It has been pointed out that some waterbodies face “oligotrophication” owing to a decrease in nutrient loads. In this study, we predicted the effect of a change in future nutrient loads on variables such as the biomass of upper-trophic-level species, using the food chain model. The target area is Lake Biwa, where fish catches have fallen in recent years concurrent with a decrease in nutrient loads. Three models with different structures were developed and 100 patterns of parameter sets were selected for each model by the Monte Carlo method. As a result, the change in the biomass of phytoplankton, regardless of the model structure, tended to be roughly proportional to the change in nutrient loads in general. On the other hand, for the fish, differences in model structures and their prey strongly affected the biomass, and although inflow load increased, the biomass decreased in some cases. Considering the uncertainty of the prediction, we suggested that the addition of nutrients with the aim of increasing the fish populations would cause undesirable results in Lake Biwa such as a combination of deteriorating water quality and no increase in the fish populations.

For phosphorus recovery, we used the technique of bacterial leaching to elute phosphorus from night soil sludge incineration ash using sulfur-oxidizing bacteria. The purpose of this study was to obtain practically enriched strains of bacteria suitable for the local environment without a complicated isolation operation and to confirm a simple and economical medium composition. Three bacterial strains were enriched at night soil treatment facilities by using the medium for sulfur-oxidizing bacteria. Two enriched strains had a greater ability to generate sulfuric acid and elute phosphorus than Acidithiobacillus thiooxidans NBRC13701 (NBRC) which was used for comparison. Clone library analysis indicated that seven and five kinds of Acidithiobacillus spp. strain were included in these enriched strains, respectively. The ability of another enriched strain for sulfuric acid generation and phosphorus elution did not reach that of NBRC, but it was thought that this enriched strain included only A. caldus with a higher optimal growth temperature than those of the others. With regard to the medium composition, seven of the 11 original components could be omitted. For sulfur, an important substrate, inexpensive desulfurization sulfur could be used. The ability of sulfuric acid generation was unaffected by these changes, but the medium preparation cost was reduced to 1/18.

In consideration of the changes in indicator bacteria in the environmental standard and wastewater effluent standard, fluctuations in the concentrations of E. coli and total coliform in raw sewage and secondary treated sewage at three wastewater treatment plants and fluctuations in the resistance to UV disinfection were investigated. Regarding the concentrations of E. coli and total coliform, there were no significant fluctuations in either raw or treated sewage with seasonal variation, water collection system, and treatment method. As a result of UV inactivation of secondary treated water, it was found that the UV resistance of E. coli was higher than that of total coliform. However, there was no significant difference in UV resistance calculated using the concentration after photo-reactivation. Moreove, no significant difference was found between seasonal variation, diurnal fluctuation, and treatment plants for these tolerances. According to the result of similar experiments on raw sewage, the UV resistances of E. coli and total coliform were equivalent, and the resistances calculated using the concentration after photo-reactivation were also the same.

The tidal flat in Hatsutsu-ura bay located in Oku-Matsushima, Miyagi prefecture, was disturbed by the Tohoku-oki tsunami generated by the Great East Japan Earthquake of 2011. The population of benthic organisms in the tidal flat, including clams, was greatly reduced by the disturbance, and subsequently, the sediment environment did not recover. In this study, to clarify the influence of embankment construction in the coastal area on the changes in the sediment environment during the recovery process after the earthquake, cluster analysis and principal component analysis using the metal composition of tidal sediment were conducted. The influence of the input from the drainage outlet of the embankment construction site was observed in the inner part of the bay, and another influx from outside of the bay was also observed at the entrance of the bay. In addition, we investigated the spatial distribution of these influxes in tidal sediment. The influx from the drainage outlet mainly affected the inner part of the bay, whereas the influx from outside of the bay mainly affected the bay entrance. In the central part of the bay, a relatively small effect of these influxes compared with other parts was observed.

Ibaraki Prefecture produces the largest volume of lotus root in Japan. The Teno area in Tsuchiura City (Ibaraki Prefecture) is the first to develop an infrastructure consisting of a concrete levee and to separate irrigation and drainage canals in Japanese lotus paddy fields. This was carried out over the period from 1995 through 2015. In this study, we studied the changes in runoff loads from lotus paddy fields due to the improvement of agricultural infrastructure in this area. Runoff loads of suspended solids (SS) , chemical oxygen demand (COD) and total nitrogen (TN) were the largest in March and April. This result is attributed to the manuring using basal fertilization and calcium cyanamid in this period. On the other hand, the runoff load of total phosphorus (TP) was maximum in July and August. As a cause, the elution of phosphate-phosphorus from lotus paddy soils and bottom sediments in drainage canals under lowered dissolved oxygen concentrations can be considered. Furthermore, annual balanced losses of COD, TN, and TP from lotus paddy fields were increased compared with those before the improvement of agricultural infrastructure. The separation of irrigation and drainage canals decreased soil sedimentation, which resulted in increases in losses of COD, TN, and TP from lotus paddy fields.

Spectral analyses [UV absorbance:dissolved organic carbon (DOC) ratios, three-dimensional excitation emission matrix (3DEEM) ] and chemical analysis (fatty acid analysis) were carried out to investigate the characteristics of organic matter in and around Isahaya Bay regulating reservoir. As a result, it was revealed that soil-derived organic matter was the dominant source of dissolved organic matter (DOM) in and around the area. It was also shown that protein and humic substances were components of labile DOM and refractory DOM, respectively. In terms of particulate organic matter (POM) , fatty acid analysis indicated that organic matter derived from phytoplankton was the main source of labile POM. In addition, organic matter from terrestrial plants were most likely to be more refractory than that from phytoplankton.