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Title: Large-scale effects induced by salt marsh and seagrass loss in shallow tidal lagoons
Author: Donatelli, Carmine
ISNI:       0000 0004 9358 6265
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2020
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Global environmental change is currently threatening many estuaries and tidal lagoons worldwide with significant ecological and socio-economical losses for our coastal communities. Several studies have emphasized the coastal protection functions of intertidal and subtidal vegetated surfaces, but their influence on the resilience of tidal back-barrier basins is understudied. Understanding the non-linear feedbacks and the large-scale effects induced by the disappearence of salt marshes and seagrass beds on sediment dynamics and hydrodynamic circulation is a critical step to predicting future impacts of sea-level rise on coastal areas and is highly topical given the current interest in wetland restoration around the world. Here, I have first explored the effects associated with salt marsh removal on sediment transport processes and tidal dynamics in shallow estuaries, employing a metaanalysis of high-resolution numerical modeling results in six lagoon-type estuaries spanning the entire Northeastern shore of the USA. In the second part of this work, I have unraveled the fate of salt marsh-derived sediments generated by wave-induced edge erosion in a small estuary located in New York City using the numerical framework COAWST. Finally, I have explored how changes in bottom friction associated with seagrass disappearance affect the sediment budget of coastal bays through local and regional changes in hydrodynamics. The main results from this dissertation highlighted that: I) salt marsh loss reduces the ability of shallow estuaries to retain sediment inputs through changes in the regional scale hydrodynamics; II) a fascinating non-linear relationship exists between salt marsh sediment trapping capacity and salt marsh size, which strongly affects the adaptive capacity of these coastal ecosystems to sea-level rise; III) only a small fraction of the sediment generated by salt marsh lateral erosion is trapped by vegetated marsh platforms; IV) reductions in seagrass coverage destabilize estuarine systems, increasing the flood phase in areas affected by seagrass disappearance and increasing bed-shear stress values across the entire back-barrier basin; V) seagrass beds reduce the wave thrust acting along salt marsh boundaries; VI) the location of the seagrass patch, in addition to its areal extent, plays an important role in attenuating wave energy along the shoreline; and VI) seagrass presence decreases the suspended sediment concentrations in the water column and consequently the sediment stock on salt marsh platforms.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral