GM6.3

Coastal wetlands are among some of the most biologically productive ecosystems on the planet. Not only do they sequester large amounts of carbon and improve water quality, but they also provide a buffer between the ocean and coastal communities protecting them from effects of climate change such as accelerated sea level rise or increased storm frequency. Over the past century, increased salt marsh area loss was observed through the formation of internal open water bodies, so-called ponds, emerging in established wetlands such as temperate salt marshes fringing the US Mid-Atlantic coast. However, detailed causes leading to pond formation and their implications for salt marsh survival are still subject to debates. This study focused on disentangling the impact of bio-geomorphological gradients, governing sediment, and plant species composition on the formation of ponds. Marsh platforms are composed of a mosaic of plant species differing in growth properties related to tolerance in inundation stress and soil anoxia. Salt marsh sediment characteristics were shown to change with increasing distance from the open water sediment source creating specific spatial gradients. We carried out stratified field surveys on plant species distribution and sediment characteristics (e.g., organic matter content and compressibility) and compared results to a controlled mesocosm experiment identifying the plant-species growth response to differences in inundation time. The combination of field and laboratory measurements enables us to evaluate how bio-geomorphological gradients consisting of species-specific plant properties (plant growth and mortality) and sediment characteristics can explain pond formation and marsh degradation.

How to cite: Schwarz, C.: On the impact of bio-geomorphological gradients on salt marsh survival, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1286, https://doi.org/10.5194/egusphere-egu22-1286, 2022.

Relative sea level rise (RSLR) is widely regarded as a threat to highly valued coastal wetlands such as tidal marsh and mangrove ecosystems. In certain places around the world, coastal wetlands already show signs of submergence due to RSLR, while in other places these wetlands instead show a certain ability to adapt to RSLR through sediment accretion and resulting surface elevation gain. Identifying the factors that drive the global variability in coastal wetland adaptability to RSLR is thus a major scientific and societal challenge. Regional- to global-scale empirical assessments and model projections have revealed that the rate of RSLR itself, the tidal range and sediment supply are major drivers of wetland adaptability. Yet, these assessments ignore the role of the tidal pattern, which varies around the world from semi-diurnal to diurnal. Here, we present a meta-data analysis, including 423 tidal marsh and mangrove sites around the world, to assess the relative influence of tidal patterns, on globally observed rates of wetland elevation change in comparison with local RSLR rates. We demonstrate that the tidal pattern contributes importantly to explain the variability in wetland adaptability to RSLR. Specifically, coastal wetlands occurring under predominantly diurnal tides are more subject to elevation deficits relative to RSLR, as compared to wetlands under predominantly semi-diurnal tides. Using a tidal wetland accretion model, we further illustrate that less frequent, diurnal tides trigger lower sediment accretion rates, hence higher wetland vulnerability to RSLR, across a wide range of scenarios of RSLR rates, tidal ranges, and sediment supply. Our findings highlight the tidal pattern as a previously overlooked yet important driver of coastal wetland adaptability to RSLR and offer new perspectives on the understanding and projection of coastal wetland responses to future RSLR. We also call for new research as tidal patterns may also affect other key wetland ecosystem functions and services.    

How to cite: Belliard, J.-P., Gourgue, O., Govers, G., Kirwan, M., and Temmerman, S.: Semi-diurnal vs. diurnal tides: implications for coastal wetland adaptability to sea level rise, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11483, https://doi.org/10.5194/egusphere-egu22-11483, 2022.

The resilience of saltmarshes mainly depends on their ability to gain elevation by sediment accretion to keep pace with sea level rise, and tidal channels play a crucial role in the transport of sediments towards their interior. While feedbacks between geomorphology and vegetation are increasingly recognized as key drivers shaping a variety of tidal channel network structures, the resulting impact on long-term sediment accretion over the vegetated platforms has been poorly studied so far. Here, we compare two saltmarsh species with contrasting colonization strategies and morphological traits: Spartina marshes, characterized by patchy colonization patterns, encroaching tidal flats in small, isolated patches (1-10 m²) that slowly grow laterally (few m/year) with dense stands of tall stems; Salicornia marshes, characterized by more homogeneous colonization patterns, establishing quickly over large areas (100-1000 m²) with much less dense and shorter stems. Through different model scenarios (without vegetation, with Spartina plant traits, and with Salicornia plant traits), we investigate the impact of saltmarsh vegetation on self-organization of tidal channel networks, and the resulting consequences on long-term sediment accretion over the vegetated platforms, while disentangling the role of plant morphological traits (stem density, height, diameter) from colonization traits (patchy vs. homogeneous). In agreement with previous literature, we find that saltmarsh vegetation (especially denser Spartina) increases channel density (a measure of alleged efficiency with which channel networks serve the vegetated platforms, solely based on their geometric characteristics). However, by contrast with what is usually assumed, our results reveal that higher channel density does not necessarily lead to higher sediment accretion rates over the platforms. That is because vegetation (especially denser Spartina) increases friction and hinders sediment transport towards the platform interiors, leading to the formation of levees close to the channels and depressions away from them. Our results also suggest that plant colonization traits (patchy vs. homogeneous) have a dominant impact on sediment accretion during the colonization phase, but that plant morphological traits (stem density, height, diameter) prevail on the long term.

How to cite: Gourgue, O., Belliard, J.-P., Xu, Y., Fagherazzi, S., and Temmerman, S.: Vegetation hinders sediment transport towards saltmarsh interior, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10906, https://doi.org/10.5194/egusphere-egu22-10906, 2022.

Tidal marshes are coastal landforms daily flooded by sea water. Their fate is strongly conditioned by the future relative sea level rise, intrinsically linked to climate change. The significant ecological and socioeconomic value of these ecosystems is a compelling reason to improve our understanding of marsh platform dynamics relative to the mean sea level. Among various factors influencing the elevation of these depositional landforms, sedimentation and compaction of the marsh body itself play a major role. In particular, it has been observed that marsh soils undergo large autocompaction due to high porosity and compressibility. Hence, characterization of marsh geomechanical properties is of paramount importance to develop reliable long-term predictions. With the aim of characterizing the geomechanical features of tidal marshes in the Venice Lagoon (Italy), a campaign of in-situ loading experiments has been recently carried out. In each experiment, eight 500-l tanks were cyclically filled and emptied with lagoon water, applying loads of various duration and entities on marsh platform. A monitoring system, based on pressure and displacement transducers, tracks the marsh response to the applied loads. This work describes the modeling activities developed to interpret these measurements from the in-situ experiments. The simulations have been carried out using a 3D poro-mechanical model solving Biot’s equations by a mixed finite-element formulation. A power law is used to describe the soil compressibility vs effective stress relationship, and main parameters are initially defined based on oedometric tests carried out on a few samples cored from the marshes. Mechanical hysteresis is also accounted for. The model calibration allows to satisfactory match the available pressure and deformations records. In particular, the numerical simulation accurately accounts for the behavior of (vertically) heterogenous marsh deposits as revealed by core interpretation. Based on these promising results, we are looking towards using the calibrated constitutive relationships in long-term biomorpho-geomechanical analyses, to forecast the fate of the marshes in the Lagoon of Venice.

How to cite: Baldan, S., Andrea, F., Claudia, Z., Philip S. J., M., Veronica, G., Massimiliano, F., and Pietro, T.: Poro-mechanical modelling of in-situ loading experiments on Venice Lagoon marshes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7550, https://doi.org/10.5194/egusphere-egu22-7550, 2022.

Coastal salt marshes are unique and complex geomorphological systems, which must accrete to keep pace with sea-level rise. Even though we know the importance of vegetation and organic matter accumulation in the marsh accretion process, we lack an understanding of spatially-distributed saltmarsh dynamics that include feedbacks with vegetation, especially for sites characterized by high species diversity. Remote sensing retrievals of wetland topography, spatial distribution of species, and vegetation biomass and productivity provide an ideal solution, providing observations over the wide range of scales of interest. Here we present the results obtained using LiDAR and hyperspectral data collected via Unmanned Aerial Vehicles (UAVs) on the San Felice saltmarsh (Venice lagoon, Italy). The selected study site hosts at least twelve species of halophytes grouped into five main associations. UAVs data were collected in September 2021, while a simultaneous field survey provided spatially-distributed georeferenced data and samples on the distribution of vegetation associations, above- and below-ground biomass, vegetation height, bulk density and organic carbon content of the soil. Results suggest that, for different plant associations, LiDAR data can be used to retrieve the aboveground biomass and estimate the belowground biomass (through allometric relations), hence providing a spatially-distributed assessment of the vegetation biomass across the marsh. Combining this information with the organic carbon content obtained by soil analyses, we estimate the combined above- and below-ground carbon stock of the salt marsh. The results obtained using hyperspectral data suggest that vegetation indexes defined on appropriate spectral bands correlate with the LiDAR biomass information and ground truth data. Using these results, observations from UAVs and satellites can be combined to bridge data from the plant to the wetland scale and beyond.

How to cite: Silvestri, S., Cuenca Portillo, R. P., Rufo, O., Assiri, M., Avendaño, S., Murray, A. B., and Marani, M.: Saltmarsh vegetation biomass distribution from drones: a case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2025, https://doi.org/10.5194/egusphere-egu22-2025, 2022.

Coastal meadows provide a wide range of ecosystem services (ES) worldwide. Primary production in coastal meadows is a key ecosystem function that drives the supply of ES such as carbon (C) sequestration as well as food provision for livestock. Beyond their role as carbon sinks, high species diversity and complex structure of coastal meadow landscapes comprise an important habitat for populations of wildfowl, waders, amphibians, and arthropods. The quality of these habitats partly depends on sward structural heterogeneity, which is mostly determined by low intensity grazing.

In order to better target conservation efforts in these ecosystems, it is necessary to develop highly accurate models that account for the spatial nature of ecosystem structure, processes and functions. In this study, above-ground biomass was predicted at very high spatial resolution in nine study sites in Estonia. A combination of UAV-derived multispectral and rgb datasets were used to produce vegetation indices and micro topographic models. A Sensefly Ebee UAV equipped with a Parrot Sequoia 1.2 megapixel monochromatic multi-spectral sensor and a senseFly S.O.D.A camera was used to obtain images at 10 cm and 3.5 cm ground sampling distance. A random forest algorithm was used to generate above-ground biomass maps based on biomass samples collected at study sites. The contribution of each predictor variable to the models was subsequently assessed. The models successfully predicted above-ground biomass at very high accuracies.

In order to assess grassland structural heterogeneity, each above-ground biomass map was clustered into discrete sward units using a Large Mean-Shift segmentation algorithm. The clustered above-ground biomass maps were further analysed using a set of five landscape indices that characterize different components of landscape configuration, patch size and heterogeneity. Grassland structural heterogeneity was subsequently related to management history at each study site, showing that continuous, monospecific grazing management tends to simplify grassland structure, which could in turn reduce the supply of a key regulation and maintenance ecosystem services: nursery and reproduction habitat for waders. These results also indicate that UAV-based surveys can serve as reliable grassland monitoring tools and could aid in the development of site-specific management strategies.

How to cite: Villoslada, M., Bergamo, T., Ward, R., Joyce, C., and Sepp, K.: A UAV-based approach for biomass prediction and sward structure characterization in coastal meadows, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8301, https://doi.org/10.5194/egusphere-egu22-8301, 2022.

The ability to trap and accumulate sediment and thereby to change the bathymetry makes coastal wetlands bioengineers of their own environment. While wind and wave attenuation directly contribute to hazard mitigation, the influence on bathymetry and thus shoreline change acts on longer time scales. In addition, sediment trapping impacts not only hazard mitigation but also blue carbon storage or the nutrient removal potential. The wetland in Stein at the Kiel Bay (German Baltic Sea) is a primary example of a site that offers ‘nature based coastal protection’, while at the same time the site is exposed to increasing anthropogenic pressures. Space for natural development at the study site is limited as the wetland is squeezed by a dyke in the hinterland, a marina and construction sites in the east, a popular tourist beach in the west and waterway dredging in the north. We aim to achieve a deeper understanding of short-term vs long-term processes of sediment trapping and vegetation propagation at this site.

We are combining remote sensing methods with vegetation mapping in field and on-site measurements (e.g. water level, oxygen saturation and waves). Vegetation mapping exposed a striking biodiversity with inter alia Tripolium pannonicum, Atriplex littoralis, Lathyrus japonicus, Bolboschoenus maritimus or Honckenya peploides besides the dominating Phragmites australis. Habitat variety is further enhanced by a manifold topography with small-scale basins, micro-cliffs and micro-depressions. Aerial images from 2007 to 2019 are analyzed to get insights into past development of vegetation patches and shoreline evolution. Preliminary results reveal that the wetland edge is relatively stable, while beach lake size varies significantly. However, this data lacks the spatiotemporal resolution to identify whether changes occurred gradually or after extreme events such as storm surges or winter ice. In contrast, our weekly to monthly UAV flights offer sufficient spatial and temporal resolution to monitor changes in microtopography. We anticipate that our results will help to better understand ecosystem dynamics as a response of gradual and abrupt disturbances, which may foster confidence in more sustainable coastal adaptation strategies.

How to cite: Karstens, S., Kiesel, J., Petersen, L., Etter, K., Vafeidis, A., and Gross, F.: Multifunctionality of coastal wetlands in a hazard context, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3403, https://doi.org/10.5194/egusphere-egu22-3403, 2022.

Scotland’s saltmarshes bury and store organic carbon (OC) for extensive periods of time, and thus, could potentially contribute as a natural solution to combat climate change. Recent studies have calculated that the top 10cm of Scottish saltmarshes hold approximately 367,888 ± 102,278 tonnes of OC ^[1]. Despite this new understanding of the surficial OC stock, the rate at which OC is buried is largely unknown. This study focusses on 10 contrasting saltmarshes around Scotland and presents an in-depth analysis of their total organic carbon (TOC) stocks and burial rates. Chronology data (provided by radioisotope analysis) provides information on the age of saltmarsh soils, as well as OC accumulation rates. Additionally, stable isotope analysis (δ¹³C and δ¹⁵N) allows improved understanding of carbon sources. Sediment carbon analysis, sediment descriptions and vegetation surveys were used to generate TOC stocks for each saltmarsh. The results showed that between 8,253 and 91,028 tonnes of OC is stored in these contrasting saltmarshes and OC burial rates range between 29.1 and 142.5 gC m^-2 yr^-1. This work highlights the role that saltmarshes play as a natural component in coastal climate mitigation and their wider significance as blue carbon environments contributing to Scotland’s natural capital.

[1] Austin, W., Smeaton, C., Riegel, S., Ruranska, P., Miller, L (2021). Blue carbon stock in Scottish saltmarsh soils. Scottish Marine and Freshwater Science, 12 (13)

How to cite: Miller, L., Smeaton, C., and Austin, W.: Scotland’s national saltmarsh carbon resources: an assessment of organic carbon stocks and burial rates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-655, https://doi.org/10.5194/egusphere-egu22-655, 2022.

Sea-level rise intensifies saltwater influx into coastal wetlands causing osmotic stress and probably changing vegetation composition. To determine especially the impact of salinity pulses as occurring during flooding events, dominant peatland macrophytes, Typha latifolia, Carex acutiformis, Schoenoplectus tabernaemontani and Phragmites australis, were exposed to different salinity regimes, consisting of control (permanently freshwater and permanently brackish water) and brackish-water treated groups with different durations of alternating exposure before returning to freshwater conditions (2 days brackish then 2 days fresh; 4 days brackish then 4 days fresh; 2 days brackish then 4 days fresh).  We measured plant height, leaf area and chlorophyll fluorescence weekly and determined the root:shoot ratio and photosynthetic pigment concentrations upon termination of study.

Salinity suppressed the growth of T. latifolia and C. acutiformis resulting in shorter plants, smaller mean leaf area and higher root:shoot ratios whereas photosynthetic pigment ratios and chlorophyll fluorescence were not affected. Moreover, shorter, but frequent salinity pulses (alternate 2 days brackish water then 2 days freshwater, and 2 days brackish water then 4 days freshwater) decreased the height of T. latifolia while C. acutiformis did not react negatively. Height and root:shoot ratio of both P. australis and S. tabernaemontani were neither affected by salinity nor by the frequency of salinity pulses. Also photosynthetic pigment ratios and chlorophyll fluorescence yield did not differ between treatments in S. tabernaemontani. In contrast, P. australis showed signs of successful acclimation through decreased chlorophyll a:carotenoid ratio and high chlorophyll fluorescence yield under both low and high irradiances. These results imply that with increasing seawater influx into coastal peatlands, T. latifolia and C. acutiformis will probably experience growth retardation or may even be replaced eventually by S. tabernaemontani or P. australis since they are more resilient against salinity and frequent salinity pulses.

How to cite: Batistel, C., Porsche, C., Jurasinski, G., and Schubert, H.: Response of four peatland emergent macrophytes to salinity and short salinity pulses, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5241, https://doi.org/10.5194/egusphere-egu22-5241, 2022.

Salt marshes sequester large amounts of “blue carbon” helping to mitigate climate change. This negative climate feedback, however, may be partially offset by increases in emissions of the potent greenhouse gases (GHGs) CH₄ and N₂O from marsh soils, which some studies have shown to vary with temperature, nutrient availability and vegetation zones. Additionally, these ecosystems may have the capacity to remove reactive nitrogen potentially reducing nutrient pollution in coastal zones. Salt marshes of the northern Northwest Atlantic are typically vegetated by Spartina alterniflora at the lowermost elevations and Spartina patens at higher elevations. On the Mississippi Delta, in the northern Gulf of Mexico, Spartina alterniflora is typically found in the most saline marshes, whereas Spartina patens is found at slightly lower salinities. We evaluated the response of GHG production and denitrification to elevated temperature and nutrients through laboratory incubations of intact soil cores. Cores were collected from Spartina patens and Spartina alterniflora zones in the St. Lawrence River estuary, Quebec and in the Barataria-Terrebonne Basin, Louisiana, areas with distinctly different climates. We used ¹⁵N-NO₃^- and ¹⁵N-NH₄⁺ tracers to partition the sources of N₂O produced by denitrification and nitrification, respectively,  as well as total N₂ production by denitrification using the ¹⁵N-GAS Flux method. We also measured potential fluxes of CH₄, N₂O and CO₂. Incubation experiments were performed under ambient conditions and with elevated temperature and nutrient conditions. Different environmental conditions between vegetation zones and climatic regions are expected to result in different fluxes of CH₄ and N₂O, and rates of denitrification. Elevated temperature and nutrients are expected to increase GHG fluxes, however, it is unclear how net N₂ production, as a remedy for nitrate attenuation in marshes, will respond. Our aim is to increase our understanding of the impact of increased temperature and nitrogen loading on nitrogen removal capacity and the GHG climate feedback in different vegetation zones of salt marshes of two climatic regions.

How to cite: Comer-Warner, S., Ullah, S., Stagg, C., Quirk, T., Swarzenski, C., Bulseco, A., and Chmura, G.: The response of greenhouse gas fluxes and nutrient filtration potential to increases in temperature and nutrient loading from salt marsh soils across a climatic gradient, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1119, https://doi.org/10.5194/egusphere-egu22-1119, 2022.

Coastal wetland systems are a priority habitat, according to the EU Habitats Directive (1992). They consist of a range of plant communities and in Europe can include salt marshes, coastal wet grasslands, swamp vegetation on the seaward edge, and scrub vegetation on the landward side. Coastal wetlands provide numerous essential ecosystem services, including supporting high biodiversity, high productivity, flood defense and wave attenuation as well as carbon and nitrogen sequestration and storage. Despite their ecological importance coastal wetlands have been subjected to habitat degradation and loss throughout their distribution as well as decreases in ecosystem service provision, and this is likely to be exacerbated by climate change. There has been increasing interest in the ability of coastal wetlands to store and sequester carbon and nitrogen as a highly important ecosystem service that may help mitigate climate change.

We collected topsoil cores from three Baltic coastal meadows following stratified random sampling for each plant community: Lower Shore (LS), Upper Shore (US), Tall Grass (TG) and Open Pioneer (OP). A total of 10 cores per plant community per site were collected. Sampling cylinders (88.2 ml capacity; 40 mm height; 53 mm internal diameter) were used to collect undisturbed soil material. Organic carbon content (SOC) was determined by the Tjurin (wet combustion) method and total nitrogen (Ntot) content with the Kjeldahl method.

Our results show that organic carbon content and total nitrogen are site and plant community specific. The specificity is likely driven by sedimentary and geomorphic constraints such as rates and duration of inundation and allochthonous organic inputs, which highlights how increasing rates of sea level rise and frequency of extreme flooding events will likely impact carbon and nitrogen storage in coastal wetlands. This also shows that not all sites provide the same level of these ecosystem services and should carbon metrics be applied for conservation purposes in the future, site specific studies and monitoring of carbon sequestration will be required.

How to cite: Rodrigues-Morgado, M., Villoslada Peciña, M., D. Ward, R., F. Bergamo, T., and Sepp, K.: Carbon and Nitrogen storage in Baltic coastal wetlands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2913, https://doi.org/10.5194/egusphere-egu22-2913, 2022.

Coastal wetlands are important components in the global carbon cycle; however, little is known regarding the carbon sink and source capacity of coastal wetlands in the northern high latitudes, nor their importance in the global methane budget. In this study, we investigate methane and carbon dioxide fluxes from coastal wetlands located along the mouth of the Kenai River of Southcentral Alaska. We measured methane fluxes with a portable greenhouse gas analyzer and a custom-made gas flux chamber along four transects with varying moisture, salinity, and tidal conditions during August 2021. To better understand the drivers of these fluxes, we also collected soil samples, recorded the vegetation composition, and measured salinity at each site. Preliminary results indicate that methane fluxes are lower in areas frequently inundated by tides as compared to areas with minimal to no tidal influence. In addition, we use these data to investigate the effects of salinity and moisture on coastal wetland methane and carbon dioxide fluxes. The overarching goal of this study is to understand whether Northern coastal wetlands are likely to become carbon sinks or sources with ongoing climate change and how future sea level rise will affect the methane and carbon dioxide emissions from these ecosystems at the land-ocean interface.

How to cite: Fuchs, M., Treat, C., Schwarzer, J., Jones, M., Tyler, N., Frolking, S., and Walter Anthony, K.: Methane fluxes from Northern coastal wetlands on the Kenai Peninsula, Alaska, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9878, https://doi.org/10.5194/egusphere-egu22-9878, 2022.

Tidal marshes are vegetated coastal ecosystems that are heavily influenced by estuarine gradients such as tidal inundation and salinity. The sequestration potential of these blue carbon ecosystems relies on the balance between the input and degradation of soil organic matter. At the root-soil interface, plant activity greatly impacts the physicochemical and biological properties of the surrounding soil through interactions with soil microbiota. The transport of oxygen into the anoxic sediments and exudation of metabolic substrates by wetland species demonstrate two key mechanisms by which plants can prime the microbial decomposition of organic matter. Previous studies have observed markedly distinct modulation of rhizosphere processes even amongst closely related species. Using planar optodes, these biogeochemical processes can be visualized and quantified as 2D images via dynamic quenching of O₂ and CO₂-sensitive fluorophores. This technique enables real-time spatial and temporal mapping of these analytes with minimal disturbance to the belowground biomass. Characterizing these profiles for marsh vegetation under hydrological stress may inform future predictions about species performance under the ongoing threat of accelerated sea level rise. In a microcosm experiment, three salt marsh species will be used in a transplant study to investigate the effect of inundation stress on O₂ and CO₂ dynamics in the rhizosphere over alternating light-dark cycles. By combining physiological measurements with morphological attributes, we aim to catalogue plant trait information that can used in scaled-up projections of long-term ecosystem functioning in wetlands.

How to cite: Wilson, M., Jensen, K., and Mueller, P.: Flooding Effect on Rhizosphere Processes in Salt Marsh Plants: Visualizing Spatio-temporal Dynamics of O2 and CO2 using Planar Optodes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12469, https://doi.org/10.5194/egusphere-egu22-12469, 2022.

This presentation will examine factors influencing the restoration trajectory of tidal wetland restoration projects in Nova Scotia, Canada, and considerations for long term resilience.  Rates of relative sea level rise in Nova Scotia are projected up to 1.5 m by 2100 (RCP 8.5) and restoration of tidal wetlands are important for climate change adaptation and mitigation.  Over the last 15 years, CBWES, Saint Mary’s University and the Province have restored close to 400 ha of tidal wetland habitat by enlarging culverts or realigning dyke infrastructure.  Comprehensive pre and 5-year post restoration monitoring and insights from the Making Room for Wetlands project reveal marked differences in the rate of vegetation recolonization, surface elevation change and overall restoration trajectory between Atlantic and Fundy marshes.   Differences are also recorded between sites in the Lower Bay (6 m tidal range) and Upper Bay of Fundy (16 m tidal range).  This presentation will focus on the influence of sediment supply, tidal range (inundation frequency and duration), restoration design and seasonal timing of re-introduction of tidal flow on the rate of vegetation recolonization and implications for long term resilience.  

How to cite: van Proosdij, D., Graham, J., Bowron, T., Lewis, S., Elliot, M., Poirier, E., Ellis, K., Lundholm, J., and Pett, B.: Making Room for Wetlands- Considerations for Long Term Resilience, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12832, https://doi.org/10.5194/egusphere-egu22-12832, 2022.

The archipelago of San Andrés, Providencia and Santa Catalina (SAI), southwestern Caribbean islands (Colombia), declared as a Biosphere Reserve by the UNESCO, is highly vulnerable to tropical storms, meteorological tides, coastal flooding and the effects of sea level rise, which are substantially increasing in a context of climate change. In 2020, for the first time in the Colombian history, a hurricane reached category 5 on its territory, destroying the island of Providencia and damaging San Andrés Island. However, historical and future hydroclimatic events trends along with potential mitigation effects of nature-based solutions with mangroves are still very little known and studied in this part of the Caribbean Sea.

Our study analyzes historical (1960s-2020) and future (2050, across low and high mitigation IPCC scenarios) trends in duration, frequency and intensity of extreme rainfall, wind, floods, hurricanes and tropical storms, and discusses their relationship with the regulation ecosystem services in terms of regulation of erosion, flood control and protection against storms, provided by the SAI mangrove forest ecosystems. Using the InVEST Coastal Vulnerability model with new in-situ data for this specific region, we estimate the vulnerability of the Archipelago (in terms of affected inhabitants, damaged houses, loss of property value) to extreme climate without, with current and with maximal mangrove area.

Our work highlights the urgent need to restore and expand the mangrove forest areas in the Archipelago as a measure of both mitigation and adaptation to climate change and extreme weather events. Investments in reducing the vulnerability of the island's inhabitants to the harmful effects of climate change must combine several strategies (climate mitigation, nature-based solutions, waste management, territorial planning, etc.) to reduce environmental damage, economic and social aspects of one of the largest marine protected areas on Earth.

How to cite: Quesada, B., Esteban Cantillo, O. J., and Clerici, N.: Hydroclimatic extremes regulation by mangroves in a highly vulnerable small Caribbean Island, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5891, https://doi.org/10.5194/egusphere-egu22-5891, 2022.

Saltmarshes are acknowledged to be important coastal ecosystems for various ecosystem services they provide. Some of these services contribute to coastal protection which is increasingly accounted for in coastal protection and management strategies. To do so, it is necessary to project the coastal protection capacity of salt marshes into the future when climate change will not only affect hydrodynamic forcing onto the coast but also environmental parameters such as CO₂ content and temperature of the water.

In this study, we exposed the two salt marsh species Spartina anglica and Elymus athericus as examples for the pioneer zone and mid marsh, respectively, to enhanced CO₂ (800 ppm) and temperature (+3°) levels in the water in a mesocosm experiment for three months. These parameters were changed individually as well as in combination to mimic a future climate scenario and compared against a control treatment with ambient conditions. At the end of the experiment the effect on plant stem growth and biomechanics was assessed using a three point bending test. These plant traits feed into the interaction of vegetation with hydrodynamics and thus form the basis for wave and flow attenuation as important coastal protection ecosystem service.

Our results show that Elymus athericus did not respond to any of the treatments with respect to stem diameter, bending modulus, flexural rigidity and breaking force, suggesting that it is insensitive to such future climate changes. Spartina anglica does show an increase in diameter for all treatments compared to the control, but this increase only became statistically significant (α=0.05) for the combined CO₂ and temperature treatment. Bending modulus as indicator for the stem’s material composition showed inconclusive results for the two heights along the stem studied with a decrease under the future climate scenario 5 cm above ground and an increase at 15 cm above ground. Flexural rigidity, incorporating both the geometry as well as the plant material, showed an increase under the future climate scenario at both locations compared to the other treatments, but only at 15 cm above ground was this increase statistically significant. The maximum force experienced during the bending test and thus the force at which structural failure is experienced did not differ between treatments at all.

Overall it can be concluded that even though some differences between the future climate scenario and present conditions could be found, all values still lie within the natural trait ranges found for the two species and thus traits relevant for the plant’s interaction with hydrodynamics and the resulting ecosystem services wave and flow attenuation appear to be unaffected by CO₂ and temperature increases in the water due to climate change. Consequently, it can be anticipated that capacity of salt marshes to provide coastal protection ecosystem services will remain constantly high and will only be affected by future changes in hydrodynamic forcing.

How to cite: Paul, M., Bischoff, C., and Koop-Jakobsen, K.: Coastal protection capacity of saltmarshes remains high in the future, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2520, https://doi.org/10.5194/egusphere-egu22-2520, 2022.

Facing the consequences of climate change like sea level rise and an intensified storminess, salt marshes will play an increasingly important role in future coastal protection. The vegetation of salt marshes contributes significantly to the protection function as the plants reduce erosion and act as obstruction to hydrodynamic forces resulting in wave attenutation. Yet, how other global change factors such as higher temperatures will affect salt marshes and their potential to protect our coasts against high wave intensities, e.g. during storm surges, is largely unknown.

In a world-unique whole ecosystem warming experiment (MERIT) we increased air and soil temperature in a salt marsh at the German North Sea coast. Here, we aimed to examine effects of warming on plant characteristics critical for withstanding hydrodynamic forces. Besides quantifying biomechanical and biochemical properties, that are known to affect plant rigidity, we additionally measured spectral reflectance to assess the NDVI of the canopy. This was done to quantify the expected shifts in the growing season due to warming (i.e. earlier green-up in spring and/or delayed senescence in autumn) that would possibly coincide with the storm surge season in NW European salt marshes. Results of this study will contribute to a better understanding of future marsh resilience and wave attenuation capacity in a warmer world.

How to cite: Reents, S., Jensen, K., Rich, R., Thomsen, S., and Nolte, S.: The effect of experimental warming on the resistance of salt-marsh vegetation to hydrodynamic forcing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9967, https://doi.org/10.5194/egusphere-egu22-9967, 2022.

Globally, increased coastal flooding is considered as one of the main consequences of climate change in coastal zones. To mitigate coastal flood risks nature-based solutions that complement traditional engineering approaches are increasingly considered as a key adaptation strategy. A widespread form of a coastal nature-based solution is managed realignment (MR), i.e. the inland realignment of coastal defences and the creation of coastal ecosystems (mostly saltmarshes) in the intervening space. However, these approaches involve giving-up previously reclaimed, now agricultural, land to the sea, often resulting in low local-community support. This is not only because coastal retreat may conflict with community values and interests, but also due to low public trust in the success of nature-based adaptation.

Here, we show that the available evidence underlining the coastal protection function of MRs is primarily based on research from natural, mostly large, saltmarshes, where wave heights during storms and tidal surges are effectively attenuated, while available evidence for the effectiveness of MRs is very limited. This means that often local communities have no conclusive evidence of the schemes’ actual flood-risk reduction potential. Indeed, the little available evidence on the coastal protection function of MRs suggests that only MRs exceeding a particular size may be effective in reducing coastal flood risks, hence local community support is becoming even more important. We therefore propose a novel co-production process for the planning and implementation of MRs, where coastal communities are involved in the production of knowledge to establish the coastal protection function of MRs.

How to cite: Schuerch, M., Mossman, H., Christie, E., and Moore, H.: The coastal protection function of Managed Realignments – a review of the available evidence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10434, https://doi.org/10.5194/egusphere-egu22-10434, 2022.

Coastal wetlands are intrinsically heterogeneous and typically composed of a mosaic of ecosystem patches with different vegetation types. The patch type and vegetation density affect hydraulics, nutrient processing, and greenhouse-gases budgets. We studied carbon sequestration and nitrogen and phosphorus accumulation rates in a lake-estuarine wetland at different patch types across a microtopographic gradient and levels of influence from the main channel. Rapid lake level rise (~1 m/decade) at our field site, OWC, an estuarine marsh by Lake Erie shore in OH, USA, led to rapid increase in wetland water elevation. These were followed by changes in the patch types at each location within the wetland. We developed an approach to classify vegetation patch types from seasonal timeseries of NDVI from the HLS (harmonized Landsat-Sentinel) remote sensing dataset. We classify the location and extent of vegetation patches over the last decade and found rapid transition from cattail to floating-leaf vegetation. And while the bathymetry (the topography of the wetland bottom) was relatively constant, the rapid changes to water elevation and vegetation meant that the current patch-type identity did not provide a consistent indication of the local ecosystem characteristics over a timeframe of several years.

Using a microtopographic (hydrological) rather than vegetation-type (ecological) characterization of our soil core locations, we found that nitrogen accumulation mirrored carbon relative distribution, with larger rates at the shallow and deep locations than at the intermediate-depth ones. Both carbon sequestration and nitrogen accumulation rates were greater the farther they were from the main channel. Phosphorus accumulation rates were larger at the deeper microtopographic level than in the intermediate and shallow ones. Phosphorus accumulation did not vary in response to the influence of the main channel. Our results highlight the relevance of watershed-level management practices of phosphorus and nitrogen runoff to control carbon sequestration and nutrient accumulation in wetlands. Climate-change-induced water-elevation changes emphasize the relevance of microtopographic considerations in wetland-related projects, such as maximizing deep pools to enhance phosphorus accumulation. 

How to cite: Bohrer, G., Ju, Y., and Villa, J.: The role of ecohydrological patch types in carbon sequestration and nutrient uptake rate in a lake estuarine wetland experiencing rapid water-level rise, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10078, https://doi.org/10.5194/egusphere-egu22-10078, 2022.

Wetland restoration has become a fundamental part of the EU strategy for biodiversity and climate action. Far from the long-lasting experience of Central Europe, many of the Southern European countries are still in the early stages of wetland restoration, renaturalization or realignment. Indeed, the passive wetland restoration strategy based on the reconversion of abandoned salt pans to wetlands became popular in Portugal over the last decade. In such period we estimate that only 30 ha of natural/passive and managed renaturalization have been conducted in the two main coastal lagoons of Portugal, Ria Formosa and Ria de Aveiro, with a potential for upscaling close to 400 ha.

In this study, we analyzed the long-term lateral adjustment of renaturalized wetlands based on remote sensing data. During ten years of natural evolution, we identified four main ecogeomorphologic states in these environments: (1) hydrodynamic readjustment and sediment infilling; (2) channelization; (3) mud or sand flats construction/destruction and pioneer vegetation colonization; and (4) vertical accretion and replacement of the tidal flat by the low marsh. The morphological development of the tidal flat (and its colonization by primary producers) was relative fast, occurring in the first 1-2 years after renaturalization, whereas the development of a bimodal interface between tidal flat and low marsh occurred at slower rates (colonization with pioneer vegetation started ~ 3 years after renaturalization). Saltmarsh areas increase at rates ranging between 500 and 1 000 m²/year in the surveyed salt pans. The degree of habitat formation and ecological succession (and services delivery) has been relatively fast, but the full benefits remain to be realized. Currently, there is no effective management strategy for renaturalized wetlands in Portugal, meaning there are no standard indicators to benchmark the success of observed and conducted interventions. The past adopted renaturalization imposed low initial costs, but long-term losses are likely, as most of them might not be a sustainable long-term solution to cope with sea-level rise and carbon accumulation.

There is now a strong environmental and policy momentum to renaturalize new areas and actively restore wetlands in Portugal. With that in mind overcomes the pressing need for interdisciplinary research on restored wetlands adjustment, merging observations and resilience assessment schemes, as well as the development of biogemorphologic indicators of evolution (including ecological successions) after renaturalization/restoration interventions. Also, interdisciplinary research (from natural and social sciences) must be combined with national and regional management plans and policies.

How to cite: Carrasco, A. R. and Sousa, A. I.: Tracking ecogeomorphologic states in renaturalized wetlands in Portugal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4476, https://doi.org/10.5194/egusphere-egu22-4476, 2022.

Ecological development, through species colonisation and the evolution of community structure, is considered a fundamental indicator of success in salt marsh restoration, and thus has been studied extensively. However, previous studies have reported mixed success, suggesting restoration techniques are not always effective. As such, it is essential further research is carried out to inform the design of future projects. This requirement is compounded by commitments to increase the number of realignment projects to mitigate losses of salt marsh due to sea level rise, as well as improve the provision of ecosystem services. This study  assesses the ecological development of a restoration site in the UK in the first three years following its creation.

The Adur estuary is a macrotidal estuary in West Sussex, UK and contains a regionally rare and significant area of salt marsh, which is protected by national legislation. The restored site sits landward of the established marsh at a higher elevation than the adjacent mid marsh plant community. Ecological surveys were carried out biannually in 2019, 2020 and 2021 using 33 quadrats along 11 transects, with each transect passing from new marsh into established upper and low marsh communities. In each quadrat, the presence and percentage cover of each plant species was recorded. Additionally, drone flights were carried out to provide 10 cm resolution imagery of the new and established marsh in both 2020 and 2021. Species composition of the new and established communities in each year were compared to determine ecological development. Additionally, the drone imagery was used to calculate the Normalised Difference Vegetation Index to provide an indicator of vegetation cover across areas not covered by quadrat surveys.

Quadrat surveys indicate significant initial development of the restoration site, with mean cover of bare ground decreasing from 72% in 2019 to 34% in 2021. Additionally, the number of species has increased, from 6 in 2019 to 9 in 2021. However, conditions still differ from the established marsh, with the dominance of Halimione portulacoides not yet present. Additionally, vegetation cover is lower in the new marsh, which was also detected in the drone imagery.

The results of this study demonstrate that the restoration site has developed over three years, as is evidenced by the decrease in bare ground and increase in halophytic species, thus suggesting restoration design has been effective. However, the current lack of dominant Halimione portulacoides cover shows a disparity with the adjacent established upper community, although the species has increased in the new marsh over the study period. Further study will reveal whether this development continues towards comparable conditions.

Monitoring of the site will be continued with further ecological surveys in 2022, 2023 and 2024. Additionally, an automated approach to community mapping will be developed using machine learning algorithms combined with the drone imagery, which will also be carried on until 2024. This automated approach to community mapping has the potential to provide rapid ecological assessments for restoration sites whilst also increasing the reliability of surveys.

How to cite: Agate, J., Ward, R., Joyce, C., and Burnside, N.: Ecological development of a salt marsh restoration site, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4780, https://doi.org/10.5194/egusphere-egu22-4780, 2022.

Tidal marshes are fundamental ecosystems to be preserved and restored to maintain their vital services to the environment and human life. For this reason, many restoration projects have been implemented in the Lagoon of Venice (Italy) to reestablish former tidal marshlands. One fundamental point of the marsh restoration design is the determination of its long-term elevation. This is crucial for the ecological functioning of the system as well as the ability of the landform to keep pace with a rising sea level. Past marsh reconstruction projects have not always been successful. Significant areas become permanently submerged by the sea only few years after their construction and/or vegetation cover remains more patchy and less biodiverse than on natural marshes. Two design parameters which have not received sufficient attention in restoration projects are autocompaction of nourishment sediments and subsidence of underlying strata. To this aim, the planned elevation at the end of the nourishment phase, i.e.  the volume of sediments used to build-up the marsh, must take into consideration nourishment autocompaction and land subsidence of the underlying lagoon bottom caused by the nourishment load. To enable monitoring of these dynamics of elevation change, we developed a novel Nourishment Elevation Change (NEC) station to investigate compaction and subsidence of an artificial marsh under development in the central basin of the Lagoon of Venice. Each NEC station is made of four steel bars set into the lagoon subsurface down to a 2-m depth. Their role is to keep a central steel pole free to move vertically with respect to its specific foundation level. The foundation consists of a plate resting either on the top of the pristine lagoon bottom or an anchor inserted into the subsurface to a depth of interest, e.g., 1 m.  As the nourishment areas become inaccessible after its development, the pole is marked with a black-and-white striping to be able to measure its movements from a distance and equipped with a horizontal plate on top of the pole. A monitoring network consisting of 10 NECs was established in the artificial marsh area of about 61.000 m² before the nourishment. The NEC station elevation is monitored with a mm-accuracy topographic intersection technique using a total station. Two stable benchmarks positioned in a nearby existing marsh are used as reference. The maximum distance between the NECs and the benchmarks amounts to 300 m. In addition, the NECs are monitored using aerial drone photogrammetry. The change over time of the distance between NEC top plate and the marsh platform allows quantifying the nourishment autocompaction.  The topographic intersection surveys have been ongoing every two weeks since the nourishment started in October 2021. Over the first month of sediment filling a maximum subsidence of about 7 cm has been measured by the NEC station located closest to the nourishment pipe. The other NECs, which are not yet affected by sediment deposition, remained stable. The NEC monitoring system seems promising and will provide quantitative information on the elevation dynamics of newly created artificial marshes.

How to cite: Zoccarato, C., Teatini, P., Minderhoud, P., Fabris, M., Menin, A., Monego, M., Bertolini, C., and Da Mosto, J.: Innovative Nourishment Elevation Change (NEC) stations for monitoring and optimizing marshland restoration projects: prototype application in the Lagoon of Venice (Italy)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7450, https://doi.org/10.5194/egusphere-egu22-7450, 2022.

Nature-based solutions have become tremendously popular over the past few years. They are popular among large financing institutions such as the WorldBank and the Asian Development Bank up to very local governmental bodies that have heard of the many benefits these Nature-based solutions deliver. However, the supposed benefits of Nature-based solutions depend strongly on how, where and with what purpose these solutions are designed. The massive introduction of Nature-based solutions has led to many interesting and innovative projects that created multiple benefits. On the other hand, it has also led to projects in which the Nature-based component was not so clear, and the benefits were uncertain. This leads us to the question: are Nature-based solutions a way to solve all your challenges in the coastal zone and if they don’t, can we still call them a Nature-based solution? And, what do we actually mean with a Nature-based solution. We would like to tap on these questions with some examples of real projects and conceptual designs.

The projects and designs are all based in coastal areas where Nature-based solutions often take the form of wetlands or extended foreshores. These wetlands consist of mangrove systems in the tropics and salt-marsh systems in more temperate regions. The projects had different goals and different scales, they provided different benefits, but they all have in common that they were called a Nature-based solution. Depending on the goals and specific demands we encountered various interesting challenges. The final designs show that Nature-based solutions come in many sizes, shapes and forms. Sometimes they have the possibility to change livelihoods of people at a landscape scale and sometimes they only added a little green fringe.

How to cite: dankers, P.: Wetlands and foreshores: The solution to all your challenges, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5565, https://doi.org/10.5194/egusphere-egu22-5565, 2022.