HR: 1340h
AN: H13D-1534    [Abstracts]
TI: "Sticky Business": the Influence of Surface Biofilm on Particle Deposition and Infiltration in Streams
AU: * Salant, N L
EM: nira@alum.dartmouth.org
AF: Department of Geography University of British Columbia, #217-1984 West Mall, Vancouver, BC V6T 1Z2, Canada
AU: Hassan, M A
EM: mhassan@geog.ubc.ca
AF: Department of Geography University of British Columbia, #217-1984 West Mall, Vancouver, BC V6T 1Z2, Canada
AB: Fine particulate matter is an important component of many streambed processes. For example, the deposition and infiltration of fine inorganic sediment has been repeatedly shown to degrade benthic habitat for fish and other organisms (Hynes, 1970). In contrast, fine organic particles are a significant source of carbon to benthic organisms (Webster et al., 1987). The mechanisms and rates of particle entrainment and deposition are highly complex and ill-predicted by simple physical relations. For example, a number of field studies have shown that measured rates of particle deposition often differ from still-water particle settling velocities calculated from particle size and density (e.g. Cushing et al., 1993). Several studies have proposed that adhesion of particles to surface biofilm may explain why deposition rates are faster than predicted, but few have investigated this phenomenon (Battin et al., 2003). In addition, although biofilms have been shown to significantly alter near-bed and interstitial flow velocities (Dodds and Biggs, 2002), the effect of these changes on particle depositionhas not been explored. Biofilm is pervasive in rivers and streams throughout the world, thus it may play an important, and heretofore underestimated, role in the deposition of fine particles to the streambed. This study tests the hypothesis that biofilm amount and structure may alter fine particle deposition, entrainment, and infiltration by either direct adhesion or by changes to near-bed hydraulics. A series of experiments are being conducted in a small recirculating flume to test how the amount and structure of surface biofilm influences the water column distribution, surface deposition, and infiltration of fine particles under two different flow levels (‘high' and ‘low'). Two types of surface biofilm are being tested: open-weave, filamentous assemblages and low-profile, mucilaginous forms; both are compared to a reference substrate without biofilm. Natural rocks hosting filamentous assemblages are collected from nearby channels and used to replace the surface layer of flume substrate. Low-profile forms are cultivated on a cobble-gravel substrate in an artificial stream system and tested at each of three growth stages. Immediately following a dose of fine particles (< 125 µm ground silica), short-term rates of particle deposition are determined by continuous measurements of near-bed particle concentrations. Hourly vertical concentration, grain size profiles, and 3-D velocity profiles are measured for the duration of the experiment (8h). Infiltration rate is determined from bed samplers sealed from the flow at 1, 2, 4, and 8 hours. At the end of each experiment, three surface samples are collected and analyzed for ash-weight, ash-free dry weight, and chlorophyll a. Four stratified bed samples and samplers are removed, dried, sieved and weighed to determine the amount and depth of fine particle infiltration into the bed with time and surface condition. Preliminary results indicate that particle deposition is significantly enhanced by biofilm presence relative to surfaces without biofilm; this effect is greater for mucilaginous forms. However, near-bed shear stresses and velocity profiles are not significantly altered by either mucilaginous or filamentous forms; bed topography has a dominant effect. Results also indicate that particle deposition is more strongly influenced by surface condition (e.g. particle size, biofilm presence) than by flow level or duration. Particle infiltration below the surface, however, is more a function of pore space and flow level than biofilm coverage on the streambed surface.
DE: 1813 Eco-hydrology
DE: 1838 Infiltration
DE: 1851 Plant ecology (0476)
DE: 1861 Sedimentation (4863)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting