1. An Integration of Numerical Modeling and Paleoenvironmental Analysis Reveals the Effects of Embankment Construction on Long‐Term Salt Marsh Accretion.
- Author
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Pannozzo, N., Smedley, Rachel K., Chiverrell, Richard C., Carnacina, Iacopo, and Leonardi, Nicoletta
- Subjects
THERMOLUMINESCENCE dating ,NUMERICAL integration ,SALT marshes ,OPTICALLY stimulated luminescence dating ,EMBANKMENTS ,ESTUARY hydrodynamics - Abstract
There are still numerous uncertainties over the influence of anthropogenic interventions on salt marsh dynamics. This study uses the Ribble Estuary as a test case and an integrated approach of numerical modeling and paleoenvironmental analysis to investigate the contribution of embankment construction to long‐term marsh accretion. Accretion rates derived using optically stimulated luminescence dating (OSL) were combined with a multi‐proxy paleoenvironmental investigation on sediment cores extracted from the salt marsh, the mobile seafloor of the central Irish Sea and the river catchment area. These analyses provided a first evolutionary perspective on the Ribble Estuary preceding any management interventions. The paleoenvironmental analyses were then compared to simulations conducted using the hydrodynamic model Delft3D to investigate the effects of embankment construction on estuarine hydrodynamics and morphodynamics of the salt marsh over the period constrained by the OSL. The numerical simulations showed that embankments were responsible for an overall intensification of the ebb currents in the system which promoted sediment export. The paleoenvironmental analyses showed that the marsh has been accreting at a rate of 4.61 to 0.86 cm yr−1 over the last ca. 190 years and that the high sedimentation rate was caused by a naturally high rate of sediment supply. The model‐data integration showed that the effects of the embankment construction on sediment transport did not compromise the long‐term resilience of the salt marsh because of the high rates of sediment supply and the river dredging which enhanced the flood dominance of the tide near the tidal flat. Plain Language Summary: Salt marshes are important ecosystems and can help protect the coastline from flooding. Sediment availability is important to help the establishment and maintenance of salt marshes. Large quantities of sediments can help salt marshes to expand and grow in elevation. Instead, the removal of sediments can cause marsh erosion. Management interventions along a coastline can influence the movement of sediments and determine how much sediments can reach (or not reach) the marsh platform. This study found that in the Ribble Estuary, a site renowned for its high rate of sediment supply, the construction of embankments promoted sediment export out of the estuary, but the high sedimentation rates caused by a natural high rate of sediment supply from the ocean, aided by river dredging, allowed long‐term marsh accretion despite the embankments presence, meaning that the marsh continued to grow in elevation over time. Key Points: The construction of embankments along an estuary can reduce salt marsh accretion by promoting sediment exportEmbankments do not necessarily compromise the long‐term resilience of salt marshes when high rates of sediment supply are presentChannel dredging can promote sediment import and reduce the effects of embankment construction on sediment transport [ABSTRACT FROM AUTHOR]
- Published
- 2022
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