title: Saltmarsh resilience in a changing climate: geomorphological and biological processes in natural and managed salt marshes in the North East of Scotland
Creators: name: Francoz, Charlotte
Publisher: name: University of Glasgow
Year: 2023

description: Salt marshes are regarded as one of the world's most productive ecosystems due to the unique habitat they provide, which is essential to our ecological structure, and their ability to act as sinks for organic and inorganic sediment. Salt marshes have long attracted human settlement and exploitation due to their location along the coast, on the sheltered shores typical of estuaries and tidal inlets. The permanent loss of saltmarsh ecosystems is between 25 and 50 percent of theirglobal historical coverage, and the decline continues globally. This is exacerbated by rising temperatures, sea level rise, and increasing storm intensity, which erode salt marshes. Since 1945, roughly 15 percent of saltmarsh area in the United Kingdom has been lost due to human intervention, primarily agricultural and industrial reclamation, and is now being exacerbated by coastal erosion and sea level rise. Saltmarsh formation and development are influenced by the interdependence of physical and biological processes, whereas vertical growth and saltmarsh stability are highly dependent on sediment supply and tidal range. However, the cumulative impact of human disturbance and sea level rise on the fundamental saltmarsh dynamics remains obscure and must be better understood at both the local and global scales. This thesis aims to improve understanding of the processes, mechanisms and patterns that 1) favour saltmarsh formation and development 2) enable saltmarsh capacity to recover from environment and anthropological disturbances 3) promote some of the regulating and supporting services salt marshes provide. My thesis has carried out a biogeomorphological appraisal of the first salt marsh managed realignment in Scotland since its breaching in 2003 in comparison with two adjacent natural salt marshes across different time scales. The study has employed a methodology to assess jointly managed/anthropogenically modified and natural salt marshes at different temporal scales. A set of managed and adjacent natural salt marshes within the same salt marsh system at Nigg Bay, NE Scotland provided a comparative case study of the links between sediment availability, vegetation presence and saltmarsh stability over time and space. Above ground changes in vegetation and sedimentation patterns were quantified over different timescales from short (annual) to longer (centennial) timescale using a combination of field measurements: sediment deposition, sedimentation plates and DEM time series in tandem with vegetation sampling. This multi-method approach has proven to be a powerful tool to analyse spatial distribution patterns of sediment accretion. Below ground physical and biological changes were explored using a combination of traditional sedimentary techniques and applying Luminescence to salt marsh for the first time, to gain knowledge on the possible mechanisms driving these changes. These results were used to assess the potential implications on the supporting and regulating benefits that salt marshes provide, as such contributing to saltmarsh blue carbon inventories for natural and managed realignment salt marsh in Scotland; and, on capacity of marshes to keep up with rising sea levels. The cumulative results of my thesis work highlight that natural salt marshes have limited space to respond to environmental changes, which reduces their long-term resiliency. In terms of sea level rise, the marsh is responding due to the accommodation space provided by the managed realignment. Furthermore, the study has developed a new application of Optically Stimulated Luminescence (OSL) that challenges the results of conventional techniques and allows exploration of modern sediment material registering the impacts of recent climate change. This work thus adds an important dataset to the Scottish context and more broadly to the growing literature on the ability for managed realignment sites to replicate natural saltmarsh functions and thus ecosystem services.