Conceptualization of Sediment Transfers Between Macrotidal Estuaries and
Coastal Seas
Abstract
Sediment fluxes at the estuary-sea interface modulate estuary
morphologies and impact particle matter exchanges between marine and
continental sources along the land-sea continuum. However,
meteorological forcing (e.g., extreme events) and human activities
(e.g., estuary deepening) drive pressures on estuary physical
functioning, hence threatening estuarine habitats and their ecosystem
services. There is an increasing societal need to better predict the
potential trajectories of estuarine sediment fluxes resulting from
natural and anthropogenic pressures. Nevertheless, it is difficult to
derive generalizations from site-specific studies; thus, multi-site
approaches appear necessary to move toward a global conceptualization of
estuarine sediment transfers. This study explores 10-year numerical
hindcasts of three contrasted macrotidal estuaries (Gironde, Loire, and
Seine estuaries; France) to disentangle the relative contributions of
hydrometeorological and morphological forcing on net sediment fluxes
between estuaries and coastal seas. Our results highlight that intense
wave events induce fine sediment (≤100 μm) export to the sea but coarser
sediment (≥210 μm) import within the estuary. Remarkably, moderate to
large river flows support mud import within the estuary. In addition,
the Seine Estuary morphological changes due to human activities (i.e.,
estuary deepening and narrowing) increase fine sediment import within
the estuary, shifting the estuary from an exporting to importing system.
We propose a conceptualization of mud flux response to river flow and
wave forcing, as well as anthropogenic pressures. It provides valuable
insights into particle transfers along the land-sea continuum,
contributing to a better understanding of estuarine ecosystem
trajectories under global changes.