Unraveling the impacts of meteorological and anthropogenic changes on sediment fluxes along an estuary-sea continuum

Abstract

Sediment fluxes at the estuary-sea interface strongly impact particle matter exchanges between marine and continental sources along the land-sea continuum. However, human activities drive pressures on estuary physical functioning, hence threatening estuarine habitats and their ecosystem services. This study explores a 22-year numerical hindcast of the macrotidal Seine Estuary (France), experiencing contrasted meteorological conditions and anthropogenic changes (i.e., estuary deepening and narrowing). The hindcast was thoroughly validated for both water column and sediment bed dynamics and showed good capacities to simulate annual sediment budgets observed from 1990 to 2015. We aim at disentangling the relative contributions of meteorological and human-induced morphological changes on net sediment fluxes between the estuary and its adjacent coastal sea. 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. Although intense river discharges induce mud export to the sea, moderate to large river discharges prove to support mud import within the estuary. Wave and river discharge events were less intense in 2005–2015 than in 1990–2000, reducing fine sediment export to the sea. The estuary deepening and narrowing due to human activities increased 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 discharge 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.

Reclamation of Tidal Flats Within Tidal Basins Alters Centennial Morphodynamic Adaptation to Sea‐Level Rise

“…The sediment transport rate is larger and the associated morphodynamic development is faster under smaller grain size, given that sediment transport increases with decreasing grain size (Engelund & Hansen, 1967). Similar findings have been reported in other studies (e.g., Grasso et al, 2021), and this topic merits further in-depth investigation. In contrast, the channels inside the tidal basin become more regularly meandering, the tidal flats become more extensive, and the distributary channels over the ebb-tidal delta become less braided when adding 10% mud to the noncohesive sand (Figure S11 in Supporting Information SI).…”

Analysis of fine grained sand and shale sedimentary characteristics in estuary based on sediment dynamics

“…The channel mainly developed in the middle of the river. The tidal sand bar is in the shape of fine strips, and the segmentation of the sand bar is not obvious, which is agreed with the results proposed by Poppeschi et al (2021) and Grasso et al (2021). In the coarse-grained estuarine model, there are many rivers in the inner-river estuary, the curvature of tidal channel is higher, and the sand bar segmentation is stronger.…”