Abstract
Coastal wetland ecosystems and biodiversity are susceptible to changes in salinity brought about by the local effects of climate change, meteorological extremes, coastal evolution and human intervention. This study investigates changes in the salinity of surface water and the associated impacts on back-barrier wetlands as a result of breaching of a barrier beach and under the compound action of different surge heights, accelerated sea-level rise (SLR), river discharge and rainfall. We show that barrier breaching can have significant effects in terms of vegetation die-back even without the occurrence of large storm surges or in the absence of SLR, and that rainfall alone is unlikely to be sufficient to mitigate increased salinity due to direct tidal flushing. Results demonstrate that an increase in sea level corresponding to the RCP8.5 scenario for year 2100 causes a greater impact in terms of reedbed loss than storm surges up to 2 m with no SLR. In mitigation of the consequent changes in wetland ecology, regulation of relatively small and continuous river discharge can be regarded as a strategy for the management of coastal back-barrier wetland habitats and for the maintenance of brackish ecosystems. As such, this study provides a tool for scoping the potential impacts of storms, climate change and alternative management strategies on existing wetland habitats and species.
Highlights
Wetlands are commonly found along low energy coastal environments, and provide important ecosystem services and economic benefits (e.g., Gedan et al 2009, 2011; Ndebele and Forgie 2017; Li et al 2018)
Our results show that the current reedbed extent is likely to shrink over the long term under the threat of increased salinity in the wetland, which agrees with previous finding suggesting that the expansion of P. australis is limited by high salinities (Chambers et al 1999)
This research explores the potential state of a coastal wetland with a barrier breach either due to coastal erosion consequent upon accelerated sea-level rise, instantaneous breaching during a storm, or as a result of human intervention
Summary
Wetlands are commonly found along low energy coastal environments, and provide important ecosystem services and economic benefits (e.g., Gedan et al 2009, 2011; Ndebele and Forgie 2017; Li et al 2018). Various environmental factors, predicted wetland loss by the end of the century has been estimated to be around 0 to 50% (Gilman et al 2006; McFadden et al 2007; Alongi 2008; Kirwan et al 2016) This is likely to be an underestimate given that sealevel rise over this century could double previous projections (Grinsted et al 2015; Bamber et al 2019).
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