EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Open Access Biogeosciences Discuss., 10, 2767–2790, 2013 Open Access www.biogeosciences-discuss.net/10/2767/2013/ Biogeosciences Biogeosciences BGD doi:10.5194/bgd-10-2767-2013 Discussions © Author(s) 2013. CC Attribution 3.0 License. 10, 2767–2790, 2013 Open Access Open Access Climate This discussion paper is/has been underClimate review for the journal Biogeosciences (BG). 134 of the Past Export of Cs and Please refer to the correspondingof finalthe Past paper in BG if available. 137 Discussions Cs in the Fukushima river in Open Access 134 137 Open Access September 2011 Export of CsEarth System and Cs in theEarth System Dynamics Dynamics S. Nagao et al. Fukushima river systems at heavyDiscussions rains Open Access Open Access by Typhoon RokeGeoscientific in SeptemberGeoscientific 2011 Title Page Instrumentation Instrumentation S. Nagao1, M. Kanamori2,Methods S. Ochiai and1, S. Tomihara3, K. FukushiMethods4, and and Abstract Introduction Data Systems Data Systems M. Yamamoto1 Discussions Conclusions References Open Access Open Access 1Low Level Radioactivity Laboratory, Institute of Nature and EnvironmentalGeoscientific Technology, Geoscientific Tables Figures Kanazawa University, Nomi, Ishikawa 923–1224, Japan Model Development 2 Model Development Graduate School of Natural Science and Technology, Kanazawa University,Discussions Kakuma, Kanazawa, Ishikawa 920–1192, Japan J I Open Access 3Aquamarine Fukuhsima, Onahama, Iwaki, FukushimaOpen Access 971–8101, Japan 4 Hydrology and Hydrology and J I Division of Earth Dynamics,Earth Institute System of Nature and Environmental Technology,Earth System Kanazawa University, Kakuma, Kanazawa, Ishikawa 920–1192, Japan Back Close Sciences Sciences Received: 31 December 2012 – Accepted: 15 January 2013 – Published: 15Discussions February 2013 Full Screen / Esc Open Access Open Access Correspondence to: S. Nagao (nagao37@staff.kanazawa-u.ac.jp) Ocean Science Ocean Science Printer-friendly Version Published by Copernicus Publications on behalf of the European GeosciencesDiscussions Union. Interactive Discussion Open Access Open Access 2767 Solid Earth Solid Earth Discussions Open Access Open Access The Cryosphere The Cryosphere Discussions Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract BGD Effects of a heavy rain event on radiocesium export were studied at stations on the Natsui River and the Same River in Fukushima Prefecture, Japan after Typhoon 10, 2767–2790, 2013 Roke during 21–22 September 2011, six months after the Fukushima Daiichi Nuclear 134 137 5 Power Plant accident. Radioactivity of Cs and Cs in river waters was 0.011– Export of 134Cs and −1 0.098 Bq L at normal flow conditions during July–September in 2011, but it increased 137Cs in the −1 to 0.85 Bq L in high flow conditions by heavy rains occurring with the typhoon. The Fukushima river in 134 137 particulate fractions of Cs and Cs were 21–56 % in the normal flow condition, but September 2011 were close to 100 % after the typhoon. These results indicate that the pulse input of 10 radiocesium associated with suspended particles from land to coastal ocean occurred S. Nagao et al. by the heavy rain event. Export flux of 134Cs and 137Cs by the heavy rain accounts for 30–50 % of annual radiocesium flux in 2011. Results show that rain events are one factor controlling the transport and dispersion of radiocesium in river watersheds and Title Page coastal marine environments. Abstract Introduction Conclusions References 15 1 Introduction Tables Figures A nuclear accident at the Fukushima Daiichi Nuclear Power Plant (NPP) occurred 134 after the 2011 Tohoku earthquake and tsunami. About 15 PBq of both Cs and J I 137Cs was released from the NPP as a result of venting operations and hydrogen explosions (Japanese Government, 2011; Chino et al., 2011). Surface deposition of J I 134 137 20 Cs and Cs reveals considerable external radioactivity in a zone extending north- Back Close west from the NPP, about 20 km wide and 50–70 km long inside the 80 km zone of the NPP (MEXT, 2011; Yoshida and Takahashi, 2012). Moderate radioactivity (100– Full Screen / Esc 600 kBqm−2) was also found in the Naka-dori region. The deposition pattern is ex- 134 137 plained by emission rates of Cs and Cs coupled with wind direction and precipi- Printer-friendly Version 25 tation (Morino et al., 2011). Interactive Discussion 2768 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | A major part of radiocesium deposited on the ground surface is present at the sur- face to 5 cm depth (MEXT, 2012a; Koarashi et al., 2012). Chemical extraction of 134Cs BGD and 137Cs from selected soil samples has indicated that both radionuclides in the soil 10, 2767–2790, 2013 are only slightly water soluble. Even the fraction extracted with 1 M ammonium acetate 134 137 5 was only approximately 10 % (Matsunaga et al., 2013). However, Cs and Cs have been transported from contaminated watersheds to rivers in Fukushima Prefecture af- Export of 134Cs and ter the Fukushima Daiichi NPP accident (MEXT, 2012a; Sakaguchi et al., 2012). Similar 137Cs in the outcomes were observed at the Pripyat and Dnieper Rivers in Ukraine after the Cher- Fukushima river in nobyl accident in 1986 (IAEA, 2006a). The migration of 137Cs has decreased markedly September 2011 10 over time in river waters from Ukraine (IAEA, 2006a; IAEA, 2006b) and Finland (Saxen´ and Ilus, 2001). The radioactivity of 137Cs shows little change from upstream to down- S. Nagao et al. stream of the exclusion zone in the Pripyat River of the Chernobyl area (IAEA, 2006a). An increase in radioactivity of 134Cs and 137Cs in river waters was also found in the Title Page Chernobyl area during a spring flood event (IAEA, 2006a,b) and in northwest Italy from 15 a delayed release in summer during ice and snow melting in mountain areas (Spez- Abstract Introduction zano et al., 1994). The transport of materials generally depends on watershed condi- tions such as vegetation, slope, soil types, and spring snow-melting. It is important to Conclusions References clarify migration behavior of radiocesium and its controlling factors for future prediction Tables Figures of its dispersion in Fukushima Prefecture, Japan. 20 To elucidate the short-term to long-term impacts of the Fukushima Daiichi NPP ac- J I cident on ecosystems of river and coastal marine environments, the Japanese Gov- 134 137 ernment has been monitoring the radioactivity of Cs and Cs in river systems J I in Fukushima Prefecture (MEXT, 2012b). Japanese rivers have a short length, high Back Close riverbed slope, and high river regime coefficient, which is the ratio of maximum /mini- 25 mum discharge (Suetsugu, 2005). Annual mean precipitation was high, 1718 mm dur- Full Screen / Esc ing 1971–2000 because of “tsuyu” (the rainy season in Japan), typhoon and snow- melting events in spring (MLTI, 2012). Matsunaga et al. (1991) reported that the ra- Printer-friendly Version dioactivity of 137Cs derived from fallout increased at high flow conditions in the Kuji River because of rain events. Nagano et al. (2003) pointed out that variations of Interactive Discussion 2769 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | suspended and dissolved form concentrations of elements in the Kuji River waters were formulated as a function of the water discharge rates. Therefore, it is important BGD to evaluate effects of rain events on export of radiocesium from land to ocean in the 10, 2767–2790, 2013 Fukushima area. 134 137 5 This study was conducted to investigate the transport of Cs and Cs in river systems in Fukushima Prefecture after rain events. This report describes the moni- Export of 134Cs and toring results of radioactivity of 134Cs and 137Cs in river waters at two rivers after the 137Cs in the heavy rain event by a typhoon in September 2011. Field experiments were conducted Fukushima river in at the Natsui River and the Same River in the southern part of Fukushima Prefecture, September 2011 10 Japan. We discussed transport behavior of radiocesium and estimated its export flux from inland to coastal areas. S. Nagao et al. 2 Materials and methods Title Page Typhoon Roke (T1115) struck Japan on 21 September and subsequently weakened Abstract Introduction to an extra-strong tropical cyclone on 22 September 2011 (JMA, 2011). The typhoon Conclusions References 15 precipitated more than 400 mm of rain daily in parts of eastern and western Japan (JMA, 2011). Fukushima Prefecture had rainfall of 100–200 mm during 15–22 Septem- Tables Figures ber. The daily rainfall on 21 September was 137 mm by the impact of Typhoon Roke at Iwaki city, located in the southern coastal region of Fukushima and in a watershed of J I the Natsui River. This value is about one-tenth of the annual mean rainfall (1409 mm J I 20 for 1981–2010: JMA, 2012). The sampling location is presented in Fig. 1. This study investigated Natsui River and Back Close Same River flowing through a less-contaminated area (< 100 kBqm−2: MEXT, 2011) to the Pacific coast. The Natsui River watershed area is 749 km2. That of the Same River Full Screen / Esc is 600 km2. The Natsui River length is 67 km. That of the Same River is 58 km. The 3 −1 25 annual mean water discharge data in 2011 were 17.6 m s for the Natsui River and Printer-friendly Version 21.4 m3 s−1 for the Same River (Fukushima Prefectural Government, 2012).