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ITS2.4/HS12.1

This session provides a platform for cross-disciplinary science that addresses the continuum of the river and its catchment to the coastal sea. We invite studies across geographical borders; from the source to the sea including groundwater, and across the freshwater-marine water transition. The session welcomes studies that link environmental and social science, address the impacts of climate change and extreme events, and of human activities on water and sediment quality and quantity, hydromorphology, biodiversity, ecosystem functioning and ecosystem services of River-Sea systems, and that provide solutions for sustainable management of the River-Sea social-ecological system.
We need to fully understand how River-Sea-Systems function. How are River-Sea-Systems changing due to human pressures? What is the impact of processes in the catchment on 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 socio-ecologic 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 jointly enable intensive human use and environmental protection in river-sea systems requires holistic and integrative research approaches with the ultimate goal of enhanced system understanding.

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Co-organized by BG4/GM6/NH5/OS2/SSP3, co-sponsored by IAS
Convener: Jana Friedrich | Co-conveners: Debora Bellafiore, Dietrich Borchardt, Andrea D'Alpaos, Michael Rode
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| Mon, 04 May, 14:00–15:45 (CEST)

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Chat time: Monday, 4 May 2020, 14:00–15:45

Chairperson: Jana Friedrich & Debora Bellafiore
D2556 |
EGU2020-13344
Another drought or more pesky humans? Anthropogenic impacts leave drought-like sedimentological signatures in offshore sediments
(withdrawn)
Akos Kalman, Timor Katz, Alysse Mathalon, Paul Hill, and Beverly Goodman-Tchernov
D2557 |
EGU2020-9015
Florian Zander, Julia Gebert, Rob N. J. Comans, Alexander Groengroeft, Timo J. Heimovaara, and Annette Eschenbach

The project BIOMUD, part of the scientific network MUDNET (www.tudelft.nl/mudnet), investigates the decomposition of sediment organic matter (SOM) in the Port of Hamburg. The microbial turnover of sediment organic matter under reducing conditions leads to the formation of methane, carbon dioxide and others gases causing a change in the sediment rheological parameters. BIOMUD is aiming to explain the effect of organic matter lability on the rheological properties impacting the navigable depth of the harbour.

Samples of freshly deposited material were taken in 2018 and 2019 at nine locations in a transect of 30 km through the Port of Hamburg. Analyses included abiotic parameters (among others grain size distribution, standard pore water properties, standard solid properties, stable isotopes, mineral composition) and biotic parameters (among others anaerobic and aerobic organic matter degradation, DNA, protein and lipid content, microbial population). At four locations, physical density fractions and chemical organic matter fractions were analysed.

The quality of organic matter was described by normalising carbon released from microbial degradation under both aerobic and anaerobic conditions to the share of total organic carbon (mg C/g TOC). Organic matter pools with different degradation rates were used to quantify the lability of organic matter. The share of faster degradable (more labile) pools correlated strongly with the size of the hydrophilic DOC fraction, confirming results of Straathof et al. (2014) who investigated dissolved organic carbon pools in compost. The hydrophilic DOC fraction was closely correlated to the polysaccharide concentration, explaining the input of easily degradable organic matter. Moreover, the amount of organic carbon present in the sediment’s light density fraction < 1.4 g/cm3 strongly correlated with the hydrophilic DOC fraction and, less strongly, with organic matter lability. High organic matter quality, i.e. the labile, easily degradable fraction, was further related to the chlorophyll concentration in the water column but also the ammonium concentration in the sediment’s pore water.

It was hypothesised that the observed toposequence of decreasing organic matter quality from upstream to downstream could be explained by a chronosequence of increasing degradation and therefore ageing of organic matter as the sediment passes through the harbour area. Further, it was hypothesized that the harbour received organic matter of higher degradability, originating from phytoplankton biomass, from the upstream part of the Elbe river, whereas the input from the tidal downstream area provided organic matter of lower quality (degradability).

This study was funded by Hamburg Port Authority.

D2558 |
EGU2020-18362
Johannes Pein, Ute Daewel, Emil Stanev, and Corinna Schrum

The present day Elbe estuary ecosystem dynamics are largely determined by high loads of river borne inorganic and organic nitrogen. Similar to most European tidal rivers, the Elbe estuary is highly eutrophied. The eutrophication leads to high primary production in the shallow limnic reach, followed by heterotrophic decay, sedimentation and summertime oxygen depletion in the deepened channel and harbor area. For several decades, the estuary has been subject to adverse trends regarding the forcing of the heterotrophic turnover: While the ambient temperature increases, the nitrogen loads are decreasing (Radach and Pätsch, 2008). The projected long-term and climatic changes imply these trends to continue (Radach and Pätsch, 2008; Huang et al., 2010). In this study we use an unstructured 3D coupled bio-physical model of the Elbe estuary to study the effect of long-term changes of riverine nitrogen loads onto the estuarine ecosystem. As a first step we change the riverine nitrogen forcing i) reducing equally the dissolved inorganic and organic nitrogen loads by 50 % each, ii) reducing the inorganic load and organic loads by 80 % and 40 %, respectively, iii) reducing both inorganic and organic loads towards pre-industrial levels (Serna et al., 2010). Our results indicate a decrease of primary production and heterotrophic turnover under all scenarios. The decrease of primary production is mainly due to reduced diatom growth. Consequently summertime nitrification and oxygen depletion also decrease. This effect is more pronounced in case of equal reduction of inorganic and organic loads than of strong reduction of inorganic nitrogen loads only. Other than diatoms, cyano-bacteria are less affected by applied changes and associated biomass even increases in comparison with the reference case under scenario ii). In the second part of the study we will increase the temperature forcing to determine to which degree the projected increase of ambient temperatures will affect the projected reduced nitrogen turnover.

D2559 |
EGU2020-8950
Jose Rodriguez, Eliana Jorquera, Patricia Saco, and Angelo Breda

Coastal wetlands are at the interface between land and sea, receiving water, sediment and nutrients from upstream catchments and also being subject to tides, wave and changing sea levels. Analysis of their future evolution requires the analysis of the entire catchment to coast system, including the effects of climate variability and change and land use changes. We have developed a modelling framework that is able to include both catchment and coastal processes into the evolution of coastal wetlands by coupling an ecogeomorphological wetland evolution model with a hydrosedimentological catchment model to include both tidal and catchment runoff inputs. We drive the model with storm events and sea-level variations and analyse scenarios of future climate and land use for a catchment in Vanua Levu, Fiji that includes a mangrove wetland at the catchment outlet. We inform our model with field, remote sensing and historical data on land use, tides, sediment and nutrient transport and cyclone activity.

D2560 |
EGU2020-6846
Marco Bracaglia, Rosalia Santoleri, Gianluca Volpe, Simone Colella, Federica Braga, Debora Bellafiore, and Vittorio Ernesto Brando

Inherent optical properties (IOPs) and concentrations of the sea water components are key quantities in supporting the monitoring of the water quality and the study of the ecosystem functioning. In coastal waters, those quantities have a large spatial and temporal variability, due to river discharges and meteo-marine conditions, such as wind, wave and current, and their interaction with shallow water bathymetry. This short term variability can be adequately captured only using Geostationary Ocean Colour (OC) satellites, absent over the European seas.

In this study, to compensate the lack of an OC geostationary sensor over the North Adriatic Sea (NAS), the Virtual Geostationary Ocean Colour Sensor (VGOCS) dataset has been used. VGOCS contains data from several OC polar satellites, making available multiple images a day of the NAS, approaching the temporal resolution of a geostationary sensor.

Generally, data from different satellite sensors are characterized by different uncertainty sources and consequently, looking at two satellite images, it is not easy to ascertain how much of the observed differences are due to real processes. In the VGOCS dataset, the inter-sensor differences are reduced, as the satellite data were adjusted with a multi-linear regression algorithm based on in situ reflectance acquired in the gulf of Venice. Consequently, the use of the adjusted spectra as input in the retrieval of the IOPs and the concentrations allows performing a reliable analysis of the short-time bio-optical variability of the basin.

In this work, we demonstrate the suitability of VGOCS to better characterise the river-sea interaction and to understand the influence of the river forcing on the short time variability of IOPs and concentrations in the coastal areas. This variability will be analysed for different case studies characterised by a different regime of river discharges, using meteorological, hydrological, and oceanographic fields as ancillary variables. This new approach and the availability of this new set of data represent an opportunity for interdisciplinary studies, in support to and interacting also with modelling implementations in river-sea areas.

D2561 |
EGU2020-8587
Eero Asmala, Christopher Osburn, Ryan Paerl, and Hans Paerl

The transport of dissolved organic carbon from land to ocean is a large and dynamic component of the global carbon cycle. Export of dissolved organic carbon from watersheds is largely controlled by hydrology, and is exacerbated by increasing major rainfall and storm events, causing pulses of terrestrial dissolved organic carbon (DOC) to be shunted through rivers downstream to estuaries. Despite this increasing trend, the fate of the pulsed terrestrial DOC in estuaries remains uncertain. Here we present DOC data from 1999 to 2017 in Neuse River Estuary (NC, USA) and analyze the effect of six tropical cyclones (TC) during that period on the quantity and fate of DOC in the estuary. We find that that TCs promote a considerable increase in DOC concentration near the river mouth at the entrance to the estuary, on average an increase of 200 µmol l-1 due to storms was observed. TC-induced increases in DOC are apparent throughout the estuary, and the duration of these elevated DOC concentrations ranges from one month at the river mouth to over six months in lower estuary. Our results suggest that despite the fast mineralization rates, the terrestrial DOC is processed only to a minor extent relative to the pulsed amount entering the estuary. We conclude that the vast quantity of organic carbon delivered to estuaries by TCs transform estuaries from active biogeochemical processing “reactors” of organic carbon to appear more like passive shunts due to the sheer amount of pulsed material rapidly flushed through the estuary.

D2562 |
EGU2020-20824
Aisling Corkery, Guanghai Gao, John O'Sullivan, Liam Reynolds, Laura Sala-Comorera, Niamh Martin, Jayne Stephens, Tristan Nolan, Wim Meijer, Bartholemew Masterson, Conor Muldoon, and Gregory O'Hare

This paper presents the development and preliminary results of a deterministic modelling system for bathing water quality assessment in Dublin Bay, Ireland.  The system integrates functional capacity for simulating the transport and fate of diffuse agricultural pollutants (utilising both the NAM rainfall-runoff model in conjunction with MIKE 11), discharges from the Dublin urban drainage network (through MIKE Urban and InfoWorks software), and the ultimate fate of pollutants in Dublin Bay (coastal domain modelling utilises the 3-dimensional MIKE 3 code).  The work presented forms part of the EU INTERREG funded Acclimatize project (www.acclimatize.eu) that is investigating the longer-term water quality pressures in Dublin Bay that may arise in the context of a changing climate (particularly that from predicted changes in precipitation totals and patterns).  Model calibration and validation has been underpinned by extensive data collection from within the catchments discharging to Dublin Bay and from the bay area itself.  Catchment data includes the observing of hydrometeorological variables for establishing relationships to measured flows and water quality at catchment and sub-catchment scales.  Coastal data relates to water quality, coastal hydrodynamics (current speed and direction collected from ADCP deployments at multiple monitoring points in the bay), temperature and salinity.  A nested modelling approach where the modelled domain is nested in a larger Irish Sea model has been adopted.  Tidal constituents along the seaward boundaries of this nested model have been calibrated to correlate well with tidal measurements from a set of established tide gauges within the modelled domain.  Bottom friction was calibrated to produce good correlations of measured and simulated current speed and direction.  Preliminary results indicate that the transport of faecal indicator bacteria within the study area is adequately represented for spring and neap tide conditions.

D2563 |
EGU2020-19093
| Highlight
Sina Bold, Jana Friedrich, Peter Heininger, Chris Bradley, Andrew Tyler, Adrian Stanica, and Danubius-pp Consortium

More than three quarters of the Earth's land surface is connected to the ocean by rivers. This natural connection between land and ocean by rivers, estuaries and deltas, as well as coastal seas, is essential for humankind in providing key ecosystem services (incl. food and water). However, the quantity and quality of water and sediment transported along the river-sea continuum is changing fundamentally with implications for the structure and functioning of associated ecosystems that are in turn affecting the continued provision of ecosystems services.

DANUBIUS-RI, the International Centre for Advanced Studies on River-Sea Systems, is a distributed research infrastructure (RI) integrating studies of rivers and their catchments, transitional waters, such as estuaries, deltas and lagoons, and their adjacent coastal seas (i.e. River-Sea Systems). DANUBIUS-RI’s vision is to achieve healthy River-Sea Systems and advance their sustainable management in order to live within the planet’s ecological limits by 2050. DANUBIUS-RI’s mission is to facilitate excellent research from the river source to the sea by (1) providing access to state-of-the art facilities, methods and tools, as well as samples and data; (2) bringing together relevant expertise to advance process and system understanding and to enhance stakeholder engagement; and (3) enabling the development of integrated management and policy-making in River-Sea Systems. DANUBIUS-RI’s mission-oriented, integrated, interdisciplinary and participatory approach seeks to change the process and system understanding of River-Sea Systems and their respective management.

DANUBIUS-RI’s Science & Innovation Agenda is guiding the RI’s evolution as it progresses from preparation through implementation to operation. It describes DANUBIUS-RI’s vision, mission and approach, and provides a scientific framework for the RI’s design and highlights the research priorities for the first five years. The framework includes interrelated key challenges in River-Sea Systems, such as global change including climate change and extreme events, changes in hydromorphology, the quantity and quality of water and sediment across the river-sea continuum as well as the structure and functioning of associated ecosystems. DANUBIUS-RI’s research priorities are in line with forthcoming missions of Horizon Europe, which have been applied to River-Sea Systems (1): “Achieving healthy inland, transitional and coastal waters” including the research priorities (a) Water Quantity, (b) Sediment Balance, (c) Nutrients and Pollutants, (d) Biodiversity, (e) Ecosystem Services; and (2): “Adapting to Climate Change: Enhancing Resilience of River-Sea Systems” including the research priorities (f) Climate Change, (g) Extreme Events.

In 2016, the European Strategy Forum for Research Infrastructures (ESFRI) included DANUBIUS-RI in its roadmap highlighting the need for a research infrastructure at the freshwater-marine interface. The Horizon 2020 project DANUBIUS-PP (Preparatory Phase) has built the scientific, legal and financial foundation to enable DANUBIUS-RI to proceed to implementation (www.danubius-pp.eu.

D2564 |
EGU2020-18320
Jana Friedrich, Sina Bold, Peter Heininger, Chris Bradley, Andrew Tyler, Adrian Stanica, and Danubius-PP Consortium

DANUBIUS-RI, the International Centre for Advanced Studies on River- Sea Systems, is a distributed environmental research infrastructure on the Roadmap of the European Strategy Forum on Research Infrastructures (ESFRI). DANUBIUS-RI offers a new paradigm in aquatic science: the River- Sea continuum approach. It aims to provide an integrated research infrastructure with interdisciplinary expertise encompassing: remote and in-situ observation systems (including ships), experimental facilities, laboratories, modelling tools and resources for knowledge exchange along freshwater-seawater continua throughout Europe, from river source to sea. The Science and Innovation Agenda of DANUBIUS (SIA), presented in a tandem presentation, provides the scientific rationale that underpins the technical and organisational design of the research infrastructure, hence the components and their interaction. The research needs and priorities identified in the SIA shape the design of the infrastructure to ensure DANUBIUS-RI provides the interdisciplinary expertise, tools and capacities required.

This presentation describes the DANUBIUS-RI components, their functions and interactions, the governance structure and services of the RI to demonstrate how DANUBIUS-RI will transform its mission into science and services for the benefit of healthy River-Sea Systems.

The DANUBIUS-RI Components comprise the Hub, Data Centre, Nodes, Supersites, e-Learning Office and Technology Transfer Office, distributed across Europe. DANUBIUS-ERIC, as legal entity, provides the effective governance framework: it coordinates, manages, harmonizes and communicates the activities carried out by the DANUBIUS-RI Components.

The DANUBIUS Commons will be a key element of DANUBIUS-RI: a set of harmonised regulations, methods, procedures and standards for scientific and non-scientific activities, to guarantee the integrity, relevance, consistency and elevated quality of DANUBIUSRI’s products and services. The DANUBIUS Commons will provide the framework to ensure that the outputs of DANUBIUS-RI are compatible, comparable, and exchangeable throughout the research infrastructure, and within the user community.

The DANUBIUS-RI Services span a range of disciplines, which is essential to address the major research questions and challenges in River-Sea Systems. Seven categories of services have been developed: (1) digital and non-digital data; 2) tools, methods and expert support; (3) study and measurements; (4) diagnostic and impact; (5) solution development; tests, audit, validation and certification; and (7) training.

DANUBIUS-RI will cooperate closely with other research infrastructures, including ICOS-ERIC, EMSOERIC, EURO-ARGO ERIC, LifeWatch ERIC and eLTER; with research infrastructure networks such as HYDRALAB and JERICO; with River Basin and Regional Seas Commissions; with data programmes and initiatives such as the European Copernicus programme, EUMETSAT and SeaDataNet; and with research programmes and initiatives such as JPI Water and JPI Oceans.

DANUBIUS-RI has completed its preparatory phase (DANUBIUS-PP) at the end of 2019, and now started its implementation. The first components successfully applied for EU infrastructural funding (EFRE). DANUBIUS-RI is expected to be operational by 2023.

D2565 |
EGU2020-22281
Eva Feldbacher, Stefan Schmutz, Gabriele Weigelhofer, and Thomas Hein

Austria has a share in three international river basins (Danube, Elbe, Rhine), but by far the most of its territory (> 96%) drains into the Danube. This Austrian territory accounts for 10% of the total area of the Danube River Basin and belongs entirely to the Upper Danube Basins, which extends from the source of the Danube in Germany to Bratislava at Austria’s eastern border to Slovakia. Austria contributes approx. 25% (ca. 50 km³/a ) to the total yearly discharge of the Danube into the Black Sea (ca. 200 km³/a).

Human activities have severely altered the Upper Danube catchment, impacting both the main stem and the main pre-alpine tributaries. Due to the Upper Danube’s considerable natural gradient and mountainous character, this part of the Danube is extensively used for hydropower production. Ten large (> 10 MW) hydropower plants are situated along the Austrian Danube (out of a total of 41), and only two Danube stretches can still be characterized as free-flowing (Wachau, Nationalpark Donau-Auen).  Besides energy generation, other human activities such as agriculture, shipping, industrialisation, urbanisation and tourism, have been and still are changing the process and system dynamics of the Upper Danube.  Climate change is additionally affecting this already heavily impacted River System.

The Upper Danube Austria and its pre-alpine network of tributaries is therefore an ideal case study region to investigate the multiple effects of human activities on riverine systems and was chosen as a “supersite” within Danubius-RI, the “International Centre for Advanced Studies on River-Sea Systems”. Danubius-RI is being developed as distributed Research Infrastructures with the goal to support interdisciplinary and integrated research on river-sea systems. DANUBIUS-RI aims to enable and support research addressing the conflicts between society’s demands, environmental change and environmental protection for river -sea systems worldwide and brings together research on freshwaters and the interface to marine waters, drawing on existing research excellence across Europe.

The supersite “Upper Danube Austria and its pre-alpine network of tributaries” covers the freshwater spectrum within the river-sea continuum, ranging from alpine and pre-alpine headwater streams along major Danube tributaries to the Danube River, including adjacent floodplains in the Upper Danube catchment. The research focus lies on the interactive effects of climate change, land use pressures, and hydromorphological alterations on the biodiversity, ecological functions, and the ecosystem service provision of streams and rivers in the Upper Danube basin and their role within the catchment.

The Supersite “Upper Danube Austria and its pre-alpine network of tributaries” joins forces of eight Austrian research institutions and is led by WasserCluster Lunz and the Institute for Hydrobiology and Aquatic Ecosystem Management (IHG) at the University of Natural Resources and Life Sciences, Vienna (BOKU). Research on sustainable management and restoration of riverine landscapes (WFD, FD, HD, Biodiversity  Strategy) in the Upper Danube Catchment is an important contribution to a healthy River-Sea System of the Danube River Basin as a whole.

D2566 |
EGU2020-22494
Peter Robins, Lisa Harrison, Mariam Elnahrawi, Matt Lewis, Tom Coulthard, and Gemma Coxon

Coastal flooding worldwide causes the vast majority of natural disasters; for the UK costing £2.2 billion/year. Fluvial and surge-tide extremes can occur synchronously resulting in combination flooding hazards in estuaries, intensifying the flood risk beyond fluvial-only or surge-only events. Worse, this flood risk has the potential to increase further in the future as the frequency and/or intensity of these drivers change, combined with projected sea-level rise. Yet, the sensitivity of contrasting estuaries to combination and compound flooding hazards at sub-daily scales – now and in the future – is unclear. Here, we investigate the dependence between fluvial and surge interactions at sub-daily scales for contrasting catchment and estuary types (Humber vs. Dyfi, UK), using 50+ years of data: 15-min fluvial flows and hourly sea levels. Additionally, we simulate intra-estuary (<50 m resolution) sensitivities to combination flooding hazards based on: (1) realistic extreme events (worst-on-record); (2) realistic events with shifted timings of the drivers to maximise flooding; and (3) modified drivers representing projected climate change.

For well-documented flooding events, we show significant correlation between skew surge and peak fluvial flow, for the Dyfi (small catchment and estuary with a fast fluvial response on the west coast of Britain), with a higher dependence during autumn/winter months. In contrast, we show no dependence for the Humber (large catchment and estuary with a slow fluvial response on the east coast of Britain). Cross-correlation results, however, did show correlation with a time lag (~10 hours). For the Dyfi, flood extent was sensitive to the relative timing of the fluvial and surge-tide drivers. In contrast, the relative timing of these drivers did not affect flooding in the Humber. However, extreme fluvial flows in the Humber actually reduced water levels in the outer estuary, compared with a surge-only event. Projected future changes in these drivers by 2100 are likely to increase combination flooding hazards: sea-level rise scenarios predicted substantial and widespread flooding in both estuaries. However, similar increases in storm surge resulted in a greater seawater influx, altering the character of the flooding. Projected changes in fluvial volumes were the weakest driver of estuarine flooding. On the west coast of Britain containing many small/steep catchments, combination flooding hazards from fluvial and surges extremes occurring together is likely. Moreover, high-resolution data and hydrodynamic modelling are necessary to resolve the impact and inform flood mitigation methodology.

D2567 |
EGU2020-14936
Coline Poppeschi, Maximilian Unterberger, Guillaume Charria, Peggy Rimmelin-Maury, Eric Goberville, Nicolas Barrier, Emilie Grossteffan, Michel Repecaud, Loïc Quemener, Sébastien Theetten, Sébastien Petton, Jean-François Le Roux, and Paul Tréguer

Extreme event occurrences and impacts in coastal waters of western Europe

 

Coline Poppeschi1, Maximilian Unterberger1, Guillaume Charria1, Peggy Rimmelin-Maury2, Eric Goberville3, Nicolas Barrier5, Emilie Grossteffan2, Michel Repecaud6, Loïc Quemener6, Sébastien Theetten1, Sébastien Petton7, Jean-François Le Roux1, Paul Tréguer4

 

1 Ifremer, Univ. Brest, CNRS, IRD, Laboratoire d'Océanographie Physique et Spatiale (LOPS), IUEM, 29280 Brest, France.

2 OSU-Institut Universitaire Européen de la Mer (IUEM), UMS3113, F-29280, Plouzané, France.

3 Muséum National d’Histoire Naturelle, UMR 7208 BOREA, Sorbonne Université, CNRS, UCN, UA, IRD, Paris, France.

4 IUEM, UMR-CNRS 6539 Laboratoire de l’Environnement Marin (LEMAR), OSU IUEM, F-29280, Plouzané, France.

5 MARBEC, Université de Montpellier, Centre National de la Recherche Scientifique (CNRS), Ifremer, Institut de Recherche pour le Développement (IRD), F-34203 Sète, France.

6 Ifremer, Centre de Brest, REM/RDT/DCM, F-29280, Plouzané, France.

7 Ifremer, Centre de Brest, RBE/PFOM/LPI, F-29840, Argenton en Landunvez, France.

 

Abstract

            The occurrence and the impact of the atmospheric extreme events in coastal waters of western Europe is evolving. Responses of the coastal environment to those events and evolutions need to be explored and explained. In this framework, the hydrodynamical and biogeochemical processes driven by extreme events in the bay of Brest are studied to better estimate their impacts on the local ecosystem. We are analyzing long-term in situ observations (since 2000), sampled at high and low frequencies, from the COAST-HF and SOMLIT network sites, located at the entrance to the bay of Brest. This study is divided into two main parts: the detection and characterization of extreme events, followed by the analysis of a realistic numerical simulation of these events to understand the underlying ocean processes. We focus on freshwater events during the winter months (December, January, February and March), considering the season with most of extreme event occurrence. The relationship between local extreme events and variability at larger scales, considering climate indices such as the North Atlantic Oscillation (NAO), is detailed. A comparison between the low frequency data from the SOMLIT network and the high frequency data from the COAST-HF network is carried out, highlighting the potential of high frequency measurements for the detection of extreme events. A comparison between in situ data and two numerical simulations of different resolutions is also performed over salinity time series. The interannual variability of extreme event occurrences and features in a context of climate change is also discussed. The link between these extreme low salinity events and the winter nitrate levels in the bay of Brest is shown. Then, we investigate the relationship between extreme events and biology in the coastal environment.

 

Keywords

In-situ observations, High and low frequency measurements, Extreme events, Numerical simulations, Bay of Brest, Weather regimes.

D2568 |
EGU2020-6670
Alexander Wachholz, Seifeddine Jomaa, Olaf Büttner, Robert Reinecke, Michael Rode, and Dietrich Borchardt

Due to global climate change, the past decade has been the warmest for Germany since the beginning of climate records. Not only air temperature but also precipitation patterns are changing and therefore influencing the hydrologic cycle. This will certainly influence the chemical status of ground- and surface water bodies as mobilization, dilution and chemical reactions of contaminants are altered. However, it is uncertain if those alterations will impact water quality for better or worse and how they occur spatially. Since water management in Europe is handled at the regional scale, we suggest that an investigation is needed at the same scale to capture and quantify the different responses of the chemical status of water bodies to climate change and extreme weather conditions. In this study, we use open-access data to (1) quantify changes in temperature, precipitation, streamflow and groundwater levels for the past 40 - 60 years and (2) assess their impacts on nutrient concentrations in surface- and groundwater bodies. To disentangle management from climate effects we pay special attention to extreme weather conditions in the past decade. Referring to the Water Framework Directive, we chose the river basin district Elbe as our area of interest. Preliminary results indicate that especially the nitrate concentrations in surface water bodies of the Elbe catchment were positively affected in the last two years, while no significant impact on nitrate levels in shallow groundwater bodies was witnessed. However, many wells showed the first significant increase in water table depth in both years since 1985, raising the question of how fast groundwater-surface water interactions will change in the next years.

D2569 |
EGU2020-5655
Norbert Kamjunke, Michael Rode, Martina Baborowski, Vanessa Kunz, Oliver Lechtenfeld, Peter Herzsprung, and Markus Weitere

Large rivers play a relevant role in the nutrient turnover from land to ocean. Here, highly dynamic planktonic processes are more important compared to streams making it necessary to link the dynamics of nutrient turnover to control mechanisms of phytoplankton. We investigated the basic conditions leading to high phytoplankton biomass and corresponding nutrient dynamics in the eutrophic River Elbe (Germany). In a first step, we performed six Lagrangian samplings in the lower river part at different hydrological conditions. While nutrient concentration remained high at low algal densities in autumn and at moderate discharge in summer, high algal concentrations occurred at low discharge in summer. Under these conditions, concentrations of silica and nitrate decreased and rates of nitrate assimilation were high. Soluble reactive phosphorus was depleted and particulate phosphorus increased inversely. Rising molar C:P ratios of seston indicated a phosphorus limitation of phytoplankton. Global radiation combined with discharge had a strong predictive power to explain maximum chlorophyll concentration. In a second step, we estimated nutrient turnover exemplarily for N during the campaign with the lowest discharge. Mass balance calculations revealed a total nitrate uptake of 455 mg N m-2d-1 which was clearly dominated by assimilatory phytoplankton uptake whereas denitrification and other benthic processes were only of minor importance. Phytoplankton density, which showed a sigmoidal longitudinal development, dominantly explained gross primary production, related assimilatory nutrient uptake and respiration. Chlorophyll a concentration and bacterial abundance affected the composition of dissolved organic matter and were positively related to a number of CHO and CHNO components with high H/C and low O/C ratios but negatively to several CHOS surfactants. In conclusion, nutrient uptake in the large river strongly depends on the growth conditions for phytoplankton, which are favored during summer drought conditions.

D2570 |
EGU2020-1447
Jianzhong Ge, Shenyang Shi, Changsheng Chen, and Richard Bellerby

Coastal ecosystems are strongly influenced by terrestrial and oceanic inputs of water, sediment and nutrients. Terrestrial nutrients in freshwater discharge are particularly important for mega-river estuaries. A remarkable increase in nutrient loads transported from the Changjiang River through the estuary to the shelf has been observed from 1999 to 2016. The Finite-Volume Community Ocean Model and the European Regional Seas Ecosystem Model were coupled to assess the interannual variability of nutrients and phytoplankton under these flux dynamics. The system exhibited a rapid ecosystem response to the changing river nutrient contribution. Singular vector decomposition (SVD) analysis demonstratedthat abundant nitrate from the river was diluted by low-nitrate water transported from the oceanic domain. In contrast, phosphate exhibited local variation, suggesting the estuarine ecosystem was phosphate-limited. The SVD results showed that there were no significant correlations between the suspended sediment and nutrients, but a significant correlation between sediment and phytoplankton. The nutrient structure of the river discharge resulted in the dominance of non-diatom species in the phytoplankton bloom from spring to autumn. The ratio of diatom and dinoflagellate populations showed a rapid feedback response to the strong oscillations in river nutrient input. High diatom primary production occurred near the sediment front, whereas dinoflagellate bloom extended significantly offshore. Both diatoms and dinoflagellates had major peaks representing spring blooms from empirical orthogonal function Mode 1 and 2, and secondary peaks from Mode 2 in the autumn, which coincided with the autumn bloom.

D2571 |
EGU2020-1915
Jianhua Gao

    Human activity has led to rapid changes in the erosion and deposition conditions and boundaries of the different units within the Changjiang–ECS S2S conveying system, thereby resulting in major changes in the source-sink pattern of the entire S2S conveying system. After 2003, the insufficient sediment supply disequilibrated the mass balance relationship between the estuary-coast-shelf deposition systems, thereby resulting in alteration in siltation and erosion state and sea bed sediment types, and the adjustment of the geomorphology evolvement. In addition, currently, the upper reach of the Changjiang became disconnected from the Changjiang–ECS S2S conveying system to become an independent S2S conveying system. Thus, the length of the Changjiang–ECS S2S conveying system is shortened, and the source area within this S2S conveying system has significantly increased.

D2572 |
EGU2020-14404
Zhicheng Yang, Sonia Silvestri, Marco Marani, and Andrea D’Alpaos

Salt marshes are biogeomorphic systems that provide important ecosystem services such as carbon sequestration and prevention of coastal erosion. These ecosystems are, however, threatened by increasing sea levels and human pressure. Improving current knowledge of salt-marsh response to changes in the environmental forcing is a key step to understand and predict salt-marsh evolution, especially under accelerated sea level rise scenarios and increasing human pressure. Towards this goal, we have analyzed field observations of marsh topographic changes and halophytic vegetation distribution with elevation collected over 20 years (between 2000 and 2019) in a representative marsh in the Venice lagoon (Italy).

Our results suggest that: 1) on average, marsh elevation with respect to local mean sea level decreased , (i.e. the surface accretion rate was lower than the rate of sea level rise); 2) elevational frequency distributions are characteristic for different halophytic vegetation species, highlighting different ecological realized niches that change in time; 3) although the preferential elevations at which different species have changed in time, the sequence of vegetation species with increasing soil elevation was preserved and simply shifted upward; 4) we observed different vegetation migration rates for the different species, suggesting that the migration process is species-specific. In particular, vegetation species colonizing marsh edges (Juncus and Inula) migrated faster facing to changes in sea levels than Limonium and Spartina , while Sarcocornia was characterized by delayed migration in response to sea level changes. These results bear significant implications for long-term biogeomorphic evolution of tidal environments.

D2573 |
EGU2020-26
Lin Lin

Damming rivers has been identified as one of the most intense artificial perturbations on carbon transportation along the river continuum. To quantify the damming effect on the riverine carbon flux in the upper Mekong River, seasonal carbon fluxes were monitored in a subtropical valley-type reservoir (the Gongguoqiao Reservoir) in 2016. Annually, around 20% of the incoming carbon was sequestered within the reservoir with most of the carbon retention occurring in the rainy season. Since higher rainfalls and water discharge brought large amounts of terrestrial carbon into the reservoir in summer, the concentrations of dissolved organic carbon (DIC), particulate inorganic carbon (PIC) and particulate organic carbon (POC) in the topwater show significant decreasing trends from the river inlet to the outlet (p<0.01). During the cooler dry season (winter), however, the damming effect was much weaker. Precipitation of PIC owing to the alkaline environment and decelerated flow velocity contributed over half of the carbon retention in the reservoir. Correlation between suspended sediment concentration and carbon concentrations reveals that heavy sedimentation also resulted in the sequestration of particulate carbon. Yet the damming impact on the flux of dissolved organic carbon (DOC) was relatively weak due to the short water retention time and refractory nature of allochthonous carbon. The anti-season operation of the dam allowed little time for the decomposition of the incoming DOC in the rainy season. The differentiation processing of the carbon flow significantly increased the dissolved carbon proportion in the outflow. The dams could be acting as filters and the effect might be exacerbated in the cascading system. Accumulation of dissolved organic carbon possibly can accelerate eutrophication processes in the downstream reservoirs and thus altered the aquatic carbon dynamics in the downstream river channels. 

D2574 |
EGU2020-8373
Celine Gommet, Ronny Lauerwald, Philippe Ciais, and Pierre Regnier

Inland waters receive important amounts of dissolved organic carbon (DOC) from surrounding soils, which drives an important net-heterotrophy and subsequent CO2 emission from these systems.  At the same time, this DOC transfer decreases the soil carbon sequestration capacity, which may limit the efficiency of the land carbon sink. The variation of DOC stocks and fluxes in time and space is modeled using the ORCHILEAK model that couples terrestrial ecosystem processes, carbon emissions from soils to headwater streams by runoff and drainage, as well as carbon decomposition and transport in rivers until export to the coastal ocean. The runs were performed at the resolution of 0.5°, taking advantage of the relatively dense observations of soil and river DOC available for European catchments.  The model was first evaluated for the hydrology by comparing the discharge at different stations along several large European rivers. The DOC measurements were used to calibrate the different parameters of the ORCHILEAK model and to evaluate the model results. ORCHILEAK was then used to generate the first European map of DOC stocks and leaching for the four seasons. We estimate a soil DOC stock at 71 TgC and a DOC leaching flux of 7,8 TgC/yr, largely dominated by runoff exports during the winter season. Our model results also allow to identify the underlying processes controlling the fraction of terrestrial NPP exported to the European inland water network. The next step will be to use the model to hindcast historical DOC fluxes and predict their evolution over the 21st century using climate change and land use projections from the SSP-RCP scenarios developed for the IPCC assessment report.

D2575 |
EGU2020-8875
Louise Rewrie, Yoana Voynova, Holger Brix, and Burkard Baschek

Seasonal and annual nitrate and phosphate loads were determined from FerryBox measurements to investigate the high seasonal and inter-annual variability of carbon and nutrient exchange between the Elbe estuary and North Sea. At the inner continental shelf, high biological activity is driven by riverine nutrient inputs, which can contribute to the net carbon dioxide (CO2) uptake. It is possible that in tidal systems this newly formed phytoplankton is transported back into the estuary over the flood tide, and this organic matter can be remineralized in the intertidal region. At present, the influence of this tidally driven mechanism on the nutrient exports and primary production in the coastal zone is not fully characterized, hence carbon sources and sinks at the estuary-coastal boundary may not be well accounted for.

The coupling between nutrient inputs from the Elbe estuary to adjacent coastal waters and the subsequent biological activity are now being investigated with a high-frequency dataset provided by a FerryBox situated at the mouth of the estuary. The FerryBox continuously measures physical and biogeochemical parameters every 10 to 60 minutes. Prelimary seasonal and nutrient (nitrate and phosphate) loads from the Elbe estuary to the coastal waters were calculated with FerryBox data between 2014 and 2017. The nutrient loads exhibited high seasonal and inter-annual variability. For example, in summer 2014 nitrate loads reached 100 x 107 mol yr-1 whereas, in summer 2017 nitrate loads were 50 x 107 mol yr-1, which cannot be explained by river discharge alone. Such changes in nutrient loads are likely to influence primary production rates in the adjacent coastal waters and impact CO2 uptake and therefore carbon cycling.

Time-series analysis is employed to determine patterns in oxygen changes in relation to photosynthesis and respiration, along with nutrient fluctuations, between 2014 and 2017. Salinity is used to differentiate between the coastal and estuarine end members, with low and high salinity representing flood tide (estuarine waters) and ebb tide (coastal waters), respectively. Changes in dissolved oxygen concentrations are used to estimate primary production (P) and community respiration (R) rates in the water column. The P/R ratio provides the ability to classify the community into autotrophic and heterotrophic systems. Results of this analysis will show the role of varying nutrient loads in supporting primary production in the coastal waters, along with estimating net ecosystem metabolism, and therefore give us a better understanding of nutrient and carbon cycling. 

D2576 |
EGU2020-2128
Yu Zhang

Metabolism, transportation, and redistribution difference of atrazine and acetochlor from estuary to bay

Yu Zhang a, Wei Ouyanga, Zihan Wanga, Zewei Guoa, Zeshan Wua, Mats Tysklindb, Chunye Lina,

Baodong Wangc, Ming Xinc

a State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China

b Environmental Chemistry, Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden

c The First Institute of Oceanography, State Oceanic Administration, 6 Xianxialing Road, Qingdao, 266061, China

Abstract

Agricultural activities are the cause of pollution in several watersheds, mainly due to the discharge of herbicides. Herbicides suffer continual degradation and they present special patterns during the transport from watershed to bay. The spatial distribution of atrazine, its dealkylated chlorotriazine metabolites, and acetochlor in water, suspended particulate sediment (SPS), and surface sediment were investigated from estuary to bay. The concentrations of atrazine and deethyl-atrazine(DEA) and deisopropy-latrazine (DIA) were generally higher in the coastal zone than estuary and bay. The water distance of metabolites demonstrated that atrazine degradation was active from estuary to bay and DIA had the shortest half-distance of 1.6 km. In contrast, acetochlor concentration decreased with an increase of seawater depth and had the longer half-distance of 8.5 km than atrazine and its metabolites. Didealkyl-atrazine (DDA) had the highest concentration in SPS (7.6 ng/L) and sediment (7.0 ng/g) among all these herbicides, which indicated that it had the biggest sorption capacity. Both the spatial distribution and the vertical contents in water, SPS, and sediment demonstrated that these herbicides presented different response during the transport from the estuary to bay. Despite the significant difference in contents of atrazine, DEA, DIA, and acetochlor in the water and sediment, their spatially averaged value in SPS was very close, indicating that SPS had saturated sorption capability. The water-particle phase partition coefficient (Kp) analysis indicated that the partition process was more active in the estuary than in the bay for atrazine and its metabolites, and the metabolites had stronger capacity than the atrazine. The Kp of acetochlor was the highest among the herbicides, which illustrated that acetochlor was strongly phase partitioned in the coastal and bay zones, thereby causing similar distribution of acetochlor in the three matrices. The correlation between Kp and the corresponding octanol-water partitioning coefficient indicated that the hydrophobicity of atrazine and its metabolites were important factors for the partition between seawater and SPS. The current tides and bathymetry were the critical factors in determining the spatial distribution of herbicides in the water and sediment, resulting in low load in the estuary zone.

Key words: Typical herbicides; Phase partition; Diffuse pollution; Suspended particulate sediment; Semiclosed bay

 
D2577 |
EGU2020-5986
Elie Dhivert, François Gibon, Karine Hochart, and Bertrand Devillers

In application of the EU Water Framework Directive, many actions have been undertaken in order to reduce pollution levels in river systems. However, for certain catchments, the resilience process is not occurring as expected. In the Bienne River basin, metals discharge has plummeted since the 1990s, following the implementation of a better industrial waste management, as well as an important industrial restructuring. Nevertheless, this river has been regularly affected by massive fish mortality over the 2012-2019 period. This phenomenon, never identified before, is becoming recurrent. Organic tissues sampled in dead fish contained high concentrations of metals in association with other toxics. In this context, this study introduces a transdisciplinary approach in order to: (i) analyse spatial and temporal evolutions of pollutions in the Bienne River, (ii) evaluate potential ecotoxicological impacts associated, (iii) identify interactions with local hydro-climatic changes. Metallic and organic pollutants were analysed over different stations and at multi-temporal scales, associating sedimentary archives, suspended matters and passive water samplers. These analyses highlight the impact on the river quality of both current and legacy pollutions, particularly during prolonged low-water periods and high discharge events. Ecotoxicological analyses emphasize a severe risk level in the case of polluted sediments remobilization, especially because of heavy metals and PAH contamination. Geochemical evidence of such remobilization events has been recorded over the last decade in a sedimentary core sampled in the downstream part of the Bienne River. Hydrological data recorded in the Bienne River gauging stations since 1971 attests of an important year-to-year variability, although changes in the river discharge distribution are ongoing. Data has shown a higher frequency of both the lowest and the highest outflows over the 2012-2019 period compared to the rest of the hydrological recording. Hydro-climatic variables coming from in-situ measurements and satellite data (GPM-IMERG6) has also shown significant modifications in the rainfall regime over this period, especially in the augmentation of dry spells and heavy rainfall episodes. Those modifications agree well with the discharge change observations. This study brings out knock-on impacts of combined geochemical, ecotoxicological and hydro-sedimentary issues on the fate of aquatic ecosystems, especially under the influence of local hydro-climatic changes and their implications on hydrological regimes. Those results aim at reducing uncertainties concerning the evolution of the river quality by highlighting such a tipping point for environmental conditions. In addition, such a study helps us to grasp the complexity of local stakes regarding the multiple interests of a wide range of stakeholders and policy makers involved on the field.

D2578 |
EGU2020-13793
Feifei Deng, Stefen Hellmann, Tristan Zimmerman, and Daniel Pröfrock

River systems in Germany are under an increasing pressure due to human activities and the changing global climate in the recent decade. Human activities, such as agriculture and industrial manufacturing, for instance have supplied contaminates to many rivers, which has greatly affected the river ecosystem. Extreme events, as a result of the changing global climate, such as the more frequent extraordinary floods and droughts, are playing an increasingly significant role in the chemical compositions of the different river systems. To protect these unique river ecosystems, it is important to identify the contribution of these various sources of pressure and quantitatively assess their relative impacts on the different river systems.

Here, we will explore the potential of using the Sr, Nd, and Pb isotopes as a fingerprinting tool to quantify the relative contributions from both natural and anthropogenic sources supplying the materials to the river system. Sediment samples were collected from the river Weser, the longest river that lies entirely within Germany. The river Weser is formed by the junction of two rivers, Werra and Fulda, and flows towards its estuary in the North Sea. With a mean discharge of 327 m3/s, it is one of the main rivers discharging into the North Sea. With its two headwaters and tributaries also sampled, sampling locations cover a geographical area of agricultural land and industrial sites, and expand to coastal areas of the North Sea. It is therefore ideal to evaluate the impact of various sources of human activities and the changing climate on the river system, and to provide insight into the contribution of river system to the ocean.

Sediment samples were analysed for their elemental compositions to evaluate the load of each chemical composition in the river Weser. Isotopic ratios of Sr, Nd, and Pb were measured on MC-ICP-MS (Multi-collector-Inductively Coupled Plasma-Mass Spectrometry) with the newly-developed automated prepFAST sample purification method (Retzmann et al., 2017). The Sr, Nd and Pb isotope results reported here are the first such dataset obtained from the river Weser sediment. Combined with the statistical analysis, such as the principal component analysis, the dataset allows the evaluation of the contribution of various sources to the load of the river Weser, and enables the quantification of the flux of the river to the North Sea, and an estimate of the contribution of the river system to contaminants transported into the coastal zone. These estimates will also be of interest to stakeholders and governments for targeted management interventions of the socio-economically important Weser river system.

 

References

Retzmann, A., Zimmermann, T., Pröfrock, D., Prohaska, T., Irrgeher, J., 2017. A fully automated simultaneous single-stage separation of Sr, Pb, and Nd using DGA Resin for the isotopic analysis of marine sediments. Analytical and Bioanalytical Chemistry 409, 5463-5480.

D2579 |
EGU2020-21706
Simone Toller, Salvatore Dominech, Enrico Dinelli, Shouye Yang, Lucilla Capotondi, Francesco Riminucci, and Ivo Vasumini

Sediment samples were collected in 2019 from Fiumi Uniti catchment in Italy in an area between the Romagna Apennines and the Adriatic Sea. The sampling phase included the collection of sediments from the Ridracoli reservoir, a large artificial basin located at 480 m a.s.l. made by construction of a dam on the Bidente river and used as the main drinking water supply of the region and for hydropower production, as well as river sediments within the whole catchment that includes the dam (Bidente, Ronco and Fiumi Uniti rivers and tributaries) and marine sediments from the Adriatic sea. In addition, we collected in the reservoir area rock and soil samples to define the element behaviour during weathering and transport.

Here we report data on chemical concentrations from different matrices within the area of Ridracoli reservoir as well as chemical characterization of sediments downstream the dam along the rivers. The chemical analyses were carried out at the State Key Laboratory of Marine Geology in Shanghai, where samples underwent a two-step digestion to assess the mobile and residual fraction using a first leaching step with 1N HCl and a second one with pure HNO3 and HF, respectively.

The chemical differences between rock, soils and sediments inside the reservoir showed a system of element mobility that can be compared to the geochemistry of surrounding sediments to assess pathways of geochemical cycles of elements. The ratio between concentrations of different matrices shows an enrichment in soils compared to rock for some elements (>1.3; Li, V, Cr, Mn, Sr, Cd, U) and slightly depletion in lake sediments compared to rocks (0.8-0.9). The REE ratio between lake sediments and other matrices (i.e., rocks, soils, and stream sediments) equals to 0.7-0.8, while for other trace elements (Li, V, Mn, Fe, Ni) is 1.1-1.2 showing an opposite behaviour.

More mobile elements assessed using the ratio between the first step of leaching and the total composition, are Mn (0.7 of extractability) and Sr (0.8) followed by Co, Cu, Se Cd and Pb (around 0.3-0.4). The more stable elements (higher in the residual) are Ti, Rb, Zr, Cs (max 0.015). Cu and Pb seems to be more mobile in sediments than rock and soil, whereas the mobility of other analytes doesn’t seem to be affected by the different matrices. REE are quite mobile showing good extractability for Eu, Gd, Tb, Dy. Spider diagrams of REE were normalized to PAAS (Post Archean Australian Shale) and show similar shapes with Gd peaks. A difference can be seen between rocks (values around 0.8 and 1.2) and sediments, with the latter showing higher values (1.2 and 1.4).

The importance of this study relies on the implications that human activities have on river systems thanks to sediment quality and on the functioning of the river-sea system in Romagna and specifically in Ridracoli reservoir catchment.

D2580 |
EGU2020-22064
Julia Gebert and Florian Zander

Under anaerobic conditions, degradation of organic matter in river sediments leads to gas formation, with organic carbon being released mainly as CH4 and CO2. Gas bubbles reduce sediment density, viscosity and shear strength, impede sonic depth finding and are suspected to affect the sediments’ rheological properties. Moreover, methane (CH4) is a potent greenhouse gas with a global warming potential (GWP100) of 28-36. Therefore, the climate impact may vary greatly depending on the way sediments are managed (for example, type and frequency of dredging and relocation in the water body or treatment on land). The objective of this paper is therefore to quantify the time-dependent stability, or inversely, the lability of sediment organic matter (SOM) as a basis for prediction of effects on sediment mechanical properties and on the release of greenhouse gases.

Within two years, over 200 samples of predominantly fine-grained sediment were collected from nine locations within a 30 km transect through the Port of Hamburg. All samples were, amongst other analyses, subjected to long-term (> 250 days) aerobic and anaerobic incubation for measurement of SOM degradation, yielding a comprehensive data set on the time-dependent change in degradation rates and the corresponding size of differently degradable SOM pools. SOM degradability exhibited a pronounced spatial variability with an approximately tenfold higher anaerobic and a roughly fivefold higher aerobic degradability of upstream SOM compared to downstream SOM. Lower δ13C values, higher DNA concentrations and a higher share of organic carbon in the light density fraction as well as elevated chlorophyll concentrations in the water phase support the hypothesis of increased biological sources of SOM at upstream locations and increased SOM degradability in shallow compared to deep layers (Zander et al., 2020).

First statistical and time series analyses indicate that

  • Long-term SOM lability appears to be predictable from short-term measurements.
  • The relationship between short-term and long-term SOM degradation is site-specific and also differs for layers of different age (depth). This supports the above-mentioned variability between sites regarding the size of differently degradable carbon pools, as well as for the depth profile at any one site.
  • The relevance of the available electron acceptors (redox conditions) for SOM degradation, i.e. the ratio between carbon release under aerobic and anaerobic conditions, differs less by site but more so by layers of different age (depth). This is plausible as especially the top layers are exposed to more variability in redox conditions than the deeper layers that are always under reducing conditions.

Zander, F., Heimovaara, T., Gebert, J. (2020): Spatial variability of organic matter degradability in tidal Elbe sediments. Journal of Soils and Sediments, accepted for publication.

D2581 |
EGU2020-1973
hyen goo cho

The Central South Sea Mud (CSSM), developed in the Seomjin River estuary, is known to be supplied with sediments from Heuksan Mud Belt (HMB) and Seomjin River. However, in order to form a mud belt, more sediments must be supplied than supplied in the above areas. In this study, clay minerals, major elements analyzes were performed on cores 16PCT-GC01 and 16PCT-GC03 in order to investigate the transition in the provenance and transport pathway of sediments in CSSM. The Huanghe sediments are characterized by higher smectite and the Changjiang sediments are characterized by higher illite. Korean river sediments contain more kaolinite and chlorite than those of chinese rivers. Korean river sediments have higher Al, Fe, K concentraion than Chinese river sediments and Chinese rivers have higher Ca, Mg, Na than those of Korean rivers. Therefore, clay minerals and major elements can be a useful indicator for provenance. Based on our results, CSSM can be divided into three sediment units. Unit 3, which corresponds to the lowstand stage, is interpreted that sediments from Huanghe were supplied to the study area by coastal or tidal currents. Unit 2, which corresponds to the transgressive stage, is interpreted to have a weaker Huanghe effect and a stronger Changjiang and Korean rivers effect. Unit 1, which corresponds to the highstand stage when the sea level is the same as present and current circulation system is formed, is interpreted that sediments from Changjiang and Korean rivers are supplied to the research area through the current.

D2582 |
EGU2020-3816
Chendong Ge and Zhenqiang Ji

The morphological characteristics of quartz inclusions in sediments from five locations in the upper, middle and lower reaches of the Changjiang River are analyzed. The source indication of sediments is discussed through the differences in shape, size, quantity, gas percentage and genetic type. From upstream to downstream, the characteristics of quartz inclusions in sediments are different. The inclusion types appearing in the samples from upstream to estuary are gradually enriched. The sediment influx from the tributaries of the Changjiang River makes new types of quartz inclusions appearing in the downstream and estuary. In terms of quantity and size, most quartz inclusions are concentrated in the range of 2-4 μm in size and 10-150/mm3 in number. The number and size range of different positions are also different. In SGJS-01 collected from Shigu, is 2-18 μm, the number is 2-166 per volume. In YBCJ-01, YZD-63 and YZD-10 samples collected from Yibin, Yichang and Wuhan, the size is 2-15μm, 2-10μm, 2-12μm and the number is 1-270, 2-220 and 1-308 per volume. The primary inclusions of SGJS-01 in Shigu is 14%, higher than that of primary inclusions in the middle and lower reaches, and that of YBCJ-01 in Yibin decreases to 6%, and for YZD-63, YZD-10 and HK-01 they were 8%, 6% and 5% respectively. The change of the primary inclusion proportion reflects the difference of source rock types of sediments. The difference of source rocks of sediments can be reflected in the type, size, quantity and proportion of primary inclusions. The characteristics of quartz inclusions could be a new way to explore the source of sediments.