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Geophysical Monograph Series

 

Keywords

  • fluvial geomorphology
  • sediment transport
  • fish habitat
  • fine sediment
  • restoration
  • human impact

Index Terms

  • 1825 Hydrology: Geomorphology: fluvial
  • 1862 Hydrology: Sediment transport
  • 1856 Hydrology: River channels
  • 1813 Hydrology: Eco-hydrology

Article

GEOPHYSICAL MONOGRAPH SERIES, VOL. 194, PP. 337-352, 2011

Salmon as Biogeomorphic Agents in Gravel Bed Rivers: The Effect of Fish on Sediment Mobility and Spawning Habitat

M. A. Hassan, E. L. Petticrew, D. R. Montgomery, A. S. Gottesfeld, and J. F. Rex

Spawning salmon have been known to affect streambed texture, influence sediment transport, and play an important geomorphological role in streams and rivers. We examined the impact of salmon and floods on channel morphology, bed material dispersion and yield, bed surface texture and stability, fine-sediment dynamics, and nutrient retention of small gravel bed streams. Repeated channel surveys indicate that salmonids change postflood channel morphology, creating a hummocky bed surface through several cycles of redd creation. In streams with dense populations of sockeye salmon, the whole surface of spawning reaches may be modified, bars are excavated, and pools are filled. Analyses of coarse and fine sediment show that salmon increase sediment mobility by disturbing fine materials and preventing the development of an armored bed surface. Carbon-nitrogen ratios of the suspended sediment at the field sites and the gravel stored sediment in the flume indicate that salmon carcasses are the primary source of nitrogen to these systems. Further, the data suggest that the fine-grain bed sediments, in particular, are good retainers of salmon organic matter and thus function as nutrient stores for subsequent salmon generations. The study shows a sharp increase in the biochemical oxygen demand when salmon decay products combine with fine sediment and settle to the gravel bed; thus, the influx of nutrients and reworked gravel may aid in sustaining the salmon stocks and other biotic activity. Consequently, bed excavation by salmon plays a major geomorphic role in streams and improves the overall health of the ecosystem.

Citation: Hassan, M. A., E. L. Petticrew, D. R. Montgomery, A. S. Gottesfeld, and J. F. Rex (2011), Salmon as biogeomorphic agents in gravel bed rivers: The effect of fish on sediment mobility and spawning habitat, in Stream Restoration in Dynamic Fluvial Systems: Scientific Approaches, Analyses, and Tools, Geophys. Monogr. Ser., vol. 194, edited by A. Simon, S. J. Bennett and J. M. Castro, pp. 337–352, AGU, Washington, D. C., doi:10.1029/2010GM000968.

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