The goal of the proposed research is to evaluate the resilience of coastal wetlands to sea level rise over multiple time scales and under the compound action of typhoons activity and sea level rise by combining numerical modelling and field work activities on the Chingming Eco-Island, China.
Coastal wetlands are delicate ecosystems located at the boundary between sea and land and play a number of crucially important socio-economic roles. For instance, coastal wetlands are important for protecting coastal communities from violent storms and typhoons, preventing flooding and coastal erosion thanks to their capability to dampen waves and storm surge energy (Leonardi et al., 2018).
The current paradigm is that coastal wetlands and their ecosystem services are threatened by accelerated sea level rise. However, there are many uncertainties about the factors affecting salt-marsh resilience and their regular cycles of erosion-accretion. Recent results indicate that detailed sediment budgets can help assess the long-term fate of coastal wetlands because such budgets represent spatially integrated measures of competing constructive and destructive forces. For instance, a sustained sediment deficit can indicate the drowning and/or lateral contraction of the marsh (Ganju et al., 2017).
We will focus on Chingming Eco-Island, China. The Changjiang Estuary represents an ideal test case to explore our hypothesis because of the drastic changes in sediment supply from the river allow exploring wetlands morphological changes for a condition of relative abundance and scarcity of sediments, and under the occurrence of multiple typhoons per year. Indeed, the annual sediment discharge in the Changjiang Estuary experienced a drastic decline after the construction of the TGD in 2003, being less than 100 Mt in 2006 and 2011, compared to an average of 423 Mt before 2003 (Mei et al., 2015, 2016).
We will test the following hypotheses:
H1: For coastal wetlands, the resilience to sea level rise is limited by the sediment supply to the system. This supply depends on both sediments coming from the river and from the ocean. Sediments coming from the ocean can play a major role in wetlands stability.
H2: In the Changjiang Estuary the contribution of the ocean to the delivery of sediments has mitigated and temporarily “hidden” the impact of the three Gorges Dams construction which is why in many coastal areas there has been no erosion despite a large decrease in sediment supply. However, after this initial lag time, it is expected that starvation from riverine sediments will become recognizable and cause large wetlands degradation.
These hypotheses will be tested by conducting ensemble simulations and by comparing model results with field measurements collected by the State Key Laboratory.
The basic numerical models setup is already available (Figure 1) but it will be modified to account for different sea level rise scenarios and to include typhoons occurrence. Preliminary field measurements of velocity, suspended sediment concentration and LiDAR measurements of tidal flats in the area are also available. It is expected for the student to contribute to the collection of new LiDAR measurements during the visiting period.
To apply for this opportunity, please visit: https://www.liverpool.ac.uk/study/postgraduate-research/how-to-apply/
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Ganju, N.K., Defne, Z., Kirwan, M.L., Fagherazzi, S., D’Alpaos, A. and Carniello, L., 2017. Spatially integrative metrics reveal hidden vulnerability of microtidal salt marshes. Nature communications, 8, p.14156.
Leonardi, N., Carnacina, I., Donatelli, C., Ganju, N.K., Plater, A.J., Schuerch, M. and Temmerman, S., 2018. Dynamic interactions between coastal storms and salt marshes: A review.
Geomorphology, 301, pp.92-107.
Mei, X., Dai, Z., Du, J., Chen, J. 2015. Linkage between Three Gorges Dam impacts and the dramatic recessions in China’s largest freshwater lake, Poyang Lake. Scientific Reports 5, 18197.
Mei, X., Dai, Z., Wei, W., Gao, J. 2016. Dams induced stage-discharge relationship variations in the upper Yangtze River basin. Hydrology Research. 47, 157-170.