Biostabilization in Sandy Carbonate Environments Detected from Multi-Seasonal Turbidity Time Series

Shamim Mohammad Murshid, Louisiana State University, Baton Rouge, LA, United States and Giulio Mariotti, Louisiana State University, Baton Rouge, United States
We investigated how microbial mats can reduce sediment resuspension in sandy carbonate environments. We collected hourly wave measurements and near-bed turbidity from July 2017 to March 2018 in Hamelin Pool, a shallow microtidal embayment in Western Australia. We searched for the presence of biostabilization by looking for seasonal variations in sediment dynamics. First, we considered the relationship between burst-averaged turbidity and burst-averaged bed shear stress. A lower turbidity for the same bed shear stress was taken as an indicator of biostabilization. Second, we considered the rate of ripple migration. The latter was measured using a novel approach, i.e., by calculating the rate at which the phase lag between the pressure signal and the turbidity signal changed within a wave burst. This analysis was possible because the turbidity signal had a clear modulation at the dominant wave frequency (2-3 s), which indicates that the turbidity was capturing the oscillatory sediment plume over wave ripples. The ability to record this high-frequency signal was likely due to the absence of mud, whose presence, even in small amounts, creates a background noise and prevents to record within a single wave cycle. As for the first method, a reduction in the ripple migration rate for a given bed shear stress was taken as an indicator of biostabilization.