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

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.     

The influence of environmental variability on silicate exchange rates between sediment and water in a shallow-water coastal ecosystem,the Seto Inland Sea,Japan

Silicate regeneration was determined in a shallow-water coastal ecosystem (Shido Bay, the Seto Inland Sea, Japan) during 1999-2000. The present study was carried out directly by core incubation and by determining gradients of dissolved silicate (DSi) in the pore water. Incubated fluxes ranged from 25.5 to 132.6 mgSim(-2)d(-1), and were 1.6-21.6 times greater than diffusive fluxes (5.4-43.3 mgSim(-2)d(-1)). The disparity between fluxes measured by core incubation and modeling pore water indicated that other physical, chemical or biological processes, in addition to diffusion of DSi from below, contribute to DSi fluxes measured during the incubation of undisturbed cores. A regression analysis revealed that water temperature and salinity explained 24% and 23%, respectively, of season to season variability in incubated fluxes. Microphytobenthos was responsible for 37% of the variability in measured rate of DSi fluxes, with greatly reducing DSi release rates due to their own DSi demand. Moreover, the inverse relationship between the DSi fluxes and biogenic silica (Bio-Si) concentrations in the surface sediment, suggested that about 41% of the variability in the DSi fluxes were explained by Bio-Si concentrations in the surface sediment. As a result, Shido Bay showed silicate regeneration of incubated cores to be a consequence of Bio-Si dissolution depending on microphytobenthos, temperature and salinity, while diffusive fluxes appeared to be limited by DSi in the pore water. An annual average of DSi flux (68.7+/-32.9 mgSim(-2)d(-1)) from the sediments to the water column corresponds to 38% of DSi, required for primary production by phytoplankton in Shido Bay.     

The paradox of smooth and abrupt bends in two-dimensional in-plane shear-crack mechanics

It is pointed out, in the context of the boundary integral equation method (BIEM), that, in the mechanics of 2-D curved in-plane shear cracks, a smooth curve, along which the crack orientation changes continuously, and an abrupt kink, across which it changes discontinuously, are not equivalent to each other. The discrepancy is illustrated by numerical results, and a set of conceptual models is used to demonstrate analytically how the equations that govern the crack mechanics have inherently distinct forms depending on whether the crack orientation changes continuously or abruptly across a bend, as long as one abides by the principles of linear elasticity theory. This has serious implications for the numerical treatment of a curved crack, which can be modelled as a chain of finite elements that are connected either smoothly or at abrupt kinks, the two methods producing different numerical outcomes. No similar paradox arises in the cases of anti-plane shear or open in-plane cracks.     

Classification of Japanese rivers by heavy metals in bottom mud

Bottom mud was collected from the upper and lower reaches of 92 rivers in Japan to determine the distribution of 0.5N-HCI-soluble heavy metals. The average concentrations of Cu, Zn, Pb, and Cd in the mud from the lower reaches were from two to three times higher than those in the upper reaches. Japanese rivers were classified according to the degree of heavy metal pollution by using the values of 0.5N-HCI-soluble metals in the lower reaches of rivers. The content of 0.5N-HCI-soluble heavy metals in the mud of the upper reaches was used as the standard value. The classification of rivers was made by a cluster analysis according to Euclidian distance. As a result, rivers in Japan could be classified into three groups based on the degree of metal pollution, and the classification was in agreement with the pollution index.     

Online hybrid test by internet linkage of distributed test‐analysis domains

Online hybrid tests (called the online tests), particularly when combined with substructuring techniques, are able to conduct large‐scale tests. An extension of this technique is to combine multiple loading tests conducted in remote locations and to integrate the tests with large numerical analysis codes. In this study, a new Internet online test system is developed in which a physical test is conducted in one place, the associated numerical analysis is performed in a remote location, and the two locations communicate over the Internet. To implement the system, a technique that links test and analysis domains located at different places is proposed, and an Internet data exchange interface is devised to allow data communication across Internet. A practical method that utilizes standard protocols implemented by operating systems for sharing files and folders is adopted to ensure stable and robust communication between remotely located servers that commonly protect themselves by strict firewalls. To combine the online test with a finite element program formulated in an incremental form and adopting an implicit integration scheme, a tangent stiffness prediction procedure is proposed. In this procedure, a tangent stiffness is estimated based on a few previous steps of experimental data. Using the system devised, tests on a base‐isolated structure were carried out. Here, the base‐isolation layer was taken as the tested part and tested in Kyoto University, Japan, and the superstructure was modelled by means of a finite element program and analysed in a computer located in Osaka University. A series of physical Internet online tests were carried out, with the integration time interval and the method of tangent stiffness prediction as the major parameters. The tests demonstrated that the Internet communication was very stable and robust, without malfunctions. The proposed method of stiffness prediction was effective even when the experimental hysteresis curves exhibited complex behaviour, thereby ensuring accurate simulation for the earthquake response of the entire structure. Copyright © 2005 John Wiley & Sons, Ltd.     

Dissolved free amino acids in coastal seawater using a modified fluorometric method

The method of Parsonset al. (1984) for measuring dissolved free amino acids (DFAA) in coastal seawater was modified. We found considerable interference in DFAA determination from ammonia dissolved in coastal seawater, although the interference of urea could be ignored. For DFAA analysis for coastal seawater samples, ammonia determinations for the same sample are needed to correct DFAA values. For coastal surface seawater samples from all over the Seto Inland Sea, Japan, values of DFAA ranged from undetectable to 1.87 μg-at N/l when corrected for ammonia, while uncorrected values ranged from undetectable to 2.61 μg-at N/l. DFAA, urea, nitrate+nitrite, ammonia and DON concentrations in surface seawater collected in the Seto Inland Sea were analyzed simultaneously. DFAA at four seasons constituted from 1.4 to 10.1% of DON, with a mean value of 6.5%. The concentration of urea was similar to that of DFAA and often higher than that of ammonium, although generally lower than that of nitrate.     

Standing stocks and production rates of phytoplankton and abundance of bacteria in the Seto Inland Sea, Japan

Standing stocks and production rates of phytoplankton and abundance of bacteria were investigated at 39 stations in the Seto Inland Sea, Japan during four crulses in October 1993, January, April and June 1994. Primary productivity was measured by the¹³C tracer method. Photosynthetic rate varied from 0.41 to 32.1 μgC/1/h with an average value of 4.67 μgC/l/h. Annual primary production was estimated to be 218 gC/m²/year. Annual primary production in this study was 1.8 times as high as the values which were previously reported at same area. The reason for the disagreement between our primary production value and previous values is not thought to be due to the difference of methods used for measuring primary production or the different Chl.a concentrations but to the method of estimating the primary production in the euphotic zone from thein vitro measurements. The distribution of bacterial cells in surface seawater was examined during the same cruises. Bacterial cell density ranged from 0.32 to 3.4×10⁶ cells/ml. The density was relatively high in the eutrophic regions of Hiroshima Bay and Osaka Bay In addition, a high density of bacteria was also observed in an area within Suo Nada where Chl.a was relatively low. The disparity between Chla and bacterial density in Suo Nada suggests that bacterial abundance can be controlled by the availability of substrates other than phytoplankton exudate.     

Simple estimation of penetration rate of light in intertidal sediments

A simple estimation of light penetration in tidal flat sediments was developed using various sediment size fractions and their attenuation rate of irradiance. The attenuation coefficients of the sediment size fractions of 63–125, 125–250, 250–500, 500–1000 μm and 1000–2000 μm were 8.10, 4.08, 2.92, 2.12 and 1.44 mm⁻¹, respectively. Using the average attenuation coefficient of the particle size fractions in the sediment, the calculated attenuation coefficient agreed well with the actual attenuation coefficient. The method presented gives a photo-parameter to predict productivity in intertidal sediments, given only the particle size fraction.     

Long-term (36-year) observations on the dynamics of the fish-killing raphidophyte Chattonella in Harima-Nada,eastern Seto Inland Sea,Japan

Long-term changes of the fish-killing raphidophyte Chattonella spp. (Chattonella antiqua, Chattonella marina and Chattonella ovata) were examined in relation to environmental factors at 19 sampling stations in Harima-Nada, eastern Seto Inland Sea, Japan, for 36 years from 1973 to 2008. Long-term trends in the dynamics of Chattonella populations were considered to relate to environmental factors such as nutrient concentrations and water temperature. High nutrient levels during the period from the 1970s to the early 1980s have contributed to the high cell density and large-scale red tides of Chattonella spp. in Harima-Nada. However, nutrient levels exhibited a decreasing trend thereafter, and it is thought that Chattonella spp. cannot form large-scale blooms under the present conditions. After the mid-1990s, the occurrence period of vegetative cells of Chattonella spp. has been several weeks or 1 month earlier than that of the 1970s and early 1980s, and the appearance frequency of Chattonella spp. has increased in the northern coastal area, although the cell density and the spatial scale of the distribution have become lower and smaller than those in the previous decades. It is suggested that the timing of germination of Chattonella cysts has become earlier as a result of the increase in water temperature, and the chances of vegetative growth have also increased, especially at the northern coast where most of large rivers discharge into the Harima-Nada. In addition, the present results revealed that fewer diatoms were also one of the significant factors for the high abundance of Chattonella spp. in Harima-Nada.