Impacts of temporal variations in sediment availability on the long-term ability of coastal salt marshes to adapt to global sea level rise
Palaeontology
Final Report Abstract
Coastal salt marshes, and coastal wetlands more generally, are considered important ecosystems with respect to the provisioning of ecosystem services, such as atmospheric carbon sequestration, coastal protection and habitat creation. They are highly sensitive to environmental change, including both terrestrial and marine drivers (e.g. global sea level rise (SLR)). In fact, some assessments expect coastal wetlands to almost disappear globally for some of the high-end SLR scenarios. The ability of coastal wetlands to adapt to future SLR crucially depends on their ability to vertically accrete sediment at the same pace as sea level rises. The most important parameters influencing this ability are the rate of SLR, tidal range and sediment availability. Furthermore, the accumulation of sediment on vegetated wetlands has been linked to vegetation characteristics (e.g. vegetation height and plant biomass) affecting the biophysical interactions between the sediment suspended in the water inundating the wetland and the vegetation. During this project, the responses of coastal wetlands, and coastal salt marshes in particular, have been investigated on various temporal and spatial scales in order to (i) improve our process understand of sediment deposition on vegetated coastal wetlands and (ii) enhance our ability to predict the future of coastal wetlands under the influence of the projected 21st century SLR. On a local, short-term scale, the direct influence of vegetation height and biomass on sediment deposition was investigated. The project also considered the likely origin of the sediment deposited on the wetland surface. On the large (global), long-term (until 2100) scale, the impact of SLR on global coastal wetland area was studied by accounting for the most important drivers controlling the long-term stability of these systems. The results of the field experiments confirmed the overwhelming importance of sediment supply dynamics to coastal wetland functioning. The importance of sediment supply seems not to be limited to the enhanced amount of sediment being available for deposition, but the sediment also seems to be depositing more efficiently under a regime of higher sediment supply. A possible explanation for this behaviour could lie in the formation of larger flocs with higher settling velocities, thought to be developed when suspended sediment concentrations are high. Meanwhile, vegetation height and plant biomass did not show any relationship with sediment deposition, suggesting that variations in vegetation characteristics on coastal wetlands, here explicitly shown for salt marshes only, may not significantly impact sediment deposition patterns. Global-scale wetland modelling, for the first time integrating sediment deposition as a function of sediment supply as well as the potential of coastal wetlands to migrate inland, revealed how important both processes are for the stability of coastal wetlands under the influence of future SLR. While previous global models and assessments, for the worst-case scenarios, have suggested global coastal wetland losses of up to 90%, the model developed during this project estimates losses of only up 30%. Much of this difference is caused by explicitly accounting for higher sediment deposition rates under increased rates of SLR. The results of this project have relevance for both the development of local-scale, processbased coastal wetland models as well as for the assessment of how our coasts and the associated ecosystem services will respond to future SLR. An improved understanding of how coastal wetlands vertically grow under the influence of global SLR will help coastal manager to maintain and restore coastal wetlands, which will crucially determine the future appearance and safety along our coasts and may help to mitigate climate change.
Publications
- (2017): Quantification of vegetation-induced allochthonous sediment deposition on coastal salt marshes, EGU General Assembly Conference Abstracts 19, 1424
Schuerch, M., Reef, R., Christie, E., Möller, I., Spencer, T. and Mayerle, R.
- (2018): Changing sediment dynamics of a mature backbarrier salt marsh in response to sea-level rise and storm events. Frontiers in Marine Science 5, 155
Schuerch, M., Dolch, T., Bisgwa, J. and Vafeidis, A. T.
(See online at https://doi.org/10.3389/fmars.2018.00155) - (2018): Future response of global coastal wetlands to sea-level rise. Nature 561(7722), 231–234
Schuerch, M., Spencer, T., Temmerman, S., Kirwan, M. L., Wolff, C., Lincke, D., McOwen, C. J., Pickering, M. D., Reef, R., Vafeidis, A. T., Hinkel, J., Nicholls, R. J. and Brown, S.
(See online at https://doi.org/10.1038/s41586-018-0476-5) - (2018): Identifying the drivers for temporal variations in salt marsh sedimentation: a case study from the UK east coast. Geophysical Research Abstracts 20, 8670
Schuerch, M. and Spencer, T.
- (2018): The effect of vegetation height and biomass on the sediment budget of a Eurpean saltmarsh. Estuarine, Coastal and Shelf Science 202, 125-133
Reef, R., Schuerch, M., Christie, E.K., Möller, I. and Spencer, T.
(See online at https://doi.org/10.1016/j.ecss.2017.12.016)
