HR: 15:10h
AN: H42J-07    [PDF]
TI: Network Disturbance Theory: Spatial and Temporal Organization of Physical Heterogeneity in Rivers
AU: * Benda, L
EM: leebenda@aol.com
AF: Earth Systems Institute, 3040 NW 57th St., Seattle, WA 98107 United States
AU: Poff, L
EM: poff@lamar.colostate.edu
AF: Department of Biology, Colorado State University, Fort Collins, CO 80523 United States
AU: Miller, D
EM: danmiller@earthsystems.net
AF: Earth Systems Institute, 3040 NW 57th St., Seattle, WA 98107 United States
AU: Dunne, T
EM: tdunne@bren.ucsb.edu
AF: Donald Bren School of Environmental Science and Management, 3510 Bren Hall University of California, Santa Barbara, CA 93106 United States
AU: Reeves, G
EM: greeves@fs.fed.us
AF: U. S. F. S./Forest Sciences Lab, 3200 Jefferson Way, Corvallis, OR 97331 United States
AU: Pess, G
EM: George.Pess@noaa.gov
AF: National Marine Fisheries Service, 2725 Montlake Blvd East, Seattle, WA 98112 United States
AU: Pollock, M
EM: Michael.Pollock@noaa.gov
AF: National Marine Fisheries Service, 2725 Montlake Blvd East, Seattle, WA 98112 United States
AB: Beginning with the premise that extreme events, or "disturbances" in the parlance of ecologists (i.e., storms, fires, floods, and punctuated erosion and sediment transport), are intrinsic to many landscapes and river systems across the world, we develop new theory on the interaction between disturbances and branching river networks. The interaction of disturbances with network geometry is central to the question of how habitat heterogeneity forms within riverine corridors, a principle underlying the emerging ecosystem concept of "riverscapes". We explore that interaction by examining how tributary confluences interrupt gradual downstream changes in channel morphology leading to locally increased physical heterogeneity. Punctuated erosion during storms and following fires and episodic floods leads to discontinuous inputs of water, sediment, and organic material at confluences that modify channel and valley-floor morphology for tens of meters to kilometers, including substrate sizes, channel hydraulic geometry, floodplain widths, fans, terraces, and log jams. Based on 14 studies that documented these confluence effects at 168 junctions spanning 6 orders of magnitude in drainage area, it appears that the probability of confluence effects increases with increasing size ratio of tributary to mainstem river. This simple scaling relationship indicates that the downstream increase in tributary basin size found in many watersheds results in a downstream increase in the spacing between confluences that have morphological effects, identifying a control on the spatial scale of confluence-related heterogeneity in rivers. Therefore, when a river network is viewed as a population of tributaries and confluences, the extent to which a network interrupts downstream continua of physical and biological processes (and the degree of habitat heterogeneity) should depend on network geometry, basin shape, drainage density, and basin size. For example, oval-shaped basins (containing dendritic networks) should favor confluence effects and therefore increased heterogeneity while rectilinear basins (containing trellis networks) should not. Moreover, basins with higher drainage (and junction) density should lead to a higher degree of network-generated morphological heterogeneity. The frequency and magnitude of floods and accelerated sediment supply that maintain confluence effects - in probability distributions containing extreme events - should also scale with basin size, leading to an age distribution of confluence-related landforms (i.e., fans, terraces, bars) that is predicted to be dominated by older features in headwaters. Additionally, the age distribution of confluence-related features should become younger with increasing distance downstream. These new theoretical insights yield testable hypotheses that should motivate and support studies on the role of extreme events, or disturbances, in river systems.
DE: 1824 Geomorphology (1625)
DE: 1848 Networks
DE: 1869 Stochastic processes
SC: Hydrology [H]
MN: 2003 Fall Meeting