GIS (Geographical information system) We investigated the relationships between land use and water quality for 18 rivers in Wakayama prefecture, western Japan. Nonpoint-source pollution was identified in the northern and central parts of Wakayama prefecture and is likely related to the low coverage of residential sewerage systems. Elevated levels of nonpoint-source pollution in the central areas are correlated with orchard cultivation and result from crop-specific differences in fertilization

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... tes and natural factors such as precipitation and soil productivity. In contrast, water quality in the southern parts of the prefecture is minimally affected by nonpoint-source pollution, as this area is heavily forested and thus less affected by human activity.