Ibaraki Prefecture produces the largest volume of lotus root in Japan. In a previous study, we reported that the runoff load of total phosphorus (TP) in the Teno area, Tsuchiura city, Ibaraki Prefecture, became maximum in summer. Therefore, in this study, we investigated lotus paddy field with abundant green algae in the Teno area, focusing on the concentrations of dissolved oxygen (DO) , TP, and phosphate (PO₄-P) . As a result, DO in the green-algae-abundant lotus paddy field became supersaturated with increasing amount of green algae. On the other hand, DO in the green-algae-abundant lotus paddy field showed a concentration decrease to less than 4 mg L^-1 with increasing amount of lotus leaves in summer. Furthermore, the concentration of TP with DO of less than 4 mg L^-1 was about twice that after the lotus was harvested. The green-algae-abundant lotus paddy field had a significantly higher percentage of PO₄-P in TP than the Sakai River agricultural water that was used. These results indicated that the green-algae-abundant lotus paddy field exhibited a reduced DO concentration and increased elution of phosphate from the paddy soil in summer. As a consequence, the concentration of TP in the green-algae-abundant lotus paddy field was increased in summer.

Assuming application in areas with difficulties in installing, maintaining and operating large-scale water supply systems, the effectiveness of decentralized systems was examined by a one-year field test of disinfection apparatuses equipped with ultraviolet light-emitting diodes (UV-LED) at a faucet supplying untreated water from a mountain stream. The untreated water was sporadically positive with Escherichia coli and had a high heterotrophic plate count (HPC) of bacteria exceeding the target value of drinking water, indicating the need of disinfection process for potable use. In UV-LED treated water, both the concentration and the positive ratio of bacteria decreased, and the maximum concentration of positive samples for E. coli, total coliforms, standard plate count and HPC were 0.5, 1.0, 6.0 and 485 CFU mL^-1, respectively. One model of the UV-LED apparatus achieved all-negative detection of E. coli throughout the one-year test period. No apparatus showed any notable trend of performance deterioration for HPC inactivation with operation time, and scale formation was not apparent inside the body of the apparatuses after the test. This study shows the potential of UV-LED apparatuses as an option of decentralized water treatment technologies.

Carbendazim is the hydrolysate of benomyl and thiophanate-methyl, which are the active ingredients of pesticides, in the environment. Carbendazim has been detected in environmental water and sediment in Japan, and there is concern that it may have chronic effects on benthic organisms living in aquatic environments. In this study, the Japanese native chironomids Chironomus yoshimatsui were exposed to carbendazim from the first instar larval stage to emergence using a sediment-water system prepared by spiking carbendazim into the sediment. During exposure, the emergence ratio and development rate of C. yoshimatsui were measured. As a result, the no-observed-effect concentration based on the sediment concentration (NOEC_sed) of carbendazim for C. yoshimatsui was 3.07 mg kg^-1, which was 170 times higher than the highest concentration of 0.018 mg kg^-1 in the Japanese environmental sediment. Therefore, it is necessary to consider the results of this study when evaluating the toxicities of benomyl and thiophanate-methyl in sediment in the future.

The annual average chemical oxygen demand (COD) in the Lake Inbanuma is about 10 mg L^-1 for recent years. The amounts of wastewater loads from households and industry have been decreasing. However, the percentage of the inflow load from nonpoint sources is increasing. The paddy fields situated in the Lake Inbanuma basin is one of these nonpoint sources for which the nonpoint load is still unknown. Throughout the year, the investigation of the emission load from paddy fields situated in the Lake Inbanuma basin was conducted at the irrigation and drainage pump station. The annual effluent loads of COD, total nitrogen (T-N) , and total phosphorus (T-P) were 47.8 kg ha^-1 yr^-1, 6.8 kg ha^-1 yr^-1, and 0.61 kg ha^-1 yr^-1, respectively. These values were smaller than data for other regions. The results suggested that the reduction in load in the Lake Inbanuma is due to water being partially circulated as a result of water being pumped up from the drainage canal. The annual balance loads of COD, T-N, and T-P were -107.3 kg ha^-1 yr^-1, -28.4 kg ha^-1 yr^-1, and -1.3 kg ha^-1 yr^-1, respectively, which show a reduction type.