Effect of long-term water velocity changes on streambed biofilm activity

This study demonstrates that long-term changes in water velocity affected the amount of biofilm biomass associated with a sand-free cobble streambed. Streambed biofilms were grown and acclimated to several different water velocities in an artificial stream. The rate at which each acclimated biofilm removed substrate from the water column was assessed by performing well-controlled, batch biodegradation tests. Substrate removal rates for each tested acclimation velocity were corrected for mass transport effects. Any differences in the mass-transport-corrected removal rates for the acclimated biofilms were due to variations in streambed biofilm biomass. Experimental results indicated that higher streambed biofilm biomass levels were found at the faster acclimation velocities. Such results imply that the rate of biodegradable contaminant removal in shallow biofilm-dominated streams is a function of the present water velocity (determines mass transport regime) and historical water velocities (determines streambed biofilm biomass levels).