HR: 12:05h
AN: H42A-08    [Abstracts]
TI: Watershed processes, fish habitat, and salmonid distribution in the Tonsina River (Copper River watershed), Alaska
AU: * Booth, D B
EM: dbooth@stillwatersci.com
AF: Stillwater Sciences, 2855 Telegraph Avenue, Berkeley, CA 94705, United States
AU: * Booth, D B
EM: dbooth@stillwatersci.com
AF: Department of Earth and Space Sciences, University of Washington Box 351310, Seattle, WA 98195, United States
AU: Ligon, F K
EM: frank@stillwatersci.com
AF: Stillwater Sciences, 2855 Telegraph Avenue, Berkeley, CA 94705, United States
AU: Sloat, M R
EM: matt@stillwatersci.com
AF: Stillwater Sciences, 2855 Telegraph Avenue, Berkeley, CA 94705, United States
AU: Amerson, B
EM: byron@stillwatersci.com
AF: Stillwater Sciences, 2855 Telegraph Avenue, Berkeley, CA 94705, United States
AU: Ralph, S C
EM: ralph@stillwatersci.com
AF: Stillwater Sciences, 2855 Telegraph Avenue, Berkeley, CA 94705, United States
AB: The Copper River watershed is a critical resource for northeastern Pacific salmon, with annual escapements in the millions. The Tonsina River basin, a diverse 2100-km² tributary to the Copper River that supports important salmonid populations, offers an opportunity to integrate watershed-scale channel network data with field reconnaissance of physical processes and observed distribution of salmonid species. Our long-term goals are to characterize habitats critical to different salmonid life stages, describe the geologic context and current geologic processes that support those habitats in key channel reaches, and predict their watershed-wide distribution. The overarching motivation for these goals is resource conservation, particularly in the face of increased human activity and long-term climate change. Channel geomorphology within the Tonsina River basin reflects inherited glacial topography. Combinations of drainage areas, slopes, channel confinement, and sediment-delivery processes are unique to this environment, giving rise to channel "types" that are recognizable but that do not occur in the same positions in the channel network as in nonglaciated landscapes. We also recognize certain channel forms providing fish habitat without analog in a nonglacial landscape, notably relict floodplain potholes from once-stranded and long-melted ice blocks. Salmonid species dominated different channel types within the watershed network. Sockeye salmon juveniles were abundant in the low-gradient, turbid mainstem; Chinook juveniles were also captured in the lower mainstem, with abundant evidence of spawning farther downstream. Coho juveniles were abundant in upper, relatively large tributaries, even those channels with cobble-boulder substrates and minimal woody debris that provide habitats more commonly utilized by Chinook in low-latitude systems. More detailed field sampling also revealed that patterns of species composition and abundance appeared related to small-scale differences in physical habitat features. For example, juvenile coho salmon used interstitial spaces between unembedded cobbles and boulders but were absent from adjacent habitat with high embeddedness. Thus high delivery rates of coarse sediment sustain critical rearing habitat that would otherwise be relatively inhospitable to fish. Using Chinook salmon as a focal species, we have integrated field- and map-based analyses to predict basin- scale geomorphic and biological constraints on the distribution of suitable spawning and rearing habitat. These analyses provide rapid guidance for where focused investigations or monitoring of key habitats should occur, a particularly important outcome where watersheds are large and field logistics are challenging. The predicted extent of suitable stream habitat within the study area represents a relatively minor fraction (ca. 10 percent) of the total stream channel network, suggesting that production of salmon from the study area depends on the maintenance of quality habitat in discrete, and relatively rare, reaches.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 1630 Impacts of global change (1225)
DE: 1825 Geomorphology: fluvial (1625)
DE: 1834 Human impacts
DE: 1879 Watershed
SC: Hydrology [H]
MN: 2007 Fall Meeting