Investigating Fine Particle Resuspension through Dynamic Flow and Sediment Mobilization Laboratory Experiments

Fine particles are prevalent in rivers and their transport directly influences biogeochemical processes and the function of stream ecosystems. We used a custom hydraulic system consisting of sand with separate influent and effluent surface water regions to study fine particle tr ansport through sediments, representing hyporheic exchange flow . The surface water divider reached approximately five centimeters into the sediment forcing water (and fine particles) to flow through the sand without sediment mobilization. Fluorescent f ine particles (DayGlo AX-11-5 Aurora Pink Pigment) were added under steady low flow conditions . The n 4 experiments were performed attempting to resuspend particles: 1) increase d steady flow, 2) oscillating flow without altering the flow direction, 3) oscillating flow with 80% forward and 20% backward flow directions , and 4) manual sediment disturbance on the influent side. During each experiment we monitored the effluent and influent concentrations and spatial fine particle deposition levels within the sediment. Fine particle remobilization was not observed during increased steady flow or oscillating flow conditions. However, when oscillating flow was increased and caused water to flow both forw ard and backwards, increased fine particles were observed in the influent water reservoir . Particle resuspension could have resulted from either the change in flow direction that dislodged deposited particles or the low levels of sediment mobilization obser ved on the influent side . The last experiment with a systematic disturbance of the top one inch of the influent sediment resulted in substantial fine particle resuspension, observable within the influent, effluent, and sediment deposition patterns. These results emphasize the transient retention of fine particles in streambed sediments and the key role that sediment mobilization plays in fine particle resuspension.