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Effects of plowing on vertical distribution of radioactive Cs and soil physicochemical properties in temperate pastures

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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-plowed pasture at the Kawatabi Field Science Center of Tohoku University, 150 km north of the Nuclear power plant. Air dose rate was measured at the top, middle, and bottom of the slope of each pasture. A profile pit (1 m x 3 m) was excavated at each location. Plants, litter and soil samples (from 0 cm to the parent material layer) were collected from all locations during the summer of 2014 to determine the radioactive Cs concentration. Particle size distribution and bulk density of the soil samples were also measured. Air dose rate was higher on the non-plowed (0.090–0.097 mSv/h) than that on the plowed (0.047–0.073 mSv/h) pastures. Radioactive Cs concentration was high in the litter layer (207–475 Bq/kg dry matter [DM]) and the topsoil (0–2.5 cm depth; 412–1139 Bq/kg DM) in the non-plowed pasture. In the plowed pastures, these variables did not differ within the 0–40 cm layer. In the non-plowed pasture, there were high sand (37.0%) and low silt (61.4%) proportions at 10–20 cm and the topsoil had a high bulk density. In the plowed pastures, these variables were similar within the 0–20 cm layer. The bulk density (P < 0.001) and organic matter content (P < 0.05) had significant relationships with the concentration of radioactive Cs. These results indicate that plowing reduced air dose rate.
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PRACTICAL REPORT
Effects of plowing on vertical distribution of radioactive Cs
and soil physicochemical properties in temperate pastures
Mikhail Komissarov
1
, Shin-ichiro Ogura
2
, Hiroaki Kato
3
and Masanori Saito
2
1 Ufa Institute of Biology, Russian Academy of Sciences, Ufa, Russia
2 Graduate School of Agricultural Science, Tohoku University, Osaki, Japan
3 Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki, Japan
Keywords
Decontamination; physicochemical property;
plowing; soil depth; temperate pasture.
Correspondence
Shin-ichiro Ogura, Graduate School of
Agricultural Science, Tohoku University, 232-3
Yomogita, Naruko-onsen, Osaki 989-6711,
Japan.
Email: shin-ichiro.ogura.e1@tohoku.ac.jp
Received 6 February 2017;
accepted 30 April 2017.
doi: 10.1111/grs.12172
Abstract
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-plowed pasture at the Kawatabi
Field Science Center of Tohoku University, 150 km north of the nuclear power
plant. Air dose rate was measured at the top, middle, and bottom of the slope
of each pasture. A profile pit (1 m 93 m) was excavated at each location.
Plants, litter and soil samples (from 0 cm to the parent material layer) were col-
lected from all locations during the summer of 2014 to determine the radioac-
tive Cs concentration. Particle size distribution and bulk density of the soil
samples were also measured. Air dose rate was higher on the non-plowed
(0.0900.097 lSv h
1
) than that on the plowed (0.0470.073 lSv h
1
) pastures.
Radioactive Cs concentration was high in the litter layer (207475 Bq kg
1
dry
matter [DM]) and the topsoil (02.5 cm depth; 4121139 Bq kg
1
DM) in the
non-plowed pasture. In the plowed pastures, these variables did not differ
within the 040 cm layer. In the non-plowed pasture, there were high sand
(37.0%) and low silt (61.4%) proportions at 1020 cm and the topsoil had a
high bulk density. In the plowed pastures, these variables were similar within
the 020 cm layer. The bulk density (P<0.001) and organic matter content
(P<0.05) had significant relationships with the concentration of radioactive
Cs. These results indicate that plowing reduced air dose rate.
Introduction
The Great East Japan Earthquake and tsunami on 11
March 2011, caused damage to the Fukushima Daiichi
Nuclear Power Plant (NPP), resulting in serious radioac-
tive pollution throughout Eastern Japan. The radioactive
fallout extensively polluted agricultural lands, including
permanent pastures and meadows, with radioactive Cs
(MEXT, 2011).
Measuring radioactive Cs fallout in agricultural areas is
important to assess the risk of food contamination. In par-
ticular, a characterization of the vertical distribution of
radioactive Cs in soil is important because it strongly
affects the transfer of radioactive Cs to crops and forages.
The roots of pasture plants such as grasses and legumes
can extend to depths of 100 cm, but the majority of the
root system occurs between 0 and 20 cm (Evans 1978;
Greenwood and Hutchinson 1998; Crush et al. 2005).
Thus, reduction or decontamination of radioactive Cs
from the 020 cm soil layer is essential for reducing the
contamination risk in pastures. Radioactive fallouts were
deposited on the litter layer and soil surfaces in forests
(Koarashi et al. 2012; Tanaka et al. 2012; Nakanishi et al.
2014), grasslands (Ramzaev et al. 2013; Ogura et al. 2014)
and paddy fields (Endo et al. 2013; Lepage et al. 2015)
after the 2011 NPP accident. Plowing can effectively
decontaminate or reduce the radioactive pollution of crops
harvested from those farmlands by moving the polluted
©2017 Japanese Society of Grassland Science, Grassland Science 1
Japanese Society of Grassland Science ISSN1744-6961
Japanese Society of Grassland Science
surface layers to deeper locations (James and Menzel 1973;
IAEA 1999). He and Walling (1997) showed that radioac-
tive fallouts were distributed more evenly in mechanically
plowed soils than they were in non-plowed (NP) soils.
Plowing and cultivation of contaminated farmlands are
also effective at reducing the air dose rate (Ogura et al.
2014). In paddy fields, radioactive Cs concentration
remained high in topsoils, even after plowing (Harada and
Nonaka 2012; Endo et al. 2013; Sakai et al. 2014). There is
little information on the effects of plowing on the vertical
distribution of radioactive Cs in pasture soils.
The remediation of farmlands must account for
radioactive Cs migration because this horizontal and ver-
tical migration can pollute crops even after decontamina-
tion activities. Matsunaga et al. (2013) reported low Cs
migration rates, even during rainy seasons. In contrast,
Riesen et al. (1999) found that the radioactive Cs activity
in soil was higher at sites with more rainfall after the
NPP accident than at those with less rainfall. In paddy
fields, rainfall promotes migration and erosion of fine soil
particles (Tanaka et al. 2013), which strongly adsorb
radioactive Cs (Matsunaga et al. 2013; Sakai et al. 2014;
Yoshimura et al. 2015). Thus, it is important to deter-
mine how plowing affects the water permeability of soils
and subsequent migration of radioactive Cs in pastures.
The objective of this study was to investigate the effects
of plowing on the vertical migration of radioactive Cs,
soil physicochemical properties and water permeability in
pastures. This study also examined the relationships
between radioactive Cs concentrations and soil physico-
chemical properties.
Materials and methods
Study site
This study was conducted at the Kawatabi Field Science
Center (FSC), Graduate School of Agricultural Science,
Tohoku University, Japan (38°440N, 140°150E, 224258 m
above sea level). The FSC is located 150 km from the
Fukushima Daiichi NPP. The climate in this region is
temperate, with a mean annual temperature of 10.2°C
and a mean annual rainfall of 1660 mm, based on records
from 1979 to 2000 (Japan Meteorological Agency, 2016).
The soil is classified as a Haplic, non-allophanic Andosol
(Classification Committee of Cultivated Soils, 1995) or as
Alic Hapludands (Soil Survey Staff, 1999).
In arable areas of the FSC, four pastures of varying
sizes and management histories were chosen for this
study (Table 1). Three pastures (13-1, 13-3 and 14-2)
were plowed to the depth of 25 cm in 20122013 to
decontaminate the radioactive fallout. Surface vegetation
was incorporated in plowed layer. Then, temperate grasses
(Dactylis glomerata L. [orchard grass], Festuca arundinacea
Schreb. [tall fescue]) were sown. In these three pastures,
soil surface was almost fully covered by the sown grasses
when the measurements were conducted. One pasture
(21-2) was not plowed when this study was conducted.
All of these pastures are slightly tilted (46°), and the
slopes lengths (i.e., distance from the highest to the lowest
edge) ranged from 144 m to 318 m. Chemical fertilizer
and cattle manure compost were applied to the decontam-
inated pastures in 20122013 as basal fertilizers. In pasture
14-2, slight gully erosion arose after the plowing.
Field and laboratory measurements
A measurement line was fixed in the center of each pas-
ture along the slope from June to July 2014. The length,
angle, and exposition of the slope were determined with a
tapeline, alidade and compass. At the beginning of the
study, vegetation condition was assessed by measuring
plant cover at 1-m intervals along each line within
0.5 m 90.5 m quadrats. Vegetation cover ranged
between 52 and 99%, and the dominant plant species
were D. glomerata,F. arundinacea,Agrostis alba L. (red-
top), Phalaris arundinacea (reed canary grass), Echino-
chloa crus-galli (L.) P. Beauv (common barnyard grass),
Trifolium repens L. (white clover), and Rumex obtusifolius
L. (broad-leaved dock).
Air radiation dose rate (lSv h
1
) was measured with
an environmental radiation monitor (csurvey meter
TCS-172B, Hitachi-Aloka Medical, Ltd., Tokyo, Japan) at
1 m above the ground surface at each location (top, mid-
dle and bottom) in the pastures. Air radiation dose rate
was measured at the beginning of each month during the
growing season (May to October 2014).
Profile pits (1 m 93 m) were excavated in each pas-
ture at the top (the highest location of the fixed line),
middle (intermediate location) and bottom (the lowest
location) of the slope from June to July 2014. One pit
was excavated at each location. Soil samples were taken
from three different parts of each profile pit at different
layers (02.5 cm, 2.55 cm, then at 5-cm intervals until
the parent material layer). The three samples were then
combined to represent the pit location. After removing
stones and plant roots, these soil samples were dried in
an oven at 105°C and sieved using a 2-mm screen. At
each sampling location, the litter layer and the dominant
plants species growing on and within a 10-m radius of
the pit were collected and separated into aboveground
parts and roots. The samples of aboveground parts, litter
layer, and roots were dried again at 105°C and sieved
through a 2-mm screen.
The physicochemical properties of the soil were deter-
mined for those fractions of soil samples with particle size
©2017 Japanese Society of Grassland Science, Grassland Science2
Migration of radioactive Cs by plowing M. Komissarov et al.
diameters <2 mm. The particle size distribution (sand:
>50 lm, silt: 250 lm, and clay: <2lm) was analyzed
using a laser diffraction particle size analyzer (SALD-
3100, Shimadzu Co., Ltd., Kyoto, Japan). Soil bulk den-
sity was determined from the dry weight and volume of
the soil in each layer. Organic matter (OM) content of
the samples was determined by incineration at 450°C for
8h.
Radioactive Cs concentration was determined with a
gamma counter (WIZARD2 2480, PerkinElmer, Waltham,
USA) equipped with a sodium iodide (NaI) detector.
Each sample was homogeneously mixed by a spatula, then
loaded into a 20-mL plastic vial, then weighed and mea-
sured for 30 min. The radioactive Cs concentration was
expressed as the total concentration of
134
Cs and
137
Cs
per unit of dry matter (DM) (Bq kg
1
DM). The stan-
dard deviation of each measurement from the gamma
counter was less than 10%. All measured activities were
corrected for radioactive decay to each sampling date.
Statistical analysis
The differences between bulk density, OM content and
radioactive Cs concentration among soil layers were com-
pared by Tukey’s multiple range test. In this analysis, the
020 cm soil layer was used because the transfer of
radioactive Cs to plants is the greatest at these depths
(Ogura et al. 2014). The locations (top, middle and bot-
tom) were regarded as replicates within each pasture.
The concentration of radioactive Cs in the above-
ground plants, litter layer and soil layers were correlated
to the mean air dose rate at individual locations. In this
analysis, soils from 040 cm were used because at these
depths all of the radioactive Cs concentrations were
greater than the detection limit.
Regression analysis was used to determine the relation-
ships between the soil physicochemical properties (soil
particle size, bulk density, and OM content). For this
analysis, soil samples from 020 cm in all four pastures
were used. The fitness of function was compared using
linear, quadratic, exponential and logarithmic models.
Regression analysis was also used to test the relationships
between radioactive Cs concentrations and the physico-
chemical properties of the soil. This analysis used the data
from the three plowed pastures to evaluate the effects of
soil characteristics on the vertical distribution of radioac-
tive Cs in soil layers after plowing. All analyses were per-
formed with IBM SPSS statistics v. 21 (IBM Corporation,
New York, USA) (IBM Corporation 2012).
Results
The air dose rate of the pastures ranged from 0.047
0.097 lSv h
1
(Table 2). The value was higher on the NP
pasture (0.0900.097 lSv h
1
) than it was on the plowed
pastures (0.0470.073 lSv h
1
).
The concentration of radioactive Cs in the plants, litter
layer, roots and soils differed among pastures and locations
Table 1 Characterization of the experimental pastures
Pasture
number
Pasture
management
Area
(ha)
Angle of
slope
(degree)
Exposition and
azimuth
relative
to slope
direction
Length of
slope (m)
Chemical
fertilizer
(kg ha
1
year
1
)
Cattle
manure
compost
(Mg ha
1)
Vegetation cover§(%)
Dominant plant
speciesTop Middle Bottom
13-1 Plowed
Sep 2012
(PO-12)
3.2 6 192 208 51-265-51 20 86 80 70 Dactylis glomerata
Agrostis alba
Phalaris
arundinacea
13-3 Plowed
Apr 2012,
cultivated
Sep 2012
(PC-12)
2.0 7 220 144 51-265-51 20 94 95 96 Festuca
arundinacea
Echinochloa
crus-galli
14-2 Plowed Sep
2013 (PO-13)
3.4 7 189 318 51-265-51 20 52 54 73 Agrostis alba
Trifolium repens
Rumex
obtusifolius
21-2 Non-plowed
(NP)
3.0 4 188 220 ––95 98 99 D. glomerata
0°= north, 90°= east, 180°= south and 270°= west. The amount of NP
2
O
5
K
2
O. §“Top”, “Middle” and “Bottom” are the highest, inter-
mediate and lowest location along each slope. Herbicide was applied in mid-July 2013.
©2017 Japanese Society of Grassland Science, Grassland Science 3
M. Komissarov et al. Migration of radioactive Cs by plowing
Table 2 The concentration of radioactive Cs in the soil, aboveground plant parts, litter layer and roots at each location in the pastures
Pasture management Plowed Sep 2012
Plowed Apr 2012,
cultivated Sep 2012 Plowed Sep 2013 Non-plowed
Correlation
coefficient
of air dose
rate SignificanceTop Middle Bottom Top Middle Bottom Top Middle Bottom Top Middle Bottom
Air dose rate (lSv h
1
) 0.057 0.073 0.073 0.060 0.067 0.070 0.063 0.047 0.057 0.093 0.090 0.097
Radioactive Cs concentration (Bq kg
1
)
Plant 55 44 72 70 26 35 106 52 24 34 138 41 0.150 NS
Litter layer -73 99 –––200 86 82 475 207 284 0.718 *
Roots 166 105 119 203 70 45 72 199 95 52 679 92 0.203 NS
Soil depth§
02.5 275 607 369 332 181 367 117 43 39 412 592 1139 0.807 ***
2.55 218 380 282 223 203 322 110 70 34 93 56 62 0.130 NS
510 149 492 173 202 207 245 28 29 251 31 39 37 0.219 NS
1020 182 132 260 36 470 114 31 151 455 21 32 31 0.432 NS
2030 36 22 28 34 57 25 52 32 79 29 22 13 0.554 NS
3040 17 8 24 23 20 16 17 12 13 21 18 20 0.350 NS
4050 16 14 5 10 13191216 11 14
5060 15 16 12 19 17 15 ––16
6070 20 12 18 18 18 13 –– –
7080 14 –– – 9––––– –
8090 11 –– –15 ––––– –
90100 13 –– – 9––––– –
040 total 876 1642 1136 849 1138 1088 356 337 871 606 759 1302 0.326 NS
*P<0.05, ***P<0.001 (correlation analysis, n=12). NS: not significant; Below the detection limit; §Depth from the surface (cm).
©2017 Japanese Society of Grassland Science, Grassland Science4
Migration of radioactive Cs by plowing M. Komissarov et al.
(Table 2). High values in the litter layer (207475 Bq kg
1
DM) and the topsoil (02.5 cm depth; 4121139 Bq kg
1
DM) were observed in the NP pasture. The concentration
of radioactive Cs in the 040 cm soil layer did not differ
between the three plowed pastures (Plowed Sep 2012 [PO-
12], Plowed Apr 2012, cultivated Sep 2012 [PC-12] and
Plowed Sep 2013 [PO-13]), whereas it was significantly
higher in the topsoil than in the deeper layers (2.540 cm)
in the NP pasture (P<0.05). The three plowed pastures
also had higher radioactive Cs concentrations in the deeper
soil layers (60100 cm) than did the NP pasture.
There was a significant relationship between air dose
rate and concentration of radioactive Cs in the litter layer
(P<0.05) and the topsoil (P<0.001) (Table 2).
The physicochemical properties of the soils differed
among the pastures (Figure 1). In the plowed pastures,
the proportion of soil particles, bulk density, and soil
OM content were similar within the 020 cm layer. In
contrast, within the 1020 cm layer in the NP pasture,
the proportions of sand and silt were 37.0 and 61.4%,
respectively. The bulk density in the NP pasture topsoil
was significantly higher than that in the deeper layers in
the NP pasture (P<0.05).
There was a negative linear relationship between OM
content and bulk density (P<0.05) (Figure 2). The con-
centration of radioactive Cs within the soil was
significantly related to soil bulk density (P<0.001) and
soil OM (exponential, P<0.05).
Discussion
In this study, high concentrations of radioactive Cs were
observed in the litter and topsoil layers of the NP pasture.
This result is consistent with those of previous studies
conducted in agricultural areas of northeastern Japan
after the Fukushima Daiichi NPP accident (Koarashi et al.
2012; Tanaka et al. 2012; Endo et al. 2013; Ramzaev et al.
2013; Nakanishi et al. 2014; Lepage et al. 2015). Ogura
et al. (2014) showed that radioactive Cs concentrations
were higher in plant roots and rootmat soils (15 cm)
than those in the litter and subsurface soils.
This study investigated the effects of plowing on the
vertical distribution of soil properties and radioactive Cs
concentrations. In the NP pasture, soil OM content was
lowest in the topsoil and the proportion of sand was
highest in the 1020 cm layer (Figure 1). In contrast, in
the plowed pastures, these soil properties and the concen-
tration of radioactive Cs were distributed homogeneously
throughout the 520 cm layer. A similar situation was
found in soil layers of paddy fields where the lands were
tilled by farmers after the deposition of radionuclides
(Lepage et al. 2015). In some sampling locations (PO-12
Figure 1 Vertical distribution of proportion of soil particles, bulk density, and organic matter content in the pasture soils. Different letters within
each graph are significantly different (n=3, P<0.05).
©2017 Japanese Society of Grassland Science, Grassland Science 5
M. Komissarov et al. Migration of radioactive Cs by plowing
bottom, PC-12 middle, and PO-13 middle and bottom),
the concentration of radioactive Cs in the 1020 cm layer
was higher than that in the upper layers, indicating that
plowing caused the migration of topsoil layers into the
deeper layers. Most radioactive Cs remains on the soil
surface and is immobilized after deposition, despite heavy
rainfall in croplands, grasslands, and forests (Matsunaga
et al. 2013), and even in paddy fields (Lepage et al.
2015). Mabit et al. (2008) estimated that the
137
Cs con-
centration in an agricultural field varied according to
depth. On average, approximately 65% of the total
137
Cs
was concentrated in the top 020 cm, 25% in the 20
30 cm layer, and less than 10% was in the deepest layer
(3040 cm) under the plowed surface. In a cultivated
field where the upper soil layer was mixed by plowing,
the concentration of
137
Cs was distributed homogeneously
over the cultivated layers, remaining even after cultivation
(Schimmack and Bunzl 1986). Plowing of the contami-
nated soil dilutes radionuclides in a larger soil volume
(IAEA, 1999), and it enhances contact of radioactive Cs
with soil particles, thus increasing fixation to frayed-edge
sites of the clay minerals (Cremers et al. 1988). Therefore,
plowing is clearly a highly effective method for decontam-
inating farmlands.
The concentration of radioactive Cs was significantly
related to soil bulk density (negative correlation), and it
also showed a mild exponential relationship to soil OM
content (Figure 2). This may suggest heterogeneity of
plowed soil layer. Since plowing did not homogenously
mix a whole soil layer up to 20 cm, the previous surface
layer with higher concentration of radioactive Cs, higher
OM content and lower bulk density might remain in
some parts of plowed layers. This further reminds us of
the possibility that plant may absorb radioactive Cs from
patches of higher radioactive Cs even after plowing.
The air dose rate was significantly related to the con-
centration of radioactive Cs in the litter and topsoil,
which were approximately 3050% lower in the plowed
pastures than in the NP pasture. This indicates that plow-
ing decreased the air dose rate due to either the migration
of radioactive Cs to deeper soil layers or to its dilution
throughout the 020 cm soil layer.
This study showed that radioactive Cs was deposited
on litter and topsoil in pastures after the NPP accident.
The topsoil layers contained higher OM content with
lower bulk density than did the deeper soils. Plowing
redistributed the topsoil into deeper layers and diluted
the radioactive Cs, thereby significantly reducing the air
Figure 2 Relationships between bulk density, organic matter content, and radioactive Cs concentration within 020 cm of the plowed pasture
soils.
©2017 Japanese Society of Grassland Science, Grassland Science6
Migration of radioactive Cs by plowing M. Komissarov et al.
dose rate. These results are consistent with previous stud-
ies (James and Menzel 1973; He and Walling 1997; IAEA,
1999). However, these studies did not investigate the
effect of water permeability on Cs migration rates. Migra-
tion of radioactive Cs deposited on agricultural areas is
slow or negligible because of adsorption onto soil parti-
cles (Nakanishi et al. 2014; Takahashi et al. 2015), even
in rainy seasons (Matsunaga et al. 2013). The vertical
migration rate of radioactive Cs can be very slow (0
0.35 cm year
1
) (Arapis and Karandinos 2004; Almgren
and Isaksson 2006). The effect of slope on the migration
of radioactive Cs was negligible, similar to a study by
Arapis and Karandinos (2004), wherein they did not
observe migration along slopes in semi-natural ecosys-
tems. Plowing is therefore an effective way to decontami-
nate pastures.
Acknowledgments
This research was supported by the “Japan-Russia Youth
Exchange Center” Foundation (JREX Fellowship program).
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©2017 Japanese Society of Grassland Science, Grassland Science8
Migration of radioactive Cs by plowing M. Komissarov et al.
... To prevent radioactive cesium (Cs) contamination of forage crops, various countermeasures were examined and then immediately implemented (Tsuiki & Maeda 2012a, 2012b, Kobayashi et al. 2013, Harada et al. 2014, Ogura et al. 2014, Yamamoto et al. 2014, Shinano 2015, Sunaga et al. 2015, Kobayashi et al. 2016, Komissarov et al. 2017. Those studies and subsequent implementation of countermeasures utilized information and knowledge mainly obtained after the Chernobyl accident in 1986 (Alexakhin 1993, Konoplev et al. 1993, Lembrechts 1993, Lönsjö et al.1989, Nisbet et al. 1993, Segal 1993, Roed et al. 1996, Fesenko et al. 2007). ...
... In Experiment 1, at one block among the three, 19% of total radioactive Cs of the three soil layers was distributed in the layer of 10 cm-20 cm. Many studies conducted after the Chernobyl and FDNPP accidents have reported very slow vertical migration of radioactive Cs, and that most radioactive Cs remained in the upper soil layers under non-plowed conditions (Arapis et al. 1997, Shiozawa et al. 2011, Tsuiki and Maeda 2012a, Yamaguchi et al. 2012, Kobayashi et al. 2013, Matsunaga et al. 2013, Ogura et al. 2014, Komissarov et al. 2017. Therefore, the detection of radioactive Cs in the lower layer before plowing indicated the occurrence of crosscontamination during soil sampling. ...
... Cross-contamination in the soil sampling procedures was also observed in the studies by Milbourn et al. (1959) andMilbourn (1960). However, in this study, the vertical distribution of radioactive Cs in the soil differed significantly among the tillage treatments, and the tendency of vertical distribution was similar to that reported by Hoshino et al. (2015) and Komissarov et al. (2017). Therefore, in this study, radioactive Cs in the soil surface layer (0 cm-10 cm) was effectively moved into deeper layers at 10 cm-20 cm and 20 cm-30 cm due to plowing for the CT and DT treatments. ...
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Whole-crop silage corn and Italian ryegrass were cultivated during summer and winter in fields contaminated by radionuclide fallout caused by the Fukushima Daiichi Nuclear Power Plant accident, with three different tillage treatments: shallow tillage treatment (tilled with a rotary tiller to a depth of about 10 cm), conventional tillage treatment (plowed with a normal moldboard plow to a depth of about 20 cm and harrowed with a rotary tiller to a depth of about 15 cm), and deep tillage treatment (plowed with a moldboard plow to a depth of about 35 cm and harrowed with a rotary tiller to a depth of about 15 cm). Vertical distribution of radioactive cesium (Cs) in the soil layers of 0 cm-10 cm, 10 cm-20 cm, and 20 cm-30 cm, and concentrations of radioactive Cs in forage samples were compared among the tillage treatments, as well as the soil chemical properties of those soil layers. Radioactive Cs in the soil surface layer (0 cm-10 cm) moved into the deeper layers at 10 cm-20 cm and 20 cm-30 cm due to plowing in the conventional and deep tillage treatments. However, significant differences were not observed for both species, either in the radioactive Cs concentration in forage samples or the radioactive Cs transfer factor from soil to plants among the tillage treatments. Moreover, the radioactive Cs concentrations in those plants and their TFs were relatively low for both species. These results suggest that radioactive Cs transfer was reduced by mixing the surface soil, even in the shallow tillage treatment. Furthermore, the exchangeable K2O content of soil was higher than 0.32 g/kg DW in all soil layers of the experimental fields, and such high content of exchangeable K2O in the soil was apparently another major reason why radioactive Cs uptake by both species was significantly restricted in all tillage treatments.
... Endl., Cupressaceae). Foothills and alpine meadows in Japan are used as pastures (Komissarov, Ogura, Kato, & Masanori, 2017). ...
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... A general tendency for an increase in the air dose rate increase down the slope corresponds to increasing concentration of radiocesium in the upper soil layers in this direction. Earlier, we showed [28] that the close correlation between these indicators (R = 0.81, P = 0.95) in the study area is statistically reliable. ...
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This study aimed to examine the influence of snowmelt on soil erosion processes in mountainous landscapes in the Miyagi prefecture of Japan. The investigated slopes had different expositions and were covered with grasslands and forests. The snowpack thickness, soil frost depth, volume of surface runoff, physicochemical properties of the soil and sediments, cesium composition of the snow and meltwater, and air dose rate were determined. In mid-February, snow cover reached its maximum thickness (100–179 cm). In the forest, the snow depth was always lower by 15–20 cm. The soil did not freeze in winter in any of the plots. Surface runoff was observed only in the grassland plots and depended on the slope aspect. The total volume of surface runoff ranged from 31 to 52 mm and snowmelt soil losses ranged from 2 to 9 kg ha−1 DM. Radiocesium concentrations in runoff samples ranged from 0.1 to 8.4 Bq L−1, below the standard limit for drinking water in Japan (10 Bq L−1). The average organic matter content of the sampled sediments was 0.4%, higher than that in the surface soil. The silt fraction in sediments became dominant for particle size distribution, and the activity concentration of total radiocesium was, on average, 250 Bq kg−1. The air dose rate was always lower than the maximum permissible level (0.2 μSv h−1) and varied from 0.02 to 0.09 μSv h−1 in winter, and from 0.08 to 0.13 μSv h−1 at times of the year without snow.
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The accident at Fukushima Dai-Ichi Nuclear Power Station (NPS) extensively contaminated the agricultural land in the Tohoku region of Japan with radioactive cesium [sum of cesium-134 (134Cs) and cesium-137 (137Cs)]. We evaluated the status of radioactive cesium (Cs) contamination in soil and plants at the Field Science Center of Tohoku University, northern Miyagi prefecture, 150 km north of the NPS. In seven pastures with different management, we examined: (1) the distribution of radioactive Cs in soil, (2) the concentration of radioactive Cs in various herbaceous plant species and (3) the change in radioactive Cs content of plants as they matured. We collected samples of litter, root mat layer (root mat soil and plant roots), and subsurface soil (0–5 cm beneath the root mat) at two to three locations in each pasture in December 2011 and May 2012. The aboveground parts of herbaceous plants (four grasses, two legumes, and one forb species) were collected from May 9 to June 20, 2012, at 14-d intervals, from one to five fixed sampling locations in each pasture. The distribution of radioactive Cs in soil differed among pastures to some degree: a large proportion of radioactive Cs was distributed in the root mat layer. Pasture management greatly influenced the radioactive Cs content of herbaceous plants (p 3 kBq kg−1 dry weight) on May 9 and significantly decreased with maturity (p
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We investigated the biological accumulation of radiocesium in tadpoles [Rana (Pelophylax) porosa porosa] in rice paddies with and without decontamination practice at Fukushima. Radiocesium was accumulated in surface part of soils both in the control and decontaminated paddies one year after decontamination. Mean (134)Cs and (137)Cs concentrations in tadpoles in the control and decontaminated paddies were 3000 and 4500, and 600 and 890 Bq/kg dry weight, respectively. Radiocesium concentrations in surface soil (0-5 cm depth) and tadpoles in the decontaminated paddy were five times smaller than in the control paddy. These results suggest that decontamination practice can reduce radiocesium concentrations in both soil and tadpoles. However, at the decontaminated paddy, radiocesium concentrations in surface soils became 3.8 times greater one year after decontamination, which indicates that monitoring the subsequent movement of radiocesium in rice paddies and surrounding areas is essential for examining contamination propagation.
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The spatial variability of soil erosion was studied through the use of fallout radionuclides (FRNs) and geostatistics. The spatial correlation structures of radiocesium (137Cs), soil redistribution and organic matter (OM) content have been established in a 2.16 ha agricultural field located 30 km east of Quebec City, Canada.A significant relationship was found between 137Cs (Bq m− 2) and OM (%) in the 0–20 cm soil depth (n = 42; r2 = 0.63, p < 0.001), highlighting the relation between these two parameters.The conversion of the areal activities of 137Cs into soil redistribution (t ha− 1 yr− 1) was done using the Mass Balance Model 2 (MBM 2). The magnitude of soil redistribution, at the sampled points, ranged from an erosion rate of 62 t ha− 1 yr− 1 to a deposition of 17 t ha− 1 yr− 1.Geostatistics coupled with a geographic information system (GIS) were used to create a map of soil redistribution, based on the spatial variability of FRNs, and to establish a sediment budget. Prior to mapping, semivariograms were produced, taking into account the autocorrelation present in the data. A significant autocorrelation and reliable variograms were obtained for the three tested parameters (137Cs, OM content and soil redistribution) (0.87 ≤ r2 ≤ 0.95; 0.7 ≤ Scale/Sill ≤ 0.96 and 4% ≤ ‘nugget-to-sill’ < 20%). Using the Kriging interpolation and ‘area weighted mean’ of the soil redistribution map, a sediment budget was estimated for the whole field. A net sediment output was estimated as 16.6 t ha− 1 yr− 1, for a sediment delivery ratio (SDR) of 99%. This high SDR is believed to reflect the joint impact of tillage, water and snowmelt erosion on the net sediment production.Approximately 85% of the agricultural field surface was estimated to be affected by erosion rates approaching or exceeding the suggested tolerance level of 6 t ha− 1 yr− 1 for most Canadian soils.The geostatistics concept is a powerful tool in soil science and especially for FRNs use in order to characterize the spatial variability of erosion and sedimentation processes.
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A magnitude 9.0 earthquake and subsequent large tsunami hit the northeastern coast of Japan on March 11, 2011. This resulted in serious damage to the reactors of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), operated by the Tokyo Electric Power Company. Large amounts of radionuclides were released from the FDNPP, a proportion of which were deposited onto the ground. In this study, we investigated soil radiocesium contamination of rice fields in Aga and Minamiuonuma, Niigata, ~ 130 and 200 km away from the FDNPP, respectively, as Niigata is one of the largest rice growing regions in Japan. Soil samples were collected from the plow layer of five rice fields in August and September, 5–6 months after the FDNPP accident. Results showed that radiocesium concentrations (the sum of Cs-134 and Cs-137) in the rice soil samples were ~ 300 Bq (kg dry soil)− 1. All samples contained a Cs-134/Cs-137 activity ratio of 0.68–0.96 after correction to March 11, 2011, showing that the radiocesium released from the FDNPP were deposited on these areas. Although the rice fields had been disturbed by farming processes after the FDNPP accident, the depth distribution of radiocesium concentrations in the plow layers showed higher concentrations in the upper soil layers. This suggests that spring tillage, flooding and puddling performed before rice transplantation may not disperse radiocesium deposited on the surface through the whole plow layer. In addition, the planar distribution of radiocesium concentrations was examined near the water inlet in one of the rice fields. Highest activities were found aligned with the direction of irrigation water discharge, indicating that radioactivity levels in rice fields may be elevated by an influx of additional radionuclides, probably in irrigation water, during farming.