Scaphirhynchus Conference: Alabama, Pallid, and Shovelnose Sturgeon

St. Louis, Missouri, 11-13 January 2005

28.  QUANTIFICATION OF FLUID AND BED DYNAMICS FOR CHARACTERIZING BENTHIC PHYSICAL HABITAT IN LARGE RIVERS.

David Gaeuman, National Research Council Associate, Columbia Environmental Research Center, 4200 New Haven Rd., Columbia, MO 65201; Phone 573-441-2978; FAX 573-876-1904; dgaeuman@usgs.gov

Robert B. Jacobson, Columbia Environmental Research Center, 4200 New Haven Rd., Columbia, MO 65201; Phone 573-876-1844; FAX 573-876-1904; rjacobson@usgs.gov

Harold E. Johnson, III, Columbia Environmental Research Center, 4200 New Haven Rd., Columbia, MO 65201; Phone 573-441-2976; FAX 573-876-1904; hejohnson@usgs.gov

Sturgeon are believed to use benthic habitats in areas where mean flow velocities are relatively high.  Because near-bed environmental conditions in these areas are extremely difficult to measure, these habitats are frequently summarized in terms of flow depth, mean flow velocity, and substrate composition.  However, dynamic conditions at the stream bed, including substrate stability, sediment transport intensity, and the structure of near-bed fluid flow, may be more directly relevant when characterizing benthic habitat.  Recent studies in the Lower Missouri River demonstrate the feasibility of using acoustic Doppler technology to characterize dynamic benthic habitats by measuring near-bed sediment transport intensity.  The apparent velocity of the stream bed due to near-bed sediment transport is measured using the bottom-track positioning capability of a commercial acoustic Doppler current profiler (ADCP), compared to precise global positioning system (GPS) positions.  Physical sampling of bedload sediment transport confirmed that the apparent bed velocity corresponds to the transport of sandy sediment near the stream bed.  High rates of bed-sediment transport presumably constitute rather severe environmental conditions from the standpoint of benthic organisms.  Our analyses also show that ADCP bed velocities are representative of fluid flow velocities in the near-bed region, so that fluid velocity measurements can be extended closer to the bed than is conventionally possible.  Acoustic assessments of benthic conditions in the Missouri River were conducted at scales ranging from the stream reach to individual bedforms.  Preliminary reach-scale results suggest that relatively high sediment transport intensities can occur in habitat units where sturgeon are commonly located.  At the local scale, transport intensities are greatest near bedform crests, and least in the intervening troughs.  Zones of low transport intensity were found to persist in areas with extremely high mean bed velocities and high fluid shears stresses.  Opportunistic use of these low-intensity zones could potentially allow sturgeon to make use of portions of the channel where the average local conditions on the bed are severe.