<p>The 2011 Fukushima-Daiichi nuclear power plant (FDNNP) accident resulted in the atmospheric releases of large quantities of man-made radionuclides. According to [1], Matua Island, located at a distance of more than 1000 km from FDNPP, was also subjected to minor radioactive contamination. Matua Island, 52.6 sq.km, a recent volcano with the highest point of 1446 m a.s.l. is located in the center of the Kuril Islands Arc. Volcanic soils are formed on stratified gravelly-stony tephra more than 60 cm thick, underlain by thin layers of volcanic slags. The latest catastrophic eruption which changed the landscape of the island occurred in 2009.</p><p>Studies of the vertical distribution of the Cs-137 in soils were carried out on four landscape catenas. The length of the catenas from the sea shore deep into the island ranged from 700 m (maximum height a.s.l. &#160;70 m) to 3.3 km (height a.s.l. &#160;450 m).</p><p>Soil core samples were taken in &#160;summer 2017 at a depth of tephra, which was located at a depth of 10 to 25 cm. Soil was sliced into separate layers with a step of 2 to 5 cm.</p><p>The measurement activity concentrations of the Cs-137 in the soil samples were carried out on a low-background gamma spectrometer Canberra Industries. &#160;The counting time&#160; was fixed not less than 24 h to ensure that the statistical measurement error is small.</p><p>Cs-134, the &#171;Fukushima&#8221; fallout marker, due to the decay, was not detected. Therefore, it is difficult to accurately assess the Cs-137 contribution from the FDNNP accident from a global fallout.</p><p>The vertical distribution of Cs-137 is characterized by extreme heterogeneity, which reflects both the primary fallout conditions and the landscape conditions of the likely lateral redistribution. For &#1089;atena 1 with a length of 1 km and an altitude&#160; of 400 m, the number of pickets (P0, P1, etc. &#8211; the numbering of pickets goes downhill), the specific activity of Cs-137 (Bq/kg) and the depth of the layer (cm) are given as follows: P0-27 Bq/kg (2-4 cm); P1 - 64 Bq/kg (6-8 cm); P2 &#8211; 70 Bq/kg (8-10 cm); P3 - 53 Bq/kg (4-6 cm); P4 - 15 Bq/kg (0-5 cm).&#160; Similar spatial&#160; heterogeneity of the specific activity of Cs-137 and its depth penetration was also found for catena 3 with a length of 1250 m and a height of 75 m (the numbering of pickets goes up the slope): P1-137 Bq/kg (17-20 cm); P2-76 Bq/kg (0-5 cm); P3 - 35 Bq/kg (0-4 cm); P4 - 43 Bq/kg (3-6 cm); P6 &#8211; 24 Bq/kg (5-10 cm).</p><p>The distribution of Cs-137 in individual soil layers was used to evaluate the empirically found shapes of the vertical profiles of radionuclide concentration. Cs-137 is believed here to be a&#160; very valuable tracer&#160; that&#160; can be used to test&#160; variability of vertical geochemical migration in Matua&#160; landscapes.</p><p>[1]. Ramzaev V.P., Barkovsky A.N., Gromov A.V., Ivanov S.A., Kaduka M.V. Fukushima fallout in Sakhalin Region, Russia, part 1: <sup>137</sup>Cs and <sup>134</sup>Cs in grassland soils. Radiation Hygiene, 2018, Vol. 11, No. 1, pp. 25-42.</p>
A Comparison of Stress Susceptibility of Sea Urchins and Sea Cucumbers in Aquaculture Conditions