HR: 1340h
AN: H53B-1230    [Abstracts]
TI: Geomorphic and Ecologic Interactions of Large Wood and Pacific Salmonid Redds Across Habitat Units on a Regulated California River
AU: * Senter, A E
EM: aesenter@ucdavis.edu
AF: University of California at Davis, 1 Shields Avenue, Davis, CA 95616, United States
AU: Pasternack, G B
EM: gpast@ucdavis.edu
AF: University of California at Davis, 1 Shields Avenue, Davis, CA 95616, United States
AB: Large wood pieces (LW, >1 m length, >10 cm diameter) are important components of geomorphic and ecologic dynamics within river systems. Physical presence of LW within a bankful channel can influence flow, sediment deposition and scour patterns, and storage of organic matter, whereas ecologic elements of LW include hydraulic variability, habitat, and nutrient sources for aquatic species. In regulated rivers hydrologic connectivity has been lost and ecosystem dynamics disrupted, yet lower reaches continue to serve as habitat, and now as headwaters, for a myriad of species including anadromous salmonids returning to spawn and complete their life-cycles. Regardless of condition, lower reaches of regulated rivers must serve as ecosystem hotspots in response to anthropogenic manipulations of the watershed. In this research, interactions between large wood, Pacific salmonid redds, and aquatic habitat units (i.e. riffle, run, glide, and pool as defined by depth and velocity) were explored in a regulated, mid-sized (i.e. channel width is greater than most tree heights), Mediterranean-climate (i.e. smaller, softer-wood trees dominate the landscape) river draining a portion of the Sierra Nevada of California. Because watershed connectivity has been severed, riparian zones highly altered, and LW removal remains common, LW levels are thought to be very low in regulated ecosystems. The study hypothesis was that a dynamic and healthy ecosystem might have areas of low, optimal, and overabundances of wood, which would correlate to low, optimal, and low redd abundances, respectively. On the other hand, in an ecosystem where connectivity is diminished, an increase in the amount of LW may potentially convert otherwise unsuitable spawning habitat to highly preferred spawning habitat. In exploring the dynamics of wood and redds at the habitat unit scale, characteristics of 530 LW pieces, locations of 650 redds, and habitat units along a 7.5 km reach directly below a dam were mapped during a spawning season. Findings suggest that fall-run Chinook salmon preferentially spawned in riffles often where LW was present, but also spawned in glides and occasionally runs, and across all these habitats both with and without LW. No spawning was observed in pools. LW was present in all habitat types, but not in every habitat unit occurrence. There were no areas in the study reach with an overabundance (i.e. complete coverage of channel bed) of LW, nor did LW presence appear to prohibit redd activity in spawning habitats. Further research is needed to determine what quantities of LW might be considered optimal in below-dam ecosystems where suitable spawning habitat is needed.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 1813 Eco-hydrology
DE: 1825 Geomorphology: fluvial (1625)
DE: 1856 River channels (0483, 0744)
SC: Hydrology [H]
MN: 2007 Fall Meeting