Nutritive salts have to be removed from not only wastewater but also non-point water sources to inhibit the eutrophication of enclosed waters in the environment. However, efficient removal methods for nutritive salts from non-point sources have not yet been established. Here the authors reported that Mg-Al-Cl forms a hydrotalcite compound (HT) which has a high selectivity and a large adsorbing capacity for phosphate anions. Thus the authors developed some concrete materials mixed with HT for the removal of phosphorous from rivers, which is a main transport medium of nutritive salts in the non-point water sources. Four types of concrete blocks and mortar block, such as normal type, air-entraining type, large porous type and small porous type, were prepared by mixing cement with HT. The compressive strengths and phosphorous adsorption capacities of the blocks were investigated. The obtained results are as follows. 1) The compressive strengths of the concrete blocks and mortar blocks decreased with an increase in the amount of the HT mixed. However, the compressive strength of the porous-type concrete (HT-POC) and porous-type mortar (HT-POM) were almost equivalent to the strength value of 10 N·mm^-2 by keeping the HT amounts below 100 and 160 kg·m^-3, respectively. 2) HT-POC and HT-POM were found to have a large removal capacity and a rapid removal rate for phosphate anions with a wide range of concentrations at neutral pH. 3) Phosphate anions were removed through the anion exchange reaction of HT mixed in the concrete. 4) The amounts of phosphate anions removed by HT-POC and HT-POM were six and three times larger respectively than that of controls. 5) HT-POC and HT-POM adsorbed phosphate anion under the condition of coexisting CO₃^2- and SO₄^2-, which inhibited the phosphate anion exchange reaction of HT. These results suggest that HT-POC and HT-POM have a high feasibility as superior purification materials for the removal of phosphate anion from rivers.

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The purpose of this study is to clarify the effects of submerged breakwater on an artificial tidal flat ecosystem. The studied tidal flat ecosystem is composed of three zones, that is, low-, high-and no-submerged-breakwater zones.
The frequencies of shear stress being higher than the critical value (0.1N m^-2) for silt transport in the low- and high-submerged-breakwater zones were lower than that in the no-submerged-breakwater zone. The silt and organic carbon contents in the low-and high-submerged-breakwater zones were higher than those in the no-submerged-breakwater zone. The slopes, reduction zone and permeability of sediment in the submerged breakwater zones were almost the same as those in natural tidal flats at Hiroshima Bay. However, the no-submerged-breakwater zone showed a sharper slope. The total population density of macrobenthos in the low-and high-submerged-breakwater zones were about twice as high as that in the no-submerged-breakwater zone. The dominant macrobenthic species in the submerged breakwater zones were Ceratonereis erthraeensis and Mediomastus sp., which are common in natural tidal flats at Hiroshima Bay. These results suggest that the construction of submerged breakwaters could change both the physiochemical and biological properties of artificial tidal flats similarly to those of natural tidal flats at Hiroshima Bay.

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Volatile chlorinated hydrocarbons, such as tetrachloroethylene (or perchloroethylene, PCE), have been found in many sites and in groundwater, and the pollution by these chemicals has also been observed in Kanazawa city. In this study, field surveys were conducted and the characteristics of groundwater flow in this area were examined using a key diagram of chemical composition of well water samples and multivariate analysis. The groundwater flow was divided into three categories corresponding to the quality of well water samples. Based on the study of groundwater flow, the concentrations of PCE and its degradation products (trichloroethylene (TCE) and cis-1,2-dichloroethylene (cis-DCE)) in well water samples were investigated as a function of distance from the tentative source of contamination. The total concentration of the three compounds and the degradation level which was evaluated from the molar fraction of the products (TCE+cis-DCE), were closely related to the distance from the source of contamination.

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The budgets of nitrogen, suspended solids and chlorophyll a were studied in June, August and October 2001 at the north pond of Osaka Nanko Bird Sanctuary. The output of suspended solids to coastal water exceeded its input to the pond, while chlorophyll a was intercepted within the pond through tidal exchange. The dissolved inorganic nitrogen imported into the pond was temporally incorporated into the biomass and was then exported in the form of dissolved organic nitrogen. Particulate nitrogen was abundant as a resource of nitrogenous nutrients output to coastal water in the summer of 2001. These phenomena are thought to correlate with biological activities such as feeding, fixation and decomposition by benthic animals, seaweeds and benthic microalgae.

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Large-scale oil spills have significant impacts on the both natural environment and society. The purpose of this study is to determine the optimum composition of a dispersant for removal of oil and clarify the effects of dispersants on biodegradation of PAH. The optimum composition of the dispersant for sandy beach sediments contaminated by 5 wt. % fuel oil C is 22% Brij 30 as the surfactant and 78% decaline as the solvent. The dispersant at its optimum composition remove greater amounts oil than commercial dispersant. Both dispersants could accelerate biodegradation of PAH in oil. The acceleration of biodegradation of PAHs is more significant for the dispersant with an dispersant at its optimum composition than for commercially available dispersant of the third generation. The acceleration of biodegradation of PAH appear to be due to washout of oil by the dispersant.

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