Salt marsh resilience to sea-level rise and increased storm intensity

Salt marshes are widely recognised as ecosystems with high economic and environmental value. However, it is still unclear how salt marshes will respond to the combined impact of future sea-level rise and possible increases in storm intensity (Schuerch et al. 2013). This study investigates marsh resilience under the combined impact of various storm surge and sea-level scenarios by using a sediment budget approach. The current paradigm is that a positive sediment budget supports the accretion of salt marshes and, therefore, its survival, while a negative sediment budget causes marsh degradation (Ganju et al. 2015). The Ribble Estuary, North-West England, was used as test case, and the hydrodynamic model Delft3D was used to simulate the response of the salt marsh system to the above scenarios. We conclude that the resilience of salt marshes and estuarine systems is enhanced under the effect of storm surges, as they promote flood dominance and trigger a net import of sediment.&#160; Conversely, sea-level rise threatens marsh stability, by promoting ebb dominance and triggering a net export of sediment. Ultimately, when storm surge and sea-level scenarios are combined, results show that storms with the highest intensities have the potential to counteract the negative impact of sea-level rise by masking its effects on the sediment budget.AcknowledgementsWe acknowledge the support of the School of Environmental Sciences, University of Liverpool.ReferencesGanju, N.K., Kirwan, M.L., Dickhudt, P.J., Guntenspergen, G.R., Cahoon, D.R. and Kroeger, K.D. 2015. &#8220;Sediment transport-based metrics of wetland stability&#8221;. Geophysical Research Letters, 42(19), 7992-8000.Schuerch, M., Vafeidis, A., Slawig, T. and Temmerman, S. 2013. &#8220;Modeling the influence of changing storm patterns on the ability of a salt marsh to keep pace with sea level rise&#8221;.&#160;Journal of Geophysical Research-Earth Surface, 118(1),&#160;84-96.

Download Full-text

Quantifying vertical deformation of salt marsh substrates and their recovery during and after storm surge inundation

10.5194/egusphere-egu21-10682 ◽

2021 ◽

Author(s):

Helen Brooks ◽

Iris Moeller ◽

Tom Spencer ◽

Katherine Royse ◽

Simon Price ◽

...

Keyword(s):

Ecosystem Services ◽

Salt Marsh ◽

Sea Level Rise ◽

Normal Stress ◽

Sea Level ◽

Storm Surge ◽

Salt Marshes ◽

Dynamic Responses ◽

Ecosystem Functions ◽

Vertical Deformation

Salt marshes are globally-distributed, intertidal wetlands. These wetlands provide vital ecosystem functions (providing habitats, filtering water and attenuating waves and currents) that can translate into valuable ecosystem services. Alongside the existence of suitable horizontal accommodation space, the ability of the salt marsh platform to accrete or increase in elevation at a rate commensurate with current and projected future rates of sea-level rise is critical to ensuring future saltmarsh functioning.While several studies have assessed whether marsh surface and subsurface processes can keep pace with sea-level rise, few have measured whether, and to what extent, a marsh substrate may consolidate during a storm surge and whether such deformation is permanent or recoverable. This is of key importance given that the frequency and/or magnitude of storm surges is expected to change over the next few decades in some locations. We apply strictly-controlled oedometer tests to understand the response of salt marsh substrates to an applied normal stress (such as that exerted by a storm surge). We compare sediment samples from Tillingham marsh, eastern England, where the sediment is clay/silt-dominated, to samples from Warton marsh, Morecambe Bay, North West England, where the sediment is sand/silt-dominated.This research provides, for the first time, insight into the response of two compositionally-different UK marsh substrates to the application of normal stress, such as that induced by hydrostatic loading during extreme inundation events. We demonstrate that both the expected magnitude of axial displacement and the potential to recover vertical deformation after the event are affected by the particle size distribution and the void ratio, as well as past stress conditions on the marsh (particularly as a result of desiccation). The potential for irrecoverable vertical deformation in response to storm surge loading has not previously been identified in salt marsh studies.The results of this research will improve the ability of future models of marsh geomorphological evolution to better represent these dynamic responses and their implications for the provision of ecosystem services. This research also challenges existing studies which often do not fully parameterise these dynamic responses when considering salt marsh morphodynamics.

Download Full-text

Salt marshes adjustment to anthropogenic pressures and sea-level rise

10.5194/egusphere-egu21-9107 ◽

2021 ◽

Author(s):

A. Rita Carrasco ◽

Katerina Kombiadou ◽

Miguel Amado

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Salt Marshes ◽

Anthropogenic Pressures ◽

The Past ◽

Ria Formosa ◽

Sediment Loads ◽

Human Interventions ◽

South Portugal ◽

And Sea Level

It is predictable that salt marshes in regions, where sediment loads are high, should be stable against a broader range of relative sea level scenarios than those in sediment-poor systems. Despite extensive theoretical and laboratory studies, additional syntheses of marsh &#8216;persistence&#8217; indicators under human interventions and accelerated sea-level rise rates are still needed. This study investigates the recent lateral changes occurring in lagoon-type marshes of the Ria Formosa lagoon (south Portugal) in the presence of human interventions and sea-level rise, to identify the major drivers for past marsh evolution and to estimate potential future trends. The conducted analysis assessed the past geomorphological adjustment based on imagery analysis and assessed its potential future adjustment to sea-level rise (~100 years) based on modelled land cover changes (by employing the SLAMM model within two sea-level rise scenarios).Salt marshes in the Ria Formosa showed slow lateral growth rates over the last 70 years (<1 mm&#8729;yr-1), with localized erosion along the main navigable channels associated with dredging activities. Higher change rates were noted near the inlets, with stronger progradation near the natural inlets of the system, fed by sediment influx pulses. Any potential influence of sea-level increase to an intensification of marsh-edge erosion in the past, could not be distinguished from human-induced pressures in the area. No significant sediment was exchanged between the salt marshes and tidal flats, and no self-organization pattern between them was observed in past. The related analysis showed that landcover changes in the salt marsh areas are likely to be more prominent in the future. The obtained results showed evidence of non-linearity in marsh response to high sea-level rise rates, which could indicate to the presence of critical thresholds and potential negative feedbacks within the system, with significant implications to marsh resilience.

Download Full-text

Salt Marshes and sea level rise: marsh dynamics in relation to accretion processes and accretion enhancement techniques

Studies in Environmental Science - Climate Change Research - Evaluation and Policy Implications, Proceedings of the International Climate Change Research Conference ◽

10.1016/s0166-1116(06)80111-1 ◽

1995 ◽

pp. 823-826 ◽

Cited By ~ 1

Author(s):

Erik-Jan Houwing ◽

Joost H.J. Terwindt

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Salt Marshes ◽

And Sea Level

Download Full-text

High-Resolution Coastal Elevation Data: The Key to Planning for Storm Surge and Sea Level Rise

Geospatial Technologies and Homeland Security - The GeoJournal Library ◽

10.1007/978-1-4020-8507-9_11 ◽

2008 ◽

pp. 229-240

Author(s):

Mark Monmonier

Keyword(s):

High Resolution ◽

Sea Level Rise ◽

Sea Level ◽

Storm Surge ◽

Elevation Data ◽

And Sea Level

Download Full-text

Venice lagoon salt marsh vulnerability and halophytic vegetation vertical migration in response to sea level rise

10.5194/egusphere-egu2020-14404 ◽

2020 ◽

Author(s):

Zhicheng Yang ◽

Sonia Silvestri ◽

Marco Marani ◽

Andrea D’Alpaos

Keyword(s):

Salt Marsh ◽

Sea Level Rise ◽

Sea Level ◽

Salt Marshes ◽

Current Knowledge ◽

Venice Lagoon ◽

Sea Level Changes ◽

Human Pressure ◽

Sea Levels ◽

Vegetation Species

Salt marshes are biogeomorphic systems that provide important ecosystem services such as carbon sequestration and prevention of coastal erosion. These ecosystems are, however, threatened by increasing sea levels and human pressure. Improving current knowledge of salt-marsh response to changes in the environmental forcing is a key step to understand and predict salt-marsh evolution, especially under accelerated sea level rise scenarios and increasing human pressure. Towards this goal, we have analyzed field observations of marsh topographic changes and halophytic vegetation distribution with elevation collected over 20 years (between 2000 and 2019) in a representative marsh in the Venice lagoon (Italy).Our results suggest that: 1) on average, marsh elevation with respect to local mean sea level decreased , (i.e. the surface accretion rate was lower than the rate of sea level rise); 2) elevational frequency distributions are characteristic for different halophytic vegetation species, highlighting different ecological realized niches that change in time; 3) although the preferential elevations at which different species have changed in time, the sequence of vegetation species with increasing soil elevation was preserved and simply shifted upward; 4) we observed different vegetation migration rates for the different species, suggesting that the migration process is species-specific. In particular, vegetation species colonizing marsh edges (Juncus and Inula) migrated faster facing to changes in sea levels than Limonium and Spartina , while Sarcocornia was characterized by delayed migration in response to sea level changes. These results bear significant implications for long-term biogeomorphic evolution of tidal environments.

Download Full-text

Impact of salt marsh and seagrass beds on the sediemnt buget and resilience of coatsal areas

10.5194/egusphere-egu2020-9659 ◽

2020 ◽

Author(s):

Nicoletta Leonardi ◽

Carmine Donatelli ◽

Xiahoe Zhang ◽

Neil Ganju ◽

Sergio Fagherazzi

Keyword(s):

Salt Marsh ◽

Water Resources ◽

Salt Marshes ◽

Numerical Models ◽

Sediment Budget ◽

Coastal Protection ◽

Seagrass Beds ◽

Geophysical Research ◽

Coastal System ◽

Depositional Patterns

Salt marshes and seagrass beds can offer sustainable coastal protection solutions and several ecosystem co-benefits. The delicate balance regulating salt marsh stability depends on several factors including the sediment added to and removed from the coastal system (Donatelli et al., 2018, 2019; Zhang et al., 2019). &#160;Despite the importance of these sediment budget dynamics, many feedbacks between salt marsh presence and sediment availability are still unclear. Here, we use numerical models to simulate changes in depositional patterns of six estuaries along the U.S. coastline to investigate how salt marsh and seagrass beds removal and restoration can alter the sediment budget and resilience of coastal environments.&#160;Donatelli, C., Ganju, N.K., Kalra, T.S., Fagherazzi, S. and Leonardi, N., 2019. Changes in hydrodynamics and wave energy as a result of seagrass decline along the shoreline of a microtidal back-barrier estuary.&#160;Advances in Water Resources,&#160;128, pp.183-192.Zhang, X., Leonardi, N., Donatelli, C. and Fagherazzi, S., 2019. Fate of cohesive sediments in a marsh-dominated estuary.&#160;Advances in water resources,&#160;125, pp.32-40.Donatelli, C., Ganju, N.K., Fagherazzi, S. and Leonardi, N., 2018. Seagrass impact on sediment exchange between tidal flats and salt marsh, and the sediment budget of shallow bays.&#160;Geophysical Research Letters,&#160;45(10), pp.4933-4943.

Download Full-text