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| Titel |
Radiocesium wash-off associated with soil erosion from various land uses after the Fukushima Dai-ichi NPP accident |
| VerfasserIn |
Yoshifumi Wakiyama, Yuichi Onda, Kazuya Yoshimura, Hiroaki Kato, Alexei Konoplev, Mark Zheleznyak |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094754
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| Publikation (Nr.) |
 EGU/EGU2014-10185.pdf |
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| Zusammenfassung |
| Soil erosion is the initial process which drives radiocesium into the aquatic systems and
therefore the quantification 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 various
land uses. Seven runoff plots were established in four landscapes; uncultivated
farmland (Farmland A1, Farmland B1), cultivated farmland (Farmland A2, Farmland
B2), grassland (Grassland A, Grassland B) and Japanese cedar forest (Forest) in
Kawamata town, an area affected by the Fukushima Dai-ichi Nuclear Power Plant
accident. The discharged sediments were collected approximately every two weeks.
In laboratories, collected sediments were dried and weighed for calculating soil
erosion rates (kg m-2) and served for measurements of radiocesium concentration
(Bq kg-1) with HPGe detectors. The erosivity factor of the Universal Soil Loss
Equation (R-factor: MJ mm ha-1 hr-1 yr-1) was calculated based on the data of
precipitation. Standardized soil erosion rates (kg m-2 MJ-1 mm-1 ha hr yr), observed soil
erosion rates divided by R-factor, was 1.8 x 10-4 in Farmland A1, 6.0 x 10-4 in
Farmland A2, 1.5 x 10-3 in Farmland B1, 8.3 x 10-4 in Farmland B2, 9.6 x 10-6 in
Grassland A, 5.9 x 10-6 in Grassland B and 2.3 x 10-6 in Forest. These erosion
rates were basically proportional to their vegetation cover of soil surfaces except
for cultivated farmlands. Concentrations of Cs-137 in eroded sediments basically
depended on the local deposition of Cs-137 and varied enormously with ranging
several orders of magnitude in all the landscapes. For the observation period of
time decreasing trends in concentrations of Cs-137 in eroded sediments were not
obvious. To compare these results with those of Chernobyl, we calculated normalized
“solid” wash-off coefficient (m2 g-1) with dividing the mean total concentration of
Cs-137 in sediments by local deposition of Cs-137 (Konoplev et al., 1992). The
coefficient was 4.4 x 10-5 in Farmland A1, 1.3 x 10-5 in Farmland A2, 6.4 x 10-5 in
Farmland B1, 1.0 x 10-5 in Farmland B2, 2.2 x 10-5 in Grassland A, 1.0 x 10-5 in
Grassland B and 8.2 x 10-5 in Forest. High erodibilities and relatively low values of
normalized wash-off coefficients in cultivated farmlands can be attributed to the
mixing of surface soil by ploughing. These values almost corresponded to those of
Chernobyl. It was found that the total “solid” wash-off coefficient of radiocesium from
farmlands is high and for 2 years period of time after the accident reaches 10%.
Generally high precipitation in the region and steep slopes promote higher wash-off of
radiocesium as compared to the Chernobyl case. Also, normalized wash-off coefficients
exhibited relatively less volatility than erodibilities in the landscapes. These results
suggest that soil erosion management is crucial for mitigating risks of radiocesium. |
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