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From the source to the sea – rivers, estuaries, deltas, marshlands, and coastal seas under global change

This session provides a platform for interdisciplinary science addressing the continuum from the river source to the sea. A systems approach is indispensable for science-based solutions to sustainably manage complex River-Sea social-ecological systems. Studies linking environmental and social sciences and crossing geographical borders are particularly invited: from the river source and its catchment through estuaries, deltas and marshlands across the freshwater-marine water transition into the coastal sea, including surface-groundwater interaction. Studies addressing the impacts of climate change and extreme events and the impact of human activities on water and sediment quality and quantity, hydromorphology, biodiversity, ecosystem functioning and services of River-Sea continua are of particular interest.

We need to understand how River-Sea Systems function and to address many open questions. How are River-Sea continua changing due to human pressures? What is the impact of processes in the catchment on coastal and marine systems function, and vice versa? How can we discern between human-induced changes or those driven by natural processes from climate-induced variability and extreme events? What will the tipping points of social-ecological system states be and what will they look like? How can we better characterise river-sea systems from the latest generation Earth observation to citizen science based observatories. How can we predict short and long-term changes in River-Sea-Systems to manage them sustainably? What is the limit to which it is possible to predict the natural and human-influenced evolution of River-Sea-Systems? The increasing demand to balance intensive human use and environmental protection in River-Sea Systems requires holistic and integrative research approaches with the ultimate goal of enhanced system understanding as the knowledge base for sustainable management solutions.

Co-organized by BG4/OS2
Convener: Jana Friedrich | Co-conveners: Debora Bellafiore, Andrea D'Alpaos, Michael Rode, Christian Schwarz
| Tue, 24 May, 13:20–15:52 (CEST)
Room 2.44

Tue, 24 May, 13:20–14:50

Chairpersons: Jana Friedrich, Debora Bellafiore, Andrea D'Alpaos


Martin Struck et al.

The Rhine as Europe’s most important waterway is navigable for about 800 km. Over centuries, it has experienced numerous human interventions along this length, from barrage construction in the upper part, through river straightening and regulation, and implementation of flood defence measures along most of its course, to land reclamation in its delta, to name just a few. The large number of changes brought along major environmental issues, namely an overall tendency to insufficient sediment amounts, widespread loss of habitats and biodiversity, and the sensitivity to flooding. Nowadays, the Rhine is an intensively managed river with important industries along its banks and a highly cultivated and densely populated catchment and delta. It is therefore a fundamental challenge to reach an agreement between its role as a waterway, the manifold of other human uses and environmental demands, to improve its ecological condition.

From its last barrage at Iffezheim, the Rhine is free-flowing and crosses the border between Germany and the Netherlands after about 530 km, where it soon connects with the Meuse to form the Rhine-Meuse delta. In this setting, Dutch and German partners take a new approach to address urgent issues on a transboundary level. As part of the pan-European research infrastructure DANUBIUS-RI, two natural laboratories, called the Middle Rhine Supersite (GER) and the Rhine-Meuse Delta Supersite (NL), are being set up to facilitate interdisciplinary research on questions regarding system understanding and ecological improvement of the river to foster the identification of possible solutions. DANUBIUS-RI, the “International Centre for Advanced Studies on River-Sea Systems”, is being developed with the goal to support interdisciplinary and integrated research on river-sea systems. It aims to enable, support and bring together research addressing the conflicts between societal demands, environmental change and environmental protection along the continuum from freshwaters to marine waters, by providing easy access to a wide range of fundamental and comparable data from a diverse set of European river-sea systems. It will also facilitate physical access to these systems through multiple supersites.

A first pilot project at the Rhine, supported by INTERREG regional funding of the Euregio Rhine-Waal, involves partners of both the Dutch and the German supersite and focuses on the comparison of sediment measurement and data processing methods in both countries. The goal of this ‘Living-Lab Rhine’ (LILAR) project is to enable a better transboundary use and comparison of the data to eventually improve the overall understanding of the Rhine sediment regime and to strengthen the transboundary efforts regarding sediment measurements and potentially even river management between Germany and the Netherlands.

How to cite: Struck, M., Huber, N., Hillebrand, G., Onjira, P., Winterscheid, A., Brils, J., Schielen, R., Mol, J.-W., Bode, C., van den Hoek, A., and Siering, F.: Living-Lab Rhine – A new approach to transboundary research along the free-flowing Rhine, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7103, https://doi.org/10.5194/egusphere-egu22-7103, 2022.

Antonia Menzione and Marco Mancini

Over the last decades numerous models for sediment transport prediction have been proposed with application to fluvial transport or littoral transport. However, the morpho-dynamic interactions that occur at the river mouth are still largely unexplored given different concurring phenomena, deriving from both river hydraulics and marine hydrodynamics. Knowing the magnitude of these phenomena is important to analyse and predict sediment discharge and deposition, erosion and potential effects on biological processes. The paper investigates the possibility to assess the behaviour of suspended sediment pattern at river mouth using numerical models and satellite images, providing a platform for the prediction of the effect of climate change in estuarine morpho-dynamic.

For this purpose, the hydrodynamic model (TELEMAC-2D) and the sediment transport model (SISYPHE) are coupled and their simulated suspended sediment maps are compared with the satellite Sentinel 2 images of SSC (suspended solid concentration) supporting the advection diffusion model coefficients calibration. 

TELEMAC-2D, a module of TELEMAC, solves the Saint-Venant equations and allows to evaluate the depth of the water, the depth-averaged tidal currents and the velocity components. Based on the outputs of the hydrodynamic simulation, the SISYPHE module simulates the transport of the fine sediments by calculating the erosion / sedimentation fluxes, concentration in the water column and layer thickness of deposited fine sediments using the Krone and Partheniades formulation, as well as the bedload flux calculated as a function of the friction and the bed shear stress.The estimate of suspended solids from remote sensing data is performed based on the relationship between SSC and spectral reflectance.

The case study in consideration is the estuary of the River Piave (3000 sq km), which flows from the eastern Italian Alps to the North Adriatic Sea. The impacts and influence of the different drivers (fluvial current, tidal currents, etc.) on the concentration, dispersion pattern and deposition of sediment are discussed.

How to cite: Menzione, A. and Mancini, M.: Modelling of sediment transport pattern in the estuary of the Piave River, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10612, https://doi.org/10.5194/egusphere-egu22-10612, 2022.

Joonas Virtasalo et al.

Rivers draining the acid sulphate soils of western Finland are known to deliver large amounts of trace metals (e.g. Al, Cd, Co, Cu, La, Mn, Ni and Zn) with detrimental environmental consequences to the recipient estuaries in the eastern Gulf of Bothnia, northern Baltic Sea. However, the distribution of these metals in the coastal sea area, and the relevant metal transport mechanisms have been less studied.

This study investigates the spatial and temporal distribution of metals in sediments at 9 sites in the Kvarken Archipelago, which is the recipient of Laihianjoki and Sulvanjoki rivers that are among the most acid sulphate soil impacted rivers in Europe. Metal contents increase in the studied cores during the 1960s and 1970s due to the intensive artificial drainage of the acid sulphate soil landscape. The metal deposition has remained at high levels since the 1980s and the metal enrichment in seafloor sediments is currently visible at least 25 km seaward from the river mouths. Comparison to sediment quality guidelines shows that the metal contents are very likely to cause detrimental effects on marine biota more than 12 km out from the river mouths. The dynamic sedimentary environment of the shallow archipelago makes these sediments potential future sources of metals to the ecosystem. Finally, the strong association of metals and nutrients in the same sediment grain size class of 2–6 µm suggests that the transformation of dissolved organic matter and metals to metal-organic aggregates at the river mouths is the key mechanism of seaward trace metal transport, in addition to co-precipitation with Mn-oxyhydroxides identified in previous studies. These findings are important for the estimation of environmental risks and the management of biologically-sensitive coastal sea ecosystems.

This study resulted from the SmartSea project, funded by the Strategic Research Council at the Academy of Finland (grant number 292 985). M.E.Å. additionally acknowledges the Swedish Research Council Formas (grant number 2018-00760). The study has utilized research infrastructure facilities provided by FINMARI (Finnish Marine Research Infrastructure network).

Original publication: Virtasalo, J. J., Österholm, P., Kotilainen, A. T., and Åström, M. E.: Enrichment of trace metals from acid sulfate soils in sediments of the Kvarken Archipelago, eastern Gulf of Bothnia, Baltic Sea. Biogeosciences, 17, 6097–6113, https://doi.org/10.5194/bg-17-6097-2020, 2020.

How to cite: Virtasalo, J., Österholm, P., Kotilainen, A., and Åström, M.: Enrichment of trace metals from acid sulphate soils in sediments of the Kvarken Archipelago, eastern Gulf of Bothnia, Baltic Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8632, https://doi.org/10.5194/egusphere-egu22-8632, 2022.

Stacey L. Felgate and the Authors

Land-ocean dissolved organic carbon (DOC) fluxes are a significant and changing component of the global carbon cycle. The current paradigm assumes that these fluxes are dominated by chromophoric or ‘coloured’ material (cDOC). DOC is often characterised and quantified using optical tools which specifically target this fraction. However, multiple studies point towards a potentially sizeable non-coloured or optically ‘invisible’ DOC (iDOC) pool which is not covered by such characterisations. Only a handful of studies have directly investigated iDOC, and so its source, composition, behaviour, and geographic prevalence remain poorly understood.

Here we show that iDOC accounts for 21 % (0.23 Tg C yr-1) of annual riverine export in Great Britain (GB), with spatial variation in catchment-scale mean annual export depending upon forest cover and mean dairy cattle density. Using > 2,900 samples from across a range of geo-climatic settings across five continents we find a similar result: iDOC accounts for 26 % of the measured DOC flux in freshwaters. Our results indicate that iDOC is more prevalent in systems with a high degree of anthropogenic influence and/or a high residence time. 

We also show that estuarine DOC behaviour is driven by the contributions of cDOC and iDOC, at least within GB estuaries: cDOC almost universally exhibits conservative transport, whilst apparent non-conservative bulk DOC transport is typically caused by fluctuations in the iDOC fraction.

We conclude that iDOC is a globally significant fraction of the land-ocean carbon flux, the broad scale importance of which has been largely overlooked. This has fundamental implications for (1) our understanding of aquatic biogeochemistry and (2) the use and interpretation of optical parameters as they relate to DOC characterisation and quantification.

This work was primarily funded by the National Environment Research Council (NERC) through the SPITFIRE Doctoral Training Programme (grant number NE/L002531/1) and the Land Ocean Carbon Transfer Programme (LOCATE; grant number NE/N018087/1). 

How to cite: Felgate, S. L. and the Authors: The importance of 'invisible' dissolved organic carbon along the land-ocean aquatic continuum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13281, https://doi.org/10.5194/egusphere-egu22-13281, 2022.

Louise Rewrie et al.

Climate projections show high temperature extremes, meteorological droughts and heavy precipitation events are set to increase across Europe (Barros et al., 2014), where the decadel average has already increaed, with temperature in 2002-2011 already 1.3°C±0.1°C above the 1850-1899 mean (Barros et al., 2014). The observed seasonal precipitation pattern presents drier summers and wetter winters across Europe, also mirrored in river flow changes. Across small river catchments in Europe from 1962 to 2004, winter period showed positive trends whereas summers were characterized by negative trends in river flow (Stahl et al., 2010). Such changes can alter the residence time of an estuary. Estuaries are biogeochemical hotspots, and critical zones for carbon cycling, and changes in the hydrological balance, still largely not well characterized, may influence processes within the water column. 

The present study will assess the potential impacts of droughts on the carbonate system in the Elbe estuary. One of the largest in central Europe, the Elbe River catchment spreads over approximately 150,000 km2 in four countries. Between 2014 and 2018, regions of Northern Germany have been under drought conditions during certain months (UFZ, 2018), reducing discharge in the Elbe River. From 2014, annual Elbe river discharge has been relatively low, where 2018 exhibited the lowest annual mean river discharge of 441 m3 s-1 since 1992. Model projections show the annual river discharge for the Elbe river is likely to remain low at 410 m2 s-1 in 2046-2055 compared to >550 m2 s-1 in 1960-1990 (Krysanova et al., 2005).

Analysis of the long-term FGG Elbe (Flussgebietsgemeinschaft Elbe) records of dissolved inorganic carbon (DIC) in the mid to lower Elbe estuary show that over spring and summer months DIC values have increased with time (1997-2018). In this period, DIC increased from the freshwater to the mesohaline region, followed by a decrease to the polyhaline zone. This is opposing to previous DIC patterns in the early 1980s, where DIC decreased towards the mid-estuary after which increased to the outer estuary. An increase in DIC in the mid-estuarine region coincided with increased turbidity and extended residence time, and during the productive months with higher organic matter from upstream regions.  This could suggest that more time for heterotrophic activity and availability of labile organic matter, acts to enrich DIC within the water column in the turbid regions, thus changing carbon cycling within the estuary. Further analysis will focus on the changes in river discharge and inorganic carbon during the past two decades, thus inclusive of low discharge and drought conditions.

How to cite: Rewrie, L., Voynova, Y., Brix, H., Ollesch, G., and Baschek, B.: Influence of recent droughts on carbon cycling in the Elbe estuary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7940, https://doi.org/10.5194/egusphere-egu22-7940, 2022.

Edward R. Jones et al.

Inadequately managed wastewater is the key driver of water quality deterioration in various regions across the world, threatening both human livelihoods and ecosystem health. Furthermore, improving wastewater management practices can supplement clean water supplies and promote sustainable development. For these reasons, Sustainable Development Goal (SDG) 6.3 sets the target of halving the proportion of untreated wastewater discharged to the environment by 2030. Yet, the impact of achieving this goal on pollutant concentrations in river waters is largely unknown.

In this work, we use a newly developed high-resolution global surface water quality model (DynQual) to estimate the state and future development of water quality variables that are of key social and environmental relevance: water temperature (Tw), salinity (indicated by total dissolved solids, TDS), organic pollution (indicated by biological oxygen demand, BOD) and pathogens (indicated by faecal coliform, FC). We first simulate river water quality for a historical time period (1980 – 2015) as in-stream concentrations  of Tw, TDS, BOD and FC at 5 arc-minute spatial resolution (~10km) globally and at the daily timestep, and validate these results against (in-situ) water quality observations from monitoring stations worldwide. In a next-step, we simulate in-stream the same water quality parameters up to 2030 under two scenarios: 1) no expansion in wastewater treatment; and 2) expansions to halve the proportion of untreated wastewater globally by 2030 (i.e., as stipulated by SDG6.3). We compare these scenarios to evaluate the relative impact of halving the proportion of untreated wastewater on global water quality.

We find that in most world regions the irrigation and manufacturing sectors are the major drivers of anthropogenic salinity (TDS) loadings, whereas the largest organic (BOD) and pathogen (FC) pollution loadings originate from the domestic and intensive livestock sectors. Considering also the dilution capacity of the stream network, hotspots of salinity pollution are found in industrialised regions such as northeastern China and the contiguous United States, and in heavily irrigated regions such as northern India. Hotspots of organic and pathogen pollution are closely associated with locations downstream of large urban settlements, and especially those with limited wastewater treatment capacities. Increasing wastewater treatment capacities in line with SDG6.3 leads to substantial decreases in both pollutant loading exports and in-stream concentrations, substantially reducing the frequency and magnitude of water quality threshold exceedance.

Our work is important for identifying pollutant hotspots and supplementing available observed water quality data, which is extremely sparse in some world regions (e.g. Africa). Our framework also allows for scenario modelling under future projections of climatic and social change, as demonstrated in this work with respect to SDG6.3.

How to cite: Jones, E. R., Bierkens, M. F. P., Wanders, N., Sutanudjaja, E., van Beek, L. P. H., and van Vliet, M. T. H.: Surface water quality under the Sustainable Development Agenda – the role of improved wastewater treatment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3599, https://doi.org/10.5194/egusphere-egu22-3599, 2022.

Man-Yue Lam and Reza Ahmadian

High levels of Faecal Indicator Organisms (FIOs), such as E Coli and Enterococci, at bathing water sites are linked to disease and public health threats. Hydro-environmental models for coastal areas are important for understanding the transport and fate of FIOs, evaluating effectiveness of environmental management strategies on coastal water quality as well as predicting FIO concentrations in bathing water sites. An important aspect in hydro-environmental models is simulating bacteria decay. Bacteria such as FIOs are generally assumed to undergo a first order degradation, C(t)=C0exp(-kt),  where C(t) is bacteria concentration at time t; C0 is initial concentration; k is bacteria decay rate. The bacteria decay rate depends on factors such as temperature, solar irradiation, and suspended solid concentration. A number of bacteria decay models, with various level of complexity, have been developed and applied in different waterbodies such as coastal areas, estuaries, and rivers; there is no consensus regarding to the best model for any given scenario. Generic bacteria decay models have been also attempted but they did not outperform site-specific models. This research evaluates the performance of several bacteria decay models in a data rich test site, namely Swansea Bay, located in South-west of UK. More than 7000 FIO samples were taken at key sources and receptors and analysed over two bathing seasons in two years. Environmental data for stream flows, tide levels, meteorology and water quality are also available. These data are important for hydro-environmental model development, calibration, and validation. This research also provides insights to the key drivers of FIOs at the bathing water sites along Swansea Bay. Hydro-environmental models for the Bay were developed with TELEMAC-2D and -3D hydrodynamic solvers, developed by the Research and Development department of Electricité de France (EDF). TELEMAC-2D solves the two-dimensional Shallow Water Equations (SWE) and TELEMAC-3D solves the three-dimensional Navier Stokes Equations (NSE). The two solvers employ the finite element method on unstructured triangular meshes. The solvers have been used in hydro-environmental studies in coastal areas, lakes, and rivers. Two main decay models were considered in this study; the Stapleton model which considers irradiation and suspended solid effects and the Mancini model which considers irradiation, salinity and temperature effects. King (2019) studied the performance of these bacteria decay models at the case study site and suggested that further improvements might be achieved by combining the two models. In this research, the performance of (i) the Stapleton model, (ii) the Mancini model and (iii) a combination of Stapleton and Mancini model were evaluated against measured FIO concentrations.  It was found that one of the key limitations of the hydro-environmental models is that the hydrodynamics of the wet-dry interface in the swash zone may not be represented accurately. Modelling wet-dry interface remains a numerical challenge; there are different modelling approaches, representing different trade-offs between computational efficiency, numerically stability and scientific accuracy. To compensate for this limitation, sensitivity of FIO concentrations to sampling locations was also evaluated. Reference: (i) King JA (2019). https://orca.cardiff.ac.uk/125923/; (ii) Mancini JL (1978). https://www.jstor.org/stable/pdf/25040179.pdf; (iii) Stapleton CM et al. (2007). https://orca.cardiff.ac.uk/40376/

How to cite: Lam, M.-Y. and Ahmadian, R.: Studying transport and decay models for Faecal Indicator Organisms (FIOs) in nearshore coastal waters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12738, https://doi.org/10.5194/egusphere-egu22-12738, 2022.

Hugo Enrique Reyes Aldana et al.

River and stream metabolism have been proposed as an important tool to determine ecological status, as it encompasses most of the environmental interactions. However, some of the factors influencing it have not been studied with enough depth, which is essential to define its utility as a monitoring and diagnostic tool, especially under the variable conditions of the current global changes. One of these understudied factors is temperature, which may become problematic considering the increasing temperatures and heatwaves occasioned by climate change. For instance, increasing temperatures due to climate change or extreme events may favor the proliferation of algal species resistant to high-temperature variability occasioning blooms and altering ecosystem metabolism. Thus, there is a need to understand how temperature affects ecosystem metabolism and its components, to be able to propose better and more integrative measures to counteract negative changes and make predictions of possible scenarios. This work presents a meta-analysis of the current information that is available on the response of ecosystem metabolism to temperature and highlights some of its implications and perspectives. With this information, scientists, managers, and stakeholders might be able to have a wider perspective and propose more adequate measurements in terms of ecosystem metabolism and ecological status.

How to cite: Reyes Aldana, H. E., Graber, D., Weitere, M., Cohen, M., and Risse-Buhl, U.: The warmer the better?: the relationship between ecosystem metabolism and temperature, possible implications under climate change – a meta-analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10786, https://doi.org/10.5194/egusphere-egu22-10786, 2022.

Raymond Ward et al.

Globally, flooding is one of the most commonly occurring natural disasters and their frequency of occurrence and intensity is predicted to increase as a result of climate change and associated influences on rainfall intensity, duration and timing. The impact of floods can be exacerbated by associated damage to transport infrastructure, which can impede disaster relief activities, often where needed most. Thailand, and especially Southern Thailand suffers greatly every year and sometimes multiple times a year from flooding causing dramatic human and economic losses. In 2020 for example, after six days of heavy rains, 351 villages were affected by flooding representing a total of 16,709 households and almost 50,000 people.

Flood risk assessments are increasingly considered vital for societies across the world and as a result, flood modelling has considerably improved in recent decades with new formulations, the acquisition of extremely accurate geodesic data and powerful computers able to handle data processing.

This study used a bespoke software Flowroute for the flood risk assessment and flood modelling. This modelling software uses meteorological data and detailed GIS data to produce flood maps with return periods of 20, 50 and 100 years within the six largest catchments of the Krabi and Nakhon Si Thammarat provinces in Southern Thailand. Flood forecast models were run using downscaled regional (3km resolution) predictions under the AR6 RCP6.0 scenario, based on 20 year, 50 year and 100 year return period events.

Results showed a 16-17% increase in flooded area by 2100 compared with 2020 for the 100 year return period events in the Krabi province and a 22-38% increase in flooded area for the 100 year return period events in Nakhon Si Thammarat over the same time period.

The greatest impacts are likely to occur in the middle and lower parts of the catchments. These areas are flatter with a low angled slope in comparison to the higher parts of the catchments running into the valleys of the mountain chains. The sudden topographical changes between the upper part of the catchments and their lower parts means that during heavy rainfall, large amounts of water are very quickly drained towards a main stream that is not able to cope with it, hence water spreading over the river banks and settling more easily on those flat coastal plains. These areas are generally densely populated, used for industrial purposes and farming representing valuable assets for the economy of both provinces and the country. . Anthropic activities such as dam/weir construction or channel realignment are common in these areas and those changes exacerbate the stress on the river system created by the natural setting of these areas.

Based on the information provided by these models, authorities and managers can undertake flood mitigation measures by adapting, improving or creating new flood defences within the catchments. A variety of methodologies have been used in the UK from re-establishing the natural flow of the rivers and streams to developing retention basins along the streams.

How to cite: Ward, R., Curoy, J., Martin, D., Puch, E., Tenedor, J., Wang, Y., Almirew, N., Dudhia, J., Barlow, J., Moses, C., and Nakhapakorn, K.: Climate change driven flood modelling predictions within Southern Thailand , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4459, https://doi.org/10.5194/egusphere-egu22-4459, 2022.

Peter Robins et al.

Estuarine flooding is driven by extreme sea-levels and river discharge, either occurring independently or at the same time, or in close succession to exacerbate the hazard, known as compound events. There is a need to identify site-specific thresholds for flooding in estuaries, which represent the magnitude of key drivers over which flooding occurs. Site-specific thresholds for flooding can be used to support forecasts and warnings, emergency response and long-term management plans. This research uses historic records of flooding in estuaries around the UK combined with 40 years of historical 15-minute frequency sea-level and river discharge data to establish the magnitude and relative timing of the drivers of flooding in 11 estuaries. The results identify estuaries which are more likely to experience flooding due to extreme compound events, e.g. Conwy, N-Wales, or independent extreme events e.g. Humber, E-England. The key limitation of using historic records of flooding is that not all flooding events have been documented, and there are gaps in the record. Therefore, this research also identified the top 50 extreme sea-level and river discharge events in the historic gauge measurements at each estuary, and cross-checked these against online sources (news reports and academic literature), to establish if these events also led to flooding. A more comprehensive historic record of flooding allows more accurate thresholds for flooding to set in each estuary. Future work will utilise numerical modelling tools in 4 estuaries to simulate flooding under different sea-level and river discharge conditions to further isolate accurate thresholds.

How to cite: Robins, P., Lyddon, C., Lewis, M., Barkwith, A., Vasilopoulos, G., and Coulthard, T.: Using historic records of compound flood events to identify site-specific thresholds for flooding in UK estuaries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12938, https://doi.org/10.5194/egusphere-egu22-12938, 2022.

Ophélie David et al.

New results acquired in the south-Brittany shelf (core MD08-3204 CQ: Bay of Quiberon and core VK03-58bis: south-Glénan) allow depicting Holocene paleoenvironmental changes from 8.5 ka BP to present through a multi-proxy dataset including sedimentological and palynological data.

First, grain-size analyses and AMS-14C dates depict a common sedimentary history for both study cores. After the post-glacial sea-level (RSL) rise and related high sedimentation rates, the parallel slowdown of the RSL rise and the drop of sedimentation rates occurred between 8.3 and 5.7 ka BP. This interval leads to the establishment of a shell-condensed level, identified in the VK03-58bis core by the “Turritella layer” and interpreted as a marker for the establishment of the maximum flooding surface. Palynological data (pollen grains and dinocyst assemblages) acquired in the core MD08-3204 CQ argue for an amplification of the fluvial influence since 5.9 ka BP; the establishment of the highstand system tract (i.e. estuarine-type sedimentation on the platform) then accompanying the slowdown of the RSL rise. On the shelf, the Anthropogenic Pollen Indicators (API) amplification, is detected since 4.2 ka BP, due to the fluvial influence becoming predominant in the context of the Late Holocene.

In addition, the comparison of fluvial palynological tracers, including API, over the last 7 kyrs, with coastal-marines sites subjected to northern vs. southern Loire catchment areas, allowed to discuss a major hydro-climatic effect on the reconstructed palynological signals. Strengthened subpolar gyre dynamics (SPG), combined with recurrent positive North Atlantic Oscillation (NAO) configurations, are well-known to favour increased winter precipitation and fluvial discharge in northern Europe, such as Brittany, and conversely during weakened SPG the winter fluvial discharge is intensified over southern Europe. Interestingly, we record, at an infra-orbital timescale, major peaks of API during periods of strengthened (/weakened) SPG dynamics in sites whose catchment areas are located north (/south) of the Loire.

How to cite: David, O., Penaud, A., Vidal, M., Fersi, W., Lambert, C., Goubert, E., Herledan, M., Stéphan, P., Pailler, Y., Bourillet, J.-F., and Baltzer, A.: Palynological and sedimentological records since 8.5 ka BP on the southern Brittany platform (NW Europe): complex responses to sea-level, rapid climate and anthropogenic changes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1003, https://doi.org/10.5194/egusphere-egu22-1003, 2022.

Tue, 24 May, 15:10–16:40

Chairpersons: Christian Schwarz, Michael Rode

Roeland C. van de Vijsel et al.

River deltas harbor invaluable ecosystems as well as many of the world’s largest cities and are hotspots for economic activity. This necessitates accurate prediction of the response of delta biogeomorphology to future scenarios of changes in sea level, wave climate, river discharge dynamics and anthropogenic forcing. Valuable insights have come from long-term model predictions performed with high-complexity simulation models. Such models often predict a gradual adjustment of biogeomorphic equilibrium to changing forcing conditions. On the other hand, a growing number of studies, based on strongly idealized models, indicate the presence of tipping points where delta systems may undergo irreversible regime shifts to an alternative stable state. Examples include estuarine (hyper)turbidity, delta channel instability and ecosystem emergence or collapse. However, field observations to support either the predicted absence or presence of irreversible regime shifts in river deltas remain scarce.

Our study reviews the existing research on reversible (single equilibrium) and irreversible (multiple equilibria) transitions in delta biogeomorphology. We propose how to bridge the apparent gap between high-complexity models, which accurately capture reversible morphodynamic adjustment to small changes in forcing but are unpractical to probe wide parameter ranges for the presence of irreversible regime shifts, and idealized models, which have contrasting characteristics. We discuss (the lack of) existing field data to support morphodynamic model predictions and specify which field measurements would be needed to provide more conclusive evidence. Specific attention is given to early warning indicators for regime shifts, such as spatial patterning and critical slowing down, and which of these signals could be picked up in delta systems. Finally, we illustrate how the design of human interventions, such as channel dredging, beach nourishments and ecosystem restoration, requires fundamental knowledge of a delta’s natural resilience, as lower resilience implies higher susceptibility to irreversible regime shifts.

How to cite: van de Vijsel, R. C., Scheffer, M., and Hoitink, A. J. F. (.: Regime shifts in river deltas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12581, https://doi.org/10.5194/egusphere-egu22-12581, 2022.

Martin O. Reader et al.

River and sea ecosystem services contribute to the rapid and intensive development of delta social-ecological systems. This development, alongside other global change drivers, threatens the biodiversity of these deltas and in turn the ecosystem services that this biodiversity supports. However, biodiversity can itself mediate anthropogenic impacts by increasing ecosystem resilience. Linkages between biodiversity and ecosystem services are increasingly established, but we lack understanding of whether the mediating effects of biodiversity are global and ubiquitous, and whether they mediate global change drivers in deltas.

Here, we examine the potential for biodiversity to mediate the relationships between five anthropogenic indicators and global change drivers (population, infrastructure, land use change, climate change in temperature and precipitation) and 19 ecosystem properties and services. We assess these relationships across a global dataset of 235 large deltas. We find that in 89% of cases, greater biodiversity (species richness and the intactness of biodiversity) is connected to a weakened or reversed association between anthropogenic drivers and ecosystem services. Such weaker or reversed associations were found across different ecosystem services (e.g. food production, carbon sequestration, soil regulation), most commonly with climate change and population.

We then investigated the contribution of biodiversity and abiotic and anthropogenic drivers to delta ecosystem service supply. Ecosystem service supply was most strongly and consistently associated with abiotic drivers (mostly climatic), but biodiversity and anthropogenic drivers were also important to individual services (productivity and crop-related services respectively). Deltas showed fewer than expected associations between biotic, abiotic and anthropogenic indicators and ecosystem services, yet weakened or reversed associations were more frequent than in other social-ecological systems. Our results empirically show how biodiversity can both act as a resource and mediate social-ecological relationships, but that both of these roles could be compromised as deltas become more modified.

How to cite: Reader, M. O., Eppinga, M. B., de Boer, H. J., Petchey, O., Damm, A., and Santos, M. J.: Biodiversity mediates human-environment interactions in deltas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11383, https://doi.org/10.5194/egusphere-egu22-11383, 2022.

Rossella Belloni et al.

Connectivity describes the efficiency of material transfer between the components of a system. The definition of these components varies among different disciplines and in relation to the material under consideration.

River systems are complex and dynamic environments where multiple and highly inter-correlated processes occur at various spatial and temporal scales. Because of this reason, in-situ traditional techniques for inland waters monitoring are often inadequate to the full understanding of river processes, making the evaluation of river system and inland-marine water connectivity a challenging task.

In this study, we use high-resolution multispectral satellite data acquired by the Sentinel-2 Earth observation mission of the EU Copernicus Programme to investigate the connectivity of the lower Tiber River basin (Italy) from a sedimentological and biogeochemical point of view. To this end, Level-1C satellite imagery, collected on the study area for the period 2017-2020, were processed through the ACOLITE software to perform image atmospheric correction and to obtain water turbidity (WT) and chlorophyll-a (Chl) concentration values on multiple regions of interest along the river course up to the river mouth and the adjacent coastal area. WT and Chl are indeed key parameters for both sediment transport and water quality monitoring of inland and coastal waters. River connectivity was then evaluated by analyzing the spatio-temporal variability of seasonal climatologies of the satellite-derived parameters.

The analysis showed a significant dependence of suspended sediment transport and chlorophyll concentration on hydrological conditions; however, complex dynamics arises. From a sedimentological point of view, as expected, connectivity seems to be positively correlated with the magnitude of the hydrological events, with the highest and lowest degrees of connectivity of WT during the highest and lowest discharge events respectively (winter and summer). From a biogeochemical point of view, there seems to be an optimum window during moderate hydrological conditions (spring) that, on one hand, allow for sediment resuspension and, therefore, nutrients transport along the river course, but on the other, prevent to reach critical resuspension values that would reduce and/or hinder Chl concentration along the river course.

How to cite: Belloni, R., Pitarch, J., Adduce, C., Tarpanelli, A., and Falcini, F.: A Satellite-based analysis of Tiber River inland-marine water connectivity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6445, https://doi.org/10.5194/egusphere-egu22-6445, 2022.

Francesca Uguagliati et al.

Together with salt marshes and tidal flats, tidal channels are one of the fundamental components of tidal environments, because they crucially control the morphodynamic evolution of tidal landscapes. Despite tidal channels play a fundamental role in the hydrodynamics and morphodynamics of tidal environments, the mechanisms that govern their initiation, development, and evolution have received less attention compared to their fluvial counterparts. To address issues of conservation of tidal systems, exposed as they are to the effects of climate changes and increasing human interference, it is therefore of critical importance to improve current understanding of the origins and evolution of tidal channels, of their morphological characteristics, and of the sedimentary structures emerging from their evolution. The present work addresses this important issue, focusing on the study of the erosional and depositional patterns that can be observed in tidal channels cutting through different salt marshes of the Venice Lagoon, from north to south. In particular, we analyzed whether tidal channels are first initiated over tidal-flat surfaces and then inherited by salt marshes, or tidal channels are capable to incise the vegetated salt-marsh surfaces overwhelming the erosion resistance to channel incision provided by vegetation. This study was carried out by combining sedimentological, paleontological, and geomorphic analyses for a total of 30 meanders belonging to small tidal marsh creeks. For the sedimentological analyses, a total of 191 cores were recovered along axial transects of the 30 study bends with normally 6 cores per transect. These analyses allowed us to distinguish four main types of deposits: salt-marsh, point-bar, channel-lag and tidal-flat deposits. Their correlation emphasized the position and the size of the point bars within the different examined transects. Based on the position of the point bar and its brink trajectory within each transect we determined whether the erosive processes that led to channel primary formation occurred over a salt marsh or over a tidal-flat surface. The analyses showed that in most cases the considered channels are originated through the incision of a salt marsh. Lastly, the geomorphic analyses suggested that the analyzed saltmarsh creeks are strongly incised.

How to cite: Uguagliati, F., Tognin, D., Puppin, A., Ghinassi, M., and D'Alpaos, A.: Where do tidal channels begin? Insights from the Venice Lagoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4873, https://doi.org/10.5194/egusphere-egu22-4873, 2022.

Anna Wünsche et al.

Estuarine management requires fundamental system understanding on drivers and effects of flow and transport dynamics. Among other system descriptors, tidal asymmetry is a fundamental prop-erty, used in many ways, e.g. to define the dominant direction of sediment transport in estuaries. There are several different parametrizations of tidal asymmetry, and the number of methods of their derivation has increased in recent years. We present an attempt to discuss comparability of descriptors for tidal asymmetry. We computed descriptors from one-year measured monitoring data of the Ems estuary. Using conformal mapping we scaled each of these for comparison. A sen-sitivity analysis shows the pronounced influence of freshwater discharge on descriptors derived from velocity data and, on the other hand, the influence of wind on quantities based on duration of tidal phases. The impact of spring neap variability changes over the estuary. Our results show that observations of short periods (e.g. two tides) are not robust compared to the average of a spring neap cycle. Finally, we conclude that the classification of the estuary in terms of flood or ebb dominant sediment transport is critically dependent on location and period of the input data. Further, we discuss how to interpret hydrodynamic parameters derived from point measure-ments. The actual characterization of an estuary requires more comprehensive data, such as var-iability over cross sections, data of suspended sediment concentration and a consideration of the entire density-driven circulation.

How to cite: Wünsche, A., Becker, M., Jürges, J., Kelln, J., and Winter, C.: Comparison of tidal asymmetry descriptors – a sensitivity study based on one-year monitoring data of the Ems estuary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13455, https://doi.org/10.5194/egusphere-egu22-13455, 2022.

Insaf Draoui et al.

Compared to deltas, lakes and estuaries, rivers generally are characterized by their natural downstream flow that can often be dealt with adequately by having recourse to 1D models. The cross-section integrated Saint-Venant equations are widely used in river modeling and engineering applications. In order to ensure the mass conservation the conservative form of the equations is preferred. In this case, the flux and source terms may be formulated in several ways. It is seen, however, that not all of them lead to stable and accurate numerical results. The choice of the convenient unknown and intermediate variables allows getting an optimal stability with fewer numerical adjustments. Furthermore, in a realistic domain, two different issues should be carefully dealt with, namely the relative paucity of geometric data points and the connection to larger water bodies ( delta, lakes ...). Regarding the data interpolation, the reference level for data definition and interpolation is generalized along the river instead of associating a local reference frame to each cross-section, allowing to obtain a smooth, stable source term. As for the connection to a 2D model, a boundary-connected coupling based on flux continuity is adopted. The aforementioned modules are implemented in the framework of a discontinuous Galerkin finite-element model, i.e., the Second-generation Louvain-la-Neuve Ice-ocean Model (SLIM, www.slim-ocean.be). Validation is performed by running the model in idealized configurations. Then, the river-lakes-delta continuum of the Mahakam River (Borneo, Indonesia) is modeled and validation is based on measured water level.

How to cite: Draoui, I., Lambrechts, J., Legat, V., and Deleersnijder, E.: The discontinuous Galerkin method for coupling a 1D river model to a 2D shallow water one , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1084, https://doi.org/10.5194/egusphere-egu22-1084, 2022.