Coastal Transition Zones under Natural and Human Pressures

Science Tools

Water pollution from cooper mine Geamana, Romania (Photo: Jaanus Jagomägi, Unsplash)

"Making better use of research findings can help transforming usable information into used knowledge."

Our Science Tools provide expert users with information on new methods, approaches or indicators for baseline assessments or for the re-evaluation of complex environmental problems in the land-to-sea continuum.

A biogeochemical tool to improve our understanding of the coastal ocean CO2 sink

Bugdget Sediments

Porewater irrigation ratesfor the North Sea only, derived from Ra budget (green) and incubations with Ra (orange) or bromide (blue) as tracers (Van Dam et al., 2022, Biogeosciences)

Shallow continental shelves are highly active regions of carbon burial, remineralization, and exchange, with net fluxes relevant to the global carbon cycle. Especially reactive are those with highly permeable sediments where currents and animals act together to rapidly flush surficial sediments with oxygenated water.

Our work used three independent approaches to assess this flushing rate and found that it is likely more rapid than previously thought. Importantly, this flushing delivers oxygenated water to the sediments. In the absence of this flushing, a suite of (mostly) anaerobic processes will produce alkalinity to the water column, which in turn will cause the net removal of atmospheric CO2.

Sand grains collected from a German Bight sediment core taken during the HE541 cruise, as seen through a microscope (Van Dam et al., 2022, Biogeosciences)

Sand grains collected from a German Bight sediment core taken during the HE541 cruise, as seen through a microscope (Van Dam et al., 2022, Biogeosciences)

The enhanced flushing that we observed effectively short-circuits these anaerobic processes occurring deeper in the sediments by balancing them with re-oxidation near the surface. The effect of this is a reduced flux of alkalinity from the sediments, thereby decreasing the capacity for surface waters to remove CO2 from the atmosphere.

Our understanding of the continental shelf carbon sink can be improved with better estimates of the seasonal and spatial variability in flushing rates and associated elemental fluxes.

Van Dam, B.; Lehmann, N.; Zeller, M. A.; Neumann, A.; Pröfrock, D.; Lipka, M.; Thomas, H.,; Böttcher, M.-E. (2022). Benthic alkalinity fluxes from coastal sediments of the Baltic and North seas: comparing approaches and identifying knowledge gaps. Biogeosciences, 19(16), 3775–3789, doi: 10.5194/bg-19-3775-2022.

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A novel technique to estimate in situ diatom growth rates by using the silica deposition fluorescent probe PDMPO


Fluorescent silica frustules under the microscope

Diatoms are the main contributors to primary production and drivers of the biogeochemical cycles of carbon, silicon and other major elements in the world’s oceans. Understanding their life cycle characteristics and species specific dynamics is crucial, however, impaired by poorly quantifiable processes such as mortality. PDMPO is a fluorophore that, when applied to growing diatom cultures, is incorporated only in newly polymerized silica in diatom frustules. Thereby it provides a tool to estimate silica uptake, study diatom cell cycles but also determine mortality-independent abundance-based species specific growth rates in cultures and natural assemblages.

In this study, the theoretical framework and applicability of the PDMPO staining technique to estimate diatom species specific growth rates have been investigated. The specific growth rate estimates based on the PDMPO staining patterns (μPDMPO) were comparable and more robust than growth rates estimated from the changes in cell concentrations (μcc).

Diatomeen Husmann

Diatom frustules are like a pill box casing. A new frustule is formed within the maternal cell during cell division. If PDMPO has been added only the newly formed silica frustules will fluoresce under the microscope

This method provides reliable and robust results within a short (24 h) incubation time frame: it is mortality independent, less variable than previous approaches and the short incubation time limits the impact of the so-called “bottle” effects. The proposed standard concentration of 0.125 μM PDMPO is sufficient to stain weakly silicified diatoms under replete nutrient conditions. However, even a higher concentration (up to 0.6 μM) does not significantly impair growth rates within a 24 h. The PDMPO technique provides a robust estimate of the species population growth rate as well as, depending on sampling strategy, information on the variability of growth rates within the population.

The understanding of the factors leading to diatom species specific dynamics and the resulting differential impact on vertical fluxes and transfer to higher trophic levels is however, still limited. By using the PDMPO method, a tool was developed that has the potential to provide a better understanding of the dynamics of phytoplankton in natural assemblages and their fate in biogeochemical cycles.

Husmann, E. and Klaas, C. (2022): Testing the use of the silica deposition fluorescent probe PDMPO to estimate in situ growth rates of diatoms. In: Limnology and Oceanography Methods. Early View, doi: 10.1002/lom3.10505.

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Baseline concentrations of technology-critical elements (TCEs) in North Sea sediments

Klein et al. Fig 1

Illustration of problematic situation of TCEs

Technology-critical elements (TCEs) are elements or minerals that bear a high supply risk, while also exhibiting high demand in the economy. They represent key components for today's high-tech industries and are therefore needed in almost every sector of modern economies. Consequently, the fields of application for TCEs range from energy production over entertainment electronics to the medical sector. Since the beginning of the 2000s, the application of TCEs has increased significantly and is expected to grow even faster within the next years. In this context, the disturbed and not fully closed circular economies of these elements play a decisive role, as this aspect leads to ever-rising waste flows, which might end up in the adjacent environmental compartments in the short or long run. Therefore, TCEs are gaining increasing attention in environmental research, as they show a high potential to enter the environment as new pollutants.

Despite the high interest to investigate the occurrence and fate of TCEs in the environment, the existing data for most TCEs are still too scarce to allow accurate assessments of their potential (eco-) toxicological effects. Moreover, the lack of considerable background or reference values hampers the distinct evaluation of TCEs and their role as potential uprising emerging contaminants.

Fig 2 3 Klein et al.

Map of the study area throughout the period from 2010 to 2020 (left); Mass fractions of the TCEs niobium (Nb) and tantalum (Ta) over the investigated period and the determined reference values (right)

Therefore, the occurrence and temporal variation of TCEs over ten years in the North Sea were investigated in this study. In cooperation with the German Federal Maritime and Hydrographic Agency, the BSH, Hereon researchers analyzed sediment samples, taken between 2010 and 2020 from BSH and Hereon, from two different coastal regions of the North Sea for their TCE content. Results reveal that for all investigated TCEs the temporal, as well as spatial variation, appeared to be minimal, implying no significant anthropogenic impacts yet. Consequently, determined mass fractions of this time series were used to estimate preliminary reference values for TCE contents in North Sea sediments.

As a result, these reference values provide a reliable starting point for future studies to better assess a possible pollution situation. Hence, a retrospective analysis of older samples and further statistical evaluation may be used to determine the factual background values of the TCEs or other analytes.

Klein, O.; Zimmermann, T.; Ebeling, A.; Kruse, M.; Kirchgeorg, T.; Pröfrock, D. (2022): Occurrence and Temporal Variation of Technology-Critical Elements in North Sea Sediments - A Determination of Preliminary Reference Values. In: Archives of Environmental Contamination and Toxicology, 82 (2022), doi: 10.1007/s00244-022-00929-4.

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Combining modeling approaches and modern stable isotope measurements: A tool to determine terrestrial nutrient inputs to support environmental planning in heavily populated coastal areas

Eutrophication is a worldwide problem in marginal seas that receive high loads of nutrients from anthropogenic sources. China, with its high population density and its fast-growing megacities along the coast, is facing increasing eutrophication pressure in its coastal waters. Thus, environmental and urban planners are challenged to find sustainable solutions for cleaner and healthier ecosystems in the marine environment.

Nitrogen Science Tool Daehnke Neu

Nitrate budget of the Bohai Sea, mass fluxes (mmol x 10 9) are complemented by respective nitrate isotope values (not shown for clarity). Arrow thickness corresponds to mass fluxes. Note that the largest input flux is nitrification, i.e., recycling of nitrate (modified after Tian et al., 2022b)

In two consecutive studies, an international team of researchers evaluated for the first time the sources of reactive nitrogen in the Bohai and the Southern Yellow Sea. This type of source is an important driver of eutrophication. A combination of modeling approaches and stable isotope measurements using state-of-the-art laboratory facilities was applied to provide for a reliable and comprehensive indication for eutrophication.

The approach showed that an amazingly large fraction of nitrate in the water column stems from microbial nutrient recycling and nitrate production in the water column. At present, this input outcompetes the capacity of regional coastal sediments to remove nitrate via respiration (summarized under the term ‘denitirification’).

The terrestrial inputs from the Changjiang River and the Yellow River have exhausted the capacity of the coastal ocean zones to remove and attenuate nitrogen. If nutrient inputs continue at present levels, the study regions are facing high ecological risky and may host low-oxygen environments in the coastal zone, which may lead to severe environmental problems. These hypoxic regions are spreading in the light of global change, and are threatening coastal aquatic ecosystems around the globe.

Tian, S.; Gaye, B.; Tang, J.; Luo, Y.; Lahajnar, N.; Dähnke, K.; Sanders, T.; Xiong, T.; Zhai, W.; Emeis, K.-C. (2022a): Nitrate Regeneration and Loss in the Central Yellow Sea Bottom Water Revealed by Nitrogen Isotopes. In: Frontiers in Marine Science, Vol. 9, (2022), doi: 10.3389/fmars.2022.834953.

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Tian, S.; Gaye, B.; Tang, J.; Luo, Y.; Li, W.; Lahajnar, N.; Dähnke, K.; Sanders, T.; Xiong, T.; Zhai, W.; Emeis, K. C. (2022b): A nitrate budget of the Bohai Sea based on an isotope mass balance model. In: Biogeosciences, Vol. 19, 2397-2415 (2022), doi: 10.5194/bg-19-2397-2022.

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Suspect screening: A powerful complementary tool to shed light on “dark matter” of per- and polyfluoroalkyl substances (PFAS) Photo slideshow on PFAS study

Per- and polyfluoroalkyl substances (PFAS) are a group of several thousand human-made chemicals that have been manufactured for more than seven decades. They are used in a broad range of consumer products and industrial applications, from fast food wrappers to firefighting foams. Due to their adverse effects on human health and the environment, some well-known PFAS have been globally banned. However, potential adverse properties, environmental occurrence and fate of next-generation PFAS remain largely unknown. Using traditional compound-specific analytical methods, so-called “target analysis”, only a small amount of PFAS on the global market is monitored.

In a new study, an international team of pollution researchers used high-resolution mass spectrometry (HRMS) to complement traditional target analysis and the total oxidizable precursor (TOP) assay as a sum parameter.

Non-target Figure Joerss Rahmen

Results of target analysis, TOP assay and suspect screening as complementary analytical tools for a water sample collected in the German Alz River (Graphic by Hanna Joerss/Hereon)

Key findings

• Based on the developed suspect screening workflow, HRMS raw data was searched for 3.655 PFAS available on the global market.

• In German and Chinese river water samples, the suspect screening revealed 86 PFAS at different confidence levels. Only about 30 of them are routinely analysed in specialized labs.

• Eight substances were detected in the environment for the first time. This included C4 to C8 perfluoroalkyl dicarboxylic acids (PFdiCAs) and three perfluoroalkylether carboxylic acids (PFECAs) containing two ether bridges.

• The results indicated that a significant PFAS fraction had been missed by target analysis and TOP assay, particularly in samples taken downstream of fluoropolymer production sites.

• However, a comparison of the analytical tools also showed the limitations of HRMS-based approaches, for example the lower sensitivity compared to target analysis.

Even though five European member states are working on a restriction proposal addressing the entire group of PFAS within the framework of the European Green Deal, an analytical tool for measuring the “totality of PFAS” is not available yet. The present study underlines that the complementary use of suspect screening, target analysis and TOP assay can achieve a better coverage of “PFAS total“ compared to traditional stand-alone target analysis.

Original publication:

Joerss, H.; Menger, F.; Tang, J.; Ebinghaus, R.; Ahrens, L. (2022): Beyond the Tip of the Iceberg: Suspect Screening Reveals Point Source-Specific Patterns of Emerging and Novel Per- and Polyfluoroalkyl Substances in German and Chinese Rivers. In: Environmental Science and Technology, doi: 10.1021/acs.est.1c07987.

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Accumulated watershed sediments as pollution memories: A tool to identify peak pollution periods in deposited sediment layers to support industrial regulation

NOAH Paper Logemann et al. 2022

Occurence and decline of different pollution groups in the North Sea during the last century (Graphic: Logemann et al., 2022, Env. Pol.)

Especially during the last 100 years, a diverse cocktail of chemicals mainly from industrial sources, has been polluting the marine environment. Contaminants enter the ecosystem via rivers, the atmosphere and through direct sources. Due to prevailing currents in the sea, fine sediments are transported and accumulated strongly in distinct regions. Strong accumulation of sediments, to which pollutants preferably adhere, causes the seabed to grow by several millimetres per year. Sediments are called the memory of a watershed, as the varying exposure during different times is reflected in their deposited layers.

In a multi-partner study, pollution researchers used modern analytical equipment to identify periods of high pollution levels generating from changing industrial activities. As part of this comprehensive pollution fingerprint, sediment cores from North Sea’s main sedimentation area were taken, in the Skagerrak, where water depths cause high rates of deposition. The deep understanding of a pollution memory demonstrated that decreasing trends could be linked to the time of introductions of restrictions from regulation. Thus, the results highlight the effectiveness of environmental legislation by revealing a successive change in contamination levels over the decades. However, even after the early introduction of regulatory measures, long periods are required until pollutant concentrations return to their natural background levels.

Analysing sediment cores from the sea by using a fingerprint approach, can be promising to build up a pollution memory for the ocean in support of industrial regulation.

Logemann, A.; Reininghaus, M.; Schmidt, M.; Ebeling, A.; Zimmermann, T.; Wolschke, H.; Friedrich, J.; Brockmeyer, B.; Pröfrock, D.; Witt, G. (2022): Assessing the chemical anthropocene – Development of the legacy pollution fingerprint in the North Sea during the last century. In: Environmental Pollution, Vol. 302, 119040, (2022), doi: 10.1016/j.envpol.2022.119040.

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A tool based around a novel combination of methods reveals that tropical seagrasses are not a “miracle solution” to climate change Photo slideshow on tropical seagrass meadow experiment

Seegraswiesen Hereon Bryce-van-dam 03

A tropical seagrass meadow (Photo: Van Dam, Hereon)

Coastal management actions aimed at protecting or restoring seagrass meadows are often assumed to have the collateral benefit of removing large amounts of carbon dioxide from the atmosphere to combat climate change. Be aware, however: not all seagrass meadows are alike. Under certain conditions, some release more carbon dioxide than they absorb and are net carbon sources to the atmosphere. This is now shown in a new study by an international team of researchers, published in the scientific journal Science Advances. This study combined direct eddy covariance measurements of air-water gas exchange with geochemical approaches to build a comprehensive carbon budget for a tropical seagrass meadow in south Florida. The process of ecosystem calcification released far more CO2 to the atmosphere than was buried in sediments as “Blue Carbon.”

This study questions the reliability of Blue Carbon approaches towards net CO2 sequestration in tropical waters. But still unclear is how applicable these results are to the global scale, and what fraction of tropical seagrass meadows are net sources, rather than sinks, of CO2 to the atmosphere.f ethical rules is suggested as a way forward towards good governance in energy transitions.

Van Dam, B. R., Zeller, M. A., Lopes, C., Smyth, A.R., Böttcher, M. E., Osburn, L., Zimmerman, T., Pröfrock, D., Fourqurean, J. W., Thomas, H. (2021): Calcification-driven CO2 emissions exceed “Blue Carbon” sequestration in a carbonate seagrass meadow. Sci. Adv. 7, 1–10 (2021), doi: 10.1126/sciadv.abj1372.

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Sustainable energy transitions: An approach to examine stakeholder perception in supporting large off-shore infrastructure

Method framework Governance Study

Methodological framework to assess stakeholder perceptions in a decarbonising world

In this study, Lange and Cummins (2021) investigated the enabling conditions for energy transitions at the community level and in coastal environments. The research was based on the study of a contested offshore gas field development in Ireland. In-depth analysis, as a tool to assess stakeholder perceptions, helped to identify causes of disputes in energy governance. The methodological framework covered an intense exchange with over 70 diverse stakeholders involved within semi-structured interviews, group discussions and a marine governance workshop, including a timeline development process.

The study shows that economic development is strongly linked to the cultural fabric, not just of the country, but of the locality. Here, a lack of trust of those in power had an influence on the conflict. The establishment of an honest broker with a mandate to evaluate the application of ethical rules is suggested as a way forward towards good governance in energy transitions.

Lange, M., Cummins, V. (2021): Managing stakeholder perception and engagement in a decarbonising world, Renewable and Sustainable Energy Reviews (2021), 111740, doi: 10.1016/j.rser.2021.111740.

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Application of emission modeling tools to assess air quality improvements during Corona lockdown Radio broadcast (in German) on Deutschlandfunk (with Dr. Volker Matthias, Hereon)

Acp Paper Matthias 2

NO2 concentrations fell by more than half at many places in countries like France and Italy due to the strict lockdowns. Whereas in Germany the concentrations fell by only by up to 25 percent. Graphic: Volker Matthias et. al (2021).

In the study, Matthias et al. (2021) calculated the changes in air quality during the first lockdown based on scientific emission modelling tools. They also assessed to what extent weather conditions were responsible for the decreased emissions. The scientists found that the amount of nitrogen oxides dropped by more than half in some cases. In cities in particular, concentrations fell sharply. In addition to estimating pure emissions with and without lockdown, the calculations included weather conditions. The result shows that emissions from road traffic could be greatly reduced if significantly more people were able to work from home in the future.

Matthias, V., Quante, M., Arndt, J. A, Badeke, R., Fink, L., Petrik, R., Feldner, J., Schwarzkopf, D., Link, E.-M., Ramacher, M. O., Wedemann, R. (2021): The role of emission reductions and the meteorological situation for air quality improvements during the COVID-19 lockdown period in central Europe, J. Atmos. Chem. Phys., 21, 13931 – 13971, doi: 10.5194/acp-21-13931-2021.

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Extreme flood events: A drift-based tool enabling a synoptic assessment of spatially distributed observations based on drift simulations (see tool under 'Management Tools')

Open Drift Tool

In the work from Callies et al. (2021), our scientists have used three examples to demonstrate the added value of using numerical drift models. Central objective was to validate and synthesize spatially and timely distributed observations. The method allows the identification of those measurements that belong to the same water body at different locations. By means of an exemplary application, using continuous observation data of the FerryBox on the ferry Büsum-Helgoland, the position of the freshwater tongue after the Elbe flood in June 2013 could be reconstructed into the Elbe estuary.

Callies et al (2021) Front. M. Sci.

Callies, U., Kreus, M., Petersen, W., Voynova, Y.G. (2021): On Using Lagrangian Drift Simulations to Aid Interpretation of in situ Monitoring Data, Frontiers in Marine Science 8:666653, doi: 10.3389/fmars.2021.666653.

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In support of new SOPs - a new method for the assessment and analysis of microplastics developed

Paper Hildebrand et al 2021

In this study, our scientists have detected high concentration of microplastic particles in the Elbe waterway as it passes into the North Sea. They have for the first time applied the important guideline for the collection of measurement uncertainties for the evaluation of the investigations. In this way, the results support the development of new Standard Operating Procedures in a focal area of pollution research in support of the toolbox.

Hildebrandt, L., Zimmermann, T., Primpke, S., Fischer, D., Gerdts, G., Pröfrock, D. (2021): Comparison and uncertainty evaluation of two centrifugal separators for microplastic sampling, Journal of Hazardous Materials, Volume 414, 2021, 125482, ISSN 0304-3894,

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Neural networks can reproduce results of complex chemical transport model calculations

Neuronal learning atmospheric emissions

A neural network was created to replicate the calculation of air pollutant concentrations with complex models. This neural network "learned" based on several years of chemical transport model (CTM) simulations and was then able to calculate concentrations for other time periods very quickly. In the context of the toolbox development the research seeks to improve the scientific capacity of numerical modeling in support of assessing transport of atmospheric emissions.

Vlasenko, A., Matthias, V., Callies, U. (2021): Simulation of chemical transport model estimates by means of a neural network using meteorological data. Atmospheric Environment,

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