The impact of typhoons on sediment connectivity: lessons learnt from contaminated coastal catchments of the Fukushima Prefecture (Japan)   总被引：1，自引：0，他引：1       下载免费PDF全文

Caroline Chartin  Olivier Evrard  J. Patrick Laceby  Yuichi Onda  Catherine Ottlé  Irène Lefèvre  Olivier Cerdan 《地球表面变化过程与地形》2017,42(2):306-317

Sediment connectivity characterizes the physical transfer of sediment through different geomorphic compartments in catchments due to sediment detachment, transport and deposition. Quantifying and modelling sediment connectivity is therefore a key prerequisite to improving our understanding of the dispersion of particle‐borne contaminants, especially in catchments exposed to highly erosive climates. The objective of this study is to provide novel insights into typhoon impacts on sediment connectivity from hillslopes to rivers. The dispersion of particle‐bound caesium‐137 (¹³⁷Cs) was investigated in two coastal catchments draining the main contamination plume from the Fukushima Daiichi Nuclear Power Plant accident. Five sampling campaigns were carried out from November 2011 to November 2015, after each typhoon season. The spatial and temporal evolution of ¹³⁷Cs contamination was investigated through the calculation of ¹³⁷Cs enrichment ratios in sediment relative to nearby soils. Rainfall erosivity (EI₃₀) associated with the main typhoons that occurred prior to each sampling campaign were computed, mapped, and finally used to improve a topographic‐based index of connectivity. From 2011 to 2015, mean contamination levels in Mano and Niida catchments decreased from 11.9 kBq kg^?1 to 3.3 kBq kg^?1 and from 34.1 kBq kg^?1 to 8.0 kBq kg^?1, respectively. Regional mean EI₃₀ ranged from 262 MJ mm ha^?1 h^?1 for typhoon Jelawat (in 2012) to 1695 MJ mm ha^?1 h^?1 for typhoon Roke (in 2011). Typhoons Roke (2011) and Etau (2015) showed the highest connectivity from contaminated sources to the rivers, and induced a significant export of sediment to the ocean. In 2013 a slight increase in ¹³⁷Cs levels in river sediments occurred, likely resulting from initial decontamination works and the occurrence of two consecutive typhoons. Importantly, this research provides new insights into the connectivity of the main sources of sediments contaminated with radiocaesium in Fukushima Prefecture and their temporal evolution, which will help with ongoing decontamination efforts. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Impact of Isahaya dike construction on DO concentration in the Ariake Sea     

Soichi Yamaguchi  Yuichi Hayami 《Journal of Oceanography》2018,74(6):565-586

In the Ariake Sea, dike construction in Isahaya Bay in 1997 for reclamation and disaster prevention was thought to cause big anthropogenic impacts on the marine ecosystem. Currently, hypoxia or anoxia occurs every summer in Isahaya Bay and the inner Ariake Sea. However, the effects of the dike construction on the DO concentration are unclarified. The present study evaluated the impact of the dike construction on the DO concentration by applying a numerical ecosystem model. The present calculation showed that the dike construction could affect the DO concentration in summer in a wider area than reported before in the steady state with a neap-spring tidal cycle. In Isahaya Bay, the dike construction caused a decrease of DO concentration greater than 2.0 mg l^?1 , due to the decrease in DO supply from the  vertical diffusion process with reduction of tidal current and the intensification of the density stratification. The dike construction also affected the DO concentration in the inner Ariake Sea by decreasing the DO concentration of the water transported by the estuarine circulation and the reduction of the diffusive supply of oxygen vertically with stratification enhanced by the dike construction. For the first time, this study showed with numerical simulation that the dike construction could affect the DO concentration in a wide area of the Ariake Sea.  相似文献   

Effectivity of dissolved SF6 tracer for clarification of rainfall–runoff processes in a forested headwater catchment     

Koichi Sakakibara  Maki Tsujimura  Sho Iwagami  Yutaro Sato  Kosuke Nagano  Yuichi Onda 《水文研究》2019,33(6):892-904

Understanding rainfall‐runoff processes is crucial for prevention and prediction of water‐related natural disasters. Sulfur hexafluoride (SF₆) is a potential tracer, but few researches have applied it for rainfall‐runoff process studies. We observed multiple tracers including SF₆ in spring water at 1‐ to 2‐hr intervals during rainstorm events to investigate the effectivity of SF₆ tracer in rainfall–runoff studies through the clarification of rainfall–runoff process. The target spring is a perennial spring in a forested headwater catchment with an area of 0.045 km² in Fukushima, Japan. The relationship between the SF₆ concentration in spring water and the spring discharge volume was negative trend; the SF₆ concentration in spring water becomes low as the spring discharge volume increases especially during rainstorms. The hydrograph separation using SF₆ and chloride ion tracers was applied for determining the contribution of principal sources on rainfall–runoff water. It suggested more than 60% contribution of bedrock groundwater at the rainfall peak and high percentage contribution continued even in the hydrograph recession phase. Based on observed low SF₆ concentration in groundwater after heavy rainfall, the replacement of groundwater near the spring with bedrock groundwater is indicated as a mechanism for water discharge with low SF₆ concentration during rainfall events. Consequently, rainstorm events play an important role as triggers in discharging water stored in the deeper subsurface area. In addition, SF₆ tracer is concluded as one of the strongest tracers for examining rainfall–runoff process studies. And, therefore, this study provided new insights into the dynamics of groundwater and its responses to rainfall in terms of SF₆ concentration variance in water in headwater regions.  相似文献   

High-pressure phase transitions of CaRhO<Subscript>3</Subscript> perovskite     

Yuichi Shirako  Hiroshi Kojitani  Masaki Akaogi  Kazunari Yamaura  Eiji Takayama-Muromachi 《Physics and Chemistry of Minerals》2009,36(8):455-462

High-pressure phase transitions of CaRhO₃ perovskite were examined at pressures of 6–27 GPa and temperatures of 1,000–1,930°C, using a multi-anvil apparatus. The results indicate that CaRhO₃ perovskite successively transforms to two new high-pressure phases with increasing pressure. Rietveld analysis of powder X-ray diffraction data indicated that, in the two new phases, the phase stable at higher pressure possesses the CaIrO₃-type post-perovskite structure (space group Cmcm) with lattice parameters: a = 3.1013(1) Å, b = 9.8555(2) Å, c = 7.2643(1) Å, V _m  = 33.43(1) cm³/mol. The Rietveld analysis also indicated that CaRhO₃ perovskite has the GdFeO₃-type structure (space group Pnma) with lattice parameters: a = 5.5631(1) Å, b = 7.6308(1) Å, c = 5.3267(1) Å, V _m  = 34.04(1) cm³/mol. The third phase stable in the intermediate P, T conditions between perovskite and post-perovskite has monoclinic symmetry with the cell parameters: a = 12.490(3) Å, b = 3.1233(3) Å, c = 8.8630(7) Å, β = 103.96(1)°, V _m  = 33.66(1) cm³/mol (Z = 6). Molar volume changes from perovskite to the intermediate phase and from the intermediate phase to post-perovskite are –1.1 and –0.7%, respectively. The equilibrium phase relations determined indicate that the boundary slopes are large positive values: 29 ± 2 MPa/K for the perovskite—intermediate phase transition and 62 ± 6 MPa/K for the intermediate phase—post-perovskite transition. The structural features of the CaRhO₃ intermediate phase suggest that the phase has edge-sharing RhO₆ octahedra and may have an intermediate structure between perovskite and post-perovskite.  相似文献   

Evidence for herbivorous cave bears (Ursus spelaeus) in Goyet Cave,Belgium: implications for palaeodietary reconstruction of fossil bears using amino acid δ15N approaches          下载免费PDF全文

Yuichi I. Naito  Mietje Germonpré  Yoshito Chikaraishi  Naohiko Ohkouchi  Dorothée G. Drucker  Keith A. Hobson  Mark A. Edwards  Christoph Wißing  Hervé Bocherens 《第四纪科学杂志》2016,31(6):598-606

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Interaction between runoff – bedrock groundwater in a steep headwater catchment underlain by sedimentary bedrock fractured by gravitational deformation          下载免费PDF全文

Cristobal Padilla  Yuichi Onda  Tomoyuki Iida 《水文研究》2015,29(20):4398-4412

Recent studies have suggested the importance of the bedrock groundwater (BG) contribution in storm runoff in headwater catchments. However, few such studies have been conducted, and the study of different types of bedrock conditions is still ongoing. The role of BG in storm runoff is still poorly understood, particularly in headwater catchments underlain by relatively deep fractured bedrock. This study aims to clarify this role using hydrometric and hydrochemical observations of BG via boreholes and catchment discharge. The responses of the BG to rainfall are demonstrated to be fast and independent of the sediment cover. The BG exhibits different responses and flow paths that are largely controlled by the bedrock fracture system. The storm runoff in the studied catchment is characterized by rapid discharge response generally followed by a delayed discharge response. The peak of the delayed discharge is much faster than that observed in previous studies, and it is well correlated with the BG levels. A hydrograph separation was performed for two storm events using three end members: rainfall, shallow BG and deep BG. The results demonstrate that the delayed discharge is primarily composed of deep BG. Moreover, a significant contribution of shallow BG is observed during large precipitation events. Although we observed no physical evidence of direct contributions of BG in the catchment, the calculations presented in this study demonstrate that the BG controls the hydrological and hydrogeological response of the catchment to rainfall events. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Profiles of nonylphenol isomers in surface waters from Sri Lanka   总被引：1，自引：0，他引：1  

Guruge KS  Horii Y  Yamashita N 《Marine pollution bulletin》2011,62(4):870-873

Isomer-specific concentrations of nonylphenol (NP) and their predicted estrogenic potency were investigated in Sri Lankan waters for the first time. The total concentration of 13 NP isomers ranged from 90 to 1835 ng/L, while the predicted estrogenic equivalent concentration ranged from 0.072 to 1.38 ng 17β-estradiol (E2)/L. Bire Lake, located in the central area of the commercial capital, Colombo, had the highest contamination among the studied locations. These data show that NP levels in Sri Lankan waters are well within the recently reported concentrations in other regions of the world. The spatial differences in NP concentrations suggest that NP contamination in Sri Lanka may be widespread, and comprehensive study is vital.  相似文献   

Seepage erosion and its implication to the formation of amphitheatre valley heads: A case study at Obara,Japan     

Yuichi Onda 《地球表面变化过程与地形》1994,19(7):627-640

Seepage erosion was investigated in an amphitheatre with a semicircular valley head, steep slopes, and a flat bottom developed in granodiorite hills at Obara, Aichi prefecture, Japan. A high sediment yield occurred where the measuring sites were located at the base of the landslide debris in the base of the convex slopes, whereas sediment outflows were small where the measuring sites were located at the base of the strong convex slopes. This implies that the seepage erosion was an effective agent for removal of debris deposited at the base of the slope. Small landslides can be found at the lower slopes within the area of the observed amphitheatre. The slope stability analysis and subsurface water observation of the lower slope suggest that the small landslides in this amphitheatre are due to over-steepened slopes, and relatively insensitive to subsurface water status. Colluvium in the flat valley bottom thinly covers the bedrock surface. Therefore the topography of the amphitheatre was found to be formed by parallel retreat of slopes by the repetition of basal seepage erosion and subsequent small landslides.  相似文献