GM6.4

EDI
Coastal wetlands: Processes, interactions, management

Coastal wetland ecosystems, such as salt marshes, mangroves, seagrass beds and tidal flats, are under increasing pressure from natural and anthropogenic processes shifting climatic conditions, and are declining in area and habitat quality globally. These environments provide numerous ecosystem services, including flood risk mediation, biodiversity provision and climate change mitigation through carbon storage. Hence, the need to get a deeper understanding of processes and interactions in these environments, and how these may be altered by climate change has never been greater. This is the case for ‘managed’, restored wetlands and natural systems alike.
This session will bring together studies of coastal wetland ecosystems across climates and geomorphic settings, to enhance the understanding of ecosystem service provisioning, interactions between hydrodynamics, sediment and ecology, and identify best future management practices. Studies of all processes occurring within coastal wetlands are invited. This includes, but is not exclusive to, sediment dynamics, hydrology, hydrodynamics, biogeochemistry, morphological characterisation, geotechnical analysis, bio-morphodynamics, ecological change and evolution, impact of climate change, sea level rise, anthropogenic and management implications. Multidisciplinary approaches across spatial and temporal scales are encouraged, especially in relation to global climate change. This session aims to enhance our understanding of basic processes governing coastal wetland dynamics and to propose sustainable management solutions for contemporary environmental pressures.

Co-organized by BG4/HS13
Convener: Mark Schuerch | Co-conveners: Thorsten Balke, Helen BrooksECSECS, Ruth Reef, Christian SchwarzECSECS
vPICO presentations
| Wed, 28 Apr, 11:00–12:30 (CEST)

vPICO presentations: Wed, 28 Apr

Chairpersons: Helen Brooks, Christian Schwarz, Mark Schuerch
11:00–11:05
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EGU21-14069
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solicited
Kerrylee Rogers and Neil Saintilan

The resilience of coastal wetlands in the fate of sea-level rise is proposed to be related to the combined influence of changes in substrate organic matter volume, mineral sediment volume, auto-compaction of accumulating material and deep subsidence; however, relatively few studies have measured all of these variables. In addition, there is ongoing debate about the suitability of this data for modelling the behaviour of coastal wetlands under anticipated sea-level rise projections as temporal discrepancies in the elevation response of coastal wetlands derived from observational and stratigraphic records exist. To resolve these issues, data derived from a range of techniques sensitive to changes occurring at annual, decadal and century timescales, is presented in the context of available accommodation space, that is, the space in which tidally-borne material can accumulate. Focussing on an embayment in Victoria, Australia, analyses confirm that at annual-decadal timescales, organic matter behaves like a sponge, compressing as the overburden of material accumulates, resulting in auto-compaction that modulates the degree of surface elevation change that occurs as tidally-borne material accumulates. These processes operate concurrently and are influenced by sediment availability, yet vary on the basis of available accommodation space. At longer timescales, the influence of auto-compaction diminishes as organic matter has undergone significant compression and decomposition, yet accumulated material remains proportional to available accommodation space. These analyses confirm that temporal discrepancies in rates of substrate elevation change can be resolved by accounting for the timescale over which processes operate and the influence of sea-level rise on available accommodation space. Accordingly, models should dynamically consider rates of surface elevation change relative to available accommodation space.

How to cite: Rogers, K. and Saintilan, N.: Coastal wetland substrate elevation is dynamically related to accommodation space and influenced by sea-level rise, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14069, https://doi.org/10.5194/egusphere-egu21-14069, 2021.

11:05–11:07
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EGU21-9107
A. Rita Carrasco, Katerina Kombiadou, and Miguel Amado

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 ‘persistence’ 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∙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.

Acknowledgements:

Rita Carrasco was supported by the contract DL57/2016/CP1361/CT0002, Katerina Kombiadou was supported by the research project ENLACE (ref. PTDC/CTA-GFI/28949/2017), all funded by Fundação para a Ciência e a Tecnologia. The authors would like to acknowledge the support granted by UIDB/00350/2020 CIMA BASE.

How to cite: Carrasco, A. R., Kombiadou, K., and Amado, M.: Salt marshes adjustment to anthropogenic pressures and sea-level rise, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9107, https://doi.org/10.5194/egusphere-egu21-9107, 2021.

11:07–11:09
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EGU21-13983
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ECS
Alice Staro, Duncan FitzGerald, Zoe Hughes, Christopher Hein, Ioannis Georgiou, Kendall King, Jennifer Connell, and Christina Pondell

Coastal saltmarshes are an important and highly diverse ecosystem, shielding the mainland from erosion and flooding. Along the US East Coast these valuable wetlands are endangered due to climate change, sea-level rise, and reduced fluvial sediment fluxes. Although hurricanes are commonly an erosional agent, they may be responsible for delivering significant volumes of sediment to the marsh surface, which could aid resiliency by increasing vertical accretion. This study analyzes marsh sediment cores collected during December 2017 within the Georgia Bight, targeting deposits associated with Hurricane Irma, which caused significant wave energy and storm surge along the coast from Florida to South Carolina in September 2017.

We have focused our initial research on samples from Sapelo Island (Georgia), where Hurricane Irma produced maximum wind velocities of 17.5 m/s and a 1.3 m storm surge, inundating the marsh for 14.8 hrs. We find that Irma-related layers are between 2 and 7 cm thick and well-oxidized. These deposits typically consist of laminated mud with low organic content (LOI: 10-25%) and low bulk density (0.3-0.8 g/cm3). On average, Irma event sediment thickness is 4 times the historical average annual accretion, which in Georgia salt marshes is 1.55 mm.

A direct comparison of Irma-affiliated marsh accretion and historical rates is complicated due to differences in consolidation, rooting and vegetation, and the sedimentation history of the marsh. Nonetheless, the storm layer represents a significant addition of sediment to the marsh surface. Thus, future increases in event sedimentation, associated with increased frequency or severity of storms, could help compensate for sea-level rise and lessen the likelihood or extent of marsh loss due to submergence.

How to cite: Staro, A., FitzGerald, D., Hughes, Z., Hein, C., Georgiou, I., King, K., Connell, J., and Pondell, C.: Will hurricane sedimentation aid southeastern US saltmarsh resiliency in the face of climate change and sea-level rise?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13983, https://doi.org/10.5194/egusphere-egu21-13983, 2021.

11:09–11:11
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EGU21-10682
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ECS
Helen Brooks, Iris Moeller, Tom Spencer, Katherine Royse, Simon Price, and Matt Kirkham

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.

How to cite: Brooks, H., Moeller, I., Spencer, T., Royse, K., Price, S., and Kirkham, M.: Quantifying vertical deformation of salt marsh substrates and their recovery during and after storm surge inundation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10682, https://doi.org/10.5194/egusphere-egu21-10682, 2021.

11:11–11:13
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EGU21-4925
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ECS
Olivia Shears, Iris Möller, Tom Spencer, Ben Evans, and Kate Royse

Salt marsh ecosystems are important for supporting biodiversity, sequestering carbon and providing natural coastal protection. Evidence for their existing and potential future loss through marginal erosion is therefore of concern. However, the factors governing spatial variability in the rates of erosion at salt marsh margins – including between creek banks within individual salt marsh sites – remain relatively poorly understood. Accurate prediction of changes to the marsh edge, and thus marsh areal extent, requires more complete understanding of the dynamics and mechanisms occurring at exposed marsh fronts.

In this study, we present observations of the responses of vertical sections of marsh substrate exposed to tidal flat conditions, during a field experiment over a six-month period. Vertical sections were extracted from natural and restored sites at two salt marshes in the UK: Northey Island, eastern England, where sediment is fine-grained, and Hesketh Out Marsh West, north-west England, where sediment is typically sand/silt-dominated. The study specifically investigates the role of different sedimentology and downcore substrate properties, including lamination and rooting structures, on observed change in the exposed vertical sections. Images captured in the field are analysed using structure-from-motion photogrammetry and used to create 3-D models of surface change. This is coupled with laboratory testing of downcore sedimentary characteristics, such as particle size distribution and organic matter content.

The study finds that within-core and between-core variability in substrate response to erosive forcing appears to be partly related to variability in sedimentology. Sediment from sand-dominated layers, such as those found in the cores extracted from Hesketh Out Marsh West, was more rapidly and consistently (i.e. across the sediment cores) removed than clay-silt rich sediment. This grain-scale sediment removal resulted in specific morphological responses, whereby ‘chunks’ of substrate were lost, creating cavity areas further exposed to hydrodynamic forcing. Intrinsic biophysical characteristics, including sediment type and the presence of vegetation structures, can impact vertical connectivity within salt marsh substrates. Observations of structural change in the vertical sections over the six-month study period suggest that reduced downcore connectivity in restored salt marsh substrates results in increased desiccation, cracking and bulk sediment removal. An improved understanding of how such intrinsic substrate properties impact marsh front dynamics will facilitate more accurate predictions of marsh evolution and potential ecosystem service provision under future conditions.

How to cite: Shears, O., Möller, I., Spencer, T., Evans, B., and Royse, K.: Variability in the erosion response of vertical sections of salt marsh sediments exposed to tidal flat conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4925, https://doi.org/10.5194/egusphere-egu21-4925, 2021.

11:13–11:15
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EGU21-4169
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ECS
Riccardo Brunetta and Paolo Ciavola

In the period 1950s-60s, the Po river Delta (Northern Italy) was hit by several floods. Agricultural fields were covered by water and many of them remained submerged since. As a consequence of the massive sediment injection into the system, this lead to the birth of new tidal flats around the tip of the Delta. The evolution of these environments over 50 years was studied, as they may be taken as an example for future reconstruction of intertidal areas. The sediment distribution and the morphological evolution of a young tidal flat of about 10 ha located in the Northern part of the Po della Pila branch were studied by undertaking fieldwork since October 2018, including detailed topographic surveys using a UAV, sedimentological analyses, and a study of sediment deposition rates. An extended crevasse splay covers the central part of the flat. The granulometry is predominately fine (Silty clay and Clayey silt), except for the central area, where the sand percentage increases (Loam and Silty sand). This surface distribution is uniform down to ~10 cm; the sand percentage increases instead within the sediment column from ~10 to 25 cm next to the mouths of the channels. The tidal flat experienced a positive sediment budget and it was characterized by higher rates of accretion after the Po river floods. These observations suggest that the tidal channels are fed by sediment from the Po River branch. Orthophotos from the 1950s show that the tidal flat is about 17 - 20 years old and its formation was influenced by human intervention and river floods. The work aims at finally comparing this case study with other tidal flats and salt marshes worldwide characterized by similar and different tidal regimes, to identify the optimal elevation for vegetation to establish and flourish, to support the future restoration of these environments.

How to cite: Brunetta, R. and Ciavola, P.: Evolution of Tidal Flats in the Northern Part of the Po Delta (Italy):  A Strategy for Future Buiding-with-Nature Management, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4169, https://doi.org/10.5194/egusphere-egu21-4169, 2021.

11:15–11:17
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EGU21-7537
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ECS
Uwe Best, Mick van der Wegen, Jasper Dijkstra, Johan Reyns, and Dano Roelvink

The uncertainty surrounding the impact of sea-level-rise (SLR) and storms, which threaten the coastal hinterland, heightens the need for design guidelines on mangroves adaptation and their use in coastal safety. Mangrove forests, well known as coastal ecosystem defences, attenuate the hydrodynamic forces, reduce coastal erosion and foster conditions for increased sedimentation. However, the mechanistic understanding of the feedbacks between the vegetation and the morphodynamics and, the processes which result in the long term erosion- sedimentation during extreme wave events has been limited (Horstman 2014, Best 2017).Therefore, this research seeks to quantify the bio-physical processes governing the geomorphological evolution of mangrove-mudflat systems utilizing spatially explicit observations of mangrove population dynamics with process-based modelling. For calibration purposes and increased insight into interactions between hydrodynamics, sediment dynamics and mangroves, field observations were collected along Guyana’s coast. 

A quadrant, 1km wide and 6km in length, was established in the mangrove-mudflat coastline at Chateau Margot. This stretch of coastline is subject to a semi-diurnal tidal regime with a maximum tidal range of 3.5m during spring tide. Using the data, we developed a 2D high-resolution depth-averaged model of the field site using Delft3D-Flexible Mesh.

We coupled this model with a mangrove dynamics model capturing the development of Avicennia germinans and Laguncularia racemosa species under suitable inundation and competition regimes. With the dynamic vegetation interface linked via the Basic Model Interface (BMI) with Delft3D-FM, the initial establishment is randomized over the computation grid cells, followed by the growth, diffusion and decay of the mangroves in areas of high stresses. The coupled model simulates the geomorphological development from the interaction between the intertidal flow, waves, sediment transport and the temporal and spatial variation in the mangrove growth, drag and bio-accumulation over 100 years. 

A combination of 1D and 2D simulations to analyze the equilibrium behavior of the system as well to identify the mechanistic feedbacks critical for the development of stable belt widths. Waves are critical for the transport of mud into the mangrove belt during high tide. Inundation of the inner fringe occurs during spring tides, so the calm conditions allow for a heightened platform and species establishment. The channels form the major path for the tidal inflow during the lower tides, while the interior of the forest is an effective sediment sink during the higher tides.

RCP SLR scenarios, liner and exponential, reinforce behavioral trends for mangrove retreat and decay, with modelled tipping points realized after 1.5m increases. Results indicate mangrove adaptability hinges on the long term sedimentation responses and system conditions to promote the establishment of belt widths exceeding 300m.

How to cite: Best, U., van der Wegen, M., Dijkstra, J., Reyns, J., and Roelvink, D.: Multi-Time Scale Mangrove-Mudflat Modelling: Exploring Guyana’s Unique Dataset & Numerical Modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7537, https://doi.org/10.5194/egusphere-egu21-7537, 2021.

11:17–11:19
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EGU21-8837
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ECS
Guillaume Goodwin, Luca Carniello, Andrea D'Alpaos, Marco Marani, and Sonia Silvestri

Seagrass meadows are globally distributed ecosystems found on coastal shelves, where they typically occupy the intertidal and shallow subtidal zones. Their sensitivity to environmental changes and proximity to human activities puts them at risk of degradation; as highly valuable marine habitats and potent carbon sequestration agents, they are therefore the target of numerous conservation programmes.

The presence of seagrass strongly influences both wave and current propagation as well as sediment mobility, affecting the morphodynamics of entire estuarine systems. However, quantifying this influence is difficult, because our knowledge of seagrass cover is limited by its dynamic nature. Sensitivity to environmental factors such as nutrient load, available sunlight (mediated by turbidity) and temperature makes seagrass meadows prone to widespread changes in extent and density. Further degradation may occur stochastically through fishing and aquaculture. Conversely, seasonal cycles of high productivity allow meadows to recover and colonize new grounds through clonal and sexual reproduction. 

We propose a novel and cost-effective method to monitor seagrass cover in shallow waters across its seasonal and interannual variations. Combining machine learning and simple numerical modelling, we create a dense time-series of seagrass extent using over 100 LandSat scenes covering a 20-year-long period in the Venice Lagoon, Italy. Based on an expert-lead ecological survey (2004), we train one binary Random Forest Classifier in each of 5 environmentally-homogeneous geographical subzones, using spectral reflectance in the blue, green, red and near-infrared bands of the corresponding LandSat scene as recognition features. We then predict seagrass presence probability for LandSat scenes spanning the 1999-2019 period. Such predictions are made unstable by their sensitivity to sediment plumes as well as algal or gelbstoff blooms. Classification is therefore constrained by a simple numerical model that simulates clonal and sexual reproduction, regional die-off and punctual degradation. The model examines the potential areas colonised or degraded with respect to previous scenes, iteratively building stabilised maps of seagrass cover over time.

Results are verified using further expert-lead estival surveys of the lagoon (2009, 2010, 2017) and of the inlets of Lido, Malamocco and Chioggia (2006 to 2015), as well as 10 digitised seagrass patches for a subsample of 20 invernal scenes. Accuracy metrics improve on the raw predictions (>80% to >85%), and scene-to-scene variability is reduced(>50% to <5%). These results show that public satellite data can be used to map seagrass cover and monitor its seasonal variations. In the future, cover maps may be used to estimate carbon storage, improve sediment transport models in shallow coastal areas, or identify drivers of change in seagrass meadows.

How to cite: Goodwin, G., Carniello, L., D'Alpaos, A., Marani, M., and Silvestri, S.: Long-term seasonal dynamics of seagrass extent in a Mediterranean Lagoon (Venice, Italy) from public satellite data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8837, https://doi.org/10.5194/egusphere-egu21-8837, 2021.

11:19–11:21
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EGU21-1011
Xinyan Wang, Jiaguo Yan, Junhong Bai, Dongdong Shao, and Baoshan Cui

Algae-dominance in seagrass beds has been well recognized, however, the competitive relationship between seagrass and macroalgae along land-sea gradients and their ecological effects has received little attention. In this study, a field survey was conducted at the Yellow River Estuary to investigate the effects of macroalgal proliferation on seagrass and macrobenthic invertebrate communities. Our results suggested that strong competitive interaction existed between the two primary producers, and the positive or negative effects of macroalgae on seagrass growth varied along land-sea gradient. Furthermore, the dominant controlling factors on the biomass, density and diversity of macrobenthic invertebrate communities were found to vary accordingly, i.e., from features of the primary producers in the nearshore where macroalgae suppressed seagrass growth to hydrodynamic disturbance in the offshore where macroalgae facilitated seagrass growth. Our study emphasizes the importance to integrate interspecific competition into ecosystem-based management of seagrass ecosystem, and provides references for additional ecological indicators.

How to cite: Wang, X., Yan, J., Bai, J., Shao, D., and Cui, B.: Effects of interactions between macroalgae and seagrass on the distribution of macrobenthic invertebrate communities at the Yellow River Estuary, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1011, https://doi.org/10.5194/egusphere-egu21-1011, 2021.

11:21–11:23
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EGU21-15258
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ECS
Thaisa Bergamo, Raymond Ward, Christopher Joyce, and Kalev Sepp

Coastal meadows supply a wide range of ecosystem services, including high carbon storage, high plant species richness and a wide variety of habitat types, which supports breeding and migratory bird populations. However, global change (climate change, pollution and environmental degradation) poses several threats to the stability and ecosystem services supplied by coastal meadows. Specifically within the Baltic Sea, recent estimates foresee various degrees of sea level rise along the Estonian coast and salinity is expected to decrease in the eastern Baltic and increase in the west. In order to assess the effects of climate change in coastal wetlands, an investigation of the influence of changes in water level and salinity on coastal wetland plant communities was undertaken. Future scenarios of Estonian coastal wetlands were evaluated using a three-year mesocosm experiment simulating altered environmental conditions. The response of three plant communities (Open Pioneer, Lower Shore and Upper Shore) were assessed in terms of changes in species composition through time. The experiment included 45 mesocosms, 15 per community with 5 treatments (3 replicates per treatment) with control, altered water level and salinity. Exploratory analysis, ANOVA and NMDS, were used to assess changes in the plant communities throughout the duration of the project. Preliminary results show that Open Pioneer is more sensitive to decreased salinity. A decrease in percentage cover of species adapted to high salinity concentration (e.g. Spergularia marina) was observed. On the other hand, Lower Shore didn’t show any clear changes with the treatments. In order to obtain deeper insights, further analysis are needed to reveal complex community shifts under altered physical conditions.

How to cite: Bergamo, T., Ward, R., Joyce, C., and Sepp, K.: Impact of Climate Change on Coastal Meadows: a Mesocosm Approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15258, https://doi.org/10.5194/egusphere-egu21-15258, 2021.

11:23–11:25
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EGU21-8626
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ECS
Kara Keimer, Charlotte Steinigeweg, Viktoria Kosmalla, Oliver Lojek, David Schürenkamp, Boris Schröder, and Nils Goseberg

Biodiversity and nature conservation play an increasingly important role with growing societal awareness, which is reflected in current European legislative frameworks such as the Marine Strategy Framework Directive or the Water Framework Directive, calling for integrative solutions and restoration of good environmental status. Salt marshes provide ecosystem services which can help mitigate climate change and sea level rise threats and simultaneously address coastal squeeze problems. The periodical submergence due to tidal changes creates a special ecosystem with different zones delineated by a landward increasing marsh elevation, which are inhabited by different plant and animal communities. In addition to their ecological value, salt marshes provide coastal protection, as they dissipate wave energy and stabilize otherwise exposed coastal soil lining sea dikes.  

The "Gute Küste Niedersachsen" research project investigates which environmental properties account for livable and safe coastal conditions along temperate climate coastlines, focusing on the symbiosis of human settlements, nature conservation and sustainable coastal protection. Specifically, the identification of vegetation-mediated ecosystem services within salt marshes at the North Sea coast of Lower Saxony, Germany is addressed here. The overarching goal of the transdisciplinary project is to gain knowledge of natural or nature-based systems and their processes within real-world laboratories at the coast to incorporate proven ecosystem services into standardized coastal protection design guidelines and promote integrated coastal zone management.

Methods include field observations and experiments, hydraulic laboratory experiments and numerical simulations over the course of 5 years. During the first years, a systematic observation of vegetation regarding distribution patterns, growth, density, and bio-mechanical (e.g. flexural rigidity, area moment of inertia) as well as root properties (e.g. root length density, tensile strength) and their respective seasonality is conducted. Through comprehensive monitoring covering large areas of halophytic meadows, a physical model of heterogeneous salt marshes will be developed. Simultaneous measurements of environmental parameters covering waves, currents and soil properties yield a comprehensive data set for analysis, numerical and analytical modeling purposes. 

Hydraulic experiments modeling the wave-vegetation-soil interaction will be devised based on field data, developing dynamically and geometrically scaled vegetation surrogates. Besides vegetation properties aboveground, a focus will be on previously sparsely considered root system effects that is hypothesized to govern erosional processes in salt marshes.

How to cite: Keimer, K., Steinigeweg, C., Kosmalla, V., Lojek, O., Schürenkamp, D., Schröder, B., and Goseberg, N.: Ecosystem services in coastal wetlands: Investigating bio- and hydro-mechanical traits of salt marsh vegetation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8626, https://doi.org/10.5194/egusphere-egu21-8626, 2021.

11:25–11:27
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EGU21-7114
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ECS
|
Highlight
Maria Maza, Javier L. Lara, and Iñigo J. Losada

The estimation of wave energy dissipation produced by saltmarshes has traditionally been obtained in terms of a drag or friction force. The estimation of these forces is made taking into account the characteristics of the saltmarsh (i.e. biomechanical properties, morphology, density) and a hydrodynamic coefficient (i.e. the drag or friction coefficient). The characterization of a vegetated ecosystem by measuring leaf traits, the biomechanical properties of the plants and the number of individuals per unit area involves a lot of effort and is case-specific. In addition, hydrodynamic coefficients are selected on the basis of simplified geometry parameterizations or on calibrations performed in ad hoc studies and accurate estimates rely on their validation under real conditions.

Although for a very limited number of species, previous studies have shown that wave damping positively correlates with standing biomass. Therefore, standing biomass can be a unique variable that defines the wave energy attenuation capacity of the ecosystem. In addition, this variable has already been already characterized for many ecosystems by means of traditional plant harvesting or more recently using aerial images. Then, to further explore its relationship with the induced flow energy attenuation, a new set of experiments is proposed using real vegetation, with contrasting morphology and biomechanical properties, and subjected to different incident flow conditions. The experiments are carried out considering four species of vegetation, with contrasting biomechanical properties and morphology, and including two densities per species. Three water depths, wave heights from 0.08 to 0.18 m and wave periods from 1.5 to 4 s are tested. Capacitive free surface gauges and Acoustic Doppler Velocimeters (ADVs) are used to measure wave damping plant capacity along the meadow.

A direct relationship between the standing biomass of the meadow and plant induced wave attenuation is found for the eight vegetated conditions. In addition, a single relationship is obtained for the resultant wave damping and the eight standing biomass values. This relationship provides the basis for the use of standing biomass as a key parameter to estimate the coastal protection service provided by different saltmarsh species using a single variable that can be easily quantified from the field.

How to cite: Maza, M., Lara, J. L., and Losada, I. J.: The standing biomass of saltmarshes as a key variable for estimating their wave energy damping capacity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7114, https://doi.org/10.5194/egusphere-egu21-7114, 2021.

11:27–11:29
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EGU21-15068
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ECS
Miguel Villoslada, Thaisa Bergamo, and Raymond Ward

Coastal grasslands provide a wide range of ecosystem services worldwide. 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. Here, we present a novel set of UAV-based tools to accurately assess and map coastal grassland structure and functions. Firstly, a combination of UAV-derived datasets were used to produce vegetation indices and micro topographic models. A classification random forest algorithm was used to process the spectral and microtopography datasets and map the extent and spatial configuration of plant communities in coastal meadows in Estonia. The model accurately predicted the occurrence of plant communities with a very high kappa value.

In the second stage, a regression random forest algorithm was used to model and map above-ground biomass within the coastal grasslands sites. Subsequently, the above-ground biomass maps in combination with a mean-shift algorithm were used to assess grassland structural heterogeneity. The results were then 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., and Ward, R.: Novel UAV-based tools for assessing coastal grassland structure and function , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15068, https://doi.org/10.5194/egusphere-egu21-15068, 2021.

11:29–11:31
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EGU21-7208
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ECS
Cai Ladd, Alejandra Vovides, Christian Schwarz, Gail Chmura, Mohammad Basyuni, María Maza, and Thorsten Balke

Hydrological monitoring is crucial for management and research in coastal wetlands. However, long-term monitoring is scarce due to the high cost of conventional hydrological equipment. The development of open-source and low-power sensors over the past decade presents an opportunity for enabling long-term, high spatial resolution monitoring of hydrodynamics in the intertidal zone. Here, we present the design, calibration, and application of one such sensor: the Mini Buoy. The Mini Buoy is a battery-powered accelerometer and data logger, contained in a standard centrifuge tube. The Mini Buoy floats upright when inundated, and moves freely about a tether anchored to the substrate. Acceleration is measured along a single axis of the buoy, and motion along the axis is used to measure inundation, currents, and waves. Deployments of up to 6 months are possible, and the buoy can measure current and wave orbital velocities as low as 0.05 m/s. Mini Buoys cost less than €350 to assemble, and the materials are globally available. We present the successful application of Mini Buoys in four contrasting scenarios: (1) characterising waves under calm and stormy conditions; (2) linking saltmarsh erosion-expansion patterns with hydrological exposure; (3) identifying high-resolution spatial variability of waves and currents along a saltmarsh edge; and (4) assessing the suitability of former aquaculture ponds for mangrove restoration. Mini Buoys are also being deployed along mangrove fringes across Vietnam, India, and Bangladesh, in order to detect thresholds in hydrodynamic forcing responsible for triggering erosion or progradation events. Mini Buoys offer an exciting and novel tool for coastal management worldwide.

How to cite: Ladd, C., Vovides, A., Schwarz, C., Chmura, G., Basyuni, M., Maza, M., and Balke, T.: The Mini Buoy: a novel hydrodynamics sensor for long-term deployments in coastal wetlands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7208, https://doi.org/10.5194/egusphere-egu21-7208, 2021.

11:31–11:33
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EGU21-13953
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ECS
Steven Sandi, Jose Rodriguez, Patricia Saco, Neil Saintilan, and Gerardo Riccardi

Coastal wetland are known to be among the most efficient carbon burial environments around the worlds and given this high efficiency for carbon sequestration, wetland restoration and conservation efforts have been proposed as a way to potentially mitigate greenhouse emissions. The processes that lead to carbon sequestration can be quite complex and often depend on feedbacks between the type of vegetation in the wetlands, tidal flow regime, geomorphology and sediment availability. Coastal wetland vulnerability to submergence due to sea-level rise has been widely discussed in the current literature, and while wetlands could survive under some sea-level rise scenarios, accelerated rates of sea-level rise would most likely result in significant wetland losses. These can be less accentuated when accommodation space is available and the wetland is able to migrate inland, however, topography, physical barriers, and some anthropogenic factors can limit wetland migration thus decreasing the ability of wetlands to cope with sea-level rise. Potential losses of wetland vegetation under accelerated sea-level rise and limited capacity for wetlands to migrate inland are expected to affect the overall efficiency for carbon sequestration. We apply an eco-geomorphic model to simulate vegetation dynamics, carbon accumulation and overall change in carbon stocks for a restored mangrove-saltmarsh wetland experiencing accelerated sea-level rise under different management scenarios. Our results suggest that under accelerated sea-level rise and limited space for inland migration, vegetation might not be able to fully mature, reducing the capacity for sequestering carbon over time.

How to cite: Sandi, S., Rodriguez, J., Saco, P., Saintilan, N., and Riccardi, G.: Carbon burial capacity limited by accelerated sea-level rise in coastal wetlands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13953, https://doi.org/10.5194/egusphere-egu21-13953, 2021.

11:33–11:35
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EGU21-3701
Shu Chen and Dongqi Wang

Coasts and estuaries are key contributors to atmospheric nitrous oxide (N2O) emissions. Here, we used laboratory incubation experiments to investigate temperature (12, 25, and 35 °C) and tidal effects on N2O fluxes in sediments sampled from three contrasting latitudinal subareas along the East China Coast (ECC) (North, Mid, and South). Overall, responses of N2O emissions to increasing temperature varied among the three climatic zones. During non-flood and flooding, mean N2O fluxes in sediments sampled from the North subarea increased exponentially with temperature (49.0 ±40.6 nmol m-2 h-1 at 12 °C to 3160 ±3960 nmol m-2 h-1 at 35 °C, and 741 ±518 nmol m-2 h-1 at 12 °C to 1020 ±1400 nmol m-2 h-1 at 35 °C, respectively). However, mean N2O fluxes in sediments sampled from the South subarea decreased at higher temperatures during flooding (977 ±306 nmol m-2 h-1 at 12 °C to 68.0 ±47.5 nmol m-2 h-1 at 35 °C) and non-flood (233 ±292 nmol m-2 h-1 at 12 °C to 183 ±142 nmol m-2 h-1 at 35 °C). Under ongoing global warming, intertidal areas at temperate may act as potential sources of N2O, whereas the contribution of low latitude coastal sediments to N2O budget may decrease. In addition, there is a combined impact of temperature and tidal fluctuation on N2O emissions that controls N2O production and consumption. Our results improve understanding of the diverse feedbacks of N2O emissions from coastal area to global climate change.

How to cite: Chen, S. and Wang, D.: Effects of Temperature increase on N2O Emissions from Intertidal Area along the East China Coast, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3701, https://doi.org/10.5194/egusphere-egu21-3701, 2021.

11:35–11:37
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EGU21-3425
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ECS
Cheryl Batistel, Gerald Jurasinski, and Hendrik Schubert

Global mean sea level had been rising and accelerating in the last decades affecting coastal wetlands that are important carbon stores since they are susceptible to fluctuating water levels. Climate-change-driven sea-level rise, which is predicted to reach about one to two meters by 2100, may lead to dramatic shifts in the vegetation composition of coastal wetlands consequently influencing ecosystem functions including photosynthetic activity, biomass production, litter decomposability, and ultimately the pattern and rates of nutrient cycling, carbon storage, and greenhouse gas exchange. In this regard, aside from water level, changes in salinity that may especially influence the decomposition of dead plant material are also of prime concern.

Here, we provide a comparative evaluation of the decomposition rates of the dominant macrophytes in different nearby freshwater and brackish peatlands. We assumed that the degradability of leaf litter differs among species due to the difference in chemical composition. Two peatland sites, Schutower Moor (freshwater) and Diedrichshagen Moor (brackish) were selected to compare the decomposition rate and nutrient release of Phragmites australis, Carex sp. and Schoenoplectus tabernaemontanii as influenced by salinity. We used the litterbag method using senescent leaves or stem parts (for S. tabernaemontanii) of the macrophytes that were collected in late autumn. We deposited 30 litterbags per species per site and retrieved 5 of these per site after 1, 2, 4, 6, 8 and 12 months, respectively.

Regardless of site and species, the highest mass loss occurred in the first 35 days of decomposition with a strong decrease thereafter with almost flat slopes. The initial decay rates of the same species did not differ significantly between sites. However, the initial mass loss of the S. tabernaemontanii litter was significantly higher than the other species. This species has the highest decay coefficient of 0.008 d-1 and 0.006 d-1 in freshwater and brackish sites, respectively. These decay rates are up to four times faster compared to the other species resulting in empty litterbags a year after deployment indicating the complete decomposition of S. tabernaemontanii while other species had between 40% to 60% dry mass remaining. Initially, the carbon and nitrogen contents of S. tabernaemontanii were significantly lower than those of the other species while its initial sulfur content was significantly higher than of the other species. S. tabernaemontanii retained a relatively high amount of nitrogen, phosphorus, sulfur and magnesium throughout decomposition compared to the other species. This keeps the C:N, C:P, C:S, C:Mg and N:P ratios nearly constant from the start to the end of the study suggesting continuous microbial activities due to the availability of such nutrients in the detritus of S. tabernaemontanii. This confirms that P. australis and Carex sp. contribute to the formation of peat while S. tabernaemontanii does not.  

Litter quality showed to be a more important factor affecting decomposition than the little difference in salinity between sites (e.g. annual average of 3psu) that did not significantly affect the decomposition rate of macrophyte litter. Therefore, future similar studies should consider comparing sites with higher salinity levels.

How to cite: Batistel, C., Jurasinski, G., and Schubert, H.: Salinity effects on mass loss and nutrient release in the litter decomposition of peatland macrophytes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3425, https://doi.org/10.5194/egusphere-egu21-3425, 2021.

11:37–11:39
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EGU21-9981
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ECS
Stella Volpini, Marco Pilotti, Giulia Valerio, and Steven C. Chapra

The Natural Reserve “Torbiere del Sebino” is situated on the southern bank of Lake Iseo and is one the most meaningful wet zone for extension and ecological importance of northern Italy, belonging to the Natura2000 network.

Torbiere occupies an area of 3.60 km2 within a 14 km2 watershed where almost 12000 inhabitants live and where agricultural activities, mostly vineyards, cover almost 40% of the area; this leads to a significant anthropic pressure that over the last 50 years has compromised the system and changed the equilibria between species, enhancing eutrophication.

Despite the ecological relevance of the area, one of the most important in northern Italy, very little quantitative information is available regarding its current state and evolution in terms of water quality and hydrodynamics.  Given the critical environmental condition of the habitat, it is necessary to address the consequences of human impact on the trophic state of Torbiere.

Torbiere consists of a system of shallow lakes or ponds (average depth 1.5 m) whose main affluent is a creek (called Rì) entering from the South. A secondary occasional affluent enters the system from the East and consists of a combined sewer overflow (CSO). Finally, the main effluent is an artificial channel located in the North connecting Torbiere directly with the subalpine Lake Iseo. Although originally subdivided into a set of many interconnected ponds, the separation levees have been demolished over the last decades to enhance internal circulation, under the assumption that this would decrease the residence time and improve the water quality. However, no rational argument was used to support this decision that led to a system where similar characteristics (Secchi’s depth, turbidity, specific conductivity) are found all over the study area and where the expansion of invasive species was easier; now there is some evidence that a separate set of ponds would be better manageable to contrast the eutrophication process. To understand this process, a 3D hydrodynamic model has been set up using Delft-3D, an open source, finite difference package. 

Given the great extension of the system, the inner circulation of the water is not driven by the momentum of the affluents, instead the wind plays a major role. This forcing term presents a daily pattern: it blows from the North in the mornings and shifts to the opposite direction in the late afternoon. The water mainly flows from the South to the North. However, preliminary results by Delft 3D showed that the circulation is made complex by the wind. The model shows that opposite directions of horizontal flow velocities are found at the surface and at the bottom of the water column, showing that only the upper layers follow the direction of the wind.

By comparing the actual and previous conditions of separation of the ponds, the model aims to give an answer to whether the choice of demolishing the banks was positive or negative for the water quality of Torbiere. Once the role of the banks will be clarified, the effects of their possible restoration will be addressed.

How to cite: Volpini, S., Pilotti, M., Valerio, G., and Chapra, S. C.: Modeling the hydrodynamics of a wetland under strong anthropic pressures (Torbiere del Sebino, Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9981, https://doi.org/10.5194/egusphere-egu21-9981, 2021.

11:39–11:41
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EGU21-12119
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ECS
Amirmoez Jamaat and Ammar Safaie

Wetlands are valuable ecological resources which play an essential and important role in the ecosystem of the region. Hence, there is a crucial need for monitoring and characterization of wetland changes caused by natural and anthropogenic disturbance. In this study, we developed a remote sensing-based approach to investigate long term land use/land cover changes (LULC) of Anzali Lagoon located in the southern coast of the Caspian Sea. In recent years, Anzali Wetland has experienced severe threats by human- and climate-induced changes and is drying up at an alarming rate. Here, an enhanced LULC change detection method is presented using a seasonal harmonic analysis of satellite image based on Normalized Difference Vegetation Index (NDVI)   that combined with remotely-sensed thermal observations. Machine learning and object-oriented approaches were implemented on high-resolution satellite images to obtain a comprehensive land-use classification map of the study area. Then, wetland vegetation changes, such as marshes, were investigated during 2013 to 2020. Additionally, the long-term sea level trend in Caspian Sea was used, along with groundwater storage changes derived by GRACE satellite data, to study their impacts on wetland ecological changes. Results of the developed hybrid model indicate that the western and central parts of the wetland are more subjected to drought stress. Moreover, spatial and temporal changes in density of aquatic plants related to external stressors were identified in the wetland. The results of this study enhance a better understanding of long-term LULC changes in coastal wetlands in response to climate changes and anthropogenic activities.

 

 

How to cite: Jamaat, A. and Safaie, A.: Detection of land use-land cover changes in Anzali Wetland using a remote sensing-based approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12119, https://doi.org/10.5194/egusphere-egu21-12119, 2021.

11:41–11:43
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EGU21-15055
Chris Smillie

Salt marshes can generally be considered as sinks for metals. Research into salt marshes in Cornwall, UK suggests those estuaries heavily impacted by mining contamination are characterised by a less diverse vegetation compared with a significantly less-polluted site. Assessment using the National Vegetation Classification on the mid-marsh confirmed an Armeria maritima-dominated community was to be found in the most metal-enriched salt marsh of Restronguet Creek. However, this plant was co-dominant with Plantago maritima in the moderately contaminated marsh of Lelant and not present at all in the Camel, which has been subject to limited mining related contamination. Using canonical correspondence analysis, vegetation abundance data was compared with geochemical variables within the sediment. Metals were studied using extractions to signal bioavailability. P. maritima was not associated with the very high metal levels found in Restronguet Creek. A. maritima, had some association with soluble copper and was closer to the bulk of metals than P. maritima. As tolerance to adverse conditions and competitiveness are mutually exclusive, A. maritima, therefore, exists in a successional relationship with P. maritima. A. maritima then appears to be outcompeted by P. maritima in marshes with low metal loadings. Moderately high metal content results in a loss of competitiveness by P. maritima allowing A. maritima to co-dominate. In extremely metal-rich estuaries, however, P. maritima is unable to compete, allowing A. maritima to colonize the mid-marsh. Vegetation community may, therefore, be useful as an indicator of the level of metal contamination.

How to cite: Smillie, C.: Mining Contamination Disrupts Successional Change in Salt Marshes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15055, https://doi.org/10.5194/egusphere-egu21-15055, 2021.

11:43–11:45
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EGU21-13176
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ECS
Julián Andrés García Murcia, Fernando Jaramillo, and Sofia Wikström

Eutrophication in the Baltic Sea has been one of the major environmental issues during the last century partly due to extensive land-use change, loss of natural retention systems, and insufficient management. European legislation such as the Water Framework Directive (WFD) attempts to guide the recovery of good ecological status from freshwater to the sea, and suggests wetlands as ecosystems that can potentially contribute to achieving this goal. Wetlands are considered remarkable Nature-based Solutions (NbS) for improving water quality by diminishing the nutrient loads. This study aims to set a background context of the WFD implementation in Sweden, determine the status of constructed wetlands, and evaluate the stakeholders’ perspectives to identify the main administrative hurdles of wetland implementation in Sweden. For this purpose, we conducted a narrative review, database analysis, and semi-structured interviews with members of the institutions involved in water management. Our results show that it is essential to find synergies among the WFD and other directives to expand cross-sectoral cooperation, implement adjustments on the funding scheme that includes restoration and maintenance of natural wetlands, and increase compensation periods and cost ceiling. Likewise, it is crucial to perform significant improvements in the monitoring system, including more frequent data collection, as well as exploring new strategies to capture landowners’ interest in the implementation of NbS, such as the Catchment Officers program. Finally, we suggest paludiculture as a promising farming practice to increase proprietors’ attention on novel market alternatives, and in turn, to provide benefits for climate, water, and biodiversity.

Keywords Wetlands management · Water Framework Directive · Nature-based Solutions · Eutrophication · Semi-structured interviews · Sweden

How to cite: García Murcia, J. A., Jaramillo, F., and Wikström, S.: Hurdles for implementation of constructed wetlands as Nature-based Solutions in Sweden, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13176, https://doi.org/10.5194/egusphere-egu21-13176, 2021.

11:45–12:30