Impact of Barrier Breaching on Wetland Ecosystems under the Influence of Storm Surge, Sea-Level Rise and Freshwater Discharge

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.

Evaluating the viability of coastal wet grassland to a changing management regime through flood hazard modelling

“…As Brotherton et al (2019a) Environmental modelling provides an opportunity to explore potential impacts to vegetated communities under extreme events and sea level rise scenarios, and allows coastal management strategies to be tested. Li et al (2019) showed that a potential managed realignment at Minsmere, UK could result in the majority loss of freshwater reedbeds under even normal tidal conditions unless freshwater inputs were regulated. It is difficult to predict the precise impacts of new patterns of flooding on reedbeds and coastal wet grassland at Blakeney Freshes, given the complexities of flooding style (sudden peak v. gradual water inputs), final water depths and flood durations, and interactions between increased inundation, waterlogging and salinization (Spalding & Hester, 2007;Brotherton & Joyce, 2015).…”

Biological–physical interactions are fundamental to understanding and managing coastal dynamics

“…Third, interventions to reverse the degradation and loss of coastal habitats—such as the managed realignment of low-lying shorelines—should be seen as experimental opportunities in which to learn more about how the biological–physical system works. Thus, for example, modelling of emergent wetland habitats following natural/artificial breaching of coastal defences points to the importance of the interactions between bed elevation (and its control of hydroperiod), hydrodynamics (in terms of both inputs (inlet morphodynamics) and outputs (drainage channel networks)) and sediment erosion/deposition, and also the role of vegetation cover and root depth/structure [ 20 ]. As the outcomes of these experiments emerge, it will be important to merge such interdisciplinary information with theory, observation, experiments and replication across systems, so as to establish generality and provide opportunity to minimize the time lag from theory through to evidence-based adoption in practice [ 21 ].…”

Ecosystem Services Values at Risk on the Atlantic Coastal Zone Due to Sea-Level Rise and Socioeconomic Development

“…These biomes are usually located in low altitude areas, and, because of that, they present direct contact with the ocean, being consequently disturbed by the flooding process. Li et al (2020) highlight that those losses due to the flooding process will be irreversible, if the RCP 8.5 scenario occurs, with diverse impacts, such as vegetation dieback and increase in salinity due to direct tidal flushing.…”