Distribution of Vallisneria americana seeds and seedling light requirements in the UMR Kimber, A., C. E. Korschgen, and A. G. van der Valk. 1995. The distribution of Vallisneria americana seeds and seedling light requirements in the Upper Mississippi River. Canadian Journal of Botany 73:1966 1973. Reprinted by U.S. Geological Survey, Environmental Management Technical Center, Onalaska, Wisconsin, December 1997. LTRMP 97-R029. 8 pp. (NTIS # PB98-122393) ABSTRACT Vallisneria americana declined in backwaters of the Upper Mississippi River, U.S.A., after a drought in 1988. To determine whether viable seeds of V. americana occurred in the seed bank of navigation pool 7, Lake Onalaska, the upper 5 cm of sediment was collected from 103 sites in May 1990. These sediment samples were kept in pots at a depth of 0.4, 0.8, and 1.2 m in an outdoor pond for 12 weeks. Vallisneria americana seeds germinated from sites throughout the lake, and some seedlings produced overwintering buds by the end of the study. Seeds, spores or fragments of 12 other species of aquatic plants also germinated. Seed germination trials with fresh and stored seeds in both greenhouse and ponds in which light availability was reduced with shade cloths indicated that seed germination was insensitive to light level. To determine the light requirements for seedling survival and bud production, sediment from Lake Onalaska was incubated in ponds under neutral density shade screens reducing light to 2, 5, 9, and 25% of full sun. Seeds germinated under all shade treatments but survival was significantly higher in the 9 and 25% light treatments, and bud production was restricted to these light levels. KEYWORDS Aquatic macrophytes, seeds, germination, light response