| Vegetation has been shown to affect the hydrodynamics of surrounding water, including friction velocity, Reynolds number, and flow roughness. Recent studies indicate that benthic algae may have a similar effect in streams. Algal assemblages were allowed to colonize flumes containing substrates of different sizes. Algal species, number, volume, mat height, and dry weight biomass were measured over time. The velocity profiles of the flumes were converted to friction velocity, roughness height, and mixing length using theoretical equations. The species composition, number and volume of cells per unit surface area, and dry weight biomass of the assemblages were similar among flumes. Algal growth was accompanied by increases in friction velocity, roughness height, and mixing length, but a decrease in near-substrate velocity. The height of the algal mat appeared to be influenced by the roughness height, and possibly limited by a maximum velocity or shear upon the upper algal cells. The results suggest that increases in hydrodynamic parameters occur with mat development (and may be assemblage-specific), but do not appear to affect the species composition of the assemblages. These results may be indicative of "baseline" development, which is altered by physical and/or biological stresses under field conditions. |
