Sediment resuspension enhances nutrient exchange in intertidal mudflats

Intertidal coastal sediments are important centers for nutrient transformation,regeneration, and storage. Sediment resuspension, due to wave action or tidalcurrents, can induce nutrient release to the water column and fuel primaryproduction. Storms and extreme weather events are expected to increase due toclimate change in coastal areas, but little is known about their effect on nutrientrelease from coastal sediments. We have conducted in-situ sedimentresuspension experiments, in which erosion was simulated by a stepwiseincrease in current velocities, while measuring nutrient uptake or release infield flumes positioned on intertidal areas of a tidal bay (Eastern Scheldt) and anestuary (Western Scheldt). In both systems, the water column concentration ofammonium (NH4+) and nitrite (NO2−) increased predictably with greater erosionas estimated from pore water dilution and erosion depth. In contrast, thephosphate (PO43−) dynamics were different between systems, and those ofnitrate (NO3−) were small and variable. Notably, sediment resuspension causeda decrease in the overlying water PO43− concentration in the tidal bay, while anincrease was observed in the estuarine sediments. Our observations showed thatthe concentration of PO43− in the water column was more intensely affected byresuspension than that of NH4+ and NO2−. The present study highlights thedifferential effect of sediment resusp