Stable nitrogen isotope composition in sedimentary organic matter as a potential proxy of nitrogen sources for primary producers at a fringing coral reef     

Yu Umezawa  Toshihiro Miyajima  Isao Koike 《Journal of Oceanography》2008,64(6):899-909

The stable nitrogen isotope ratio (δ ¹⁵N) in macroalgae is effectively used as a time-integrated bioindicator to record nitrogen sources for primary producers during their growing periods in aquatic ecosystems. However, the utility of this tool is limited because the occurrence of these organisms is often restricted in space and time. To investigate the potential of chemical composition in sedimentary organic matter (SOM) as a proxy for time-integrated environmental conditions, nitrogen (N) and carbon (C) contents and their stable isotope ratios (δ ¹⁵N and δ ¹³C) were determined, and systematically cross-checked against corresponding values in macroalgae at the Shiraho fringing reef in Okinawa, Japan. Preliminary trials showed that δ ¹⁵N in SOM processed by the “wash-out method” for δ ¹³C analysis yielded similar δ ¹⁵N values to the bulk sediment, despite the loss of some SOM during the process. The amounts of organic matter and the ratio of the HCl-insoluble portion were variable within the reef, probably reflecting local vegetation and subsequent decomposition. The distribution of δ ¹⁵N and δ ¹³C in SOM showed similar trends to those of macroalgae, with mostly constant differences of 1.4‰ and −6.7‰, respectively. These differences throughout the reef appeared to be explained in terms of mixed contributions from macrophyte and epibenthic microalgae growing in different seasons and years, with their debris undergoing diagenetic alteration. Therefore, macroalgae and SOM δ-values can be used in a complementary manner, over various time scales, as indicators of the integrated effect of dissolved inorganic nitrogen (DIN) sources on coral reef ecosystems.  相似文献   

Distinguishing potential sources of arsenic released to groundwater around a fault zone containing a mine site   总被引：1，自引：1，他引：0  

Irwan Iskandar  Katsuaki Koike 《Environmental Earth Sciences》2011,63(3):595-608

Arsenic (As) contamination in groundwater in mineralized areas typically results from the oxidation of As-rich sulfide minerals in aquifers, from hydrothermal alteration of geothermal systems, or as a result of anthropogenic influences such as mining activity. The primary goal of this study was to determine the spatial and temporal variance in As concentrations in shallow groundwater in a mineralized area and to identify the main As source controlling the concentration patterns. To this end, a combination of a geostatistical technique for space–time modeling of As concentrations and a numerical simulation, which models the transport of As in groundwater, is implemented. A study site in North Sulawesi, Sulawesi Island, Indonesia was selected as it was suitable for investigating the importance of fault lines and metal mining on As contamination. Initially, stable isotope analysis was used to ascertain the groundwater source and the mixing mechanism of the shallow and deep groundwater. Geostatistical modeling revealed consistent general patterns of As concentrations during the past 10 years, with high concentrations found along a NW–SE axis. By matching the geostatistical results with the distributions of As concentrations obtained through transport modeling, the deep-seated hydrothermal system along the fault zone was found to be the major As source. Wastewater from the mine was also observed to be a local As source. Another important influence on the As concentration pattern was a river, which acted as a boundary to separate the groundwater systems into two regions.  相似文献   

Reciprocal sound transmission measurement of mean current and temperature variations in the central part (Aki-nada) of the Seto Inland Sea,Japan     

Yudi Adityawarman  Arata Kaneko  Koji Nakano  Naokazu Taniguchi  Katsuaki Komai  Xinyu Guo  Noriaki Gohda 《Journal of Oceanography》2011,67(2):173-182

A 30 km-range reciprocal sound transmission experiment was carried out on the line connecting Honshu and Shikoku (the first and fourth biggest main Japanese islands, respectively) in the central part (Aki-nada) of the Seto Inland Sea, Japan, during March–May 2010 to measure the mean current and temperature variations over the sea. The range-averaged current along the sound transmission line was estimated to have a mean and standard deviation of (3.8–4.4) ± (1.7–1.8) cm/s after converting the travel time difference data into currents, including a fortnightly tidal variation in the range of ±30 cm/s. The positive mean current implies slow water movement from the west to east through Aki-nada. The range-averaged speed of sound was estimated by converting from the mean travel time or one-way travel time into the speed of sound, and further converted into temperature for fixed values of salinity and depth, according to the standard speed of sound formula. Besides the precise measurement (to an accuracy of 0.01°C) of semidiurnal and diurnal tidal variations and seasonal warming, the temperature data showed periodic variations with periods of 7.0 and 21.1 days that had never been observed in Aki-nada before. This study suggests that reciprocal sound transmission is a powerful technique for the long-term accurate measurement of mean current and temperature variations in coastal and inland seas.  相似文献   

Hydrogeological and ground-water resource analysis using a geotechnical database     

Katsuaki Koike  Toshiaki Minta  Shinya Ishizaka  Michito Ohmi 《Natural Resources Research》1996,5(1):23-32

An application of a geotechnical database system for primary evaluation of ground-water resources in a sedimentary basin is proposed. The database consists of 1200 borehole logs including geologic columns,in situ test results, ground-water level, water quality data, and resistivity logs. The Kumamoto plain, situated in southwest Japan, is chosen as a study area. The evaluation process consists of two steps: (1) modeling of shapes of water-bearing strata, and (2) modeling of distribution of physical quantity which has some relationship with the porosity of those strata. In step (1), the shapes of upper and/or lower surface of the pyroclastic flow deposits and the andesitic lava were determined, whereas the three-dimensional distribution model of resistivity was constructed from resistivity logging data obtained from 100 boreholes and using the proposed interpolation method in the step (2). An empirical equation between the porosity and the resistivity of the lava was also identified. The integration of two types of model and the empirical equation contributed to an estimate of the total volume of the ground-water under the study area.  相似文献   

Co-kriging for modeling shallow groundwater level changes in consideration of land use/land cover pattern     

Jean Aurelien Moukana  Hisafumi Asaue  Katsuaki Koike 《Environmental Earth Sciences》2013,70(4):1495-1506

This study aimed at clarifying the relationship between the dynamics of land use/land cover (LULC) changes and decline in the groundwater levels, and specifying an LULC category strongly affecting such decline in a Quaternary sedimentary basin. Groundwater level data recorded at 26 observation wells for a 14-year period in the Kumamoto Plain, central Kyushu, southwest Japan, were used for the analysis. The general trends of LULC were detected by a satellite image classification technique and surface spline method, which highlighted the decreases in groundwater-recharge materials. As the next step, those trends of groundwater levels that were closely correlated with rainfall were removed from the level data set, and the resultant residual component levels were applied to co-kriging analysis with LULC categories. Co-kriging provided a detailed map of groundwater level variability. Furthermore, we propose a method, prediction of residual of groundwater level (PWL), to infer future residual groundwater levels from the supposed LULC pattern by co-kriging-based modeling. PWL was demonstrated to be effective because it clearly represented the decrease and increase in negative residual level areas, depending on the extent of rice fields in the past and in predicted future distribution scenarios.  相似文献   

Effectiveness of Neural Kriging for Three-Dimensional Modeling of Sparse and Strongly Biased Distribution of Geological Data with Application to Seafloor Hydrothermal Mineralization     

Koike  Katsuaki  Yono  Oak  de Sá  Vitor Ribeiro  Tomita  Shohei Albert  Nozaki  Tatsuo  Takaya  Yutaro  Komori  Shogo 《Mathematical Geosciences》2022,54(7):1183-1206

Mathematical Geosciences - Three-dimensional modeling of geoscientific data of limited amounts and strongly biased locations is difficult and impractical using almost any method. To obtain a...  相似文献   

Discriminating Weathering Degree by Integrating Optical Sensor and SAR Satellite Images for Potential Mapping of Groundwater Resources in Basement Aquifers of Semiarid Regions     

Magaia  Luís André  Koike  Katsuaki  Goto  Tada-nori  Masoud  Alaa Ahmed 《Natural Resources Research》2019,28(3):1197-1215

Natural Resources Research - Unlike in coastal and sedimentary basins, regional-scale exploration of groundwater resources using only geophysical methods is costlier in consolidated rocks such as...  相似文献   

Vertical profiles of nitrous oxide and dissolved oxygen in marine sediments     

Toshihiro Usui  Isao Koike  Norio Ogura   《Marine Chemistry》1998,59(3-4)

The whole core squeezing method was used to simultaneously obtain profiles of nitrous oxide (N₂O), nitrogenous nutrients, and dissolved oxygen in sediments of Koaziro Bay, Japan (coastal water), the East China Sea (marginal sea), and the central Pacific Ocean (open ocean). In the spring of Koaziro Bay, subsurface peaks of interstitial N₂O (0.5–3.5 cm depth) were observed, at which concentrations were higher than in the overlying water. This was also true for nitrate (NO₃⁻) and nitrite (NO₂⁻) profiles, suggesting that the transport of oxic overlying water to the depth through faunal burrows induced in situ N₂O production depending on nitrification. In the summer of Koaziro Bay, sediment concentrations of N₂O, NO₃⁻ and NO₂⁻ were lower than in the overlying water. In most East China Sea sediments, both N₂O and NO₃⁻ decreased sharply in the top 0.5–2 cm oxic layer (oxygen: 15–130 μM), which may have indicated N₂O and NO₃⁻ consumption by denitrification at anoxic microsites. N₂O peaks at subsurface depth (0.5–6.5 cm) implied in situ production of N₂O and/or its supply from the overlying water through faunal burrows. However, the occurrence of the latter process was not confirmed by the profiles of other constituents. In the central Pacific Ocean, the accumulation of N₂O and NO₃⁻ in the sediments likely resulted from nitrification. Nitrous oxide fluxes from the sediments, calculated using its gradient at the sediment–water interface and the molecular diffusion coefficient, were −45 to 6.9 nmolN m⁻² h⁻¹ in Koaziro Bay in the spring, −29 to −21 nmolN m⁻² h⁻¹ in the summer, −46 to 37 nmolN m⁻² h⁻¹ in the East China Sea, 0.17 to 0.23 nmolN m⁻² h⁻¹ in the equatorial Pacific, and <±0.2 nmolN m⁻² h⁻¹ in the subtropical North Pacific, respectively.  相似文献   

青藏高原那曲地区冰冰雹天气系统中的大气电场   总被引：12，自引：9，他引：3  

周筠 Kajik.  M 《高原气象》2000,19(3):339-347

利用１９９８年４～９月间进行的ＧＡＭＥ－ＴＩＢＥＴ青堪稿原云和降水的多普勒雷达及大气平均电场加强期观测实验资料,对青藏高原那曲地区的冰雹天气系统中的大民电场作了定量观测和研究。结果表明：在降雹过程中大气电场强度基本上系统中的大气电场强度基本上均为负值,其峰值也均强于－２２ｋＶｍ＾－１;在降雹过程中随着降雹时间的临近,大民场强度基本不断增强,但降雹开始时大气电场强度并不达到其峰值,峰值出现的时刻比开  相似文献   

青藏高原那曲地区冰雹天气系统中的大气电场     

周筠珺  陈成品  刘黎平  楚荣忠  冯锦明  张彤  宋新民  M. Kajikawa  H. Fujii  Y. Aoi  T. Koike  S. Shimizu  K. Ueno 《高原气象》2000,19(3)

利用1998年4～9月间进行的GAME-TIBET青藏高原云和降水的多普勒雷达及大气平均电场加强期观测实验资料, 对青藏高原那曲地区的冰雹天气系统中的大气电场作了定量观测和研究.结果表明: 在降雹过程中大气电场强度基本上均为负值, 其峰值也均强于-22 kVm-1; 在降雹过程中随着降雹时间的临近, 大气电场强度不断增强, 但降雹开始时大气电场强度并未达到其峰值, 峰值出现的时刻比开始降雹的时刻略有滞后; 在各降雹日中, 较强的大气电场强度基本上对应着各冰雹谱分布段较多的冰雹数目, 而这种较好的相关在各谱分布段上都表现出来; 随着降雹时间的临近, 每5 min闪电频数不断增强.在开始降雹时每5 min闪电频数平均达到43, 峰值的出现时刻略滞后于开始降雹的时刻, 这一滞后时间一般平均在3 min左右; 在降雹过程中, 单位面积中的冰雹数目与对应时段内总闪电数有着较好的对数关系, 相关系数R为0.954 0.在降雹过程的时间序列上, 冰雹云成熟期过后, 总闪电次数与冰雹降雹率成反相关.  相似文献