HR: 11:00h
AN: B42A-03    [Abstracts]
TI: Tributary Sediment Yield, Water Yield and Sediment Composition as Controls of Habitat Heterogeneity in River Networks
AU: * Rice, S
EM: s.rice@lboro.ac.uk
AF: Loughborough University, Department of Geography, Loughborough, LE11 3TU United Kingdom
AU: Ferguson, R
EM: r.i.ferguson@durham.ac.uk
AF: University of Durham, Department of Geography, Durham, DH1 3LE United Kingdom
AU: Hoey, T
EM: thoey@geog.glasgow.ac.uk
AF: University of Glasgow, Department of Geography & Geomatics, Glasgow, G12 8QQ United Kingdom
AB: There is growing evidence that the delivery of water and sediment from tributaries can, via changes in habitat, elicit biological responses in the recipient channel. In particular, greater habitat heterogeneity near confluences may support biodiversity "hotspots" of broad, ecosystem significance. However, our understanding of what controls tributary impacts is very limited. This hinders effective consideration of confluences in river management practice; a problem that is pressing because of recognition that lotic ecosystems involve bio-physical interactions across networks, rather than along simple drainage lines. To date, field data have been used to specify empirical rules relating the probability of a tributary's impact to basin properties such as relative area. This approach has the advantage that it is easily applied at landscape scales, but because basin characteristics are used as gross surrogates for sediment flux, water flux, and sediment composition, little has been learned about the operation and interaction of these primary controls. We therefore used a 1-D sediment routing model with multiple grain-size fractions to investigate mainstream responses to inputs of water and sediment at confluences. Simulations were performed for different initial conditions, using many combinations of values of three independent parameters: the ratios of tributary to mainstream water flux (QR), sediment flux (FR) and characteristic bed load grain size (DR). A primary distinction can be made between confluences that exhibit aggradation (DR > 2) and those that exhibit degradation (DR < 1 or FR = 0), but in the real world post-confluence degradation is rare and we therefore focus here on aggrading tributaries. We describe the impact of QR, FR and DR on the longitudinal spatial heterogeneity of three indicative characteristics of physical habitat: mainstream grain size, percentage sand and Froude number. To apply our results at broader scales requires specification of relations between QR, FR, DR and easily measured network or basin parameters. This issue is considered, and tentative inferences about the network-scale implications of our results are made.
DE: 0400 Biogeosciences
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1848 Networks
SC: Biogeosciences [B]
MN: 2005 Joint Assembly