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Physical drivers of saltmarsh change in enclosed microtidal estuaries

Physical drivers of saltmarsh change in enclosed microtidal estuaries
Physical drivers of saltmarsh change in enclosed microtidal estuaries
Estuaries are among the most biologically productive ecosystems on the planet, per unit area, with intertidal habitats and particularly saltmarshes providing a variety or ecosystem services and supporting large numbers of both primary and secondary producers. These habitats are globally important and are found throughout tropical to temperate climates. Micro-tidal estuaries are found throughout the world and particularly sensitive to sea-level rise, as they are limited in their ability to adjust and are considered vulnerable to future changes .Hence, at a broad scale, understanding the drivers and mechanisms of saltmarsh change in micro-tidal systems is crucial in aiding decision making in future coastal management.

This thesis explores the drivers and mechanisms of saltmarsh change through the development of a conceptual model, which is then tested using Poole Harbour, UK as a case study site. The potential drivers of saltmarsh change were investigated using a multidisciplinary approach, combining a GIS historic change analysis utilising aerial photography, charts and maps, a bathymetric analysis of the harbour morphology and a 2D hydrodynamic TELEMAC model. Spartina anglica rapidly colonised the Harbour at the end of the 19th Century increasing the saltmarsh area from approximately 120ha to over 900ha during the 1920’s, after which there was a decline in area that has continued to present day However, saltmarsh extent in 2005 was still approximately three times the extent prior to the colonisation of Spartina anglica.

Poole Harbour is large and dendritic and spatially within the Harbour separate tributaries exhibit clearly distinct saltmarsh erosion and accretion trends. Accretion was seen to occur in relatively sheltered locations with short fetches, fronted by high mudflats, in areas that are flood dominant both in terms of hypsometry as well as tidal peak flow and slack duration. Erosion was seen to occur in relatively exposed areas where the marsh top and fringing mudflats are significantly lower and local sediments have a lower shear velocity than in accretionary regions. Saltmarsh erosion tends to occur in morphologically ebb dominant areas but not exclusively, suggesting multiple drivers are in operation.

Poole Harbour is used in this study as an example of a wider global problem. At a broad scale, observations emphasise that saltmarsh changes occurring elsewhere in the UK, and potentially elsewhere in the world, may be more complex than often portrayed. Highlighting the need for detailed case by case studies, that use all the data available over a sufficient time period. Multiple drivers of change control the net evolution of saltmarsh in Poole Harbour and this is likely to be a widespread conclusion for other estuaries globally.
Gardiner, Sarah
6893acd0-97bf-4f15-9bf7-5364b6d74941
Gardiner, Sarah
6893acd0-97bf-4f15-9bf7-5364b6d74941
Nicholls, Robert
4ce1e355-cc5d-4702-8124-820932c57076

(2015) Physical drivers of saltmarsh change in enclosed microtidal estuaries. University of Southampton, Engineering and the Environment, Doctoral Thesis, 237pp.

Record type: Thesis (Doctoral)

Abstract

Estuaries are among the most biologically productive ecosystems on the planet, per unit area, with intertidal habitats and particularly saltmarshes providing a variety or ecosystem services and supporting large numbers of both primary and secondary producers. These habitats are globally important and are found throughout tropical to temperate climates. Micro-tidal estuaries are found throughout the world and particularly sensitive to sea-level rise, as they are limited in their ability to adjust and are considered vulnerable to future changes .Hence, at a broad scale, understanding the drivers and mechanisms of saltmarsh change in micro-tidal systems is crucial in aiding decision making in future coastal management.

This thesis explores the drivers and mechanisms of saltmarsh change through the development of a conceptual model, which is then tested using Poole Harbour, UK as a case study site. The potential drivers of saltmarsh change were investigated using a multidisciplinary approach, combining a GIS historic change analysis utilising aerial photography, charts and maps, a bathymetric analysis of the harbour morphology and a 2D hydrodynamic TELEMAC model. Spartina anglica rapidly colonised the Harbour at the end of the 19th Century increasing the saltmarsh area from approximately 120ha to over 900ha during the 1920’s, after which there was a decline in area that has continued to present day However, saltmarsh extent in 2005 was still approximately three times the extent prior to the colonisation of Spartina anglica.

Poole Harbour is large and dendritic and spatially within the Harbour separate tributaries exhibit clearly distinct saltmarsh erosion and accretion trends. Accretion was seen to occur in relatively sheltered locations with short fetches, fronted by high mudflats, in areas that are flood dominant both in terms of hypsometry as well as tidal peak flow and slack duration. Erosion was seen to occur in relatively exposed areas where the marsh top and fringing mudflats are significantly lower and local sediments have a lower shear velocity than in accretionary regions. Saltmarsh erosion tends to occur in morphologically ebb dominant areas but not exclusively, suggesting multiple drivers are in operation.

Poole Harbour is used in this study as an example of a wider global problem. At a broad scale, observations emphasise that saltmarsh changes occurring elsewhere in the UK, and potentially elsewhere in the world, may be more complex than often portrayed. Highlighting the need for detailed case by case studies, that use all the data available over a sufficient time period. Multiple drivers of change control the net evolution of saltmarsh in Poole Harbour and this is likely to be a widespread conclusion for other estuaries globally.

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More information

Published date: January 2015
Organisations: University of Southampton, Energy & Climate Change Group

Identifiers

Local EPrints ID: 385299
URI: http://eprints.soton.ac.uk/id/eprint/385299
PURE UUID: ca1f76a9-b12e-4697-bca8-b648502ce199
ORCID for Robert Nicholls: ORCID iD orcid.org/0000-0002-9715-1109

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Date deposited: 13 Jan 2016 11:05
Last modified: 06 Jun 2018 12:44

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