Shinji Kaneko

Vertical migration of radiocesium and clay mineral composition in five forest soils contaminated by the Fukushima nuclear accident

Abstract In forest soils contaminated by radiocesium (134Cs and 137Cs), deposition from the Fukushima nuclear accident, clay minerals might play important roles in long-term cesium (Cs) dynamics through sorption. To determine whether radiocesium can be retained within the organic layer and the upper mineral soil layers in the Fukushima region, we investigated the vertical distribution of 134Cs and 137Cs and the clay mineral composition in five soil profiles of varying radiocesium deposition levels and vegetation types. X-ray diffraction analyses and oxalate extraction suggested that hydroxy-interlayered vermiculites and short-range-ordered aluminum (Al) and iron (Fe) compounds (i.e, allophane and ferrihydrite) were major clay mineral species of the upper soil layers. The vertical soil distribution of 134Cs and 137Cs suggested that most of them were retained in the organic layer and upper mineral soil layer under different levels of deposition. Within 1.5 years after the accident, both 134Cs and 137Cs were leached from the organic layer, and most of these (59–73%) were accumulated in the upper soil layer (0–5 cm). The proportion of 137Cs (or 134Cs) leaching from the organic layer was greater at sites receiving greater amounts of precipitation. The substantial accumulation of 137Cs in the upper soil layer, irrespective of the 137Cs deposition level or clay mineral composition, suggests that sorption capacities of clays and organic matter are sufficiently high to retain 137Cs in the surface soil during at least the initial stage of contamination.

Biomass and morphology of fine roots of sugi (Cryptomeria japonica) after 3 years of nitrogen fertilization

Increasing nitrogen (N) deposition may affect carbon and nutrient dynamics in forest ecosystems. To better understand the effects of N deposition, we need to improve our knowledge of N effects on fine roots (roots <2 mm in diameter), as they are a key factor in carbon and nutrient dynamics. In this study, we fertilized 1 × 2 m plots in a sugi (Cryptomeria japonica) stand (336 kg ha-1 y-1) for 3 years and evaluated the responses of the fine roots to high N load. After fertilization, the concentration of NO3–N in the soil of N-fertilized (NF) plots was five-times as large as that in the control plots and the effect was more remarkable in the subsurface soil than in the surface soil. The biomass of fine roots <2 mm in diameter appeared to be greater in the NF plots (88 ± 19 g m-2) than in the control plots (56 ± 14 g m-2), but this difference was not statistically significant. In both plots, 76% of the biomass was accounted for by fine roots that were <1 mm in diameter. In the surface soil, the specific root length of fine roots <1 mm in diameter was significantly greater, and the diameter of those fine roots was marginally smaller, in the NF plots than in the control plots. In addition, the concentration of N in fine roots <1 mm in diameter was marginally greater in the NF plots than in the control plots. There may have been increased production of thinner fine roots or increased root branching in the NF plots. This study suggests that, in general, high N load is likely to have positive effects on sugi in terms of fine root characteristics and the effects on fine-root morphology are more evident than the effects on fine-root biomass.

Temporal changes in the radiocesium distribution in forests over the five years after the Fukushima Daiichi Nuclear Power Plant accident

To elucidate the temporal changes in the radiocesium distribution in forests contaminated by the Fukushima Daiichi Nuclear Power Plant accident, we monitored the 137Cs concentration and inventory within forests from 2011 to 2015 across nine plots containing variable tree species and different contamination levels. The 137Cs concentrations in needles and branches decreased exponentially at all coniferous plots, with effective ecological half-lives of 0.45–1.55 yr for needles and 0.83–1.69 yr for branches. By contrast, the 137Cs concentration in deciduous konara oak leaves did not change over the five years. The concentration of 137Cs in oak wood increased by 37–75%, whereas that in Japanese red pine decreased by 63% over the five years. In Japanese cedar and hinoki cypress, the 137Cs concentration in wood showed an increasing trend in half of the plots. The changes in 137Cs in the organic and mineral soil layers were not strongly related to the tree species or contamination level. Our multi-site, multi-species monitoring results revealed that the pattern of temporal changes in radiocesium in the 9 forest plots was similar overall; however, changes in 137Cs in needles/leaves and wood differed among tree species.

Composition of inorganic elements and the leaching behavior of biomass combustion ashes discharged from wood pellet boilers in Japan.

To evaluate the characteristics of wood ash as fertilizer, composition of inorganic elements and the leaching behavior were studied. The leaching behavior was evaluated by three leaching methods using different solvents (water, hydrochloric acid, and acetic acid: Japanese leaching test Nos. 18 and 19 and modified toxicity characteristic leaching procedure prescribed by the US Environmental Protection Agency). The ash composition varied according to raw materials for fuel and ash collection systems. Concentration of Na, Al, Si, and V became higher in bark ashes while that of K became higher in wood ashes. Pb, Cd, Se, and Zn were more volatile and enriched in fly ashes. Of the nutrient elements, K showed high water solubility and its phytoavailability also appeared high, although the amount of water-soluble K was low in bark ash. Ca and Mg had intermediate solubility while P was less soluble in both water and acetic acid. The amount of hazardous substances having leached was low for most, but not all the ashes, in terms of Pb, Cr and As. Nevertheless, the phytoavailability of these hazardous substances after their application to the forest appeared low, due to their amphoteric leaching behavior and the acidity of Japanese forest soils.

SOIL GENESIS ON THE RAISED CORAL REEF TERRACES OF ISHIGAKI- AND OKINAWA-ISLANDS IN THE RYUKYU ISLANDS, JAPAN : I. Relations among Soils and Geomorphic Plains and Chronosequential Change of Soil Chemical Properties

Soil forming processes on the raised coral reef terraces under humid sub-tropical maritime climate were investigated in Ishigaki- and Okinawa-islands in the Ryukyu Islands. Analyses of soil morphology and soil chemical properties showed that there is a close relationship between soil development and the relative age of the terrace plains, as follows: The soils develop from Coral Limestone Lithosols (Lithic Udorthents) on the lowest terraces, through Rendzina-like soils (Typic Rendolls) on the lower terraces, Terra fusca-Iike soils (Lithic Eutrochrepts) on the lower middle terraces, Mottled Terra fusca-like soils (Aqu-ollic Hapludalfs) on the higher middle terraces and finally to Terra rossa-like soils (Mollic Hapludalfs) on the limestone plateaux corresponding to the higher terraces. However, the status of free iron oxides in all these soils is similar to that of Red soils, reflecting the bio-climatic conditions of the humid sub-tropics. It appears therefore necessary to develop criteria that may enable t...

A method for obtaining the relationship between the amount of DNA and the fine root weight from mixtures of fine roots and soil particles

Fine root biomass can be estimated from the quantity of DNA of a target plant extracted from fine root samples using regression analysis. However, the application of this method to fine root samples mixed with soil particles (mixed samples) is difficult due to the high DNA adsorption capacity of some clay minerals. Our aim in this study was to clarify the enhancement level of the DNA extraction efficiency of an improved method, and to obtain a regression line between the amount of DNA and the root biomass from a mixed sample with similar reliability as for fine roots alone (pure root sample). We examined the amount of DNA extracted from a mixture of Zea mays L. fine roots and highly adsorbent Kanuma soil using various concentrations of a skim milk solution, which acts as an adsorption competitor for the soil particles during the DNA extraction process. The amount of DNA of Zea mays extracted from the mixed sample using 0% skim milk was lower than from the pure root sample. However, the amount of DNA extracted from the mixed sample increased with increasing concentrations of skim milk, reaching the same level as for the pure root samples and resulting in a regression line that was similar to the pure root samples. Optimal DNA extraction levels were obtained with the addition of 20 µL of a 20% skim milk solution to 30 mg of a mixed sample. We also discuss the applicability of this method to other plant species and soil types.

Characteristics of culm structure and carbon and nitrogen concentrations in dead bamboo culms of two Phyllostachys species

The tissue structure of a bamboo stem (culm) differs from that of woody species, exhibiting a large cavity in the internode surrounded by a cortex with high silica concentration. Thus, to obtain an accurate estimation of the necromass, as well as carbon (C) and nitrogen (N) stocks in dead bamboo culms, we examined the basic characteristics of culm structure as well as the C and N concentrations of decomposing culms of Phyllostachys bambusoides and P. heterocycla. We collected dead culms of the two bamboo species from 15 bamboo stands in central and southwestern Japan, and analyzed the relationship between the ratio of wall volume to culm disk volume and culm diameter, as well as the changes of C and N concentrations in dead culms with wall density, which can be used as an indicator of the degree of decomposition. The ratio of wall volume to culm volume tended to decrease with increasing culm diameter for both species. The C concentration did not change, but the N concentration increased with decreasing wall density. The wall density was related to the C/N ratio, which is a chemical parameter of the degree of decomposition. The culm structure should be considered when estimating culm density. The mean C concentration can be used for estimating the C stock of decomposing culms irrespective of decomposition level. N concentration, however, should be determined according to decomposition level for N stock estimation.

Nitrogen leaching from surface soil in a temperate mixed forest subject to intensive deer grazing

We aimed to determine the grazing impact on soil nitrogen (N) mineralization and N leaching in a temperate mixed forest on Mt. Ohdaigahara, central Japan, where Sika deer (Cervus nippon Temminck; hereafter deer) grazing has decreased biomass of Sasa nipponica Makino et Shibata (hereafter sasa) that dominates the forest understory. Soil N mineralization and N leaching of the top 0.3-m layer were measured in situ from 2006 to 2007 by an ion-exchange resin core method inside and outside a deer exclosure. Deer grazing decreased the carbon to nitrogen (C:N) ratio of sasa litter because of the declining dead culm C:N ratio and the increasing ratio of leaves with a lower C:N ratio than culms in the aboveground biomass. Grazing increased N mineralization and nitrification rates as well as annual N (ammonium-N and nitrate-N) and nitrate-N leaching. In contrast, deer grazing did not increase the total soil C and N content. The positive effect of grazing on the N mineralization rate may have resulted from a qualitative change in sasa litter due to grazing. The higher annual N leaching resulting from deer grazing may have been related to the facilitated N mineralization rate and decreased N uptake in plants, e.g., sasa with less aboveground biomass due to grazing.

Accuracy criteria for measuring carbon and nitrogen concentrations in forest soil and litter samples

Abstract To establish accuracy criteria for measurements of carbon and nitrogen concentrations in forest litter and mineral soil, we examined the change in the coefficient of variance (CV) with the number of measurement repetitions, the distribution of CVs and the effect of analytical error on the variation of CV to suggest a threshold for detecting outliers. We analyzed the measurement values of 266 soil samples and 73 litter samples collected from various forests throughout Japan. The CV changed with the number of measurement values for soil samples, but not for litter samples. This finding suggested that the accuracy criterion of the CV of two measurement values should be applied only to CVs calculated from two measurement values. When the CV was calculated from two measurement values, variation in the CV did not differ among carbon concentration classes of soil samples; however, the variation did differ among carbon concentration classes of litter samples and nitrogen concentration classes of litter and soil samples. These differences suggested that accuracy criterion should be independently decided in each carbon and nitrogen concentration class. Variation in the CV was not strongly affected by the analytical error because variation in the blank value was very small compared with variation in the CV. The distribution of the CV did not differ from the normal distribution for litter samples, but it did differ for soil samples. Thus, we used the robust Huber’s m-estimator outlier test to decide a threshold to represent the accuracy criterion. The threshold value was almost constant among carbon concentration classes both for soil and litter samples, with mean values of 3.6% and 2.6%, respectively. Conversely, the threshold of outliers of soil and litter samples varied among nitrogen concentration classes. This suggested using different thresholds for each nitrogen concentration class. Moreover, by applying the calculated thresholds we showed that outliers accounted for approximately 30% of the data in almost all carbon and nitrogen concentration classes for soil samples and less than 20% in almost all carbon and nitrogen concentration classes for litter samples.

Soil genesis on the raised coral reef terraces of Ishigaki and Okinawa-islands in the Ryukyu Islands, Japan. II: Chronosequential changes of clay mineralogical composition

Granulometric and clay mineralogical analyses were performed on soil types differing in their genesis which had been formed on the raised coral limestone terraces and plateaux under the perhumid subtropical maritime climate of the Ryukyu Islands. The amount of clay fraction in Rendzina-like soil on the lower terrace was relatively small (8-34%) and decreased with depth, while those in Terra fusca-like soils on the middle terraces and in Terra rossa-like soil on the plateau were very large (45–78%) suggesting the occurrence of clay migration. Rendzina-like soil mainly contained illite and metahalloysite with a moderate amount of mixed layered mineral consisting of illite and vermiculite, and a small amount of vermiculite, Al-vermiculite, goethite, and quartz. Clay mineral composition of Terra fusca-like and Mottled Terra fusca-like soils was similar to that of Rendzina-like soil except that the content of illite was lower in these soils. Terra rossa-like soil, on the other hand, mainly contained Al-vermicu...