GI2.3 | Transport Processes and Environmental Impact of Human-made Disturbances: Radioactive Contamination and Watershed Management
EDI
Transport Processes and Environmental Impact of Human-made Disturbances: Radioactive Contamination and Watershed Management
Co-organized by HS13
Convener: Daisuke Tsumune | Co-conveners: Fi-John Chang, Jr-Chuan Huang, Roman Bezhenar, Junko Takahashi, Hikaru Miura, Masatoshi Yamauchi
Orals
| Mon, 15 Apr, 08:30–12:30 (CEST)
 
Room 0.51
Posters on site
| Attendance Mon, 15 Apr, 16:15–18:00 (CEST) | Display Mon, 15 Apr, 14:00–18:00
 
Hall X4
Orals |
Mon, 08:30
Mon, 16:15
The session gathers multi-disciplinary transport processes triggered by human-made disturbances in the natural system. Understanding the transport processes, tracers, drivers, and possible consequences are the main concerns in understanding dynamics For example, radioactive materials from nuclear power plant accidents (e.g., Fukushima and Chernobyl) are known as polluting hazardous materials, but are also ideal markers in understanding the transport processes (dynamics and physical/chemical/biological reaction chains) from the atmosphere to the soil-water system and then to the ocean and biosystem.

With water as the key carrier after the fallout, the marker aspect particularly promoted studies in the soil-water system, e.g., effects of artificial change in the entire soil-water interface (watersheds) from the drivers to the possible consequences. Such studies help risk/quality management of human-made forcing to the nature, such as possible nuclear power plants accident (risk is increasing in Ukraine and Yellow Sea).


The following specific topics will particularly discussed:
(a) Atmospheric Input (transport and deposition of radionuclides);
(b) Responses in Soil and Forestry System (interaction and transfer to organic system);
(c) Hydrologic drivers for transport (soil-water interactions);
(d) Oceanology (long-range transport);
(e) Natural Hazards (risk assessment in possible accidents);
(f) Measurement Techniques (advanced instrumentation).

Session assets

Orals: Mon, 15 Apr | Room 0.51

Chairpersons: Junko Takahashi, Fi-John Chang, Masatoshi Yamauchi
08:30–08:35
08:35–08:45
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EGU24-2601
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ECS
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On-site presentation
Sheng Fang, Xinwen Dong, Shuhan Zhuang, and Yuhan Xu

The inverse modeling technique has been widely adopted to estimate atmospheric emissions, which aims to complement the subjective inference and provides rare retrieval when unavailable source information. The inversion generally requires the environmental observations and the source-receptor relationship constructed by an air dispersion model. But these two kinds of input lead to an ill-posed inverse problem in continuous atmospheric emissions. For the observations, the measurement network cannot capture all information on a specific emission progress, because of the nature of spatial sparse and limited temporal collections. Besides, there are inevitable model-observation discrepancies introduced by the discretization and imperfect parameters in the physical model and the diagnostic meteorology model. In this dilemma, the estimated atmospheric emissions are featured with discontinuous elements such as temporal gaps, artificial oscillations, and negative values, which are biased from the continuous emission progress in the real world.

This paper describes a regularized inversion framework to objectively address these artifacts and promote the continuity of emissions. This framework consists of the joint estimation model and the total variation (TV) regularization to handle the model-observation discrepancies and the insufficient observations respectively. The former implements site-by-site corrections by adding a diagonal matrix to the residual term of the inversion, and thus reduces the oscillations. The latter enhances a prior with the piecewise-constant feature by the L1-norm of the gradient of the emission vector, and therefore recovers the missing emissions. An adaptive parameterization scheme is tailored for the TV regularization to correct negative values.

The proposed method has been applied to the Fukushima accident to estimate the lasting emissions of 137Cs, facing the observations with nearly half temporal incomplete of the estimation period and unavoidable deviations introduced by the atmospheric dispersion model. The results produce a discrete emission profile that accurately approximates the continuous emission progress, which better matches the recognized one by expert judgments than nine published estimates, with a Pearson’s correlation coefficient of 0.92 and an index of agreement of 0.82. The estimated profile agrees with the timing of on-site gamma dose rate peaks as well. The evaluation was also conducted with respect to atmospheric simulations, providing significantly improved air concentrations and depositions, with the ten-factor agreement (FAC10) values of 0.56 and 0.99 respectively. The uncertainty analysis with respect to the regularization parameters shows a limited variation range of the estimation error (median value below 15.04%), demonstrating the potential for operational inversions with automatic parameterization.

How to cite: Fang, S., Dong, X., Zhuang, S., and Xu, Y.: Regularized framework for inverse problems in continuous atmospheric emissions: An application to the Fukushima accident, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2601, https://doi.org/10.5194/egusphere-egu24-2601, 2024.

08:45–08:55
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EGU24-3268
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On-site presentation
Yasunori Igarashi, Valentyn Protsak, Gennady Laptev, Igor Maloshtan, Dmitry Samoilov, Serhii Kirieiev, Yuichi Onda, and Alexei Konoplev

The Chornobyl wildfires of 2020 raises concerns regarding radionuclides wash-off from post fire sites. The objective of this study is to determine the speciation of 137Cs and 90Sr in the ash and soil. And to reveal the impact of the wildfires on concentrations of 137Cs and 90Sr in river water in Chornobyl. To accomplish this objective, extraction tests were conducted using ash and soil samples collected immediately after the 2020 fires to determine the water-soluble and exchangeable fractions of 137Cs and 90Sr in the ash and soil. Long-term river-water radionuclide concentration records were also analyzed.

The results showed that the solid–liquid distribution coefficient (Kd) of ash was significantly lower than that of soil for 137Cs, while for 90Sr there was no significant difference in Kd between ash and soil. Analysis of river water data indicated that 90Sr concentrations higher than the Ukrainian drinking water standard (> 2 Bq/L) were observed more frequently following wildfires in the Sakhan River catchment. The fires increased 90Sr concentrations over the following two years, particularly in the spring, when snowmelt causes substantial releases, and in the summer and autumn, when surface flows occurred. High 90Sr concentrations were observed only within the Chornobyl Exclusion Zone, so additional human uptake of or dose exposure to 90Sr from river water is not expected.

The Chornobyl wildfires, which is a short period when radioactive contamination levels are elevated in the ecosystem, affected radionuclide speciation, turning the catchment into a location where radioactive contamination levels are significantly higher than in the surrounding area for the redistribution of radionuclides.

How to cite: Igarashi, Y., Protsak, V., Laptev, G., Maloshtan, I., Samoilov, D., Kirieiev, S., Onda, Y., and Konoplev, A.: Impacts of wildfire on desorption of radionuclide and subsequent wash-offs in the Chornobyl Exclusion Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3268, https://doi.org/10.5194/egusphere-egu24-3268, 2024.

08:55–09:05
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EGU24-4338
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ECS
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On-site presentation
Donovan Anderson, Hiroaki Kato, and Yuichi Onda

This study evaluates the long-term impact of government-led decontamination efforts on air dose rates in Fukushima forests affected by the 2011 nuclear disaster. While decontamination successfully mitigated radiation risks, its influence on air dose rates over time remains understudied, particularly in comparison to non-remediated forests. A comprehensive assessment spanning 2013 to 2020 was conducted, utilizing governmental decontamination data and monitoring adjacent untreated forests. Despite initial increases post-decontamination, air dose rates generally stabilized, following a trend indicative of physical decay. The study found that dominate tree species in forests influenced dose rate reduction. Broadleaf forests maintained lower post-decontamination dose rates compared to untreated counterparts, while cedar forests experienced increased post-decontamination rates, reverting to pre-decontamination levels. Both forest types exhibited similar annual decrease trends due to physical and environmental decay, with red pine in non-decontaminated forests showing the slowest decline. Analysis of radioactive cesium concentrations in organic matter and soil revealed a gradual transfer from organic matter to soil. Decontamination reduced concentrations in organic material but had no discernible effect on soil concentrations, indicating an ongoing transfer of radioactive materials from organic matter to soil. This emphasizes the need for future remediation strategies to assess local natural restoration potential and this study offers crucial insights for refining forest decontamination strategies and underscores the importance of factoring in ecosystem dynamics in radiation remediation planning.

How to cite: Anderson, D., Kato, H., and Onda, Y.: The Influence of Remedial Actions on Ambient Dose Rates in Fukushima Forests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4338, https://doi.org/10.5194/egusphere-egu24-4338, 2024.

09:05–09:15
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EGU24-13896
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Virtual presentation
Yoshifumi Wakiyama, Shun Satoh, Hyoe Takata, Pierre-Alexis Chaboche, and Honoka Kurosawa

Previous studies indicated that high-flow events can result in substantial 137Cs exportation via river to the ocean and increase 137Cs concentrations in coastal seawater. Assessing response of marine 137Cs behavior to terrestrial 137Cs inflow will lead to a better understanding of 137Cs transfer processes in terrestrial and marine environments. This study presents results of sample collections under various flow conditions on a river system and its coastal seawater to discuss the transfer processes in detail. The study was conducted in the Ukedo river system and its coastal sea during 3rd-19 th September 2023. Water samples were collected for 13 times at two downstream points of the river system, on the mainstream (Ukedo river) and a tributary (Takase river), and 8 times at seashore locating at 500 m north from the river mouth. In the sampling period, the catchment mean rainfall was totaled 300 mm with intensive rainfalls on 4, 6 and 8 September. Collected water samples were filtrated to measure 137Cs concentration in suspended solids (Bq/kg) and dissolved 137Cs concentrations (Bq/L). 137Cs concentrations in suspended solids in Ukedo and Takase river ranged from 7.0 to 67 kBq/kg and from 2.4 to 15 kBq/kg, respectively. The concentrations at peak water discharge phases in Takase river tended to be high when ratio of rainfall amount on downstream parts to that on whole catchments were high, but vice versa in the Ukedo river. This discrepancy can be attributed to the difference in spatial distribution of 137Cs inventory between the two catchments. Dissolved 137Cs concentrations in Ukedo and Takase rivers ranged from 52 to 70 mBq/L (5 samples measured out of 13) and from 8.4 to 37 mBq/L, respectively. At the seashore, 137Cs concentrations in suspended solids and dissolved 137Cs concentration ranged from 2.0 to 95 kBq/kg and from 6.7 to 410 mBq/L, respectively. Both concentrations appeared maximum in the sample collected 5 hours after the peak river water discharge which occurred with intensive rain on 8th September. Higher dissolved 137Cs concentration in seawater than in corresponding river water for the high-flow event indicates considerable desorption of 137Cs from terrestrial suspended solids into coastal seawater. Both 137Cs concentrations in seawater decreased with time to reach the background levels in 10 days after the event despite of quite stable concentrations in rivers. These results provide important implications for quantifying 137Cs transfer processes in terrestrial-marine environments.

How to cite: Wakiyama, Y., Satoh, S., Takata, H., Chaboche, P.-A., and Kurosawa, H.: Linkage of 137Cs dynamics in river and coastal seawater during high-flow events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13896, https://doi.org/10.5194/egusphere-egu24-13896, 2024.

09:15–09:20
09:20–09:30
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EGU24-147
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On-site presentation
Aleksei Konoplev, Honoka Kurosawa, Yoshifumi Wakiyama, Yasunori Igarashi, and Kenji Nanba

Analysis of available monitoring data on seasonal variations of dissolved radiocesium concentrations in the water bodies of accidentally contaminated areas has revealed two basic mechanisms responsible for regular seasonal variations of dissolved 137Cs concentrations in water bodies (increase in summer and decrease in winter), namely temperature dependence of radiocesium desorption from sediments to solution, and ion-exchange remobilization of radiocesium by cations of ammonium generated as a result of organic matter decomposition in anoxic conditions. An equation has been derived describing seasonal variations of dissolved radiocesium in water bodies considering two basic factors: water temperature and combined concentration of basic competitive cations. In Fukushima rivers, which are mostly shallow and fast-flowing, ammonium concentration is usually negligible. For them, the predominant factor of dissolved 137Cs seasonality is the temperature dependence of 137Cs desorption. For stagnated stratified waters of ponds, lakes, and dam reservoirs in anoxic conditions, the role of ammonium in 137Cs mobilization can be comparable with that of water temperature or even be prevalent. Results of a field experimental study of dissolved 137Cs seasonality in three ponds of Okuma town in the near area of the Fukushima Daiichi nuclear power plant are presented.

This research was supported by Environmental Radioactivity Research Center (ERAN) Projects I-23-11 and I-23-12.

How to cite: Konoplev, A., Kurosawa, H., Wakiyama, Y., Igarashi, Y., and Nanba, K.: Mechanisms of seasonal variations of dissolved 137Cs concentrations in freshwaters: Fukushima and Chernobyl, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-147, https://doi.org/10.5194/egusphere-egu24-147, 2024.

09:30–09:40
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EGU24-2293
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On-site presentation
Wei Sun, Jia-Yi Liou, and Fi-John Chang

    In the face of evolving global weather patterns attributed to climate change, precise prediction of groundwater levels is increasingly essential for effective water resource management. This significance is particularly pronounced in regions like Taiwan, where groundwater is a pivotal water source. This study focuses on the Zhuoshui River basin in central Taiwan and explores a Transformer Neural Network (TNN) based on a 20-year hydrometeorological dataset at a 10-day scale to predict groundwater levels. Our investigation reveals that the innovative TNN model outperforms conventional models, such as the Convolutional Neural Network (CNN) and the Long Short-Term Memory neural network (LSTM). The TNN model's superiority is evidenced by its enhanced predictive capabilities, as measured by metrics like R2 and MAE. Notably, the TNN model excels in providing precise forecasts (MAE < 1 m) for the majority of groundwater monitoring stations, notwithstanding challenges in areas facing overexploitation.

    This groundbreaking study marks the first attempt of the TNN model to predict groundwater levels, showcasing its robust performance and broad applicability. The TNN model emerges as a valuable tool for groundwater level prediction, contributing to sustainable groundwater management and effective resource utilization amid the backdrop of climate change. With the potential to address climate-related challenges, the TNN model stands as a pivotal asset for optimizing strategies in groundwater resource management.

How to cite: Sun, W., Liou, J.-Y., and Chang, F.-J.: Revolutionizing Groundwater Level Prediction in Taiwan: Unleashing the Power of Transformer Neural Networks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2293, https://doi.org/10.5194/egusphere-egu24-2293, 2024.

09:40–09:50
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EGU24-5500
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On-site presentation
Estimating Basin Recharge and Pumping Rates Using Hydrological-Groundwater Coupled Model (SWAT-MODFLOW) - A Case Study of the Zhuoshui River Alluvial Fan in Taiwan
(withdrawn)
Li-Chi Chiang, Min-Jing Li, and Chih-Mei Lu
09:50–10:15
Coffee break
Chairpersons: Hikaru Miura, Jr-Chuan Huang, Roman Bezhenar
10:45–10:55
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EGU24-12226
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ECS
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On-site presentation
Olivia Miller, Scott Ator, Mike Hess, Daniel Jones, Patrick Longley, Morgan McDonnell, Matthew Miller, Annie Putman, Dale Robertson, David Saad, Noah Schmadel, Gregory Schwarz, Andrew Sekellick, Kenneth Skinner, Richard Smith, and Daniel Wise

Stream water-quality and its drivers vary across time and space, but we only monitor a small fraction of streams consistently over long periods of time. Such limited monitoring necessitates the development and application of spatially explicit and dynamic models to predict water quality at unmonitored locations. Historically, data and computational limitations have hindered temporally variable prediction efforts across large spatial scales. However, hybrid statistical and process models, such as Spatially Referenced Regression on Watershed attributes (SPARROW), can provide spatially explicit, accurate predictions of water quality constituents with substantially lower computational cost than process-only models while retaining process-level information that can be obscured within machine learning models. An emerging next generation of such hybrid models moves beyond temporally static predictions into dynamic predictions. Here, we present regional- and continental-scale dynamic SPARROW models developed across the United States to simulate annual salinity and seasonal nutrient loads and concentrations over decades. Dynamic SPARROW models account for temporal variability of constituent sources and processes that deliver constituents from the landscape to streams. In addition, dynamic SPARROW models quantify lagged delivery of contaminants to streams that may have accumulated in soils, groundwater, and vegetation. Results quantify that legacy sources can vary by constituent, location, and time, and provide inference into river responses and lags to management activities. For example, groundwater storage contributes between 66 and 82% of the dissolved solids load to streams in the Upper Colorado River Basin, while lagged storage contributes on average between 20% to nearly 50% of the total nutrient load to Illinois River Basin streams.  Ongoing work to expand dynamic representation of loading up to the continental United States will provide further insight into the continually evolving impacts of legacy and other sources on riverine water quality. Dynamic representation of key processes across spatial scales provides new opportunities for more informed management that can improve water quality for human and ecosystem uses.

How to cite: Miller, O., Ator, S., Hess, M., Jones, D., Longley, P., McDonnell, M., Miller, M., Putman, A., Robertson, D., Saad, D., Schmadel, N., Schwarz, G., Sekellick, A., Skinner, K., Smith, R., and Wise, D.: Perspectives on dynamic water quality modeling across continental and watershed scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12226, https://doi.org/10.5194/egusphere-egu24-12226, 2024.

10:55–11:05
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EGU24-1993
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ECS
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On-site presentation
Yanlai Zhou, Zhihao Ning, Fanqi Lin, and Fi-John Chang

Reservoir impoundment operation has far-reaching effects on the synergies between hydropower output, floodwater utilization, and carbon fluxes. However, there's a notable rise in flood risks, especially when advancing impoundment timings and lifting reservoir water levels. This study proposed a novel reservoir impoundment operation framework prioritizing flood prevention, hydropower generation, floodwater management, and carbon emission control. The Three Gorges Reservoir in the Yangtze River was selected as a case study. The results demonstrated that initiating impoundment on or after September 1st could ensure flood safety. The best scheme of reservoir impoundment operation could significantly boost synergistic benefits, enhancing hydropower output by 1.39 billion kW·h (5.3%) and the water impoundment rate by 10.2% while reducing carbon emissions by 51.65 GgCO2e/yr (15.8%) and increasing organic carbon burials by 10.03 GgCO2e/yr (10.3%), respectively, compared with the standard operation policy. This study not only provides scientific and technical support for reservoir impoundment operation benefiting water-carbon nexus synergies but also presents policymakers with viable options to pre-experience the risks and benefits for sustainable hydropower through adjusted impoundment schedules and reservoir water levels. 

How to cite: Zhou, Y., Ning, Z., Lin, F., and Chang, F.-J.: Optimizing impoundment operation of Three Georges Reservoir for enhancing hydropower output and reducing carbon emission, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1993, https://doi.org/10.5194/egusphere-egu24-1993, 2024.

11:05–11:15
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EGU24-7089
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On-site presentation
Alexandre Cauquoin, Maksym Gusyev, Yoshiki Komuro, Hayoung Bong, Atsushi Okazaki, and Kei Yoshimura

Following the accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March 2011, large quantities of radioactive materials were released into the atmosphere and ocean. Since the FDNPP nuclear accident, Tokyo Electric Power Company (TEPCO) operators have been implementing measures to reduce groundwater inflow into the FDNPP damaged reactor buildings while pumping water to cool the nuclear reactors and fuel debris. The resulting huge water volume began the discharge into the ocean from August 2023, after being treated by an Advanced Liquid Processing System (ALPS) to remove radionuclides for acceptable discharge levels except tritium. Tritium releases from the FDNPP accident and the ALPS treated water raise questions about the impact on tritium in precipitation in Japan, the removal time of anthropogenic tritium in groundwater and the oceanic transport of tritium from released ALPS treated water. 

In this two-part study, we present (1) the modeling of tritium in precipitation during the FDNPP accident using an atmosphere general circulation model (AGCM), and (2) a sensitivity simulation of tritium concentration in the ocean due to planned ALPS treated water release in the next decades by TEPCO using an ocean general circulation model (OGCM). 

For the atmospheric part, we used the isotope-enabled AGCM MIROC5-iso, in which tritium has been implemented [1], and adapted an estimated atmospheric release of iodine-131 [2] for the anthropogenic tritium source. We found good agreement with the tritium in precipitation observations in Japan for 2011 and subsequent years, despite MIROC5-iso’s rather coarse horizontal resolution (approximately 2.8°). Together with measured tritium data in Japan, our modeled results can be used to interpret mean transit times of Fukushima surface and groundwater systems and in other Asian systems (see abstract of Gusyev et al. in the same session).

For the oceanic part, we used the OGCM COCO4.9, which is the ocean component of the Model for Interdisciplinary Research on Climate, version 6 (MIROC6 [3]), and the tritium discharge scenario from TEPCO. Tritium concentration at the ocean surface reaches approximately 3 Bq/m3 near the release site and varies between 0.01 and 0.25 Bq/m3 in the North Pacific Ocean, well below the natural tritium level (approximately 50 Bq/m3 [4]). For this kind of projection simulation, the use of a fully coupled atmosphere-ocean model would make it possible to model tritium concentration in both the atmosphere and the ocean, as well as the dynamics of exchanges within and between these water cycle reservoirs.

 

[1] Cauquoin et al.: Modeling natural tritium in precipitation and its dependence on decadal variations of solar activity using the atmospheric general circulation model MIROC5-iso, J. Geophys. Res. Atmos., in review (minor revisions).

[2] Katata et al., Atmos. Chem. Phys., 15, 1029–1070, https://doi.org/10.5194/acp-15-1029-2015, 2015.

[3] Tatebe et al., Geosci. Model Dev., 12, 2727–2765, https://doi.org/10.5194/gmd-12-2727-2019, 2019.

[4] Jenkins et al., Earth Syst. Sci. Data, 11, 441–454, https://doi.org/10.5194/essd-11-441-2019, 2019.

How to cite: Cauquoin, A., Gusyev, M., Komuro, Y., Bong, H., Okazaki, A., and Yoshimura, K.: Simulation of tritium releases into the atmosphere during the Fukushima accident and into the ocean due to planned discharge of treated water, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7089, https://doi.org/10.5194/egusphere-egu24-7089, 2024.

11:15–11:25
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EGU24-13781
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On-site presentation
Yuichi Onda, Hikaru Sato, and Daisuke Tsumune

Reducing the release of radionuclides into the environment is crucial for decommissioning nuclear facilities and post-accident remediation. After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, a seawall was constructed to minimize the direct discharge of Cs-137-contaminated groundwater into the ocean. Despite this measure, unexplained seasonal variations in Cs-137 emissions continued. Notably, between 2013 and 2014, groundwater leaks from treated water storage tanks at the site led to detectable levels of tritium (H-3) in the groundwater moving downslope from the plant. Our study, conducted over 2015-2021, utilizes a watershed hydrologic tracer approach to identify the marine sources of Cs-137 and explore the underlying causes of its seasonal fluctuation.

We analyzed H-3 in FDNPP groundwater and drainage channel K, known for high Cs-137 concentrations. By correlating this data with Cs-137 levels and runoff in the channel, we deduced the proportion of surface to total flow, identifying the main sources of Cs-137 and its seasonal variability. The surface flow, indicated by H-3 presence and further subdivided by effective rainfall analysis, revealed that the flow through the plant buildings was heavily contaminated with Cs-137, constituting the primary runoff source. We found that Cs-137 concentrations in basal flow are influenced by temperature, while those in surface flow respond to rainfall.

These insights are crucial for effective cleanup strategies at FDNPP and demonstrate the broader applicability of using leakage H-3 as a tracer to identify sources of radioactive and chemical pollutants from terrestrial to marine environments in similar scenarios.

How to cite: Onda, Y., Sato, H., and Tsumune, D.: Tritium Leakage Traces the Path of Cesium from Fukushima Daiichi Nuclear Power Plant into the Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13781, https://doi.org/10.5194/egusphere-egu24-13781, 2024.

11:25–11:30
11:30–11:40
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EGU24-17332
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On-site presentation
Maksym Gusyev, Alexandre Cauquoin, Yasunori Igarashi, Hyoe Takata, Shigekazu Hirao, and Naofumi Akata

Environmental tritium (3H) radioisotope with a half-life of 12.32 years is naturally generated in the upper atmosphere by cosmic rays and enters the water cycle in the troposphere as the water molecule (HTO) to become a useful tracer in Japan and other countries. In 2011, anthropogenic 3H entered the terrestrial water cycle due to the Fukushima Daiichi Nuclear Power Plant (FDNPP) atmospheric release and discharged in Advanced Liquid Processing System (ALPS) treated water from the FDNPP site to the Pacific Ocean in 2023 raising concerns internationally. In Japan, 3H measurements in monthly precipitation have been conducted by the Government and Universities while many surface water sites were sampled twice per year across Fukushima Prefecture accumulating a decade-long record of 3H measurements. However, there are no 3H measurements in precipitation during the FDNPP accident requiring atmospheric numerical modeling to quantify anthropogenic 3H in Fukushima. To utilize 3H as a tracer in Fukushima, we combine simulated anthropogenic 3H released by the FDNPP in 2011 with the long-term time-series of 3H in precipitation from 1950 to present in the Tokyo area, which was scaled to Fukushima area. Using annual 3H in precipitation is 2.86 TU-3.70 TU with an average of 3.37 TU from 2016 to 2021 lead to the scaling factor from Tokyo area to Fukushima city between 1.30 and 1.61. For Fukushima surface water sites, measured 3H concentrations are at low levels of natural 3H concentrations and lead to insignificant doses due to drinking water exposure. In addition, we sampled several headwater catchments near Fukushima city in October 2023 for measuring 3H and estimated tritium-tracer mean transit time and subsurface water storage volume after the ALPS-treated water discharge. As a result, we demonstrate that environmental 3H radioisotope is a useful tracer with developed 3H time-series in precipitation and surface water measurements to evaluate terrestrial water cycle in Fukushima. 

How to cite: Gusyev, M., Cauquoin, A., Igarashi, Y., Takata, H., Hirao, S., and Akata, N.: Anthropogenic and natural tritium radioisotope in terrestrial water cycle of Fukushima, Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17332, https://doi.org/10.5194/egusphere-egu24-17332, 2024.

11:40–11:50
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EGU24-20396
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On-site presentation
Richard Harbron, Aleksandra Lipikhina, Kazbek Apsalikov, and Evgenia Ostroumova

Between 1949 and 1990, tests of nuclear weapons and other explosive devices were performed by the Soviet Union at the Semipalatinsk Nuclear Test Site (SNTS) in Kazakhstan, resulting in radioactive contamination of surrounding settlements. This contamination and the associated impact on the health of the local population are a subject of ongoing radioecological, radiobiological, dosimetric, and epidemiological research. Less in known about potential additional radioactive contamination of settlements SE of SNTS, close to the border with China. This region may have been contaminated by fallout from weapons tests performed by China at Lop Nor between 1964 and 1981, during which time all tests at SNTS were underground. Here, we review available evidence of this contamination, including the results of sampling campaigns performed both at the time of the Chinese tests and in recent years, and electron paramagnetic resonance (EPR) of tooth enamel.

Soil, vegetation, and milk sampling performed in the weeks following the Lop Nor tests revealed the presence of short-lived fission products, including I-131, I-133, Sr-89, Zr-95 and Ba-140 well in excess of background levels. Contamination was greatest following the thermonuclear tests on 17/06/1967 and 27/06/1973. Contemporary soil sampling in Kazakhstan and NW China suggests radioactivity levels have returned to background levels, though with ratios of Pu-240 / Pu-239, and Pu-240+239 / Cs-137 that differ from global fallout levels. Efforts to reconstruct exposure levels are ongoing, including collection of fortuitous dosimeters (e.g. bricks from settlement buildings) and teeth of exposed residents.

How to cite: Harbron, R., Lipikhina, A., Apsalikov, K., and Ostroumova, E.: Evidence of radioactive contamination of the Abai Region, Kazakhstan, from the Chinese nuclear testing program at Lop Nor, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20396, https://doi.org/10.5194/egusphere-egu24-20396, 2024.

11:50–12:00
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EGU24-10247
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On-site presentation
Vira Balabukh, Oleg Skrynyk, Sergiy Bubin, and Gennadiy Laptev

The Zaporizhzhia nuclear power plant (ZNPP) has been occupied by Russian aggressors since March 4, 2022. Its proximity to the combat zone results in a real risk of an accident with radioactivity emissions. There have been a number of blackouts at ZNPP (the most recent one was reported on December 2, 2023, lasting for approximately 5 hours), which could potentially lead to an accident with a scenario similar to that of the 2011 Fukushima Daiichi NPP disaster. The objective of this research is to assess possible contamination of the territory of Ukraine and neighboring countries by Cs-137, emitted in a hypothetical accident at ZNPP, depending on weather patterns usually observed over the domain. The assessment is based on numerical simulations of atmospheric transport, dispersion and deposition processes.

In order to obtain an input meteorology for the dispersion/deposition simulations, we chose 37 typical weather patterns out of 153 that were objectively identified in the domain during 2018-2020. Our selection aimed to keep seasonal and frequency distribution of the patterns in the sampled population. Generally, the selected patterns included 22 cyclonic, 12 anticyclonic, and 3 situations of western transport. Their mean duration was approximately 6 days. 3D meteorological data for the selected weather patterns were generated by means of the WRF v4.3 meteorological model based on ERA5 reanalysis data.

The source term parameterization was based on freely available information published in scientific papers, reports etc. Several Cs-137 emission scenarios were considered by varying an emitted fraction of the total core inventory (50% and 3.43%) and a period of time when the source was active (24, 32, and 40 hours). The dispersion/deposition calculations were performed with the CALPUFF v6 and HYSPLIT v5.2.3 atmospheric dispersion models. Using these two models, which implement different computation algorithms, allowed us to perform the verification of the computed results.

Our calculations showed that a hypothetical accident with the most conservative emission scenario (emitted 50% of the total core inventory) could lead to significant contamination of not only the territory of Ukraine but also neighboring countries. Generally, depending on the weather pattern, from 10 to 80% of the emitted Cs-137 could be deposited on the territory of Ukraine. The reduction of the total emission obviously leads to decreased absolute values of the contamination, however the fractions of deposited in Ukraine Cs-137 stay unchanged for each weather pattern.

 

The work is supported by the grant program University for Ukraine (U4U) and The Yale School of the Environment. Oleg Skrynyk also acknowledges the support from the MSCA4Ukraine fellowship program, which is funded by the European Union.

How to cite: Balabukh, V., Skrynyk, O., Bubin, S., and Laptev, G.: Possible contamination of Ukraine and neighboring countries by Cs-137 due to a hypothetical accident at the Zaporizhzhia NPP as a consequence of the Russian aggression, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10247, https://doi.org/10.5194/egusphere-egu24-10247, 2024.

12:00–12:30

Posters on site: Mon, 15 Apr, 16:15–18:00 | Hall X4

Display time: Mon, 15 Apr, 14:00–Mon, 15 Apr, 18:00
Chairpersons: Daisuke Tsumune, Roman Bezhenar, Fi-John Chang
Poster1
X4.177
|
EGU24-7677
Junko Takahashi, Satoshi Iguchi, Takuya Sasaki, and Yuichi Onda

Introduction

Radiocesium (Cs-137) deposited on forests was intercepted by the canopy, then migrated to the litter layer and eventually to the soil layer, where some of it has been absorbed by roots and circulated through the forest ecosystem for a long time. In other words, the amount of Cs-137 uptake by roots will control the long-term dynamics in the forest ecosystem in the future, temporal changes in Cs-137 in tree roots have rarely been reported. In this study, we investigated the Cs-137 concentration and inventory in the soil and very fine (VF) roots (< 0.5 mm) of Japanese cedar from 2011 to 2020.

Methods

An approximately 3 m x 3 m plot was established in a cedar forest (initial deposition 440 kBq m-2) in the Yamakiya district of Kawamata Town, Fukushima Prefecture. Litter and soil samples were collected twice a year during 2011-2012 and once a year after 2013 using a scraper plate at 0.5 cm intervals for 0-5 cm, 1 cm intervals for 5-10 cm, and 5 cm intervals for 10-20 cm. Root samples were collected by further separating only the roots with tweezers from soil samples in 2012, 2015, 2017, and 2020, and washed by ultrasonic homogenizer to remove soil particles on the root surface. The roots measured were absorptive VF roots of 0.5 mm or less of the current year's growth.

Results and discussions

The Cs-137 concentration in the litter layer was still decreasing exponentially more than 12 years after the accident, its inventory was about 0.2-0.5% of the deposited amount. The depth distribution of Cs-137 concentration in the mineral soil layers was fitted with an exponential equation until 2019, but after 2020, the peak concentration shifted slightly downward and was fitted with a hyperbolic function. The Cs-137 inventory in the soil increased over time due to the migration from the forest canopy and litter layers, whereas that in the VF roots decreased in 2020. Especially, the Cs-137 inventory in the VF roots in the 0–2 cm of soil reached 89% in 2012; however, it decreased with time to approximately 43% in 2020. This decrease in the Cs-137 concentration in the VF roots at 0–2 cm was caused by the decrease in Cs-137 concentration in the litter layers. Although the Cs-137 concentration in the VF roots below 2 cm increased with increasing Cs-137 concentration in the soil, the downward migration of Cs-137 within the soil can reduce the amount of Cs-137 absorbed by roots because the VF root biomass decreases exponentially with depth. In other words, Cs-137 can be removed from the long-term active cycles of forest ecosystems as they migrate deeper into the soil without physical decontamination. This natural downward migration process can be regarded as a “self-cleaning” of the forest ecosystem, resulting in a decrease in the air dose rate and the amount of Cs-137 absorbed by roots.

How to cite: Takahashi, J., Iguchi, S., Sasaki, T., and Onda, Y.: Downward migration of Cs-137 in soils reduce root uptake of Japanese cedar in Fukushima, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7677, https://doi.org/10.5194/egusphere-egu24-7677, 2024.

X4.178
|
EGU24-7423
Yutaro Nagata, Yuichi Onda, Junko Takahashi, and Koichi Sakakibara

The concentration of dissolved-form 137Cs in forested rivers is known to increase during rainstorms, and direct leaching from litter and soil water is considered to be a factor. There have also been many studies showing that competing ions such as K+ and NH4+ promote the elution of 137Cs. However, there are no examples of detailed measurements of 137Cs concentrations and water quality characteristics of stream water and water passing through litter during actual rainstorms. In this study, stream water, throughfall,  water passing through litter, and groundwater were sampled in a small watershed in Fukushima Prefecture, Japan, which was affected by the Fukushima Daiichi Nuclear Power Plant, to measure dissolved 137Cs and dissolved organic carbon (DOC), K+and NH4+. NH4+ was not detected in stream water. The average concentrations of dissolved137Cs, DOC and K+ were 6.36 (mBq/L), 0.51 (mg/L) and 0.14 (mg/L), respectively, while the concentrations of 137Cs and DOC doubled to 13.38 (mBq/L), 1.13 (mg/L) during rainfall event and the K+concentrations remained unchanged (0.15mg/L). The concentrations of 137Cs and DOC  in the water passing through the litter were 50 and 30 times higher than in the stream water, respectively, suggesting that the high concentrations of dissolved 137Cs at the time of runoff were formed by leaching from the litter rather than by the presence of competing ions. The amount of 137Cs and K+eluted from the litter increased in the order of near-channel, saturated zone at run-off and slope, while the amount of DOC eluted from the litter was lower near the channel. These results suggest that 137Cs, K+and DOC release from near-channel litter is lower than that from litter on the slope because of the progress of leaching due to the occurrence of saturated surface flow.

How to cite: Nagata, Y., Onda, Y., Takahashi, J., and Sakakibara, K.: Mechanisms of dissolved-form 137Cs runoff from forest source watersheds , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7423, https://doi.org/10.5194/egusphere-egu24-7423, 2024.

X4.179
|
EGU24-2292
|
ECS
Pu Yun Kow, Yu-Wen Chang, and Fi-John Chang

Climate change profoundly affects natural water resources by increasing extreme rainfall and persistent drought events. This impact has led to a rising likelihood of over-extraction of groundwater by Taiwanese farmers due to insufficient water resources. Quantifying groundwater pumping activities is challenging, thereby prompting this study to introduce a hybrid AI model combining a Convolutional-based Autoencoder with LSTM. The objective is to explore the spatiotemporal relationship between hydrometeorology and groundwater for providing a quantitative assessment of groundwater resources.

To construct the model, a comprehensive dataset spanning two decades (2000-2019) is utilized, incorporating information from 33 groundwater monitoring wells in the Jhuoshuei River basin of Taiwan. Two types of datasets, observation and simulation, are employed for a robust analysis. The hybrid AI model yields accurate three-month-ahead forecasts for shallow groundwater in the Jhuoshuei River basin, with R2 performance ranging from 0.70 to 0.87 for T+1 (short-term forecasts) and from 0.42 to 0.69 for T+3 (long-term forecasts).

The significance of these forecasts lies in their potential to empower farmers to increase crop cultivation efficiency. The long-term forecasts aid in formulating strategic plans for crop cultivation and fallow periods, promoting efficient agricultural management. Simultaneously, the short-term forecasts empower farmers to enhance irrigation efficiency, leading to a reduction in regional water consumption. This proactive approach aligns with Sustainable Development Goals (SDGs) 11 and 12, fostering sustainable water resource management practices. In essence, this hybrid AI model emerges as a valuable tool for proactive and adaptive water resource management, particularly crucial in the context of evolving climate conditions.

Keywords: Groundwater management, AI, Deep Learning, regional forecast, machine learning, SDGs, Taiwan

How to cite: Kow, P. Y., Chang, Y.-W., and Chang, F.-J.: AI-Driven Hydro-Insights: Proactive Water Resource Management for Sustainable Agriculture in the Face of Climate Change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2292, https://doi.org/10.5194/egusphere-egu24-2292, 2024.

X4.180
|
EGU24-2519
Chu-Han Chen, Meng-Hsin Lee, Hang-Yeh Lin, and Fi-John Chang

The escalating frequency of climate-related disasters underscores the imperative need for robust adaptive strategies to mitigate the impacts of extreme weather events. Crafting effective adaptive solutions, however, presents a formidable challenge. This research investigates the potential of aquavoltaic systems to enhance adaptive capacity and promote low-carbon production in fishing villages grappling with climate change. Focused on clam farming in Yunlin County, Taiwan, our study builds innovative Water-Energy-Food-Land-Climate (W-E-F-L-C) Nexus models using system dynamics (SD) techniques to compare the synergistic benefits and resource utilization efficiency between aquavoltaic systems and conventional aquacultural methods. This study meticulously catalogues factors from SD models and incorporates them into a comprehensive life cycle assessment (LCA) to scrutinize the environmental impacts of both aquavoltaic and conventional systems. Carbon emission data is rigorously calculated by LCA, revealing the carbon emissions flow resulting from interactions between these factors.

Additionally, this study conducts a scenario analysis to gain insight into how aquavoltaic and conventional aquacultural systems respond to key influencing factors such as temperature and rainfall. Our findings underscore that elevated temperatures and intensified rainfall significantly impact conventional clam farming compared to the aquavoltaic system. Aquavoltaics emerges as a robust and viable mechanism for aquaculture in the face of capricious weather conditions. Particularly noteworthy is the effectiveness of solar panels in intercepting and diverting rainwater during heavy rainfall in summer, reducing the risk of diluting pond water and thereby stabilize water quality. The shading effect induced by photovoltaic installations also contributes to moderating water temperatures, especially under direct sunlight. By synergizing physical mechanisms with advanced simulation techniques, this study propels toward a more efficient and resilient paradigm in aquaculture. Aquavoltaics demonstrate promising potential for sustainable and low-carbon production as well as promoting the resilience of fishing villages. This study not only illuminates the intricate dynamics of climate-resilient aquaculture but also stands as a milestone for the development of sustainable aquaculture practices.

How to cite: Chen, C.-H., Lee, M.-H., Lin, H.-Y., and Chang, F.-J.: Enhancing Climate-Resilient Aquaculture in Yunlin County, Taiwan: A Comparative Analysis of Aquavoltaic Systems and Conventional Methods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2519, https://doi.org/10.5194/egusphere-egu24-2519, 2024.

X4.181
|
EGU24-14216
|
ECS
Li-Chin Lee, Jr-Chuan Huang, Gabriele Weigelhofer, Thomas Hein, Yu-Lin Yu, and Pei-Hao Chen

The fate and reactivity of dissolved organic matter (DOM) in river networks is critical to understanding carbon cycling in inland water systems, and is highly regulated by physio-geographic factors and water residence time (WRT). In this study, we investigate the spatiotemporal variation of DOM concentration and composition in two SMRs in Taiwan with different landscapes and anthropogenic impacts. The WRT for these two rivers, the Keelung and Lanyang River, are around 34 and 23 hours, respectively. Dissolved organic carbon (DOC) concentration measurements and optical analyses (absorbance and fluorescence) were used to examine DOM quantity and quality along the river continuum. The comparative results showed that, along the SMR continuum, the DOC concentrations and optical indexes exhibited slight changes, with significant increases observed only at downstream sites influenced by human activities. Meanwhile, the higher biological index (BIX) and lower humification index (HIX) indicated an increase in autochthonous sources and a decrease in the degree of humic characters. In addition, we observed a positive correlation between WRT and DOC concentration variability, yet not significant for DOM compositions. When comparing the two rivers, the one with steeper topography and less human influence shows lower levels of DOC concentration and degree of humification. Overall, the SMRs seem to have lower DOC concentrations (0.26 - 1.65 mg-C L-1), lower HIX (0.28 - 0.76), and slightly higher BIX (0.8 - 1.9) on a global scale, which might be attributed to Taiwan's steep landscape and shorter water residence time, limiting soil organic carbon (SOC) production and in-stream processes rates. Through our investigation, DOC concentration and DOM composition across river networks will be better understood and potentially improve the assessment of the global carbon cycle.

How to cite: Lee, L.-C., Huang, J.-C., Weigelhofer, G., Hein, T., Yu, Y.-L., and Chen, P.-H.: Spatiotemporal Variation of DOM Concentration and Composition along the Subtropical Small River Continuum in Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14216, https://doi.org/10.5194/egusphere-egu24-14216, 2024.

X4.182
|
EGU24-17762
Pei-Hao Chen, Hasan Raja Naqvi, Guan-Zhou Lin, Tsung-Yu Lee, Li-Chin Lee, and Jr-Chuan Huang

Human-induced land-use change has profound effects on both societies and ecosystem services. For example, transitioning from forests to conventional farms using fertilizers can escalate soil nitrogen, degrade groundwater, and impair downstream ecosystems. This study explores the intricate dynamics of human-induced land-use change, focusing on the shift from forests to tea farm-dominated catchments in Taiwan, where conventional farming practices with fertilizers impact soil quality, groundwater, and downstream ecosystems. Utilizing the Soil and Water Assessment Tool (SWAT) for nutrient export analysis, our research reveals that when agricultural land use exceeds 2%, exports of nitrate, phosphate, and potassium spike significantly, ranging from 25% to 150%. Notably, agricultural land use induces a higher impact on nitrate, with concentrations surpassing those by 120% and 233% during the dry season and wet season, respectively. Tea farms, constituting a substantial portion, exhibit a nearly tenfold increase in NO3-N yield compared to forests. Implementing a modified fertilization strategy, involving application during small rainfall events, enhances nitrogen uptake and tea tree harvest yield while reducing nitrogen input by 10%. This research offers actionable recommendations for sustainable agroforestry practices by integrating river and rainwater data with SWAT modeling. By doing so, it advances our understanding of hydrological and biogeochemical processes in subtropical tea farm-dominated catchments, providing valuable insights into hydrology and biogeochemistry.

How to cite: Chen, P.-H., Naqvi, H. R., Lin, G.-Z., Lee, T.-Y., Lee, L.-C., and Huang, J.-C.: Assessment of nutrient export in agroforestry catchments dominated by tea farms in subtropical small mountainous rivers, Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17762, https://doi.org/10.5194/egusphere-egu24-17762, 2024.

Poster2
X4.183
|
EGU24-7140
Hideki Tsuji, Hironori Funaki, and Seiji Hayashi

In the region affected by the Fukushima nuclear accident in 2011, some freshwater fish shipments continue to be suspended owing to radioactive contamination (mainly 137Cs) of the aquatic environment. In predicting the future 137Cs contamination of aquatic organisms, investigations must focus on the dynamics of 137Cs in dissolved form, which is highly bioavailable and abundant in the environment. In particular, dam lakes that deposit large amounts of sediment contaminated with 137Cs and have a long residence time of water can substantially influence the dynamics of 137Cs in rivers, as suggested by prior research. This study focuses on the effect of desorption of 137Cs from lake sediment on the formation of dissolved 137Cs concentrations in dam discharge water, using the results from monitoring surveys at two dam lakes located near the Fukushima Daiichi Nuclear Power Plant.

We collected inflow and discharge water from the Matsugabo and Yokokawa dams in Fukushima Prefecture every month from 2014 and measured the concentration of dissolved and particulate 137Cs in the water using the cartridge filter method. On the basis of these results, combined with flow data from the dam lakes, we estimated the annual budgets of 137Cs (inflow/outflow) in the dam lakes. For the particulate form, annual 137Cs inflow into the lakes decreased by more than 80% in most years, indicating that most of the inflow particles sedimented. For the dissolved form, the annual discharge of 137Cs was higher than the annual inflow of 137Cs, concurring with results from a neighboring dam lake. This increment suggests 137Cs desorption from the sediment.

According to the monthly monitoring data, the dissolved 137Cs concentration in the dam discharge water at some periods showed a higher value than the peak value from the previous year. This phenomenon was observed when the reservoir storage rate of the dam lake fell below approximately 30%. To determine the main source of dissolved 137Cs in the dam lake, we investigated the horizontal distribution of the dissolved 137Cs concentrations at several points in Yokokawa dam lake and the vertical distribution of the dissolved 137Cs concentration at the center of the lake in August 2023, when the water level was very low. The concentration of dissolved 137Cs in the lake water was found to increase in the inlet part of the lake, while the concentration remained almost the same in the downstream direction from the site. The concentration of dissolved 137Cs at the center of the lake was almost unchanged vertically. This trend was different from the increase in the concentration of dissolved 137Cs in bottom water, previously observed at the same location (Tsuji et al., 2022). These results indicate that 137Cs desorption from sediment in the inlet area mainly led to the increase in the dissolved 137Cs concentrations in the lake water, in part owing to the low volume of flowing water.

How to cite: Tsuji, H., Funaki, H., and Hayashi, S.: Effect of 137Cs desorption from sediment on the formation of dissolved 137Cs concentrations in dam discharge water, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7140, https://doi.org/10.5194/egusphere-egu24-7140, 2024.

X4.184
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EGU24-14837
Yayoi Inomata and Daisuke Tsumune

The anthropogenic radionuclides such as caesium-137 (137Cs), strontium-90 (90Sr), 3H, 14C, and plutonium (Pu) were released into the global ocean as results with large scale weapon tests in the late 1950s and early 1960s. Because these anthropogenic radionuclides have been still existed in the ocean, it is necessary to investigate the behavior of these anthropogenic radionuclides due to investigate the effects of human health. In this study, the spatiotemporal variations in the 137Cs and 90Sr activity concentrations in global ocean surface seawater from 1956 to 2021 using the HAMGlobal2021: Historical Artificial radioactivity database in Marine environment, Global integrated version 2021. The global ocean was divided into 37 boxes. The 0.5-yr average value of 90Sr in the northern North Atlantic Ocean and its marginal sea, decreased exponentially in 1970–2010, just before the F1NPS accident. Estimated apparent half residence time of 137Cs and 90Sr ranged from 4.1-34.1 years and 3.6-25.2 years, respectively. Considering that longer Tap occurs larger inflow and shorter Tap occurs larger outflows/smaller inflow of radionuclide from the upstream region, 137Cs and 90Sr were inflowed into the Eastern China Sea from the subtropical western North Pacific Ocean. Inflow of 90Sr into the Sea of Japan from the Eastern China Sea were relatively smaller than those of 137Cs. Although 90Sr were decreased exponentially, these trends tended to be larger than those of 137Cs, which was investigated by our previous study (Inomata and Aoyama, 2023). This might be caused by the different behavior of 90Sr and 137Cs such as particulate form for 90Sr in the seawater.

 

Keywords: 90Sr, 137Cs, Database, surface seawater, global ocean

Reference: Inomata and Aoyama, Evaluating the transport of surface seawater from 1956 to 2021 using 137Cs deposited in the global ocean as a chemical tracer. Earth Syst. Sci. Data, 15, 1969–2007, 2023.

How to cite: Inomata, Y. and Tsumune, D.: Spatiotemporal variations of 137Cs and 90Sr in the global ocean based on the historical data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14837, https://doi.org/10.5194/egusphere-egu24-14837, 2024.

X4.185
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EGU24-7685
|
ECS
Hikaru Miura, Takashi Ishimaru, Jota Kanda, Yukari Ito, and Atsushi Kubo

Radionuclides including radioactive Cs were released into the environment due to the Fukushima Daiichi Nuclear Power Plant accident in 2011. Two years after the accident, glassy water-resistant particles incorporating radioactive Cs were first reported. Such glassy particles are called cesium-bearing microparticles (CsMPs). CsMPs have been studied because (i) they have information on the condition in the reactor at the time of the accident, and (ii) there is concern about the exposure to the humans and the other organisms.

Several types of CsMPs have been reported, which is assumed to reflect the difference in the accidental progress of each unit. It is also known that CsMPs were transported in the atmospheric plume at the time of emission and therefore have different deposition regions. Type-A CsMPs, are presumed to originate from Unit 2, deposited over a wide area including the Kanto region due to their small size (~0.1–10 µm). Type-B CsMPs, are presumed to originate from Unit 1, deposited in a limited area in the north direction because of their large size (50–400 µm). Matrix of Types-A and -B CsMPs is SiO2 but Type-A CsMPs have higher concentration of volatile elements including Cs than Type-B CsMPs due to the difference in forming process. Type-A CsMPs were formed through gas condensation, whereas Type-B CsMPs were formed through melt solidification.

The presence of CsMPs emitted from Unit 3 in the ocean was confirmed by our research. The plume at the time of the emission of radionuclides from Unit 3 was in the ocean direction, which suggests that many CsMPs from Unit 3 deposited directly into the ocean. We will report the comparison of CsMPs from marine and terrestrial sources. In addition, we reported Type-A CsMPs from suspended particles in rivers and marine samples, such as plankton net and suspended particle samples. This fact suggests that Type-A CsMPs deposited on land and transported to the ocean through rivers. The presence of CsMPs may be the cause of the overestimation of solid–water distribution coefficient for marine sediments and particulate matters and apparent high concentration factor of marine biota of radioactive Cs.

How to cite: Miura, H., Ishimaru, T., Kanda, J., Ito, Y., and Kubo, A.: Comparison of cesium-bearing microparticles from marine and terrestrial sources, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7685, https://doi.org/10.5194/egusphere-egu24-7685, 2024.

X4.186
|
EGU24-14451
Daisuke Tsumune, Takaki Tsubono, and Kazuhiro Misumi

The March 11, 2011, Great East Japan Earthquake triggered accidents at the Fukushima Daiichi Nuclear Power Plant (1F NPP), releasing radioactive substances into the ocean. Sparse observational data on 137Cs in the ocean led to interpolation and simulation for a comprehensive understanding. The primary focus was on direct release, emphasizing the need for a suitable source.

The direct release rate (Bq/day) was calculated by multiplying the seawater exchange flow rate (m3/day) and observed 137Cs concentration (Bq/m3). Using a mesh size of 735 m x 929 m x 8 m on the model, the seawater exchange flow rate at the release point was simulated. The 137Cs concentration relied on average observed radioactivity at 5, 6, and the south discharge canals near the 1F NPP. Direct release was estimated at 2.2x1014 Bq/day from March 26 to April 6, 2011, aligning with rates derived from other methods.

The seawater exchange flow rate's dependency on the model's mesh size was acknowledged. For this estimation, a 735 m x 929 m mesh size encompassing key points was considered reasonable for the seawater exchange flow rate, given the complex transport process from the release source (Unit 2 intake) to observation points (5, 6, and the south discharge point) due to port structures.

A higher resolution model with a 147 m x 186 m mesh (1/5) was used for a detailed analysis of direct release rates. The size of the sea area for determining the volume of seawater exchange flow rate can now be changed. Despite challenges in setting due to damaged ports, using the seawater exchange flow rate in a similar area as the previous resolution was deemed appropriate. The results of the validation of the release rate and the observed results by the relationship equation confirmed the consistency with the amount of seawater exchange obtained by the results of the dye tracer release experiments in the 1970s.

The release of 137Cs from the 1F NPP site persists. Estimating direct release rates up to 2016, a long-term simulation with a higher resolution model was conducted for validation. Results showed the oceanic 137Cs concentration distribution influenced by coastal currents, eddies, and the Kuroshio Current, leading to spatio-temporal variability. Validation with observed annual mean concentrations revealed good agreement. The higher resolution improved coastal transport reproducibility, addressing 137Cs radioactivity underestimation at the Fukushima 2 NPP, 10 km south of the 1F NPP.

How to cite: Tsumune, D., Tsubono, T., and Misumi, K.: Verification of direct release rate of oceanic 137Cs from Fukushima Daiichi Nuclear Power Plant Accident by higher resolution ocean dispersion model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14451, https://doi.org/10.5194/egusphere-egu24-14451, 2024.

X4.187
|
EGU24-13825
Seongbong Seo, Igor Brovchenko, Vladimir Maderich, Ivan Kovalets, Kateryna Kovalets, and Kyung Tae Jung

To cope with the increasing threat of radioactivity release accidents in the Yellow Sea a Lagrangian radionuclide transport model in the region was recently developed coupled in off-line manner with current-wave-suspended sediment modeling system (Brovchenko et al, 2022).  The radionuclide model included as an essential feature the fast adsortion-desorption processes of dissolved and particulate radionuclides in the presence of multi-ftactional sediments. Upgrade is made in this work by including fast and slow adsorption-desorption processes of radionuclides and a novel approach for lagrangian simulation of the radionuclide exchange between near-bottom water-layer and bed sediments. Lagrangian particles in the model can possess several states: dissolved in the water column, adsorbed on suspended sediment of particular size, dissolved in the pore water, adsorbed on the bed sediments of particular size. Note that, If particles are adsorbed on the sediments then it can be in two different states, namely fast and slow reversible forms; if there are Nsed sediment size classes then we have Ntot =2+4Nsed  total states of the radionuclide. Throughout the numerical integration the model calculates the probabilities to transfer into each possible state (that depends on the current state and time step) during the next time step and then chooses the new particular state by comparing with the generated uniformly distributed random number. Hypothetical accident at the Haiyang NPP in China, which is located at the coast of Yellow Sea close to Korea is considered as a scenario of accident. The atmospheric transport and deposition of radionuclides on the sea surface was simulated by the FLEXPART model. The obtained deposition fluxes were used as a source term in the Lagrangian radionuclide transport model. 3D fields of currents, suspended sediment concentration and turbulent diffusion coefficient as well as bed sediment fractional composition are identical to the previous results of the Yellow Sea (Brovchenko et. al. 2022).  Computational domain of the FLEXPART model includes bigger outer area, which covers Yellow and East China Sea, with spatial resolution of 0.15 deg, and inner area, which covers only Yellow Sea with better spatial resolution of 0.05 deg. The source term of 137Cs released due to hypothetical accident at the Haiyang NPP was obtained from the 6-day simulations of the FLEXPART model. The total amount of radioactivity that deposited on the calculation area is approximately 55 PBq. The radioactivity budget analysis reveals that almost near 50% of the 137Cs was deposited to the bottom sediments and approximately half remained in the dissolved form. About 4% of the total amount remains on the suspended sediments in one-step modelling and about 9% with the use of two-step model. The total bed contamination changed only 1% because for this period bottom contamination fluxes dominated over the bed cleaning process. More differences are expected for simulation with duration of several years when dissolved 137Cs concentration in water will decrease and bed cleaning process become more significant.

How to cite: Seo, S., Brovchenko, I., Maderich, V., Kovalets, I., Kovalets, K., and Jung, K. T.: Lagrangian radionuclide transport modeling with fast and slow adsorption-desorption processes: application to the Yellow Sea with a hypothetical atmospheric deposition , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13825, https://doi.org/10.5194/egusphere-egu24-13825, 2024.

X4.188
|
EGU24-13386
|
Highlight
Kyeong Ok Kim, Roman Bezhenar, Ivan Kovalets, Igor Brovchenko, Vladimir Maderich, and Kyonghwan Kwon

After accidents at the Chornobyl NPP in 1986 and Fukushima Daiichi NPP in 2011, it became clear that there are many causes that can lead to a nuclear accident, including techno-genic and natural disasters. There is a danger of damage to the Zaporizhzhia NPP, with the subsequent release of radioactivity into the environment, as a result of the Russian invasion of Ukraine. The coastline of the Yellow Sea and East China Sea(YSECS) is a place where 9 NPPs are in operation in China and Korea. Since they are semi-enclosed seas with a very high density of population, any potential nuclear accident in the region can significantly contaminate the marine environment and affect the health of many people.

In the current study, a set of numerical models for the first time was applied to simulate the spreading of radionuclides in the environment as a result of the hypothetical accident at the Haiyang Nuclear Power Plant in China. The scenario of accidental release with containment-bypass was considered in this work. The atmospheric transport and deposition of radionuclides on the sea surface were simulated by the FLEXPART model. The set of 1450 dispersion scenarios following hypothetical accidental releases with different start dates were calculated for the next 120 h after release start, thus covering meteorological conditions from 1 Mar 2020 to 28 Feb 2021. Scenario with the heaviest deposition densities on the Yellow Sea was selected. These results were used as a source term for three different marine dispersion model simulating the transfer and fate of Cs-137 in YSECS: the grid-based Eulerian model THREETOX, Lagrangian radionuclide transport model and compartment model POSEIDON-R. Such approach emulates the application of various models with their own settings in the event of an unexpected accidental release, similar to the Fukushima accident. For THREETOX model setup, 3D current velocities with 30 vertical layers were extracted from the KIOST-MOM model, results of which are monthly averaged and cover North Pacific. The Lagrangian radionuclide transport model used regional currents and suspended sediments concentrations from circulation model adopted for the YSECS taking into account tides and multi-fractional sediments. These two models were applied for emergency and post-emergency phases for the period from half a year to one year after deposition. The POSEIDON-R model already had a system of boxes for the North-Western Pacific covering the YSECS, East/Japan Sea and Eastern coastal area of Japan. It was applied for a long-term assessment of several decades. Obtained concentrations of Cs-137 in water, bottom sediments and partly in marine organisms were compared and the differences were analysed. Application of three marine dispersion models provides the possible ranges of radionuclide concentrations on the one hand and increases the reliability of results on the other.

How to cite: Kim, K. O., Bezhenar, R., Kovalets, I., Brovchenko, I., Maderich, V., and Kwon, K.: Multi-model simulation of the radionuclide transfer in the Yellow Sea as a result of hypothetical atmospheric deposition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13386, https://doi.org/10.5194/egusphere-egu24-13386, 2024.