Short-Term Bed-Level Dynamics of an Intertidal Shoal After Large-Scale Nourishment

Abstract

Erosion and habitat loss on intertidal flats are increasingly fought through large-scale sediment nourishment. Yet the impact of nourishment on short-term bed-level dynamics remains poorly quantified. Daily erosion–accretion events shape the immediate physical environment experienced by benthic infauna: repeated burial and re-exposure set the physical bounds of the ecological niche, making bed-level dynamics a key indicator of habitat suitability that annual bathymetric surveys fail to capture. We evaluate the impact of a large-scale (1.13 million m3) nourishment at Roggenplaat in the Eastern Scheldt, Netherlands (2019) on bed-level dynamics, comparing daily bed-level changes between nourished and adjacent non-nourished areas with millimetre precision over five years. We assess three dimensions: persistence (temporal memory of the bed-level state), volatility (the frequency and magnitude of daily change), and sensitivity (the coupling between forcing and bed-level response). Two key insights emerge. First, nourished areas showed larger daily fluctuations, but event-driven bed-level changes were indistinguishable between treatments. Second, nourishment shifted the forcing balance: storm events dominate erosion in non-nourished areas, whereas in nourished areas, spring tides alone drive both accretion and erosion. Ecologically, the elevated daily disturbance is expected to act as a community-assembly filter, selecting for mobile infauna rather than excluding colonisation. These findings suggest that, although nourishment elevates day-to-day bed-level activity, its episodic disturbance regime remains compatible with the native bed-level regime, with implications for benthic habitat assessment at future restoration sites.

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