UNDERSTANDING SEDIMENT INTERCEPTION BY BIOTA: PHYSICAL DRIVERS AND OVERALL IMPORTANCE FOR COASTAL SEDIMENTATION (Invited Presentation)

Aquatic vegetation is known to alter rates of sedimentation by changing effective settling rates through its impacts on drag and turbulence and by directly intercepting (i.e., capturing) sediment on stems and leaves. While many efforts in ecogeomorphology have invested in understanding how vegetation changes flow properties and effective settling, sediment interception remains relatively poorly understood. We undertook a multifaceted approach to understand how physical (i.e., Reynolds number, canopy characteristics, sediment characteristics) and biological (i.e., presence or absence of biofilm) factors govern sediment interception magnitudes. Controlled experiments with vegetation substitutes in a laboratory flume allowed us to isolate effects of individual drivers. A synthesis of these experimental results with those of other flume studies (84 total) allowed us to test different hypotheses, grounded in a Buckingham-Pi dimensional analysis, about the appropriate functional form for an expression for particle interception over different Reynolds number regimes and over a wider range of environmental parameters than we were able to investigate in our flume studies. Last, tracer experiments in two field flumes constructed around intact vegetation communities in the Wax Lake Delta, Louisiana enabled us to evaluate whether this functional relationship was a satisfactory predictor of particle interception in the more complex field setting. Our findings suggest that 1) vegetation density has a larger effect size on particle interception than Reynolds number within a range of Reynolds numbers realistic for coastal settings, 2) the presence of biofilm has a positive effect on interception that can exceed variability due to some physical factors, and 3) particle interception is likely to be a small component of coastal sedimentation budgets, particularly relative to effective settling. Further, our derived functional form of the equation for particle interception was consistent with those resulting from previous flume studies of interception involving multiple stems.