Abstract. We observed ³H activity concentrations and the ¹³⁷Cs activity concentrations during the SoSo 5 rivers cruise in 2014 and at the Tomioka port in 2014–2018. The ³H activity concentrations at coastal stations located close to the Fukushima coast ranged from 90 Bq m⁻³ to 175 Bq m⁻³, and decreased between 67 Bq m⁻³ to 83 Bq m⁻³ at the stations located 12–16 km from the coast. The ³H activity concentration at the estuaries and ports, except at 56 north canal of the FNPP1 site, are around 200–500 Bq m⁻³ and slightly lower than the ³H activity concentration of 500–600 Bq m⁻³ observed in the rivers. These gradients of the ³H activity concentrations in the coastal region might indicate the large effect of ³H flux through the rivers. On the other hand, the ³H activity concentration at 56N of the FNPP1 site was significantly high compared to the ³H activity concentration in surrounding waters both north and south of the FNPP1 site and in river waters. It should also be noted that the ³H activity concentrations were similar at the stations located both north and south of the FNPP1 site, while the ¹³⁷Cs activity concentrations were lower at the stations north of the FNPP1 site and higher at the stations south of the FNPP1 site. This indicated that the major sources of ¹³⁷Cs could be the FNPP1 site as the point source while the source of ³H should be more diffuse and linked to riverine inputs located north and south of the FNPP1 site. The ³H / ¹³⁷Cs activity ratios in coastal waters were 1.2–2.2 as obtained via the slopes by standardised major axis regressions between the ³H activity concentration and the ¹³⁷Cs activity concentration of SoSo samples and Tomioka Port observed in 2014–2018, which is significantly high compared to that of the released radionuclides derived from the FNPP1 site, which was 0.01 in 2011 just after the accident. The open-water ³H activity concentration contribution to coastal waters was estimated to be 67 ± 20 Bq m⁻³ and 66 ± 17 Bq m⁻³ as the intercepts also by standardised major axis regressions. These estimates are consistent with 50 Bq m⁻³ obtained at the Kuroshio region as the background levels of ³H activity concentration in open water. The ³H and ¹³⁷Cs fluxes to the coastal region of Fukushima based on the open-water movement, freshwater flux from the rivers based on their respective catchment, and mean monthly precipitation were estimated. The largest ³H flux is the open-water inflow from the north of the FNPP1 site and it reaches 52 GBq day⁻¹, while the rivers north of the FNPP1 site showed 3–5 GBq day⁻¹ fluxes. We obtained a ³H flux as 1.9–4.5 GBq day⁻¹ of ³H using the ³H activity concentration in the port, which is comparable with the fluxes obtained from the rivers located north of the FNPP1 site. While using ³H activity concentration at the 56 north canal of FNPP1, we obtained 28–86 GBq day⁻¹ fluxes, which is one order of magnitude larger than those estimated using ³H activity concentration in the FNPP1 port. One of the reasons could be the very high variability of the ³H levels at 56 north canal and in the port of FNPP1, explaining variable ³H/¹³⁷Cs activity ratio observed at 56 north canal and in the port of FNPP1. The ³H activity concentration of TFWT in the fish filets collected close to the FNPP1 site ranged from 97 ± 11 Bq m⁻³ to 144 ± 11 Bq m⁻³, which were similar to the ³H activity concentrations in the surrounding seawater, in agreement with the knowledge that the bioconcentration factor of ³H is approximately 1. In contrast, higher values were found in TOBT, which can be linked to life-history traits.

中文翻译：

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2014年福岛沿海地区的t活动浓度和行为

摘要。我们在2014年的SoSo 5河流游以及2014-2018年的富冈港观察到³ H浓度和¹³⁷ Cs浓度。位于福岛海岸附近的沿海站点的³ H浓度范围从90 Bq m ^-3到175 Bq m ^-3，在12-16 km的站点上的67 Hqm ^-3到83 Bq m ^-3降低。从海岸。除了FNPP1站点北运河的56条外，河口和港口的³ H活性浓度约为200–500 Bq m ^-3，略低于³在河流中观测到的H活度浓度为500–600 Bq m ^-3。沿海地区³ H活度浓度的这些梯度可能表明³ H通量通过河流的影响很大。在另一方面，³在FNPP1网站的56N H活性浓度显著高比³在周边海域北方和南方的FNPP1网站及在河水H活性浓度。还应注意的是，位于FNPP1站点北部和南部的站点的³ H活性浓度相似，而¹³⁷在FNPP1站点以北的站点，Cs的活动浓度较低，而在FNPP1站点以南的站点则较高。这表明¹³⁷ Cs的主要来源可能是FNPP1站点作为点源，而³ H的源应更加分散并与位于FNPP1站点北部和南部的河流输入有关。通过³ H活度浓度和¹³⁷ H之间的标准化长轴回归，通过坡度获得的沿海水域的³ H /  ¹³⁷ Cs活度比为1.2–2.22014-2018年观察到的SoSo样品和富冈港的Cs活性浓度，与事故后刚从FNPP1站点释放的放射性核素的2011年的0.01相比，这是很高的。通过标准化的主轴回归分析，对沿海水域的开放水域³ H活度浓度贡献估计为67±20 Bq m ^-3和66±17 Bq m ^-3。这些估计与在黑潮地区获得的50 Bq m ^-3一致，作为开放水中³ H活性浓度的背景水平。的³ H和¹³⁷根据露天水流向福岛沿海地区的Cs通量，根据河流各自的汇水情况估算的河流淡水通量以及月平均降水量。³ H通量最大的是FNPP1站点北部的开放水流入，达到52 GBq天^-1，而FNPP1站点以北的河流显示3–5 GBq天^-1通量。使用港口中的³ H活性浓度，我们得到³ H的1.9–4.5 GBq天^-1的³ H通量，这与从FNPP1站点以北的河流获得的通量相当。使用^3时在FNPP1北运河56处的H活度浓度，我们获得了28–86 GBq天^-1通量，这比在FNPP1港口使用³ H活度浓度估计的通量大一个数量级。原因之一可能是在北运河56和FNPP1港口的³ H水平变化很大，这解释了在北运河56和FNPP1港口观察到的³ H / ¹³⁷ Cs活度比变化。在靠近FNPP1部位收集的鱼排中TFWT的³ H活性浓度范围从97±11 Bq m ^-3到144±11 Bq m ^-3，与³与³ H的生物富集系数约为1的认识相一致，周围海水中的H活度浓度与此相反。相反，在TOBT中发现较高的值，这可能与生活史特征相关。