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

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.