THE ROLE OF FLOODS IN PARTICULATE ORGANIC MATTER DYNAMICS OF A SOUTHERN APPALACHIAN RIVER/FLOODPLAIN ECOSYSTEM

Abstract

I investigated the role of a flood in particulate organic matter (POM) dynamics of the Little Tennessee river/floodplain ecosystem in western North Carolina, USA. I measured litter inputs, leaf breakdown, floodplain litter, and aboveground herbaceous net primary production at 12 sites. Annual litter inputs (274-625 g m-2 y-1) were typical of a temperate deciduous forest, but lower than other floodplain forests in the eastern United States. Mean aboveground herbaceous net primary production ranged from 61-439 g m-2 y-1 and leaf breakdown rates of 4 tree species ranged from 0.001-0.010 d-1. Following a flood on 8 January 1998, sites were separated into three inundation classes: inundated, partially-inundated, and non-inundated. Sites inundated by a January flood had significantly less forest floor leaf litter and coarse woody debris after the flood. There was no significant change at the partially-inundated or non-inundated sites. In addition, there was no significant difference in herbaceous material between pre- and post-flood collections for any inundation classes. Litter input, leaf breakdown, and floodplain litter standing crop data suggest that flood entrainment of POM from the floodplain of Little Tennessee River is a source of POM to the active channel. The impact of floods on the floodplain POM dynamics, however, is highly dependent on the time of year and magnitude of the flood, and on the structure of floodplain tree assemblages, which is strongly influenced by anthropogenic land use. Compared to direct litterfall and instream primary production, the floodplain may be a small annual source of POM for the river.