Stream discharge and floodplain connections affect seston quality and stable isotopic signatures in a coastal plain stream

Connections of a stream to its floodplain are important ecological linkages that affect spatial and temporal dynamics of the basal resources available to primary consumers in streams. Suspended organic material and associated microorganisms (seston) vary in quality seasonally and interannually within streams because of changing inputs from riparian and floodplain sources. Researchers have investigated the quality of different size fractions of material, but these differences have not been assessed with respect to the hydrology and the geomorphic structure of streams. We investigated how quality, represented by the stoichiometric ratio C:N, and stable isotopic signature (delta C-13 and delta N-15) of 3 seston size classes varied in Ichawaynochaway Creek, a 5(th)-order tributary of the lower Flint River in the Coastal Plain of southwestern Georgia, USA. Samples were collected throughout the basin during varying flow regimes to estimate the quality and source of materials available over different temporal and spatial scales. Our results indicate significant differences in quality and stable isotopic signature based on particle size, discharge, and geomorphic structure of the stream and floodplain (constrained vs unconstrained reaches). The constrained portions of this stream occur in the lower portions of the basin. During low flow conditions, seston had higher quality with less depleted delta C-13 and more enriched delta N-15 signatures in the constrained than in the unconstrained portions of the stream. However, during high flow conditions, higher quality seston entered the stream from the adjacent floodplain in all portions of the basin. Insights gained from our study indicate how terrestrial and aquatic linkages and the natural flow regime affect the dynamics of basal resources and their availability to primary consumers in streams.