Making use of relevant Geographic Information System (GIS) data, an attempt was made to analyze the changes in the magnitude and spatial distribution of the land-based sources of nonpoint pollution loads for the entire Lake Biwa–Yodo River Basin over the 18-year period between 1991 and 2009. Specifically, the magnitudes per unit area of the runoff coefficient and of the COD, T-N and T-P pollutant loads, respectively, were computed and displayed as GIS visual images. The resulting GIS outputs indicate that the runoff coefficient increased along the riparian zones of rivers and around the lakeshore in the middle and lower basin regions, except for the mountainous regions. This implies that the pollutants flow directly into the immediately adjacent receiving waterbodies. Also, the trends of water pollutants were found to be affected by the unit load. The runoff coefficient and the COD loads were related with the progress of urbanization, indicating that the increase and decrease in T-N and T-P pollutant loads were caused by the conversion of land mainly from paddy agriculture to other agricultural purposes. In conclusion, it was confirmed that the results displayed in the form of GIS outputs are useful not only for numerical assessment but also for the assessment of spatial distributions.

Various materials have been developed to restore sludge-accumulated bivalve fishing grounds. In this study, we examined the effectiveness of using an improved material, fluvic acid iron silica material (FS material) , to treat deteriorated sediment by the photo-Fenton reaction of Fe-humic substance complexation in Lake Shibunotsunai, northern Japan. From the results of a field experiment with FS material laid on the lake bottom, the thickness of deposited mud, mud content, and ignition loss of bottom sediment were partially reduced in the FS material site compared with the control site, but the effect was much smaller than in the previous research. Laboratory experiments revealed that the effectiveness of FS material was enhanced by a high water temperature and by using a greater amount of FS material. It has been found that if there is a current in the FS material site, the decomposed sediment surface layer may peel away. As a result, it is important to consider the applicable utilization method of FS material in accordance with the locality.