Environmental change of the fluvial-estuary system in relation to Arase Dam removal of the Yatsushiro tidal flat,SW Kyushu,Japan   总被引：1，自引：0，他引：1  

Sansfica M. Young  Hiroaki Ishiga 《Environmental Earth Sciences》2014,72(7):2301-2314

Chemical composition of 24 elements for sediments and suspended solids, water parameters and the diatoms from Yatsushiro Bay tidal flat, Kuma River, and Arase Dam have been determined to examine changes from 2002 to 2013. In 2002, sediment delivered to the bay by the Kuma River was restricted by the Arase Dam; however, in April 2010 two gates were opened and also repeated seasonal flushing allowing resumption of natural sediment transport. Bulk chemical composition of the tidal flat sediments has changed since 2002, with marked decreases in concentrations of As, Zn, Pb and total sulfur. Decreased heavy metal contents in 2012 and 2013 for bay sediments after opening the dam and repeated flushing is attributed to dilution by previously impounded quartz and feldspar. Restoration of natural sediment transport by opening the dam and repeated flushing has thus brought about a recovery in the Yatsushiro marine environment.  相似文献   

Grazing impact of the copepod community in the Oyashio region of the western subarctic Pacific Ocean     

Kazutaka Takahashi  Akira Kuwata  Hiroaki Saito  Keiichiro Ide 《Progress in Oceanography》2008,78(3):222-240

The role of copepod grazing on the ecosystem dynamics in the Oyashio region, western subarctic Pacific was investigated during six cruises from June 2001 to June 2002. In situ grazing rates of the copepod community (CGR) were measured by the gut fluorescence method in respect to developmental stages of dominant species. In terms of biomass, more than 80% of the copepod community was dominated by six large calanoid species (Neocalanus cristatus, Neocalanus flemingeri, Neocalanus plumchrus, Eucalanus bungii, Metridia pacifica and Metridia okhotensis) throughout the year. Resulting from the observed pattern of the interzonal migrating copepods, the CGR in the Oyashio region was divided into three phases, i.e. spring (bloom), summer (post-bloom) and autumn-winter phase. During the spring bloom, late copepodites of the interzonal migrating species, N. cristatus, N. flemingeri and E. bungii appeared in the surface layer (0-50 m) to consume the production of the bloom, resulting in a high grazing rate of the copepod community (7.9 mg Chl m⁻² d⁻¹), though its impact on phytoplankton community was low due to the high primary productivity. During the post-bloom period, although the copepod community which was dominated by N. cristatus, N. plumchrus, M. pacifica and newly recruited E. bungii still maintained a high biomass, the CGR was generally lower (1.8-2.6 mg Chl m⁻² d⁻¹ for June and August 2001), probably due to the lower availability of phytoplankton. Nevertheless, the highest CGR was also observed during this period (10.5 mg Chl m⁻² d⁻¹ in June 2002). The high CGR on autotrophic carbon accounted for 69% of the primary production, suggesting that the copepod community in the Oyashio region potentially terminates the phytoplankton bloom. Abundant occurrence of young E. bungii, which is a characteristic phenomenon in the Oyashio region, was largely responsible for the high grazing pressure in June 2002 suggesting that success of reproduction, growth, and survival in E. bungii during the spring bloom is an important factor in controlling phytoplankton abundance during the post-bloom season. During autumn and winter, CGR was the lowest in the year (0.29-0.38 mg Chl. m⁻² d⁻¹) due to the disappearance of the interzonal migrating copepods from the surface layer. Diel migrant M. pacifica was the most important grazer during this period. The annual ingestion of the copepod community is estimated as 37.7 gC m⁻² on autotrophic carbon (converted using C:Chl ratio of 30) or 137.9 gC m⁻² on suspended particles (using C:Chl ratio of in situ value, 58-191), accounting for 13% and 46% of annual primary production, respectively. This study confirms that copepod grazing is an important pathway in carbon flow in the Oyashio region and in particular their role in the phytoplankton dynamics is significant for the termination of the spring bloom.  相似文献   

The effect of health benefits on climate change mitigation policies     

Masako Ikefuji  Jan R. Magnus  Hiroaki Sakamoto 《Climatic change》2014,126(1-2):229-243

This paper studies the interplay between climate, health, and the economy in a stylized world with eleven heterogeneous regions, with special emphasis on USA, Europe, China, India, and Africa. We introduce health impacts into a simple economic integrated assessment model where both the local cooling effect of SO ₂ and the global warming effect of CO ₂ are endogenous, and investigate how these factors affect the equilibrium path. Regions do not respond in the same way to climate change. In particular, emission abatement rates and health costs depend on the economic and geographical characteristics of each region. Two policy scenarios are considered, Nash and Optimal, for which we present both global and regional results. Results for Africa and China are highlighted.  相似文献   

Site effects by generalized inversion technique using strong motion recordings of the 2008 Wenchuan earthquake   总被引：3，自引：1，他引：2  

Yefei Ren  Ruizhi Wen  Hiroaki Yamanaka  Toshihide Kashima 《地震工程与工程振动(英文版)》2013,12(2):165-184

The generalized inversion of S-wave amplitude spectra from the free-field strong motion recordings of the China National Strong Motion Observation Network System (NSMONS) are used to evaluate the site effects in the Wenchuan area. In this regard, a total of 602 recordings from 96 aftershocks of the Wenchuan earthquake with magnitudes of M3.7-M6.5 were selected as a dataset. These recordings were obtained from 28 stations at a hypocenter distance ranging from 30 km to 150 km. The inversion results have been verified as reliable by comparing the site response at station 62WUD using the Generalized Inversion Technique (GIT) and the Standard Spectral Ratio method (SSR). For all 28 stations, the site predominant frequency F _p and the average site amplification in different frequency bands of 1.0–5.0 Hz, 5.0–10.0 Hz and 1.0–10.0 Hz have been calculated based on the inversion results. Compared with the results from the horizontal-to-vertical spectral ratio (HVSR) method, it shows that the HVSR method can reasonably estimate the site predominant frequency but underestimates the site amplification. The linear fitting between the average site amplification for each frequency band and the V _s20 (the average uppermost-20 m shear wave velocity) shows good correlation. A distance measurement called the asperity distance D _Aspt is proposed to reasonably characterize the source-to-site distance for large earthquakes. Finally, the inversed site response is used to identify the soil nonlinearity in the main shock and aftershocks of Wenchuan earthquake. In ten of the 28 stations analyzed in the main shock, the soil behaved nonlinearly, where the ground motion level is apparently beyond a threshold of PGA > 300 cm/s² or PGV > 20 cm/s, and only one station coded 51SFB has evidence of soil nonlinear behavior in the aftershocks.  相似文献   

Effects of slope gradient on runoff from bare-fallow purple soil in China under natural rainfall conditions     

Yoshitaka Komatsu  Hiroaki Kato  Bo Zhu  Tao Wang  Fan Yang  Randeep Rakwal  Yuichi Onda 《山地科学学报》2018,15(4):738-751

Purple soil is highly susceptible for overland flow and surface erosion, therefore understanding surface runoff and soil erosion processes in the purple soil region are important to mitigate flooding and erosion hazards. Slope angle is an important parameter that affects the magnitude of runoff and thus surface erosion in hilly landscapes or bare land area. However, the effect of slope on runoff generation remains unclear in many different soils including Chinese purple soil. The aim of this study was to investigate the relationship between different slope gradients and surface runoff for bare-fallow purple soil, using 5 m × 1.5 m experimental plots under natural rainfall conditions. Four experimental plots(10°, 16°, 20° and 26°) were established in theYanting Agro-ecological Experimental Station of Chinese Academy of Science in central Sichuan Basin. The plot was equipped with water storage tank to monitor water level change. Field monitoring from July 1 to October 31, 2012 observed 42 rainfall events which produced surface runoff from the experimental plots. These water level changes were converted to runoff. The representative eight rainfall events were selected for further analysis, the relationship between slope and runoff coefficient were determined using ANOVA, F-test, and z-score analysis. The results indicated a strong correlation between rainfall and runoff in cumulative amount basis. The mean value of the measured runoff coefficient for four experimental plots was around 0.1. However, no statistically significant relationship was found between slope and runoff coefficient. We reviewed the relationship between slope and runoff in many previous studiesand calculated z-score to compare with our experimental results. The results of z-score analysis indicated that both positive and negative effects of slope on runoff coefficient were obtained, however a moderate gradient(16°-20° in this study) could be a threshold of runoff generation for many different soils including the Chinese purple soil.  相似文献   

钢板桩挡墙主动土压力分布的形状效应   总被引：1，自引：0，他引：1  

刘芳  张国庆  蒋明镜  熊巨华  中山裕章 《岩土力学》2012,33(Z1):315-320

采用有限元数值试验,研究帽型钢板桩的截面形状对墙后主动土压力分布规律的影响。首先,对室内缩尺模型试验进行数值模拟,对比实测数据验证数值模型的有效性;然后,建立钢板桩挡墙数值模型,模拟该挡墙在不同位移模式下土压力变化和分布的规律,与平板挡墙计算结果进行对比,分析钢板桩截面形状对土压力分布的影响,进一步探讨形状效应的可能影响因素及机制。分析结果表明,钢板桩的截面形状影响墙后主动土压力的分布形式,影响程度与位移模式有关;墙体平动和绕墙底转动情况下,钢板桩挡墙凸出部分的主动土压力值大于凹处,但墙体绕墙顶转动情况下差异不明显;主动土压力的形状效应由土拱效应引起,截面高宽比对其影响显著,墙土摩擦角影响有限。  相似文献   

Brownish discoloration of the summit crater lake of Mt. Shinmoe-dake,Kirishima Volcano,Japan: volcanic–microbial coupled origin     

Shinji Ohsawa  Kenji Sugimori  Hiroshi Yamauchi  Tomoyuki Koeda  Hiroaki Inaba  Yoshihisa Kataoka  Tsuneomi Kagiyama 《Bulletin of Volcanology》2014,76(5):1-10

A drastic change in lake water color from blue-green to brown was observed in the summit crater lake of Mt. Shinmoe-dake, Kirishima Volcano about 8 months after its 2008 eruption. The color change lasted for about 2 months (April–June 2009). The discoloration was attributed to a brownish color suspension that had formed in the lake water. X-ray fluorescence and Fourier transform infrared analyses of a sample of the suspension identified schwertmannite (Fe₈O₈(OH)₆(SO₄)). A cultivation test of iron-oxidizing bacteria for the sampled lake water with lakebed sediment revealed that the crater lake hosts iron-oxidizing bacteria, which likely participated in schwertmannite formation. We suggest that pyrite (FeS₂) provided an energy source for the iron-oxidizing bacteria since the mineral was identified in hydrothermally altered tephra ejected by the August 2008 eruption. From consideration of these and other factors, the brownish discoloration of the summit crater lake of Mt. Shinmoe-dake was inferred to have resulted from a combined volcanic–microbial process.  相似文献   

Phytoplankton community structure,as derived from pigment signatures,in the Kuroshio Extension and adjacent regions in winter and spring     

Yuta Nishibe  Kazutaka Takahashi  Mitsuhide Sato  Taketoshi Kodama  Shigeho Kakehi  Hiroaki Saito  Ken Furuya 《Journal of Oceanography》2017,73(4):463-478

The relationships between the spatiotemporal variation in phytoplankton community structure and environmental variables were investigated in the Kuroshio Extension (KE) region from winter to spring by analysing biomarker pigments. In winter, when the mixed layer was deep, phytoplankton communities were characterised by low biomass and a relatively high dominance of cryptophytes, followed by chlorophytes and pelagophytes. In spring, phytoplankton biomass generally increased with shoaling of the mixed layer. In April, when nitrate was not exhausted, chlorophytes became the most dominant group throughout the KE region, followed by cryptophytes. In May, in the south of the KE, phytoplankton biomass decreased with the depletion of nitrate and cyanobacteria dominated, whereas at the northern edge of the KE, phytoplankton biomass remained high. A predominance of diatoms occurred sporadically at the northern edge of the first ridge with a shallow mixed layer and an elevated nutricline. In contrast, the contribution of diatoms was low at the northern edge of the second ridge, despite high levels of nitrate and silicic acid, suggesting that factors other than macronutrient depletion limited diatom production. In general, the contribution of diatoms to the total phytoplankton biomass in the KE region was small in both winter (2.9%) and spring (16%). This study showed that the phytoplankton communities in the KE region during the spring bloom were generally composed of non-diatom phytoplankton groups, chlorophytes, cryptophytes, and prasinophytes. It is necessary to identify the roles of non-diatoms in grazing food chains to more accurately evaluate the KE as a nursery area for pelagic fish.  相似文献   

The Mg-carbonate-Fe interaction:Implication for the fate of subducted carbonates and formation of diamond in the lower mantle     

Naira S.Martirosyan  Konstantin D.Litasov  Sergey S.Lobanov  Alexander F.Goncharov  Anton Shatskiy  Hiroaki Ohfuji  Vitali Prakapenka 《地学前缘(英文版)》2019,10(4):1449-1458

The fate of subducted carbonates in the lower mantle and at the core-mantle boundary was modelled via experiments in the MgCO3-Fe^0 system at 70-150 GPa and 800-2600 Kin a laser-heated diamond anvil cell.Using in situ synchrotro n X-ray diffraction and ex situ transmission electron microscopy we show that the reduction of Mg-carbonate can be exemplified by:6 MgCO3+19 Fe=8 FeO+10(Mg0.6Fe^0.4)O+Fe7 C3+3 C.The presented results suggest that the interaction of carbonates with Fe^0 or Fe^0-bearing rocks can produce Fe-carbide and diamond,which can accumulate in the D"region,depending on its carbon to Fe ratio.Due to the sluggish kinetics of the transformation,diamond can remain metastable at the core-mantle boundary(CMB)unless it is in a direct contact with Fe-metal.In addition,it can be remobilized by redox melting accompanying the generation of mantle plumes.  相似文献   

In situ stress measurements in a borehole close to the Nojima Fault   总被引：1，自引：0，他引：1  

Hiroaki Tsukahara  Ryuji Ikeda  Kiyohiko Yamamoto 《Island Arc》2001,10(3-4):261-265

Abstract In situ stress was measured close to the fault associated with the 1995 Kobe Earthquake (Hyogo-ken Nanbu earthquake; January 1995; M 7.2) using the hydraulic fracturing method. The measurements were made approximately 2 years after the earthquake. The measured points were approximately 40 m from the fault plane at depths of about 1500 m. The maximum and the minimum horizontal compressive stresses were 45 MPa and 31 MPa, respectively. The maximum compressive stress and the maximum shear stress are very small in comparison with those of other seismically active areas. The azimuth of the maximum horizontal compressive stress was estimated from the observed azimuths of well bore breakouts at depths between 1400 m and 1600 m and was found to be N135° (clockwise). The maximum stress axis is perpendicular to the fault strike, N45°. These features are interpreted in terms of a small frictional coefficient of the fault. The shear stress on the fault was released and dropped almost to zero during the earthquake and it has not yet recovered. Zero shear stress on the fault plane resulted from the perpendicular orientation of one of the principal stress to the fault plane.  相似文献