Nature-based solutions (NbS) at the coast are, by definition, methods developed to work with nature to sustainably protect, restore and/or manage the shore. They can be classified into 4 main categories such as fully natural solutions, managed natural solutions, hybrid solutions and ‘green’ engineering solutions. As part of the EU Mission: ‘Restore our ocean and waters by 2030’, the Horizon Europe-funded Atlantic-Arctic Agora (A-AAgora) project identifies innovative solutions, including NbS, to co-develop coastal restoration actions in association with nature and people, throughout 3 demonstration areas. In this context, Demo Ireland locally adapted the ‘living lab’ approach via community-led actions undertaken at Harper’s Island, Co. Cork. Managed and hybrid NbS, for instance livestock grazing, control of invasive species (Spartina), development of pollinator areas, etc…, were successfully tested, supporting coastal wetland restoration and significantly enhancing local biodiversity. NbS deployed by communities at Harper’s Island, with the support of Cork County Council, were then described and reported, allowing their replication to the whole island of Ireland, and overseas. Moreover, additional sites facing coastal erosion and tidal flooding issues were selected and monitored along the Co. Cork coastline. Preliminary results allowed us to identify the main coastal challenges for each site in association with local geomorphological patterns and hydrodynamics, in a context of climate change. The next step for the A-AAgora project in Ireland is to identify suitable NbS as sustainable solutions and long-term management actions, to tackle coastal challenges in those areas. Moreover, this ongoing work is carried-out with the collaboration of multiple stakeholders, such as scientists, decision makers and communities. While these methods have been developed at local scales in the south of Ireland, they can be reproduced and upscaled in other areas, further raising global awareness about coastal adaptation and coastal sustainable solutions/managements.

How to cite: Biausque, M., O'Suilleabháin, D., Wah-Pay, L., and Verling, E.: The use of nature-based solutions (NbS) for coastal restoration actions and biodiversity protection: the A-AAgora project for Ireland., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-516, https://doi.org/10.5194/egusphere-egu24-516, 2024.

Coastal sediments are frequently permeable due to their relatively large grains size. Knowledge on exchange processes across the sediment-water interface and metabolism in these sediments is limited however. We characterize permeable sediments at about 5 m water depth in a coastal stretch of ~3.5 km² at the southern Baltic coast off Germany. Permeability ranged from 1.4 ^.10^-12 m² to 11.3 ^.10^-11 m² (organic content: 0.1% - 0.2% dry mass). We determined total oxygen uptake, TOU, of 10 – 28 mmol O₂ m² d^-1 from in situ measurements in the dark. Benthic net primary production determined in situ varied between 1 - 14 mmol O₂ m² d^-1.
We observed an increase in volumetric oxygen uptake rates in flow-through experiments when highly reactive glucose was supplied as substrate, pointing to the pivotal role of reactive organic substrate availability. However, we could detect only marginally enhanced TOU (uptake doubled at one out of three locations) when applying stirring rates inducing pore water flow in benthic chambers under natural conditions. We conclude that stimulating effects of permeability associated with pore water flow are not detectable in benthic exchange rates below a threshold of 7 ^.10^-11 m² under field conditions. This threshold is higher than previously reported.
Ex situ experiments demonstrated that the distribution of oxygen in the sediment was affected by photosynthetic activity of microphytobenthos and by pore water flow. Benthic primary production determined by the dark-light shift method exceeded the summed fluxes of oxygen into the water and into the sediment driven by concertation gradients, and increased with light intensity as well as with organic substrate availability. These findings indicate that calculated net ecosystem metabolism can shift from autotrophy to heterotrophy owed to an increased consumption within the sediment during advection. We argue that under advective conditions the export flux of photosynthetically produced oxygen may differ from the flux under diffusive conditions. This may seriously impair photosynthesis rate determinations obtained from incubation experiments.

How to cite: Forster, S., Schade, H., and Werna, W.: Surface sediment permeability and reactivity in a shallow coastal environment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1790, https://doi.org/10.5194/egusphere-egu24-1790, 2024.

Coastal communities in North West England face numerous anthropogenic challenges, including high vulnerability to the impacts of climate change, namely enhanced coastal erosion and flooding from sea level rise (Sayers et al., 2022), and marine litter. To manage heightening climate impacts, Flood and Coastal Management has transitioned from a defence to risk-based management, including a focus on building coastal system resilience through Nature-based Solutions (NbS) rather than physical defences. Building the resilience of people, including coastal communities, is critical to this transition, whereby their voices are heard and they can better prepare for these risks (EA, 2020). However, despite the strategic intent to engage and involve people, public participation in practice has been restricted by numerous challenges, perpetuating a continued lack of public involvement in decision making or resilience building.

This interdisciplinary project investigates whether such a deficit in public engagement in decision making can be overcome through a case study citizen science project called Coast Watchers at Rossall on the North West coast, which aims to collaboratively engage people in monitoring and responding to coastal challenges. The research embarked on several study phases to iteratively design, test and evolve the citizen science project collaboratively, involving various coastal monitoring activities and social science investigations. Results suggest that it is important to account for people’s local coastal values, motivations and concerns (Earl et al., 2022) when designing a collaborative approach to public engagement.

Crucially, the work explores the extent to which coastal communities can be engaged beyond citizen science monitoring and become active participants in a resilient and collaborative coastal management. The talk will present outcomes from a series of interviews with coastal practitioners and community members in the North West, exploring the challenges and opportunities for communities to be more involved in a collaborative coastal management. Findings will be discussed within a wider context, whereby they are contributing towards a Flood and Coastal Resilience Innovation Project, Our Future Coast (EA, 2022), which seeks to engage people in adaptation planning and co-designing NbS to better protect coastal communities around the North West coast from current and future challenges.

References

Earl, J., Gormally-Sutton, A., Ilic, S. and James, M.R. (2022). ‘Best day since the bad germs came’: Exploring changing experiences in and the value of coastal blue space during the COVID-19 pandemic, a Fylde Coast case study. Coastal Studies & Society, 1(1), pp.97-119.

Environment Agency (2020) National Flood and Coastal Erosion Risk Management Strategy for England. https://www.gov.uk/government/publications/national-flood-and-coastal-erosion-risk-management-strategy-for-england--2. [14/9/23]

Environment Agency (2022) Flood and Coastal Resilience Innovation Programme. https://engageenvironmentagency.uk.engagementhq.com/innovation-programme. [7/2/23]

Sayers, P., Moss, C., Carr, S. and Payo Garcia, A. (2022) Responding to climate change around England's coast: the scale of the transformational challenge. Ocean & Coastal Management, 225.

How to cite: Earl, J., Ilic, S., Gormally-Sutton, A., and James, M. R.: Collaborative Citizen Science to Support Coastal Management, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3820, https://doi.org/10.5194/egusphere-egu24-3820, 2024.

Coastal permeable sediments cover 50-60% of the continental shelves and are important filters and bioreactors that sitting between the land and ocean. In permeable surface sediments, the dynamic porewater advection can lead to frequent redox oscillation, which significantly affects the coupled cycling of organic matter (OM) and iron. In our study, we focused on the most redox active iron fraction (extractable by 0.5 M HCl), and investigated their effects on OM degradation and retention. During the transition of redox conditions, Fe(III) oxyhydroxides were quantitatively found as the dominant electron acceptors for anaerobic OM remineralization. However, the release of reduced Fe was significantly delayed, with most Fe(II) (~96%) remaining in the solid phase either through adsorption or formation of authigenic Fe(II)-bearing minerals. Under frequent redox oscillation as typically observed in natural coastal permeable sediments, Fe(II) in the solid phase can be re-oxidized and repetitively used as electron acceptor for anaerobic OM remineralization (Iron “redox battery”). In addition, based on our field study along near- to offshore transect in the North Sea, we found that the most redox active iron trapped abundant of dissolved OM (54±20 times than DOM in porewater) that enriched in aromatic and oxygen-rich compounds. It indicates that iron may preferentially promote the retention of terrigenous and aromatic DOM in permeable sediments, thus serving as an important temporal storage for terrigenous OM in the coastal ocean. Further investigations of the dynamic Fe-OM interactions in coastal sediments are warranted to better understand carbon cycling in the coastal area. 

How to cite: Zhou, Z. and Yang, S.: Iron mediated organic matter cycling in permeable surface sediments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7418, https://doi.org/10.5194/egusphere-egu24-7418, 2024.

The Don River Delta, bordering the Taganrog Bay in the Sea of Azov, is one of the major deltas of Europe, providing important ecological and economic services. The Sea of Azov is an enclosed sea, which is also the shallowest sea on the globe (the mean depth is 7 meters) with rich biological productivity.

It was indicated recently that both the Sea of Azov (Berdnikov et al, 2023) and the Don Delta (Venevsky et al, 2023), as well as the estuary area have undergone significant environmental transformations in the last four decades. The water temperature and salinity in the sea and the estuary increased to the never observed values mostly due to climate change (Berdnikov et al, 2023) and the prevailing wind directions changed to the westerlies bringing strong upward surges to the delta. Meanwhile, the Don River runoff significantly dropped started from 2007, while fluvial sediments delivery to the Don Delta were steadily diminishing already during 70 years due to the constructions of dams, human land use and runoff regulation (Venevsky  et al, 2023). Significant amount of suspended sediments from the Taganrog Bay enters the delta and salty waters intrusions to the delta are frequent during surges driven by the westerlies. Thus, the role of marine factors in the delta and estuary area of the Don increased in the last few decades in comparison with fluvial factors. Carbon sequestration in coastal areas considered to be the so-named natural solution for climate change mitigation. Thus, it is important to estimate the past, present and future carbon balance of the Don Delta and the estuary, especially accounting that the delta undergoes changes from being fluvial dominated to marine (wave and surge) dominated one.

We are currently involved in the study focusing on the quantification of carbon pools and fluxes in the Don Delta and the estuary. The study combines modelling approach with field observations and remote sensing data. Our field data included seasonal observations for 2006-2020 of total suspended solids, salinity, concentration of dissolved and suspended organic matter, and chlorophyll-a concentration in the river-delta-estuary continuum (the Lower Don River -Delta-Taganrog Bay). Remote sensing included Landsat and Sentinel images for upward surges episodes for the same period.  We use three combined models:  a hydrological model of the Don estuary area (DonDeltaHECRAS) for simulation of the river flow and water levels during surges; model of suspended matter dynamics (DonDeltaBalanceModel), which allows us to calculate the suspended matter dynamics in the Don estuary area; and model of vegetation and soil dynamics (DonDeltaEcoModel), which is aimed at estimating the carbon accumulation in vegetation and soil in the delta. We found out that with the recent frequency of surges on average 20% of organic chemicals transported with the river runoff is deposited in the delta. Thus, marine factors affect accretion of soil within the delta and change both the carbon pools and fluxes in the delta and the estuary.

How to cite: Venevsky, S., Berdnikov, S., Gerasjuk, V., Sorokina, V., Kleshchenkov, A., Sheverdyaev, I., Kulygin, V., and Lichtanskaia, N.: Dynamics of carbon pools and fluxes in the Don River Delta, Southern (European) Russia, and the estuary under the conditions of increasing marine factors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8832, https://doi.org/10.5194/egusphere-egu24-8832, 2024.

Coastal peatlands, despite their ecological importance are at risk from a range of disturbances that render this habitat vulnerable, affecting their productivity and could potentially trigger ecosystem shift. Salinity is one of the factors affecting the structural and functional aspects of macrophytes in peatland environments. This study aims to assess the impacts of different salinity levels on the growth, biomass, and photosynthetic performance of peatland plants using a mesocosm approach. Four treatments of varying salinity were implemented: Saline (C+) with salinity of 20 ppt, Freshwater (C-) with salinity of 0 ppt, 22 and 55 pulses where the plants were exposed alternately to water with salinities of 20 ppt and 0 ppt every 2 and 5 days, respectively.  Two macrophyte species, Phragmites australis and Typha latifolia, were planted in mesocosm tanks. Over a 16-week period, various parameters including leaf length, leaf area, plant height, growth, biomass, and photosynthetic responses were monitored to evaluate the extent of salinity-induced stress. Results indicate that P. australis exhibited no significant difference in growth rates and biomass across treatments. Growth monitoring showed peak observed at the 8th week post-transplanting. Leaf area and leaf production also showed no significant variations. While shoot production increased initially, peaked at the 8th week, and declined thereafter. T. latifolia on the other hand, displayed growth rate variations favoring the freshwater (C-) and less frequent water change (55) treatments. The 55 pulses exhibited the highest absolute growth rate, but growth regressed after 8th week in treatments exposed to salinity changes. Leaf production in saline (C+) and higher frequency of water changes (22) showed a steep decline from 10th week onward. Saline treatment resulted in the lowest leaf production, leaf area, and biomass. This study contributes insights on the varying responses of macrophytes to salinity stress, demonstrating acclimation kinetics, and identifying salinity limits. 

How to cite: Go, A., Schubert, H., and Jurasinski, G.: Salinity influence on plant traits and photosynthesis in selected peatland macrophytes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9443, https://doi.org/10.5194/egusphere-egu24-9443, 2024.

Due to their shallow depth, coastal lagoons are often considered to be vertically well-mixed. However, past studies have shown that, depending on forcing conditions, vertical density stratification may in fact occur even in lagoons of only a few meters depth. Further, many coastal lagoons are faced with a multitude of anthropogenically caused pressures, including eutrophication as well as a likely increasing occurrence of summer heatwaves and other extreme atmospheric conditions due to climate change. While eutrophication leads to increased biological productivity and a subsequently increased oxygen demand, high water temperatures during heatwaves lead to reduced oxygen solubility, thus aggravating the risk of anoxic conditions within the water body. As vertical stratification acts to suppress vertical mixing, it may facilitate the occurrence of bottom oxygen depletion in such waters. Since coastal lagoons are of great ecological and economical interest due to their multiple ecosystem services, e.g., as spawning grounds for fish, it is of utmost importance to assess the conditions under which vertical stratification may occur. Only with such knowledge it will be possible to estimate the future development of coastal lagoon ecosystems. While many past studies have covered stratification of freshwater lakes during heatwaves, there is a significant gap of research covering coastal lagoons under the same conditions, where an additional forcing is added via the connection to the open sea. In particular, non-tidal, non-choked lagoons are currently understudied with respect to summer heatwaves. In our study, we therefore aim to assess the conditions under which stratification may occur in such lagoons during a mid-latitude summer heatwave. To this end, we have applied a non-dimensional parameter space analysis to a numerical, one-dimensional water column simulation of such a lagoon. Here, we present first results from this analysis.

How to cite: Reese, L., Gräwe, U., Lange, X., and Burchard, H.: Stratification in non-tidal shallow coastal lagoons during extreme summer heatwaves , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10491, https://doi.org/10.5194/egusphere-egu24-10491, 2024.

Climate change is already modifying the marine environment, and these alterations will presumably increase in the coming decades. Some of the most significant changes expected during this period include ocean warming, rise of sea level, and modifications to circulation and wind wave patterns. For instance, in the Mediterranean, ocean surface temperatures are projected to increase by 1-4 ºC by the end of the century, triggering a chain of impacts on marine ecosystems, such as species migration, significant mortality in some species, and an increase in harmful algal blooms.
Furthermore, sea levels are expected to rise, reaching values ranging from 30 cm to over 1 m by the end of the century. The consequences include the increased permanent flooding of low-lying areas, the salinization of coastal water reservoirs, and damage caused by marine storms.

In this context, despite ongoing efforts to reduce greenhouse gas emissions, it is crucial to develop realistic and effective plans for adapting to climate change. Nature-based solutions (NBS) present a particularly interesting approach to addressing climate change impacts. One NBS option suitable for reducing the impacts of climate change in coastal areas is to increase seagrass meadows through restoration interventions. The interaction of seagrasses with water flow leads to a reduction in flow energy, thereby limiting the impact of waves reaching the coast.
However, ocean warming poses a threat to seagrass meadows, as some species are particularly vulnerable to marine heatwaves. Therefore, the primary goal of the SEAFRONT project is to quantify the potential benefits of seagrass meadows in protecting the coast from future marine storms under different scenarios of global warming and seagrass evolution. SEAFRONT focuses on Spanish coastal areas, which exhibit a variety of hydrodynamical situations and seagrass coverages.
Specifically, SEAFRONT aims to 1) assess the impacts of marine storms over the last decades, evaluating the role of seagrasses; and 2) generate future scenarios of physical and economic impacts.

In this presentation, we share the results of numerical simulations focused on measuring the total water level at the shore under various scenarios. These simulations account for sea level changes, wave patterns, coastal shapes, and seagrass coverage. Additionally, we discuss the economic impacts of marine storms based on information from insurance companies.
Our initial analyses suggest that restoring seagrass meadows is a highly effective way to adapt to marine storms, countering the effects of rising sea levels. However, in areas where seagrasses already exist, losing them could lead to severe consequences, increasing the impact of marine storms.

How to cite: Jaca Estepa, J. and Jordà Sánchez, G.: Seagrass meadows provide essential coastal protection against future marine storms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11191, https://doi.org/10.5194/egusphere-egu24-11191, 2024.

River estuaries are diverse coastal ecosystems that have significant ecological, social, cultural and economic value. Estuaries worldwide are stressed by increasingly intensive human activities, also in the Baltic Sea, a European inland sea. Human pressures include e.g., dredging, port constructions, river water acidification and pollutants. In the latest assessment of threatened habitat types in Finland, coastal estuaries were assessed as an Endangered (EN) habitat complex due to historical abiotic and biotic quality changes.

As estuaries are often very shallow environments with turbid water column, it is not easy to acquire detailed seabed information from those areas. In the ongoing SeaMoreEco project we use remote sensing methods such as shipborne acoustic surveys, floating drones, flying drones and satellites, as well as seabed sampling and underwater video observations to map and monitor shallow water areas of the Gulf of Bothnia (GoB), northern Baltic Sea. We provide information e.g., on seabed geology and underwater vegetation. Here, we focus on seabed sediment data produced in the SeaMoreEco and in some other projects.

Anthropogenic radionuclides and heavy metal pollution are typical pressures widely affecting river estuaries and other marine ecosystems. For example, the fallout from the April 1986 Chernobyl nuclear power plant accident has rendered the Baltic Sea as the most polluted marine body in the world with respect to ¹³⁷Caesium (¹³⁷Cs). In the present study we determined the levels of ¹³⁷Cs activity and heavy metal content in the bottom sediments, and their spatial and vertical distribution in the subsurface sediments of the GoB.

Activity contents of ¹³⁷Cs and heavy metal contents in seabed surface sediments of the GoB have generally declined over the last decades. In some estuaries however, ¹³⁷Cs values in subsurface sediments remain at elevated levels relative to values measured from other areas of the Baltic Sea. In some areas, also the contents of heavy metals (e.g., cadmium, lead, zinc) in the subsurface sediments are quite high. This is typical for areas close to e.g., the metal industry and the areas affected by the loading from acid sulfate soils.

Data on harmful substances (e.g., radionuclides) in seabed sediments is important for coastal management and marine spatial planning while assessing risks associated with dredging and other operations. Dredging in areas where bottom sediments contain a lot of harmful substances can cause the re-mobilization and transport of these contaminants. Increasing anthropogenic pressures in coastal and marine areas will likely increase risk associated with polluted bottom sediments. Climate change might also shift many of the parameters (precipitation,  river discharge) that affect sediment distribution and pollution in the coastal and marine areas, also in the GoB.

This study is part of the Interreg Aurora funded SeaMoreEco project, the EMODnet Geology project funded by The European Climate, Environment, and Infrastructure Executive Agency (CINEA) through contract EASME/EMFF/2020/3.1.11/Lot 2/SI2.853812 - EMODnet Geology, the EMODnet Ingestion 3 project funded by the CINEA through contract CINEA/EMFAF/2021/3.4.10/02/SI2.868290, and the MAAMERI project funded by the Ministry of Environment, Finland. The study utilized research infrastructure facilities provided by FINMARI (Finnish Marine Research Infrastructure network).

How to cite: Kotilainen, A. T., Kotilainen, M. M., Jokinen, S., Sahiluoto, M., Virtasalo, J. J., and Kaskela, A. M.: Estuaries under pressure – surveying the extreme shallow water environments , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11676, https://doi.org/10.5194/egusphere-egu24-11676, 2024.

How to cite: Scroccaro, I., Laurent, C., Aveytua, L., Solidoro, C., and Canu, D.: Assessing the spatial and temporal trophic properties of the Marano and Grado Lagoon, Italy with the coupled physical-biogeochemical model SHYFEM-BFM , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15787, https://doi.org/10.5194/egusphere-egu24-15787, 2024.

Carbon loss from peatlands involves both gaseous emissions and a significant contribution from the water-bound fraction, specifically dissolved organic carbon (DOC), during mineralization and degradation processes. Our hypothesis proposes that DOC production is dependent on pore size, with elevated concentrations occurring in finer pores. To test this hypothesis, we extracted pore water at well-defined pressure heads (-60 and -600 hPa), representing macro- and mid-size pore domains, in degraded peat samples. Topsoil and subsoil samples exhibited soil organic matter contents of 34wt% and 57wt%, respectively. Remarkably, the more degraded topsoil consistently displayed significantly higher average DOC concentrations than the subsoil, with 1.5 times greater levels at -60 hPa and 2.4 times higher at -600 hPa. This trend suggests that more degraded peat soils are prone to releasing higher amounts of DOC. Furthermore, in topsoil samples, DOC concentrations were consistently higher at the -600 hPa pressure head compared to -60 hPa. To enhance our understanding, we computed hydraulic conductivities at -60 and -600 hPa using Van Genuchten parameter values, subsequently estimating the DOC load under unit gradient conditions. This calculation is particularly relevant for real-field situations, especially in partially saturated (degraded) peat soils. The hydraulic conductivity at -600 hPa was nearly a hundred times lower than at -60 hPa, leading to the conclusion that macro-pores serve as the primary pathways for DOC release in peat soils, irrespective of higher DOC concentrations in the fine pore domain.

How to cite: Lennartz, B., Cambinda, R., Liu, H., and Rezanezhad, F.: Pore-Size-Class Dependent Carbon Turnover in Peat Soils, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15930, https://doi.org/10.5194/egusphere-egu24-15930, 2024.

Coastal peatlands are unique ecosystems situated at the interface of land and sea. Past human activities, specifically drainage, have turned these carbon sink coastal regions into carbon sources. To mitigate climate change, recent management strategies focus on rewetting drained coastal peatlands. In this study, we aimed at characterizing surface and groundwaters in two coastal fens and examine the impacts of seawater input events caused by a storm surge (freshwater-rewetted) and rewetting with seawater (seawater-rewetted). Prior to the events, our findings reveal variable marine influence on surface and groundwater in the past which depends on distance from the coast, peat thickness, and possibly, drainage networks. After the storm surge, increases in specific conductivity (SC), chloride, and sulfate concentrations in surface waters persisted for up to a year. Increases in surface water dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) concentrations were also observed. In peat groundwater, a sustained increase in DOC concentrations that reached 526 mg DOC L^-1 was observed at a shallower depth (max: -0.59 masl) while a delayed increase was observed at a deeper depth (max: -1.41 masl). High dissolved carbon concentrations were still observed in peat groundwater until the end of the observation period, three years after the storm surge. For the seawater-rewetted fen, significant changes in surface water properties were observed, which included SC, chloride, pH, DOC, DIC. The initial DOC concentrations in peat groundwater decreased, but later, showed the same high concentrations similar to the storm surge flooded fen. No apparent impacts to deeper sandy aquifers from both sites were observed. Overall, storm surge flooding impact on surface water properties lasted for a limited time while rewetting with seawater significantly and drastically changed the surface waters as the peatland was transformed into a lagoon-like environment. Peat groundwater properties in both sites did not change significantly, however, depth-dependent variable increases in DOC concentrations could be expected. The increases in DOC concentrations in peat groundwater were accompanied by increased SC and decreased pH conditions. Lastly, the ongoing salinization of seawater-rewetted fens may lead to brackish-rewetted environments with higher concentrations of seawater salts and potentially create new biogeochemical reactive mixing zones of ground- and seawater.

How to cite: Racasa, E. D., Liu, H., Toro, M., and Janssen, M.: Groundwater quality in two coastal fens and the influence of storm surge flooding and rewetting with seawater, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18394, https://doi.org/10.5194/egusphere-egu24-18394, 2024.

Biological nitrogen (N) fixation is the microbial transformation of atmospheric N₂ to ammonia, which is carried out by various groups of microorganisms and in all environments. The organisms, called diazotrophs, do not rely on bioavailable combined N such as nitrate or ammonium, which are often limiting ecosystem productivity. On the other hand, their activity provides nutrients to the otherwise N-limited ocean. In the central Baltic Sea high nitrogen fixation occurs each summer in surface waters introducing up to 792 000 t N per year, but was also identified in the deep and anoxic waters. In coastal waters the heterotrophic and autotrophic N₂ fixation is not well studied and even less is known about the annual cycle and its regulation by the environment. Since coastal environments are considered to act as a filter for nutrients and organic matter, knowledge on an additional N source through N₂ fixation is of great importance.

Here, we present N₂ fixation rates for bulk water and sediment slurries (upper 5 cm), incubated for 24 hours in the dark and during a daily light cycle. We selected three stations near a peatland with outcropping peat layers and sandy sediments. Monthly sampling over the course of one year was done together with in-situ measurements of temperature, salinity, pH, nutrient concentrations and dissolved organic substances. Incubations were spiked with ¹⁵N₂ gas and incubated in the lab. The fixation rates ranged from our detection limit up to 285 nmol N L^-1 d^-1 in water and 2 nmol N g_dw^-1 d^-1 in sediments with a mean fixation rate of 11.2 nmol N L^-1 d^-1 and 0.1 nmol N g_dw^-1 d^-1 for water and sediment, respectively. We could not find significant difference between stations and overall, the rates were much lower than in the surface waters of the central Baltic Sea. Though the rates in the water observed in June 2022 agree well with the rates of a cyanobacterial bloom in late summer (4.3 – 7.8 µmol N m^-3 h^-1). The rates for the water as for the sediment showed significant positive correlation (Spearman, sig. level 0.05) with variables affected by the seasonal change as temperature, daylength, pH and oxygen saturation. during winter and spring, the rates in the water were low to non-detectable and highest in summer. Also, in the sediment the lowest rates were found during winter and highest rates in spring. In general, the light cycle treatment showed higher rates than the dark incubation, with the exception of spring where the dark incubated sediments had higher rates than the ones in a daily light cycle. The outcropping peat layer seemed to induce some variability in N₂ fixation rates, reflecting the heterogeneity of substrate which was sometimes covered with sand layers of different thickness.

Even though the rates in this study are comparably low for both water and sediment, a seasonal pattern became visible. Sediments and shallow waters clearly deserve more attention to better understand the process and the potential role as food and nitrogen source.

How to cite: Klett, A., Liskow, I., and Voss, M.: Nitrogen fixation in the shallow waters off a coastal wetland with outcropping peat, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18697, https://doi.org/10.5194/egusphere-egu24-18697, 2024.

Following the current expansion of offshore constructions for the production of renewable energy as well as shipping traffic, assessments of impacts on marine ecosystems are becoming increasingly important. Thus, accurate knowledge of the spatial and temporal distribution of animal species is mandatory regarding the preservation of biodiversity and management of offshore wind farms and further economic activities. High-resolution optical imagery of airborne remote sensing sensors enables the observation of marine birds and mammals within large ocean areas. However, the identification of features at the ocean surface as well as the separation of animals and further objects, such as wave structures, ships or buoys, requires time-consuming visual inspection of the acquired image sequences by trained personnel. Here, we apply an AI-based approach to automatically detect and classify various features above the sea surface based on aerial imagery of the German North Sea and Baltic Sea. A large number of optical images at a spatial resolution of 2 cm have been acquired by the German Federal Agency for Nature Conservation (BfN) during repeated monitoring flights since 2018. These images are preprocessed and geolocated by assigning respective auxillary informations to create an extensive database on marine animal observations. The AI method which we are developing has to be responsible both for detecting birds in images, and for tracking instances of a same element present on multiple frames in order to avoid counting an individual multiple times. Some of the main challenges which will have to be dealt with are the following. First, luminosity conditions cannot be controled and might be suboptimal in a large fraction of the images, rendering animals completely white or black, or difficult to distinguish from the background. Second, smaller animals might consist only of little pixel blobs, and thus be difficult to distinguish. Third, flying birds might have shadows, which, while bird-shaped, must not be classified as birds. Fourth, in bird flocks overlapping tricks the AI into detecting one bird instead of several ones, which renders tracking significantly more challenging. We aim at tackling the third and fourth issues by incorporating cinematic estimation of the plane‘s and animal‘s movements, and estimating the direction of the sun in each frame, into the tracking system. In the future, our system will be used by the German Federal Agency for Nature Conservation (BfN) to monitor bird and mammal populations, and evaluate the effectiveness of preservation measures. 

How to cite: Sommer, C., Seuret, M., Gourmelon, N., Christlein, V., and Braun, M.: AI classification of marine birds and mammals based on aerial imagery of the German North and Baltic Seas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19604, https://doi.org/10.5194/egusphere-egu24-19604, 2024.

Coastal peatlands have been frequently blocked from the sea and artificially drained for agriculture. With an increasing awareness of ecosystem functions, several of these coastal peatlands have been rewetted through dike removal, allowing seawater flooding. In this study, we investigated a recently rewetted peatland on the Baltic Sea coast to characterize the prevailing soils/sediments with respect to organic matter accumulation and the potential release of nutrients upon seawater flooding. Eighty disturbed soil samples were collected from two depths at different elevations (–0.90 to 0.97 m compared to sea level) and analyzed for soil organic matter (SOM) content and carbon:nitrogen (C:N) ratio. Additionally, nine undisturbed soil cores were collected from three distinct elevation groups and used in leaching experiments with alternating freshwater and Baltic Sea water. The results demonstrated a moderate to strong spatial dependence of surface elevation, SOM content, and C:N ratio. SOM content and C:N ratio were strongly negatively correlated with elevation, indicating that organic matter mineralization was restricted in low-lying areas. The results also showed that the soils at low elevations release more dissolved organic carbon (DOC) and ammonium (NH₄⁺) than soils at high elevations. For soils at low elevations, higher DOC concentrations were observed when flushing with freshwater, whereas higher NH₄⁺ concentrations were found when flushing with brackish water. Recorded NH₄⁺ concentrations in organic-rich peat reached 14.82 ± 9.25 mg L^–1, exceeding Baltic seawater (e.g., 0.03 mg L^–1) by two orders of magnitude. A potential sea level rise may increase the export of NH₄⁺ from low-lying and rewetted peat soils to the sea, impacting adjacent marine ecosystems. Overall, in coastal peatlands, geochemical processes (e.g., C and N cycling and release) are closely linked to microtopography and related patterns of organic matter content of the soil and sediments.

(The original article has been published in Geoderma, Volume 438, 116637; DOI: 10.1016/j.geoderma.2023.116637)

How to cite: Wang, M., Liu, H., Rezanezhad, F., Zak, D., and Lennartz, B.: The influence of microtopography on soil carbon accumulation and nutrient release from a rewetted coastal peatland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18426, https://doi.org/10.5194/egusphere-egu24-18426, 2024.