Hiroaki Kato

• PhD
• Professor (Associate) at University of Tsukuba

Radionuclides released and deposited because of the 2011 Fukushima Dai-ichi Nuclear Power Plant accident caused an increase in air dose rates in Fukushima Prefecture forests. Although an increase in air dose rates during rainfall was previously reported, the air dose rates in the Fukushima forests decreased during rainfall. This study aimed to deve...

To explore the processes of soil erosion at the plot scale, Digital surface model of Differences (DoD) maps (Unmanned Aerial Vehicle - Structure from Motion (UAV-SfM) method) and data from Radio Frequency Identification (RFID) tags were analysed. The comparison of differences in accuracy of UAV-SfM and 3D terrestrial laser scanner (TLS) measurement...

The March 2011 Fukushima Dai-ichi Nuclear Power Plant accident in Japan released 520 PBq of radionuclides compared to a total release of 5300 PBq from the Chornobyl Nuclear Power Plant accident. Both nuclear accidents resulted in deposition of radiocesium throughout the northern hemisphere, and a plethora of studies have been performed regarding ra...

This study investigated the spatial distribution of radiocesium deposited by the Fukushima Daiichi Nuclear Power Plant accident in a densely planted Japanese cedar stand. Systematic grid sampling was conducted to determine ¹³⁷Cs inventories in the layers of deposited organic material and mineral soil at two different spatial scales (hillslope [60 m...

Forest is an important part of the environmental system, which has a significant impact on soil hydrological characteristics and forest landscapes, because these processes are influenced by forest management and understory vegetation. Quantitative understory vegetation biomass (UVB) measurement and estimation are vital processes in forest ecology a...

In this chapter, we review the scales, levels of contamination of forest ecosystems with radiocesium, and the impact on forestry in the areas affected by the accident at the Fukushima Dai-Ichi Nuclear Power Plant. We summarize the results of the studies revealing the radiocesium dynamics in compartments of the typical forest ecosystems in the initi...

Aiming to fill a need for data regarding radiocesium transport via both branchflow and stemflow through forests impacted by radioactive fallout, this study examined the vertical variation of radiocesium flux from branchflow and stemflow through the canopies of young Japanese cedar (Cryptomeria japonica (L. f.) D. Don) and Japanese oak (Quercus serr...

Thirty-five years after the accident, large forest areas in the Chernobyl Exclusion Zone still contain huge amounts of radionuclides released from the Chernobyl Nuclear Power Plant Unit 4 in April 1986. An assessment of the radiological and radioecological consequences of persistent radioactive contamination and development of remediation strategie...

To analyse the ¹³⁷Cs distribution and migration under various fractions of organic matter layers, this study investigated easily recognizable, originally shaped organic L-fractions, and not easily recognizable, early fermented and fragmented organic F-fractions, of both oak (Quercus serrata) and cedar (Cryptomeria japonica) sampled from Osawa water...

The deposited ¹³⁷Cs is one of the long-lived radionuclides, that was released following the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, has been hydrologically transported as particulates in the terrestrial environment of the Fukushima region. The impact of freeze-thaw processes and subsequent runoff affecting the ¹³⁷Cs flux and concen...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Long-term monitoring revealed that radiocesium (137Cs) deposition that fall from the canopy with litterfall was characterized by forest types, seasonal change, and canopy closure (CC). The sum of autumn and spring 137Cs deposition values divided by the sum of summer and winter tended to have higher values in the cedar forest. The angle of view α wh...

The 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, Japan, released the largest quantity of radionuclides into the terrestrial environment since the 1986 accident at Chernobyl. This accident resulted in 2.7 PBq of radiocaesium (¹³⁷Cs) contaminated forests, agricultural lands, grasslands and urban areas, which subsequently migrated thro...

This study investigated the temporal change in vertical distributions of radiocesium inventories in Japanese forest soils during the early phase (from 2011 to 2017) following the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, using three simple parameters. We calculated the fraction in the organic layer (Fl/t), the migration center (Xc) an...

After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, immediate soil and vegetation sampling were conducted according to the action plan of nuclear emergency monitoring; however, analysing the monitoring dataset was difficult because the sampling protocols were not standardised. In this study, the sampling protocols applied just after t...

The Fukushima Dai-ichi Nuclear Power Plant Accident released large quantities of radionuclides into the atmosphere, with subsequent fallout onto wide area of land surface in Fukushima and its neighboring prefectures. Because approximately 70％ of the radiocaesium deposited on land was in forest areas, an analysis of the spatial distribution and tran...

The purpose of this chapter is to (1) provide an overview of radiocesium dynamics in forests affected by past nuclear accidents; (2) introduce the latest monitoring results of radiocesium cycling during the early phase of the Fukushima accident; and (3) discuss the potential suitability of radiocesium as a tracer of water and element cycling in for...

Approximately 70% of the total land area affected by the fallout from the Fukushima accident is forested, and therefore monitoring of the ambient dose rate in forest environments is essential to ensure that the population and natural habitats of these areas are protected from radiological hazards. However, there are little available data on the amb...

The effects of a 50% forest thinning intensity on Fukushima-derived 137Cs deposition by litterfall and its discharge by runoff in hillslope coniferous forest were monitored using four litterfall traps and a hillslope erosion plot. The observation was underway during the pre-and post-thinning periods. Results demonstrated that during the pre-thinnin...

Fukushima Daiichi Nuclear Power Plant accident resulted in radioactive contamination of forest environment over a wide area in Fukushima Prefecture and the neighboring prefectures. In this chapter, initial atmospheric deposition of radiocesium following the Fukushima accident was estimated based on the analysis of multiple dataset derived from diff...

Understanding solid 137Cs wash-off in sediment sources is important for predicting radiological risks in zones contaminated by the Fukushima Dai-ichi Nuclear Power Plant accident. Yoshimura et al. (2015) studied solid 137Cs wash-off using soil erosion plots representing different land uses in Fukushima. However, temporal trends of 137Cs activity co...

Ascertaining the initial amount of accidently released radiocesium is fundamental for determining the extent of radioactive contamination following nuclear accidents, and is of key importance to environmental transfer models. A series of the airborne monitoring surveys of radioactivity have conducted by the Japanese Ministry of Education, Culture,...

Although several studies have assessed the effects of thinning on water quality, including nitrogen (N) exports, few have examined N-saturated plantations. This study assessed the short-term effect of thinning on N exports from a N-saturated plantation forest in northern Kyushu, western Japan, that was thinned (43% of basal area) during January–Mar...

Approximately 70% of the total land area affected by the fallout from the Fukushima accident is forested, and therefore monitoring of the ambient dose rate in forest environments is essential to ensure that the population and natural habitats of these areas are protected from radiological hazards. However, there are little available data on the amb...

The study investigated temporal changes in the 137Cs concentrations in vegetal and hydrological samples collected from various forests in Yamakiya District, Kawamata Town of Fukushima prefecture over six years following the Fukushima Dai-ichi nuclear power plant accident. Cesium-137 was detected in all forest environmental samples. However, the con...

Owing to the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident a vast amount of radiocesium was released polluting the land. Afterwards, a variety of decontamination practices has been done, reducing the ambient dose rates. In this study we evaluated the effectiveness of eight forest decontamination practices by means of monitoring the radioc...

Purple soil is highly susceptible for overland flow and surface erosion, therefore understanding surface runoff and soil erosion processes in the purple soil region are important to mitigate flooding and erosion hazards. Slope angle is an important parameter that affects the magnitude of runoff and thus surface erosion in hilly landscapes or bare l...

This study determined the initial distribution of Fukushima reactor-derived radiocesium fallout in forest areas of Fukushima Prefecture based on analysis of airborne monitoring surveys by the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT). The results of the fifth airborne monitoring surveys were compared with the th...

Spatial variability of throughfall (TF) isotopic composition, used as tracer input, influences isotope hydrological applications in forested watersheds. Notwithstanding, identification of the dominant canopy factors and processes that affect the patterns of TF isotopic variability remains ambiguous. Here, we examined the spatio-temporal variability...

Cesium-137 (137Cs) migration in the litter layer consists of various processes, such as input via throughfall, output via litter decomposition, and input from deeper layers via soil organism activity. We conducted litter bag experiments over 2 years (December 2014-November 2016) to quantify the inputs and outputs of 137Cs in the litter layer in a J...

Key message Thinning resulted in evapotranspiration decrease and caused the relative contributions of each component to evapotranspiration to become very close. Abstract To increase the understanding of forest management to control water cycles, we examined the effect of 50% strip thinning on evapotranspiration (ET) and its partitioning into canop...

Throughfall (TF) is a critical component of the hydrological and biogeochemical cycles and is greatly influenced by stand structures in forested watersheds. Previous studies have examined the relationships between TF and stand structures for different species and regions. However, there remains acknowledged difficulty in estimation of TF with chang...

Spatial patterns of atmospherically deposited radiocesium on the forest floor and the temporal evolution were measured in two Japanese cedar stands and a secondary mixed broad-leaved forest in the early phase of the Fukushima Daiichi Nuclear Power Plant accident. In situ measurements of the (137)Cs gamma count were made using a portable germanium g...

The root water uptake profile (RWUP) reflects a plant’s survival strategy and controls evapotranspiration and carbon fluxes. Despite its importance, there is still no reliable method for reconstructing this profile. In this study, we applied and compared two possible approaches to a case study in a conifer plantation: an isotope-calibrated mechanis...

This study investigated the effects of plowing on the vertical migration of radioactive Cs, air dose rate, and soil physicochemical properties in temperate pastures after radioactive pollution from the 2011 Fukushima Daiichi Nuclear Power Plant accident. The study area consisted of three plowed pastures (decontamination treatment) and one non-plowe...

Land use composition and patterns influence the hydrological response in mountainous and forest catchments. In plantation forest, management operations (FMO) modify the spatial and temporal dynamics of overland flow processes. However, we found a gap in the literature focussed on modelling hydrological connectivity (HC) in plantation forest under d...

There were two sources of ionizing irradiation after the atomic bombings of Hiroshima and Nagasaki: (1) initial gamma-neutron irradiation at the moment of detonation and (2) residual radioactivity. Residual radioactivity consisted of two components: radioactive fallout containing fission products, including radioactive fissile materials from nuclea...

The radionuclide ⁵⁶Mn (T1/2=2.58 hours) is one of the dominant beta- and gamma-emitters within few hours after the neutron irradiation of soil dust following nuclear explosion in atmosphere. The effects of exposure to residual radioactivity from nuclear explosions are the subject of discussions and research of the consequences of nuclear tests and...

The Fukushima Daiichi Nuclear Power Plant accident has released massive amount of radiocesium into the terrestrial environment, and the radiocesium (Cs-137) transfer and flux through river network is important to understand the redistribution of radiocesium in terrestrial environment, which is essential for assessing the external and internal radio...

Soil water samples were sampled and dissolved 137Cs concentrations were measured at four sites with different land use (meadow land, pasture land, and young/mature cedar forest) in Yamakiya District, located ~35 km northwest of Fukushima Dai-ichi Nuclear Power Plant (FDNPP) from July 2011 to October 2012. Meadow land and pasture land are not covere...

An experiment has been conducted to evaluate the additional dose reduction by clear felling contaminated forestry in Fukushima Prefecture, Japan, and using the timber to cover the areas with wood chips. A portable gamma spectrometry system, comprising a backpack containing a 3 × 3″ NaI(Tl) detector with digital spectrometer and GPS receiver, has be...

Soil water samples were sampled and dissolved 137Cs concentrations were measured at four sites with different land use (meadow land, pasture land, and young/mature cedar forest) in Yamakiya District, located ~35 km northwest of Fukushima Dai-ichi Nuclear Power Plant (FDNPP) from July 2011 to October 2012. Meadow land and pasture land are not covere...

On 11 March 2011 a 9.0 earthquake and the resulting tsunami occurred in central-eastern Japan triggering, one day after, the Fukushima Dai-ichi nuclear power plant (DNPP) accident. Despite the bulk of radionuclides (ca. 80%) were transported offshore and out over the Pacific Ocean, significant wet and dry deposits of those radionuclides occurred ma...

Overland flow connectivity is a key factor to understand the redistribution dynamics of sediments, nutrients, radiotracers, etc., in the different compartments at channel, hillslope and catchment scales. Human organization of landscape elements has a significant control on runoff and soil redistribution processes. Construction of trails, forest roa...

The depth distribution of pre-Fukushima and Fukushima-derived 137Cs in undisturbed coniferous forest soil was investigated at four sampling dates from nine months to 18 months after the Fukushima nuclear power plant accident. The migration rate and short-term temporal variability among the sampling profiles were evaluated. Taking the time elapsed s...

We examined changes in suspended-sediment yields (SSY) after a 50 % strip thinning in headwater streams draining a Japanese cedar (Cryptomeria japonica) and cypress (Chamaecyparis obtusa) plantation forest. We applied a paired-catchment analysis to treated (K T : 17.1 ha) and control (K C : 8.9 ha) catchments. Annual suspended-sediment yield (SSYan...

Thinning results in more open-stand canopies and then immediately modifies the environmental factors that influence forest floor evaporation (Ef). Thus, the changes in Ef induced by thinning would play an important role in the forest water cycle, whereas few studies have reported this topic. This study analyzes the effect of strip thinning on Ef, i...

We examined the effect of strip thinning on the spatio-temporal variability of throughfall (TF) in a mature Japanese cypress (Chamaecyparis obtusa) stand. Strip thinning, which removed 50% of stems, was performed in a catchment in October 2011. TF was examined by setting up 20 tipping-bucket rain gauges in an experimental plot. Canopy interception...

Japanese cedar () and Japanese cypress () plantations account for approximately 30% of the total forested area in Japan. Both are arbuscular mycorrhizal trees that leach more NO in response to nitrogen (N) deposition than do forests of ectomycorrhizal trees. However, little information is available about the size of N exports from these plantations...

We evaluated the effects of 50% strip thinning on peak flow responses in 17-ha nested catchments. We observed 117 storm events from April 2010 to December 2013, including 32 events in the pre-thinning period, 15 events during the thinning operation, and 70 events in the post-thinning period. Paired-catchment analysis with multiple pairs of nested g...

Hiroaki Katoa, , , Yuichi Ondaa, Keigo Hisadomeb, Nicolas Loffredoa, Ayumi Kawamoric

We examined the effect of strip thinning on rainfall interception (Ei) in a 32-year-old Japanese cypress plantation in central Japan. Strip thinning was conducted in the catchment in October 2011; that removed 50% of the stems. The gross precipitation (Pg), throughfall (TF) and stemflow (SF) were monitored in a 12-m × 13-m plot before and after thi...

Nutrient concentrations in stream water, rainfall, throughfall, stem flow, surface flow and ground water were compared before, during, and after strip thinning (intensive 50%) in plantation forested watersheds in Tochigi, Japan. Influences were evaluated comparing four thinning-applied and two reference basins for one year before, six months during...

This study revealed the influence of change in forest canopy structure by forest management practice for throughfall generation and canopy water interception process. Throughfall and stemflow were observed in a mature Japanese cypress (Chamaecyparis obtusa) plantation before and after thinning. Decreased stem density (from 2400 to 1300 trees ha−1)...

Core soils and falling litter samples were collected in Japanese cypress forest (Chamaecyparis obtuse) to determine the litter-feed 210Pbex and organic carbon transfer from forest canopy to soil and their subsequent distribution. Of the canopy residing 210Pbex pool, litterfall annually transports 53% to the forest floor while it adds 117 g m–2 year...

Spatial distributions and temporal changes of radioactive fallout released by the Fukushima Dai-ichi Nuclear Power Plant accident have been investigated by two campaigns with three measurement schedules. The inventories (activities per unit area) of the radionuclides deposited onto ground soil were measured using portable gamma-ray spectrometers at...

The Fukushima Dai-ichi nuclear accident led to massive atmospheric deposition of radioactive substances onto the land surfaces. The spatial distribution of deposits has been estimated by Japanese authorities for gamma-emitting radionuclides through either airborne monitoring surveys (since April 2011), or in situ gamma-ray spectrometry of bare soil...

To explore the behavior of radionuclides released after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011, and the distribution of radiocesium in paddy fields, we monitored radiocesium (Cs) and suspended sediment (SS) discharge from paddy fields. We proposed a rating scale for measuring the effectiveness of surface soil remo...

Radiocaesium wash-off associated with soil erosion in different land use was monitored using USLE plots in Kawamata, Fukushima Prefecture, Japan after the Fukushima Dai-ichi Nuclear Power Plant accident. Parameters and factors relating to soil erosion and (137)Cs concentration in the eroded soil were evaluated based on the field monitoring and pres...

We investigated the contribution of three evapotranspiration (ET) components including canopy interception (Ei), tree transpiration (Et) and forest floor evaporation (Ef) and identified the sources depth of evaporated water in a Japanese cypress stand. Monitoring primarily focused on the growing season of July–October 2011. In a 12 × 13 m plot with...

Soil erosion is the initial process which drives radiocesium into the aquatic systems and therefore the quantifi-cation of radiocesium wash-off associated with soil erosion is indispensable for mitigating the risks. This study presents two year's observation of soil erosion and radiocesium wash-off to quantify differences in radiocesium behavior in...

To clarify radiocaesium migration with litterfall from the tree canopy to the forest floor, a study was conducted in the three different forests in Fukushima Prefecture where radionuclides released from the Fukushima Daiichi Nuclear Power Plant FDNPP were deposited. Concentrations of 134Cs and 137Cs in the litterfall had been periodically monitored...

We conducted a field monitoring experiment examining throughfall in Japanese cypress plantations located in Tochigi Prefecture, eastern Japan. A set of 20 tipping-bucket rain gauges and throughfall collectors were placed in a lattice-like distribution throughout a 10 × 10-m experimental plot to investigate the effect of the forest canopy on the spa...

Interception loss (E i) in forests has been studied widely. However, E i parameters and modeling as well as spatial patterns of throughfall (TF) in abandoned Japanese cypress (Chamaecyparis obtusa) plantations remain poorly documented. In this study, gross precipitation (P G), stemflow (SF), and TF were monitored in an unmanaged 32-year-old Japanes...

Forests in Fukushima and neighboring prefectures accumulated atmospheric fallout of radioactive materials after the Fukushima Daiichi Nuclear Power Plant accident. We investigated the initial behavior of Cs-137 deposited in coniferous forest plantations. Furthermore, we conducted in-situ measurements of radioactivity in coniferous and broadleaf for...

We conducted field observation in nested headwater catchments draining Japanese cypress (Chamaecyparis obtusa) and cedar (Cryptomeria japonica) forests at Tochigi prefecture for examining the effects of forest thinning on hydrological processes at different catchment scales. 50% of the stems was removed with line thinning in catchment K2 (treatment...

Previous experiences such as Chernobyl Nuclear Power Plant accident have confirmed that fallout radionuclides on the ground surface migrate through natural environment including soils and rivers. Therefore, in order to estimate future changes in radionuclide deposition, migration process of radionuclides in forests, soils, ground water, rivers shou...

The Fukushima Daiichi nuclear power plant accident resulted in extensive radioactive contamination of the forest environment in Fukushima and the neighboring prefectures. In this study, we analyzed radiocesium concentrations in rainwater, throughfall, stemflow, and litterfall to characterize the transfer of the deposited radiocesium in various fore...

Radioactive contamination has been detected in Fukushima due to the nuclear accident at Fukushima Daiichi Nuclear Power Plant (NPP) following the earthquake and tsunami on 11 March 2011. Following comprehensive investigation (FMWSE project funded by MEXT, Japan; http://fmwse.suiri.tsukuba.ac.jp/) was conducted to confirm migration of radionuclides...

The Fukushima Daiichi nuclear power plant accident resulted in extensive radioactive contamination of the forest environment in Fukushima and the neighboring prefectures. In this study, we analyzed cesium-137 concentrations in throughfall, stemflow, and litter-fall to measured the transfer of the deposited cesium-137 from canopy to forest floor in...

The Fukushima Daiichi nuclear power plant accident resulted in extensive radioactive contamination of the surrounding forests. In this study, we analyzed fallout 137Cs, 134Cs, and 131I in rainwater, throughfall, and stemflow in coniferous forest plantations immediately after the accident. We show selective fractionation of the deposited radionuclid...

The relationships of erosion-induced displaced soil organic carbon (SOC) to discharged 210Pbex and 137Cs in a hillslope forested area were investigated using runoff plots in three different forest types. A significant correlation was found between the displaced SOC and the radionuclides in each examined forest type. Compared with 137Cs, however, th...

The mega earthquake that rampaged north-east Japan on March 11, 2011 and the triggered subsequent tsunami hit the Fukushima Daiichi Nuclear power plant and resulted the discharge of about 770,000 terabecquerel radionuclide materials to the atmosphere. The distribution and deposition of the radionucides are then governed by the wind and rain followi...

After the nuclear reactor accident in Fukushima on March 11, 2011, huge amounts of radionuclide such as Caesium-137, which is an artificial radionuclide with a half-life of 30.17 years, has been produced. Most of the fallen Cs-137 infiltrated into soil together with rainfall and was absorbed by soil sediments. The potential concentration of radionu...

Soil, vegetation and other ecological compartments are expected to be highly contaminated by the deposited radionuclides after the Fukushima Daiichi nuclear power plant (NPP) accident triggered by a magnitude 9.1 earthquake and the resulting tsunami on Marchi 11, 2011. A large proportion of radionuclides which deposited on forest area are trapped b...

Radioactive contamination has been detected in Fukushima and the neighboring prefectures due to the nuclear accident at Fukushima Daiichi Nuclear Power Plant (NPP) following the earthquake and tsunami on 11 March 2011. The total deposition of radioactive materials in fallout samples for 137Cs ranged from 0.02to >10 M Bq/m2 for Cs-137. Experimental...

We investigated radionuclides deposition and fine sediment transport in a 13 ha headwater watershed, Tochigi prefecture, located in 98.94 km north of Tokyo. The study site was within Karasawa experimental forest, Tokyo University of Agriculture and Technology. We conducted fingerprinting approach, based on the activities of fallout radionuclides, i...

After Tohoku earthquake on March 11th 2011, the subsequent tsunami and the resulting Fukushima Daiichi Nuclear Power Plant disaster, gamma emitting particles, first release into the atmosphere, were quickly deposited on the soil surface, with potentially harmful level in the surroundings of the nuclear power plant. Thus, the evaluation of soil depo...

Soil, vegetation and other ecological compartments are expected to be highly contaminated by the deposited radionuclides after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident triggered by a magnitude 9.0 earthquake and the resulting tsunami on 11 March 2011. However, there is no field measurement data on the depth distributions of radio...

To investigate the spatial patterns and temporal variation of rainfall redistribution characteristics in forest plantations, field observation of throughfall was conducted in three forest stands consisting of Japanese cypress (Chamaecyparis obtuse), and Japanese cedar (Cryptomeria japonica), in Tochigi and Kochi prefecture, Japan. Throughfall in 8m...

To examine the effects of understory vegetation on infiltration capacity, a series of field infiltration test was conducted by using an oscillating nozzle rainfall simulator at 14 sites in steep Japanese cypress plantation. The simple regression analysis among the maximum final infiltration rate（ FIRmax）, percentage vegetation cover and dry weight...

In this study, two small experimental catchments were selected in semi-arid grassland in Mongolia. The Kherlen-bayan Ulaan (KBU) catchment has been subjected to intensive grazing as a wintering shelter for domestic livestock animals, and the number of livestock animals in the Baganuur (BGN) catchment has been increasing over the last few decades. T...

Mongolia is located in northeastern Asia, and approximately 75% of its total land area consists of cold, semiarid grassland that is subjected to grazing throughout the year. The flights of closely spaced terracettes marked on the steeper hillslopes (20°

本研究ではインドネシア，ブランタス川上流域のスングルダムにおける堆砂量の増加の原因を定量的に把握するため，天然放射性核種のPb-210exを土壌粒子のトレーサーとし，森林地および耕作地の土壌侵食量を推定した．また，ブランタス川源流域とレスティ・アンポロン川流域で河床堆積物を採取し，またスングルダム堆積物について，Pb-210ex濃度に基づいて潜在的な土砂供給源からの土砂流出寄与率を推定した．森林地および耕作地における平均土壌侵食量は，それぞれ0.4 t ha-1 y-1 と11.1 t ha-1 y-1 であった．また，スングルダム堆積物に対する耕作地の表面侵食による土砂流出寄与率はブランタス上流域全体では約30 ％と推定され，本流域において耕作地の表面侵食による土砂流出が主要な土砂供給源の...