Soil and sediment carbon and nitrogen in Mississippi alluvial valley and interior Flatwoods Bottomlands

Bottomland forests occur in floodplains of rivers and streams and are particularly dominant in the southeastern United States. Red oak (Quercus spp.) dominated sites in these systems are important for many wildlife species, remove pollutants, and accumulate C and nutrients. We examined red oak stands at six study sites in the Mississippi Alluvial Valley and Interior Flatwoods physiographic regions. We measured the hydroperiod at one location per site and degree of hydrologic connection to a major river, deposition of sediment and particulate C and N, and soil C and N (to 50 cm) at 10 to 20 locations within each site. Sources of organic matter appeared to change with hydrologic connection. Connected sites accumulated sediment C and N derived from eroded soil (0.05-0.23 Mg C ha-1 yr-1 and 2-15 kg N ha-1 yr-1), while disconnected sites were more likely to transfer C and N from within their respective floodplains (0.03-0.05 Mg C ha-1 yr-1 and 2-3 kg N ha-1 yr-1). In connected floodplains, sediment and soil characteristics were frequently correlated with distance to and discharge of the nearest stream. In disconnected floodplains, the distance to and discharge of the nearest stream was important in explaining soil and sediment characteristics, but the depth of mottling was frequently more important. Deposition of N and C was highest on sites within the floodplains connected to their major river. Accumulation of C appeared negligible, while accumulation of particulate N may be an important input of N to these systems.