Impact of Chronic and Massive Resuspension Mechanisms on the Microphytobenthos Dynamics in a Temperate Intertidal Mudflat

Abstract

Microphytobenthos (MPB) resuspension is a key mechanism in the transfer of organic matter from productive intertidal mudflats to terrestrial and marine systems. In this study, we infer on the contribution of physical and biological factors involved in the MPB resuspension. We use a physical‐biological coupled model forced by realistic meteorological and hydrodynamical forcings to simulate chronic (without any concomitant sediment resuspension) and massive (driven by bed failure) resuspension over a year. The model simulates mud surface temperature, MPB growth, and grazing by the gastropod Peringia ulvae. The model suggests that MPB resuspension is the highest in spring tides and at the flood beginning due to high current velocity and low water heights that promote waves‐sea bottom interactions. The seasonal export of MPB biomass is the highest in spring, up to threefold higher than in summer when the export is the lowest. The simulated seasonal dynamics of MPB resuspension results from the MPB biomass concentration in the sediment, physical disturbances, and the bioturbation activity by P. ulvae. Annually, 43% of the simulated MPB primary production is resuspended. The MPB resuspension (60.8 g C·m−2·yr−1) exceeds the loss by P. ulvae grazing (41.1 g C·m−2·yr−1). The model suggests that chronic and massive resuspension events are important in the synoptic to seasonal MPB dynamics in temperate intertidal mudflats. Accounting for such processes in the carbon budget assessment in the land‐ocean interface could bring new insights to our understanding of the role played by MPB in the coastal carbon cycle.

Mapping the Intertidal Microphytobenthos Gross Primary Production, Part II: Merging Remote Sensing and Physical-Biological Coupled Modeling

“…The spatial and temporal distribution of MPB over mudflats is highly variable, as it is driven by highly variable physical [light, mud surface temperature (MST), tides, waves, and current] and biological (grazing, biostabilization, and bioturbation) conditions (e.g., Admiraal, 1984;Blanchard et al, 1996;MacIntyre et al, 1996;Underwood, 2001; Morris and Kromkamp, 2003;Sahan et al, 2007;Salleh and McMinn, 2011;Kwon et al, 2014;Orvain et al, 2014a,b;Savelli et al, 2019). Such a variability impedes any accurate and robust assessment of the role played by MPB at the scale of the whole mudflat ecosystem and of its contribution to the carbon cycle.…”

“…Recently, remotely sensed estimates of vegetation index and of in water MPB chlorophyll a (Chl a) concentration were compared to model outputs in order to assess the model ability to simulate realistic MPB biomass levels over the Brouage mudflat (Savelli et al, 2018(Savelli et al, , 2019. Such a comparison does not exist for MPB PP.…”

Movement of Microphytobenthos and Sediment Between Mudflats and Salt Marsh During Spring Tides

“…a and sediment concentrations on the salt marsh will be a product of water depth and wave energy (Leonardi et al, 2015). The wind speed values during this study were less that those found by de Jonge and van Beusekom (1995) to cause major resuspension, but even lower speeds can resuspend surface cells and sediments loosely associated in a "fluff " layer (Savelli et al, 2019). Such resuspension of biofilm material also weakens the potential for further biostabilization, leading to further resuspension (Ubertini et al, 2015).…”

“…a concentration in the top 2-mm sediment surface before and after high-tide emersion periods during spring tides on both the transition and the salt marsh. Other studies in the Colne estuary have found significant "wash away" from mudflats during tidal cover (Bellinger et al, 2009;Taylor et al, 2013), and modeling shows this can be a significant process in MPB biomass dynamics on mudflats (Savelli et al, 2019). High levels of microspatial variability in MPB biomass (Spilmont et al, 2011;Taylor et al, 2013) may mask individual localized losses on any particular patch of sediment.…”

“…The negative effect of increased tidal range on Chl. a concentrations on the sediment surface is potentially associated with water depth and the wind speed (de Jonge and van Beusekom, 1995;van der Wal et al, 2010;Savelli et al, 2019). Wind speed is positively correlated with wave height at the study site (Redzuan, 2017), so that increases in suspended Chl.…”