We conducted a pilot-scale experiment for seaweed bed construction using concrete substrata with newly developed fly-ash (FA) porous concrete panels or conventional concrete panels from November 23, 2013 to October 14, 2017 in a coastal area of Noto Peninsula, Japan. The FA porous concrete panel was manufactured by replacing 20-40% of the cement with coal fly ash produced in a coal power plant. The total number of Ecklonia kurome sporophytes grown on two substrata after four years was 14. The erosion of central lamina began in the third year and the maturing of over 50% of E. kurome sporophytes was observed in the fourth year. A greater number of E. kurome sporophytes tended to grow on FA porous concrete panels than on normal concrete panels; the maximum density of E. kurome sporophytes attached to FA porous concrete panels was 24 individuals per square meter. The final number of E. kurome sporophytes largely differed among the sides of each substratum, which seemed to be strongly affected by waves. No grazing marks of herbivorous fishes and benthic animals were observed during the four years of growth monitoring. These results suggest that E. kurome bed construction using FA porous concrete panels in the coastal area of Noto Peninsula would be possible.

The total nitrogen concentration in chlorinated wastewater from a sewage treatment plant included a large amount of ammonium nitrogen as determined by a measurement method established by the Water Pollution Prevention Act, but it was less than the concentration of dissolved inorganic nitrogen. The total nitrogen concentration may have been underestimated because some of the chloramines in the sample changed to nitrogen gas or nitrous oxide gas under alkaline conditions. Therefore, we evaluated a novel pretreatment method for total nitrogen analysis. The recovery rate of total nitrogen in a sample including 1 mg L^-1 ammonium nitrogen and 1 mg L^-1 available chlorine from sodium hypochlorite was enhanced to 98% by the addition of 50 mmol L^-1 sodium sulfite solution, which accounted for at least 0.4 vol% of the sample. Additionally, a recovery test was carried out with some real samples. The recovery rates of total nitrogen in wastewater from the sewage treatment plant and in water from the environment around the plant were 100-104% after the addition of 50 mmol L^-1 sodium sulfite solution.

The effects of operations to increase nitrogen discharge from sewage treatment plants to prevent oligotrophication at Harima-nada in the Seto Inland Sea on concentrations of organic matter, nitrogen, and phosphorus in surface water were evaluated. First, the sea waters around the Futami treatment center, which has been conducting the operation, were analyzed. The results show that no significant changes in water quality were observed during the operation. Next, the effects of the operations of 20 sewage treatment plants at Harima-nada on the water quality were simulated using a numerical simulation model. As a result, it was estimated that dissolved inorganic nitrogen and phosphorus were taken up by phytoplankton, and organic matter and nitrogen concentrations in the entire area of Harima-nada were increased by phytoplankton advection and diffusion. The observed values could not confirm the effect of the operation to increase nitrogen discharge at the Futami treatment center owing to dilution by seawater and the drainages of other nitrogen emission sources. However, it was shown that when the number of operations to increase nitrogen discharge from sewage treatment plants increased, the water quality in a wide area of Harima-nada may be affected.

The influence of different land use types on groundwater was evaluated on the basis of the relationship between the annual water quality fluctuation and the content of stable NO₃^- isotopes in winter in five spring water samples collected from a river terrace. The compositions of two spring water samples from the edge of the terrace with forested land use on the upstream side were very similar and were not affected by anthropogenic activity. Spring water collected from the terrace surface near a paddy field was influenced by ammonium sulfate, but contained low concentrations of NO₃-N. The quality of spring water from a terrace site surrounded by agricultural land (a vegetable field) suggested the influence of chemical fertilizers, such as magnesian lime and ammonium chloride. In spring water from a terrace site where a poultry farming facility and residential area were located, the concentration of N derived from organic matter and the K⁺, Na⁺, and Cl^- ion contents were high. This pollution from domestic drainage is a cause of concern.