Influence of tidal forcings on microphytobenthic resuspension dynamics and sediment fluxes in a disturbed coastal environment.

The resuspension dynamics of microphytobenthos (MPB) and sediment fluxes were investigated in a disturbed coastal environment by employing an in situ mooring system. We aimed to identify the interrelationship between microalgal biomass and sediment particles in aspect of their (de)coupling mechanism in a tidal channel system. In specific, the Chl-a (as a proxy of MPB biomass) and the suspended sediment concentration (SSC) were simultaneously measured under natural tidal conditions at different time scales, encompassing daily to fortnightly variations. Looking for the sediment dynamics, the SSC showed a strong positive correlation (p < 0.001) with the Reynolds stress; however, this relationship was not observed for benthic Chl-a. This could be due to more dynamic characteristics of the smaller biological cells, i.e., the decoupled benthic Chl-a from the sediment particles might randomly distribute in the turbid water column above the tidal channel. Notably, the iteration between MPB coupling (prevailing in spring) and segregation (prevailing in neap) with the sediment particles across the flood and ebb tidal cycles was evident during the study period. Meantime, the onshore flux of suspended sediment was almost balanced by its offshore flux, but that of Chl-a appeared to be unbalanced due to an excessive onshore transport. Altogether, the study area seems to experience a time lag in resuspension between MPB and sediment, followed by biological trapping in the tidal channel system, which would support a productive shallow water environment. The present study is the first to address the tidal resuspension of benthic microalgae in relation to sediment dynamics in a disturbed coastal environment of the Yellow Sea.