Decrease in anthropogenic nutrients and its effect on the C/N/P molar ratio of suspended particulate matter in hypertrophic Dokai Bay (Japan) in summer     

Kenichiro Hamada  Naoko Ueda  Machiko Yamada  Kuninao Tada  Shigeru Montani 《Journal of Oceanography》2012,68(1):173-182

Biologically important nutrient concentrations in Dokai Bay have declined as a result of reductions in anthropogenic inputs of total nitrogen and total phosphorus. A decrease in nutrient concentrations affects phytoplankton growth, thereby changing the biochemical characteristics of autochthonous particulate matter. We therefore investigated changes in the C/N/P molar ratio of suspended particulate matter (SPM) in the summer, when phytoplankton growth is vigorous, before environmental quality standards (EQSs) were attained (1995–1998) and afterward (2006–2009). We found that the ratio of particulate organic nitrogen (PON) to particulate phosphorus (PP) changed in conjunction with changes in the ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus (DIP) that resulted from reductions in nutrient loading. Furthermore, we suggest that because the DIP concentration in seawater was high before EQSs were attained, inorganic phosphorus was possibly adsorbed onto SPM. After the attainment of EQSs, however, the DIP concentration fell, and PON/PP was high. Phosphorus limitation of phytoplankton growth in the mouth of the bay may explain the high PON/PP ratios after EQS attainment.  相似文献   

Eutrophication-induced changes in Lake Nakaumi,southwest Japan     

Kota Katsuki  Yasushi Miyamoto  Kazuyoshi Yamada  Hiroyuki Takata  Keiko Yamaguchi  Daisuke Nakayama  Hugo Coops  Hidenobu Kunii  Ritsuo Nomura  Boo-Keun Khim 《Journal of Paleolimnology》2008,40(4):1115-1125

Lake Nakaumi, southwest Japan, is an enclosed lagoon characterized by polyhaline and halocline conditions. Since the last century, its ecological state has been altered by eutrophication. We used a paleolimnological approach and studied multiple proxies, including chemical compounds, diatoms, foraminifera and molluscs, to infer the eutrophication history of the ecosystem. Eutrophication in Lake Nakaumi was associated with several factors, including increased nutrient loading, input of herbicides, and dike building since the 1920s. The ecological condition of this lake was divided into several stages that reflect the eutrophication process after the 1940s. A catastrophic “regime shift” from a clear state with aquatic vegetation to a turbid one with phytoplankton occurred in the early 1950s. Environmental degradation in the Honjo area, a part of Lake Nakaumi, was attributed primarily to physical changes caused by the construction of an enclosing dike. Eutrophication occurred almost simultaneously with the physical changes to the Honjo area in the 1970s. Until recently, no regime shift was observed in this area, though the core-top sediments show possible symptoms of incipient change.  相似文献   

Changes of seawater quality in Ofunto Bay,Iwate, after the 2011 off the Pacific coast of Tohoku Earthquake     

Yuichiro Yamada  Shinnosuke Kaga  Yoshimasa Kaga  Kimiaki Naiki  Shiho Watanabe 《Journal of Oceanography》2017,73(1):11-24

Ofunato Bay was a semi-closed area because of the breakwater effect at the entrance; however, the breakwater was destroyed by a massive tsunami generated by the 2011 off the Pacific coast of Tohoku Earthquake. Consequently, the physical environment of Ofunato Bay has been changed significantly, i.e., the modification of the stratified structure of seawater inside the bay and the intermittent intrusion of seawater outside the bay. These alterations of physical environment are considered to have an influence on the chemical and biological environment in Ofunato Bay. To elucidate the influence of the tsunami on the aquatic environment, we measured dissolved nutrients, chlorophyll a and dissolved oxygen concentrations, and heterotrophic bacteria abundance inside and outside of Ofunato Bay from 2012 to 2014, and compared these data with those obtained before the earthquake. As compared with before the earthquake, significant changes after the earthquake were (1) decrease of ammonium and phosphate concentrations, (2) increase of chlorophyll a concentration, (3) increase of dissolved oxygen concentration in the bottom, and (4) decrease of heterotrophic bacteria abundance. The collapse of the breakwater and consequential enhanced water exchange were considered to have brought the decrease of nutrient concentration inside the bay. Furthermore, washout of shellfish mariculture rafts by the tsunami decreased the shellfish biodeposits along with the elution of nutrients by heterotrophic bacteria. Decrease of cultivated shellfish further caused a decline in feeding pressure on phytoplankton and, subsequently, increased the phytoplankton biomass that contributed to the decrease of nutrients inside the bay.  相似文献   

The Intra-Seasonal Oscillation and its control of tropical cyclones simulated by high-resolution global atmospheric models     

M. Satoh  K. Oouchi  T. Nasuno  H. Taniguchi  Y. Yamada  H. Tomita  C. Kodama  J. Kinter  D. Achuthavarier  J. Manganello  B. Cash  T. Jung  T. Palmer  N. Wedi 《Climate Dynamics》2012,39(9-10):2185-2206

Project Athena is an international collaboration testing the efficacy of high-resolution global climate models. We compare results from 7-km mesh experiments of the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) and 10-km mesh experiments of the Integrated Forecast System (IFS), focusing on the Intra-Seasonal Oscillation (ISO) and its relationship with tropical cyclones (TC) among the boreal summer period (21 May–31 Aug) of 8?years (2001–2002, 2004–2009). In the first month of simulation, both models capture the intra-seasonal oscillatory behavior of the Indian monsoon similar to the observed boreal summer ISO in approximately half of the 8-year samples. The IFS simulates the NW–SE-oriented rainband and the westerly location better, while NICAM marginally reproduces mesoscale organized convective systems and better simulates the northward migration of the westerly peak and precipitation, particularly in 2006. The reproducibility of the evolution of MJO depends on the given year; IFS simulates the MJO signal well for 2002, while NICAM simulates it well for 2006. An empirical orthogonal function analysis shows that both models statistically reproduce MJO signals similar to observations, with slightly better phase speed reproduced by NICAM. Stronger TCs are simulated in NICAM than in IFS, and NICAM shows a wind-pressure relation for TCs closer to observations. TC cyclogenesis is active during MJO phases 3 and 4 in NICAM as in observations. The results show the potential of high-resolution global atmospheric models in reproducing some aspects of the relationship between MJO and TCs and the statistical behavior of TCs.  相似文献   

The impact of the Wangara experiment   总被引：1，自引：0，他引：1  

G. D. Hess  B. B. Hicks  Tetsuji Yamada 《Boundary-Layer Meteorology》1981,20(2):135-174

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Random response analysis of a non-linear soil-suspension bridge pier     

Y. Yamada  H. Takemiya  K. Kawano 《地震工程与结构动力学》1979,7(1):31-47

The structure analysed herein is a tower and pier system of a long-span suspension bridge. The tower shaft is modelled to allow classical normal modes decomposition in order to reduce higher modes. The pier is assumed to be rigid body free to translation as well as to rocking motion, being reacted by the surrounding soil compliance that is derived from a continuum mechanics approach. Linear and non-linear soil and structural dynamic interaction is dealt with by random vibration theory with use of the linearization technique and complex modal analysis. Primary interest is placed on the investigation of the dynamic characteristics of the total interaction system and the rms response with change of the soil condition and input excitation level. Also discussed is the approximate response analysis, using classical normal modes for the interaction system, for purposes of practical design.  相似文献   

PBL similarity profiles determined from a level-2 turbulence-closure model     

Tetsuji Yamada 《Boundary-Layer Meteorology》1979,17(3):333-351

A diagnostic model for the determination of similarity profiles of turbulence and mean-wind gradient in the planetary boundary layer is developed. Vertical profiles of a turbulence length scale and the flux Richardson number are formulated through the extension of the relationships for the constant flux layer. These profiles together with a turbulence energy equation and a similarity profile empirically determined for heat or momentum flux are used to compute the turbulence energy. Relationships previously derived from a turbulence closure model are used to compute second moments of turbulence.  相似文献   

Seismic damage estimation for low- and mid-rise buildings in japan     

C. Scawthorn  H. Iemura  Y. Yamada 《地震工程与结构动力学》1981,9(2):93-115

While much effort has been spent on analysis of individual structures, building class seismic damage estimators, of value in disaster planning, code-writing, city planning, national hazards policy formulation, etc., have been little investigated. Based largely on data from Sendai City, Japan in the 12 June, 1978 Miyagiken-oki earthquake (M_L = 7.4), estimators of seismic damage for low- and mid-rise buildings in urban Japan have been determined. For low-rise buildings, based on damage to over 60,000 buildings, damage ratios for onset of damage and collapse and for cost of damage are found to correlate best with response spectra at 0.75 s. Using published test data and average building properties, a seismic damage model explains the low-rise building behaviour and permits examination of the effect of structural changes on the estimated damage. For mid-rise buildings, damage states (0: none, 4: total) are determined as a function of maximum storey displacement, based on published natural period determinations (pre- and post-earthquake) for 189 mid-rise buildings in Sendai. The effects of structural changes on expected damage can also be estimated. With these two building class damage estimators, a large part of future seismic damage to urban Japan can be estimated, as well as the effects of various mitigation measures.  相似文献   

Estimation of water requirement per unit carbon fixed by Eucalyptus camaldulensis in semi-arid land of Western Australia     

T.Kojima  Y.Tanaka  S.Katoh  K.Tahara  N.Takahashi  K Yamada 《中国科学D辑(英文版)》2002,45(Z1)

Afforestation in arid land is a promising method for carbon fixation, but the effective utili-zation of water is highly important and required. Thus, the evaluation of the amount of water perunit carbon fixed with the tree growth is required to minimize the amount of water supplied to theplants. In this research, a tree is regarded as a carbon fixation reactor with inflows of water andnutrients from roots, and CO2 as the carbon source from leaves with outflow of water vapor fromleaves and accumulation in the tree itself. In the process of photosynthesis and respiration nutri-tional elements are dissolved in water flow in trees. They do not flow out by these reactions, butare accumulated in trees. Thus, we have treated the behaviour of nutrients as a marker to evaluatethe water/carbon ratio. Assuming that nutrient concentration is constant in sap, and the differences in the ratios ofnutrient to carbon in living trees and dead (i.e. litter fall, etc.) are negiected, the ratio of the usedwater to fixed carbon is given as the ratio of nutrient to carbon in the tree body divided by the ratioof nutrient to water in sap. However, some nutrients are translocated and concentrated within thetree and some may be discarded through litter fall. Thus it is important to examine which nutrientelement is the most suitable as the tracer. In this paper, the results of the above method applied to Eucalyptus camaldulensis in semi-arid land of Western Australia are shown. The value of water requirement per unit carbon fixationdetermined from potassium balance is between 421 kg-H2O/kg-C for mature trees and 285kg-H2O/k9-C for young trees, while the values from calcium balance are much larger than these.The cause of the discrepancy between these values is discussed based on the measured elementconcentrations in sap and trees and the plant physiology. Finally, the actual average value throughthe life of a tree is suggested to fall between the two values.  相似文献   

Volcanic Sequences Related to Kuroko Mineralization in the Hokuroku District, Northeast Japan     

Ryoichi Yamada  Takeyoshi Yoshida 《Resource Geology》2004,54(4):399-412

Abstract. Kuroko deposits are a representative volcanic‐hosted massive sulfide deposit and the Hokuroku district is economically the most important Kuroko containing province in Japan. There are two cycles of the bimodal volcanic sequence in the Hokuroku district. The pre‐ore volcanism started with basaltic activity and was followed by intensive felsic hyaloclas‐tic activity under bathyal conditions. The post‐ore sequence also began with basaltic activity intercalated with mudstone and was followed by alternating beds of pumice tuff with several lava flows and mudstone. Kuroko deposits are situated in the final period of the pre‐ore felsic volcanic sequence of the first bimodal volcanic cycle. Based on a detailed investigation of existing age data, it was concluded that the felsic volcanic sequences in the pre‐and post‐Kuroko formation can be divided into a pre‐ore dacite group (16–13.5 Ma), a D2 dacite group (lower unit of the post‐ore volcanic sequence, 12.7±0.6～ ll Ma) and a Dl dacite group (upper unit of the post‐ore sequence including quartz‐porphyry and granitoid, 11sim;10 Ma) in ascending order. Field and microscopic observations show that the pre‐ore dacite is characterized by aphyric to plagioclase‐phyric lava and the post‐ore dacitic rocks are characterized by quartz‐plagioclase‐phyric aphanitic lava and dome. These three dacite groups are petrochemically discriminated by SiO₂‐Al₂O₃ and CaO‐TiO₂ diagrams, excluding altered specimens. The distribution of the normative compositions on the Q‐An‐Ab‐Or diagram suggests that the pre‐ore dacites trend on the 5 kb cotectic line (equilibrated to 10—15 km deep) and those of the post‐ore trend along the 1 kb line (a few km deep). The secular variation of the major elements indicates that the rhyolitic members genetically related to the Kuroko formation could be the most differentiated products in the pre‐ore felsic volcanism. The distribution of Nb against SiO₂ content in the pre‐ and post‐ore bimodal volcanic cycles indicates that these two volcanisms could have been generated by different magmatic origins. The difference would have been caused by the tectonic conversion from a back‐arc to an island‐arc setting.  相似文献