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Partitioning of the nitrogen stock in a Fijian seagrass bed dominated by Syringodium isoetifolium (Ascherson) Dandy and in an adjacent area bare of macrophytic vegetation was assessed to evaluate the effect of the presence of seagrass on... more
Partitioning of the nitrogen stock in a Fijian seagrass bed dominated by Syringodium isoetifolium (Ascherson) Dandy and in an adjacent area bare of macrophytic vegetation was assessed to evaluate the effect of the presence of seagrass on coral sediment. Concentrations of major nutrients, such as nitrogen and phosphate, were as low in the water column at the seagrass bed and the bare area as they were in the open ocean. Concentrations of ammonium and dissolved organic nitrogen, however, were higher in the water within the seagrass canopy than they were in other waters. In sediments at the seagrass bed and the bare area, interstitial nitrogen, such as nitrate and dissolved organic nitrogen, was a minor component of the total nitrogen (0.3-0.05%). On the other hand, concentrations of total organic nitrogen in seagrass-bed sediment (about 70% of which was in the form of amorphous organic nitrogen and the rest of which came from living and dead seagrass) were more than three times higher than those in bare-area sediment. Concentrations of organic carbon from amorphous organic materials in seagrass-bed sediment showed no large change with depth, resulting in an apparent decrease in the carbodnitrogen atom ratio from 60 to 10. These results suggest some mechanisms to minimize the loss of nitrogen stock from the sediment of tropical seagrass beds.
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Research Interests: Geology()
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Research Interests: Geology()
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Alkenone sea surface temperature (SST) records were generated from the Ocean Drilling Program's (ODP) Sites 1014 and 1016 to examine the response of the California Current System to global climate change during the last 136 ka. The... more
Alkenone sea surface temperature (SST) records were generated from the Ocean Drilling Program's (ODP) Sites 1014 and 1016 to examine the response of the California Current System to global climate change during the last 136 ka. The temperature differences between these sites (Delta SST(NEP)=SST(ODP1014)-SST(ODP1016)) reflected the intensity of the California Current and varied between 0.4 and 6.1 °C. A high Delta SST(NEP) (weaker California Current) was found for late marine isotope stage (MIS) 2 and early MIS 5e, while a low Delta SST(NEP) (stronger California Current) was detected for mid-MIS 5e and MIS 1. Spectral analysis indicated that this variation pattern dominated 23- (precession) and 30-ka periods. Comparison of the Delta SST(NEP) and SST based on data from core MD01-2421 at the Japan margin revealed anti-phase variation; the high Delta SST(NEP) (weakening of the California Current) corresponded to the low SST at the Japan margin (the southward displacement of the NW Pacific subarctic boundary), and vice versa. This variation was synchronous with a model prediction of the tropical El Niño-Southern Oscillation behavior. These findings suggest that the intensity of the North Pacific High varied in response to precessional forcing, and also that the response has been linked with the changes of tropical ocean-atmosphere interactions.
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Research Interests: Geography, Biodiversity, Mangrove, Seagrass, Fishery, and 2 moreEcosystem and Indo Pacific(Ecosystem and Indo Pacific)
(Ecosystem and Indo Pacific)
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Ruditapes philippinarum called asari in Japanese is one of the important clams as fishery resource in Asia, and it has purification function in water. However, the number of asari has dramatically reduced due to deterioration of their... more
Ruditapes philippinarum called asari in Japanese is one of the important clams as fishery resource in Asia, and it has purification function in water. However, the number of asari has dramatically reduced due to deterioration of their habitat [1]. Therefore, revealing their distribution and life in the sediment are required for ecological assessment of asari. Adaptations of acoustic sensing to detect or identify aquatic organism have increased. For example, side scan sonar and high-resolution acoustic imaging sonar were used to map or monitor aquatic organisms on the seafloor [2, 3]. On the other hand, there are few studies of acoustic sensing to detect aquatic organisms in the sediment. In general, it is difficult to detect small object like shellfish in the sediment by standard acoustic sensing. Therefore, we have developed a new sensing method and succeeded to detect asari in the sediment using 1-MHz focus ultrasound [4]. Furthermore, we reported the importance of incident angle ...
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Coastal megacities are highly vulnerable to climate change due to asset concentration and hazard exposure, but have potential for innovative risk management taking advantage of technological, economic and political capacities and cultural... more
Coastal megacities are highly vulnerable to climate change due to asset concentration and hazard exposure, but have potential for innovative risk management taking advantage of technological, economic and political capacities and cultural assets. Tokyo is the center of one of the world’s largest urban agglomerations and one of the most hazard prone global cities. Having experienced repeated extreme events and resultant devastation, Tokyo has deployed a strategy of high technology based risk management. In the face of climate risks that amplify ongoing threats from catastrophic earthquakes, it is unclear whether the current strategy and its attendant culture and administrative structures are an enabler or a barrier for climate change adaptation. Based on 24 expert interviews, this paper examines Tokyo’s readiness to transition from its current risk management orientation aimed at disaster prevention towards more resilient of transformative states. We find the current risk management ...
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Research Interests: Agronomy, Biology, Pesticide, Wetland, Aquatic Plant, and 3 moreGermination, Paddy Field, and Glufosinate
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ABSTRACT Deposition of atmospheric nutrients is known to alter oligotrophic ecosystems such as the open ocean, but the role of such nutrients in the further deterioration of eutrophic aquatic ecosystems is largely unknown. The Hii River... more
ABSTRACT Deposition of atmospheric nutrients is known to alter oligotrophic ecosystems such as the open ocean, but the role of such nutrients in the further deterioration of eutrophic aquatic ecosystems is largely unknown. The Hii River watershed in Japan encompasses lagoons that have been eutrophic since 1980s. This study examined the atmospheric deposition of nitrogen and phosphorus in the Hii River watershed and the nitrogen and phosphorus concentrations in the Hii River over an 11-yr period. Total nitrogen (TN) concentrations of both precipitation and river water were significantly higher in cold months (November–March) than in warm months (April–October). Most of the TN was nitrate, which suggests that the TN source was atmospheric nitrogen from East Asia transported by seasonal winds. In contrast, total phosphorus (TP) concentrations of both precipitation and river water were significantly higher in warm months. Over time, the TN concentration in the river water showed a decreasing trend although the trend was not significant, while the TP concentration increased significantly. This was attributed to an increase in the atmospheric deposition of TP originating from East Asia since 2000. The increase in the deposition of atmospheric phosphorus might also have increased phosphorus leakage from the soils. In this work, the TN : TP ratios for both atmospheric deposition and river water indicate that changes in atmospheric nutrient deposition affect loading rates and N : P ratios. These changes, especially the latter, could have significant ecological effects in eutrophic systems by lowering the N : P ratios, which could induce cyanobacteria blooms.
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The coastal area of the southern Lake Baikal with the population over 35,000 people remains an attractive spot for both tourists and local residents. Despite high anthropogenic impact, a detailed assessment of water quality in this area... more
The coastal area of the southern Lake Baikal with the population over 35,000 people remains an attractive spot for both tourists and local residents. Despite high anthropogenic impact, a detailed assessment of water quality in this area has not been performed so far. Here, we performed a comprehensive evaluation of the quality of the surface, bottom and interstitial water in rivers, lacustrine water and wastewater in the southern Lake Baikal region. We analyzed 37 samples for the presence of fecal enterococci, Escherichia coli and assessed their hydrochemical parameters: concentrations of nutrients (nitrate-N, nitrite-N, ammonium-N and phosphate-P), dissolved oxygen and amount of ions (HCO3− + SO42− + Cl− + Ca2+ + Mg2+ + Na+ + K+). In addition, the temperature, pH and electrical conductivity were also measured. We found that multiple areas around South Baikal suffer from microbiological and hydrochemical pollution. We conclude that ecological situation in this area requires immediat...
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Research Interests: Medicine()
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This study reports an adaptation of acoustic sensing to detection of shellfish in the sediment. In this paper, we tried to detect Ruditapes philippinarum called asari in Japanese using a 1-MHz acoustic focus probe. Then, 2-D acoustic... more
This study reports an adaptation of acoustic sensing to detection of shellfish in the sediment. In this paper, we tried to detect Ruditapes philippinarum called asari in Japanese using a 1-MHz acoustic focus probe. Then, 2-D acoustic imaging of the shellfish in the sediment was performed, and the strong backscatter from the shell surface was detectable. Acoustic imaging was performed at some incident angles (0°, 15°, and 30°) to decrease back scatter from the sediment and increase that from the shellfish. The result shows acoustic imaging at 30° incident angle was the most efficient. Furthermore, weak scatter inside shell was also observed as good indicator for asari detection. In addition to the experiments, finite-difference time-domain (FDTD) simulation was performed to understand complex wave propagation generated by the focus probe. This simulation helped us to understand the experimental data.
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Nearshore (littoral) habitats of clear lakes with high water quality are increasingly experiencing unexplained proliferations of filamentous algae that grow on submerged surfaces. These filamentous algal blooms (FABs) are sometimes... more
Nearshore (littoral) habitats of clear lakes with high water quality are increasingly experiencing unexplained proliferations of filamentous algae that grow on submerged surfaces. These filamentous algal blooms (FABs) are sometimes associated with nutrient pollution in groundwater, but complex changes in climate, nutrient transport, lake hydrodynamics, and food web structure may also facilitate this emerging threat to clear lakes. A coordinated effort among members of the public, managers, and scientists is needed to document the occurrence of FABs, to standardize methods for measuring their severity, to adapt existing data collection networks to include nearshore habitats, and to mitigate and reverse this profound structural change in lake ecosystems. Current models of lake eutrophication do not explain this littoral greening. However, a cohesive response to it is essential for protecting some of the world's most valued lakes and the flora, fauna, and ecosystem services they su...
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Cascading effects of pesticide use It is now well known that neonicotinoids negatively affect pollinators. As research has expanded, it has become clear that these globally used insecticides directly affect other ecosystem components,... more
Cascading effects of pesticide use It is now well known that neonicotinoids negatively affect pollinators. As research has expanded, it has become clear that these globally used insecticides directly affect other ecosystem components, including vertebrates. Yamamuro et al. now show that these compounds are indirectly affecting species through trophic cascades (see the Perspective by Jensen). Since the application of neonicotinoids to agricultural fields began in the 1990s, zooplankton biomass has plummeted in a Japanese lake surrounded by these fields. This decline has led to shifts in food web structure and a collapse of two commercially harvested freshwater fish species. The authors argue that such dynamics are likely occurring widely. Science , this issue p. 620 ; see also p. 566
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Habitats, flowering characters and information of escape from cultivation were studied by investigating the populations in the field, observing plants under cultivation, examining herbarium specimens, hearing investigation and literature... more
Habitats, flowering characters and information of escape from cultivation were studied by investigating the populations in the field, observing plants under cultivation, examining herbarium specimens, hearing investigation and literature survey. Genetic diversity of Nymphoides peltata was re-examined by SSR polymorphism. Though the analysis of genetic diversity was not successful because some loci were difficult to identify, genetic polymorphism was found within the population of Lake Inawashiro and Lake Biwa, respectively. Non-flowering populations were found to grow scattered in Japan and have genetic polymorphism. The most populations of N. peltata in Lake Biwa were recorded from the attached small ponds and connected drains or rivers. Escaping populations were revealed to scatter various places.
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Even though the interaction between water movements and aquatic plant is crucial for the aquatic ecosystem management, the importance of water turbulence in this regard is not well documented. To add to our knowledge on the interaction... more
Even though the interaction between water movements and aquatic plant is crucial for the aquatic ecosystem management, the importance of water turbulence in this regard is not well documented. To add to our knowledge on the interaction between aquatic plant communities and water turbulence, this study examined turbulence, plant, sediment and water quality at the reed community (Phragmites australis) in the Lake Shinji, Japan. Observations were conducted along transects perpendicular to the shoreline. For each transect, reed communities were observed at land ward side, centre, water ward and the outside of the reed community. An elevated level of turbulence was observed outside compared to inside reed community, where the magnitude of turbulence decreased with distance into the community interior. A significant positive correlation was observed for turbulence and surface-dissolved oxygen where the latter was negatively correlated to reed density. Sediment composition was affected by ...
Research Interests: Geography, Environmental Science, Turbulence, Transect, Sediment, and 2 morePhragmites and Ekologia(Phragmites and Ekologia)
(Phragmites and Ekologia)