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Spatial changes in a macrozoobenthic community along environmental gradients in a shallow brackish lagoon facing Sendai Bay, Japan 总被引：3，自引：0，他引：3
The spatial distribution, abundance, and assemblage structure of macrozoobenthos were examined at 45 stations in a brackish lagoon (Idoura Lagoon, Japan) to examine the animal–environmental relations in estuarine soft-bottom habitats. We found a total of 23 taxa; the polychaetes Heteromastus sp., Hediste spp., and Prionospio japonica and the isopod Cyathura muromiensis numerically dominated the community. Cluster analysis and one-way analysis of similarity (ANOSIM) identified seven groups of stations that had significantly different macrozoobenthic communities; these were subsequently consolidated into five habitat groups according to their association with environmental characteristics. Canonical correspondence analysis (CCA) showed that salinity, silt-clay content, and the oxidation–reduction potential (ORP) of the sediment strongly affected the macrozoobenthos distribution pattern in the lagoon, whereas other factors (e.g., relative elevation of the habitat and sediment organic content) had much weaker effects. Similarity percentages (SIMPER) procedures indicated that the polychaete Notomastus sp. and the bivalve Macoma contabulata were specific to habitats with low salinity and reduced mud, whereas the bivalve Nuttallia olivacea was specific to sandy bottoms. Heteromastus sp. and Hediste spp. achieved their highest densities in rather oxidized sediments. The acid-volatile sulfide (AVS) content in the sediment was suggested as another possible factor affecting macrozoobenthic density. Our results clearly demonstrate that macrozoobenthic assemblages in estuarine soft-bottoms have high spatial heterogeneity on a small scale (e.g., hundreds of meters) related to physical and chemical environmental changes. Our data also suggested the importance of sediment redox condition (e.g., ORP and AVS content) and sediment grain size as structuring factors in estuarine soft-bottom communities as well as the salinity in the habitat. 相似文献
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Abstract Several linear magnetic anomalies over continental crust have been identified in and around the Japanese Islands. The anomalies are probably related to island arc tectonic structures, but identifying specific sources has been difficult. Several deep holes were drilled in and around Aso caldera, where a linear anomaly occurs along an active fault. One drillhole located on the linear anomaly encountered a zone of highly magnetized and altered basement rocks at least 100 m thick at a depth of ∼1000 m. The other hole was located away from the anomaly and did not encounter any high-magnetic zones. Rocks from the zone have exceptionally strong remanent magnetization (several tens of A/m) sub-parallel to the present field. AF demagnetization experiments indicated that the magnetization is hard and stable. Magnetic modeling indicates that the linear anomaly is caused mainly by this layer. Microscopic examination of core samples shows that the highly magnetized zone includes secondary magnetic minerals and abundant hydrothermal alterations. Temperatures determined by fluid inclusions and down-hole temperatures show that the temperature of the highly magnetized zone was elevated in the past relative to surrounding rocks. The high temperature could destroy primary magnetic minerals and replace them with secondary magnetic minerals. Thus, the past hydrothermal system may have enhanced thermo-chemical remanent magnetization. The results can produce a model indicating that there was a past hydrothermal system related to the tectonic structure. 相似文献
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Yugo Kanaya Yasuhiro Sadanaga Jun Hirokawa Yoshizumi Kajii Hajime Akimoto 《Journal of Atmospheric Chemistry》2001,38(1):73-110
An instrument for measuringtropospheric OH/HO2 radicals by laser-inducedfluorescence developed in our laboratory is presentedin detail. It is based on FAGE (fluorescence assay bygas expansion) technique and OH is both excited anddetected at 308 nm corresponding to its A-X(0,0) band.The alignment of the laser beam, the design of thesample gas inlet, and the devices for the fluorescencedetection are optimized so as to reduce the backgroundsignal while keeping the OH sensitivity as high aspossible. A thermalized position of the expanding gasbeam is probed in our system and we did not observe asevere decrease of the HOx sensitivities under humidconditions. An optical fiber is used for deliveringthe laser light to the fluorescence detection cellmounted outside at a high position. Thus the laserbeam alignment is by far simplified and is made highlyreproducible, once settled properly. For thecalibration, two methods are employed: a system withlaser absorption measurements of OH and a system ofsimultaneous photolysis of H2O and O2. Thecalibration factors are compared well within thecombined uncertainty. Using the latter system, theconversion efficiency of HO2 to OH by NO additionis measured to be around 90%. The detection limitsfor OH and HO2 (S/N = 2) are estimated to be3.3 × 106 and 3.6 × 106cm–3 at noon,respectively, with an integration time of 1 min. Theresults of test observations at our institute are alsopresented. 相似文献
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Spatio-temporal changes in macrozoobenthic assemblage structure were monitored at 8 stations in a river-affected temperate lagoon (Idoura Lagoon, Japan) from May 1997 to May 1998 to assess animal–environment relationships in estuarine soft-bottom habitats. A total of 29 taxa occurred with a predominance of a few polychaete species including Heteromastus cf. similis, Hediste spp., Pseudopolydora cf. kempi and Prionospio japonica. The community structure differed significantly among four habitat types that were characterized by different salinity, sediment characteristics, and/or bottom elevation. For each habitat, macrozoobenthic community structure changed significantly with time, which was discriminated mostly by the lower density of polyhaline opportunistic species such as P. cf. kempi in warmer period. The salinity in the study area was much lower from May to September, mainly due to irrigation discharge from paddy fields, which seemed to be a lethal factor for the polyhaline species. C/N ratio and δ13C value of the sediment implied the accumulation of river-derived organic matters during the high river flow period. Present results showed the significant effects of fluctuating river discharge on the estuarine soft-bottom habitats, suggesting a linkage among terrestrial, riverine and estuarine ecosystems. 相似文献
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