid was extracted from soil into potassium phosphate solution and separated from other components in the extract by high-performance liquid chromatography. Although the adsorption of the acid by soil prevents its quantitative recovery, the method is adequate to be applied to a study of nitrogen metabolism in rookeries. A large input of uric acid during the breeding season, its localization on the soil surface and its in situ decomposition were found to occur in the rookeries. The method is easily modified for preparative purposes, which makes it possible to perform isotopic analysis at a natural level and to elucidate further the nitrogen dynamics in the ecosystem.

Material cycling and organic evolution

Intertwined cycles of matters are proposed to be one of the essential characteristics of life. The increase in the amount of recycled matters within biological groups and the complication of the cycling network are considered to be the early development of life soon after its appearance on the Earth. From this point of view, the origin of a cell alone can not sufficiently be regarded as the origin of life. The origin of a cell must be followed by a formation of material cycling among cells, if the cells are to stay on the Earth long enough so that they could be called life.This biogeochemical viewpoint leads to a quantitative analysis of life activity. A formula is presented to exemplify the potential utility of the viewpoint. It is applied to analyses of possible early developments of life and of an impact of present human activity on the global carbon cycle. Further application of the viewpoint to a variety of biogeochemical, sociogeochemical, ecological, and environmental problems should eventually show whether there is some utility in this view.