We analyzed vegetation cover and the diversity of native and alien aquatic plants in the Lake Teganuma watershed (northeastern Chiba Prefecture). Using digital elevation model data, we established six third-order sub-watersheds, which were further divided into second-and first-order sub-watersheds. The easternmost third-order sub-watershed (Kamenari) contained large tracts of agricultural landscape. Land cover on the western sub-watersheds was more densely developed through human activity.

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... ation cover was derived from the normalized difference vegetation index (ASTER data), and extant data on distributions of aquatic species were digitized. Aquatic plant diversity and vegetation cover were substantially higher in Kamenari than in the five western sub-watersheds. Several submerged species in Kamenari are currently listed in the prefectural red data book. Only common emergent species occurred in the western areas. There was a strong correlation between vegetation cover and native species diversity in Kamenari, but not for alien species. Thus, the eastern Kamenari sub-watershed is a hot spot for aquatic plant diversity (especially native species) in the Lake Teganuma watershed.