Sources of mineral nutrition for submersed macrophyte growth Rogers, S. J., W. F. James, and J. W. Barko. 1995. Sources of mineral nutrition for submersed macrophyte growth in riverine systems: Results of initial investigations. Pages 194-200 in Proceedings, 29th Annual Meeting, Aquatic Plant Control Research Program, Vicksburg, Mississippi, November 14-17, 1994, Miscellaneous Paper A-95-3, August 1995. Reprinted by U.S. Geological Survey, Environmental Management Technical Center, Onalaska, Wisconsin, June 1997. LTRMP 97-R007. 7 pp. (NTIS #PB97-177984) ABSTRACT Widespread decline of Vallisneria americana Michx. and other submersed aquatic species occurred in portions of the Upper Mississippi River System (UMRS) during 1988 1991. These declines prompted study efforts by the LTRMP to better understand factors potentially contributing to the declines. One likely factor limiting growth is nitrogen (N) availability. In order to sustain plant growth over time, N supplies to the sediments need to be replenished as they become depleted due to plant uptake and diffusional losses. During periods of prolonged low flow hydraulic conditions, the availability of N in backwaters of the UMR may limit the productivity of Vallisneria and other species of rooted macrophytes. In this study, we began efforts to determine sources and mechanisms of nutrient replenishment, primarily N, in a backwater lake where Vallisneria had previously occupied over 1200 ha. N concentrations in plant tissues, sediments, water, and accreted materials were determined from samples collected throughout the 1994 growing season. Results of the study indicate that adequate N was available during the season to sustain plant growth, and that sediment pore water was the major source of N. Also, our data suggest that N deposition via accretion may be an important mechanism of N replenishment to the sediment surface, and combined with processes of sediment mixing, may help sustain aquatic macrophyte populations within the lake. KEYWORDS Aquatic macrophytes, mineral nutrition, nitrogen availability, Upper Mississippi River System