Soil erosion and radiocesium migration during the snowmelt period in grasslands and forested areas of Miyagi prefecture,
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Soil erosion and radiocesium migration during the snowmelt period in grasslands and forested areas of Miyagi prefecture, Japan Mikhail Komissarov
&
Shin-ichiro Ogura
Received: 5 April 2020 / Accepted: 5 August 2020 # Springer Nature Switzerland AG 2020
Abstract 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
M. Komissarov (*) Ufa Institute of Biology UFRC, Russian Academy of Sciences, Pr. Oktyabrya 69, Ufa 450054, Russia e-mail: [email protected] S. 50 μm, silt 2– 50 μm, and clay < 2 μm) in each sample was analyzed using a laser diffraction particle size analyzer (SALD3100, Shimadzu Co., Ltd., Kyoto, Japan). The bulk density was determined from the dry weight and volume of the undisturbed soil and sediment samples. The 134Cs and 137Cs activity concentration in the soil, sediments, and in the snow and runoff water was determined by gamma (γ) spectrometry using HPGe detectors (PerkinElmer WIZARD2 2480, Waltham, MA, USA). Measuring times (usually 30 min per sample) was chosen in order to achieve a statistical uncertainty less than 5%. The r-Cs concentration was expressed as the concentration of 134Cs and 137Cs per unit of dry matter (DM) (Bq·kg−1 DM). All measured activities were corrected for radioactive decay to each sampling date. In this paper, the average values of soil properties and r-Cs content in 0–2.5 cm from the three positions (top, middle, and bottom) were calculated and are presented for each plot (Table 2). It related in terms that the 90% of r-Cs at the studied plots is accumulated in surface soil (Fig. 2), and only this layer is involved in erosion processes; therefore, this research focuses on r-Cs concentration in sediments and runoff. Figure 2 also demonstrated that mostly, the highest concentration of r-Cs is found in the middle and lower parts of the slopes that indicate downslope radionuclide migration due to soil erosion and also related
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