HR: 10:35h
AN: H42A-02 INVITED    [Abstracts]
TI: Aggradation at Tributary Confluences as a Control on Biodiversity in River Networks
AU: * Rice, S P
EM: s.rice@lboro.ac.uk
AF: Loughborough University, Department of Geography, Loughborough, LE11 3TU, United Kingdom
AB: Numerical experiments utilizing a 1-D sediment routing model demonstrate that geomorphological adjustments to altered flow and sediment regimes at tributary junctions can greatly increase physical heterogeneity in the recipient channel. This helps to explain why river confluences can behave as ‘hotspots' that exhibit elevated biodiversity. In general, biodiversity is expected to increase with physical heterogeneity if other biological factors are unchanged. In the context of understanding and managing river biodiversity at network scales, interesting issues then include (1) identifying a priori that subset of tributary junctions where large physical impacts might be expected and (2) exploring how network configuration might influence the number and spatial arrangement of such confluences. Results show that main stem aggradation is the primary driver of increased physical heterogeneity in confluence zones, and this suggests that (1) and (2) can be investigated by defining the probability of main stem aggradation at confluences. Model experiments reveal that aggradation is most sensitive to the ratios of tributary to mainstream bed load flux and bed load grain size, and is less sensitive to relative discharge. This suggests that probability statements about aggradation (and thence, perhaps, biodiversity) might be derived from estimates of the relative bed load fluxes and grain sizes at the confluences throughout a network. The potential of obtaining such estimates for real and simulated networks is considered and the importance of network magnitude and topology for network-scale patterns of confluence-zone aggradation are explored. An important implication of this work is that understanding the production, delivery and routing of sediment, not just water, is important for understanding physical and biological diversity in river networks.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 1813 Eco-hydrology
DE: 1825 Geomorphology: fluvial (1625)
DE: 1856 River channels (0483, 0744)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting