Thursday, May 29, 2008 - 9:15 AM
522

Sources and retention of organic matter in a river network: The function of floodplain vs. confined segments

J. Ryan Bellmore1, Colden V. Baxter1, and Andrew M. Ray2. (1) Stream Ecology Center, Department of Biological Sciences, Idaho State University, Pocatello, ID 83209-8007, (2) Fish and Wildlife Department, Shoshone-Bannock Tribes, Fort Hall, ID 83203

Floodplains are considered hotspots of productivity and retentive features in river networks.  However, in montane systems they are typically juxtaposed with more confined segments, and the relative roles of the two segment types, and their potential interactions, have received little investigation.  We compared the sources (autochthonous and allochthonous) and retention of organic matter in five floodplain vs. five canyon-confined segments in the upper Salmon River Basin, central Idaho.  We hypothesized that floodplains would have higher aquatic chlorophyll a biomass, greater terrestrial litter input, and higher retentive capacity than confined segments.  We observed that chl-a biomass and terrestrial litter input in floodplains was actually within the range of values measured for confined segments.  As expected, retentive capacity of confined segments, both surface (measured via leaf-release methods) and subsurface (from conservative-tracer techniques) was considerably lower than that of floodplain segments.  These results show that floodplains in this region do indeed function as important retentive features.  However, production at higher trophic levels in montane floodplains, often attributed to basal productivity within these segments, is likely supplemented by organic matter delivered from upstream confined segments.  Further investigation is needed of functional interactions between different geomorphic segment types in river networks.


Web Page: Floodplain Productivity, Floodplain Retention, River Networks