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Dessirier, B., Blicher-Mathiesen, G., Andersen, H. E., Gustafsson, B., Müller-Karulis, B., Meter, K. V., . . . Humborg, C. (2023). A century of nitrogen dynamics in agricultural watersheds of Denmark. Environmental Research Letters, 18(10), Article ID 104018.
Open this publication in new window or tab >>A century of nitrogen dynamics in agricultural watersheds of Denmark
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2023 (English)In: Environmental Research Letters, E-ISSN 1748-9326, Vol. 18, no 10, article id 104018Article in journal (Refereed) Published
Abstract [en]

Intensive agriculture has been linked to increased nitrogen loads and adverse effects on downstream aquatic ecosystems. Sustained large net nitrogen surpluses have been shown in several contexts to form legacies in soil or waters, which delay the effects of reduction measures. In this study, detailed land use and agricultural statistics were used to reconstruct the annual nitrogen surpluses in three agriculture-dominated watersheds of Denmark (600-2700 km2) with well-drained loamy soils. These surpluses and long-term hydrological records were used as inputs to the process model ELEMeNT to quantify the nitrogen stores and fluxes for 1920-2020. A multi-objective calibration using timeseries of river nitrate loads, as well as other non-conventional data sources, allowed to explore the potential of these different data to constrain the nitrogen cycling model. We found the flux-weighted nitrate concentrations in the root zone percolate below croplands, a dataset not commonly used in calibrating watershed models, to be critical in reducing parameter uncertainty. Groundwater nitrate legacies built up in all three studied watersheds during 1950-1990 corresponding to & SIM;2% of the surplus (or & SIM;1 kg N ha yr-1) before they went down at a similar rate during 1990-2015. Over the same periods active soil nitrogen legacies first accumulated by approximately 10% of the surplus (& SIM;5 kg N ha yr-1), before undergoing a commensurate reduction. Both legacies appear to have been the drivers of hysteresis in the diffuse load at the catchments' outlet and hindrances to reaching water quality goals. Results indicate that the low cropland surpluses enforced during 2008-2015 had a larger impact on the diffuse river loads than the European Union's untargeted grass set-aside policy of 1993-2008. Collectively, the measures of 1990-2015 are estimated to have reset the diffuse load regimes of the watersheds back to the situation prevailing in the 1960s.

Keywords
legacy nitrogen, field surplus, diffuse load, policy
National Category
Environmental Sciences
Identifiers
urn:nbn:se:su:diva-223197 (URN)10.1088/1748-9326/acf86e (DOI)001070662000001 ()
Available from: 2023-10-24 Created: 2023-10-24 Last updated: 2024-01-17Bibliographically approved
Gustafsson, E., Carstensen, J., Fleming, V., Gustafsson, B. G., Hoikkala, L. & Rehder, G. (2023). Causes and consequences of acidification in the Baltic Sea: implications for monitoring and management. Scientific Reports, 13, Article ID 16322.
Open this publication in new window or tab >>Causes and consequences of acidification in the Baltic Sea: implications for monitoring and management
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2023 (English)In: Scientific Reports, E-ISSN 2045-2322, Vol. 13, article id 16322Article in journal (Refereed) Published
Abstract [en]

Increasing atmospheric CO2 drives ocean acidification globally. In coastal seas, acidification trends can however be either counteracted or enhanced by other processes. Ecosystem effects of acidification are so far small in the Baltic Sea, but changes should be anticipated unless CO2 emissions are curbed. Possible future acidification trends in the Baltic Sea, conditional on CO2 emissions, climate change, and changes in productivity, can be assessed by means of model simulations. There are uncertainties regarding potential consequences for marine organisms, partly because of difficulties to assign critical thresholds, but also because of knowledge gaps regarding species’ capacity to adapt. Increased temporal and spatial monitoring of inorganic carbon system parameters would allow a better understanding of current acidification trends and also improve the capacity to predict possible future changes. An additional benefit is that such measurements also provide quantitative estimates of productivity. The technology required for precise measurements of the inorganic carbon system is readily available today. Regularly updated status evaluations of acidification, and the inorganic carbon system in general, would support management when assessing climate change effects, eutrophication or characteristics of the pelagic habitats. This would, however, have to be based on a spatially and temporally sufficient monitoring program.

National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:su:diva-222985 (URN)10.1038/s41598-023-43596-8 (DOI)001138089300001 ()2-s2.0-85173094289 (Scopus ID)
Available from: 2023-10-30 Created: 2023-10-30 Last updated: 2024-02-13Bibliographically approved
Kuliński, K., Rehder, G., Asmala, E., Bartosova, A., Carstensen, J., Gustafsson, B., . . . Undeman, E. (2022). Biogeochemical functioning of the Baltic Sea. Earth System Dynamics, 13(1), 633-685
Open this publication in new window or tab >>Biogeochemical functioning of the Baltic Sea
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2022 (English)In: Earth System Dynamics, ISSN 2190-4979, E-ISSN 2190-4987, Vol. 13, no 1, p. 633-685Article, review/survey (Refereed) Published
Abstract [en]

Location, specific topography, and hydrographic setting together with climate change and strong anthropogenic pressure are the main factors shaping the biogeochemical functioning and thus also the ecological status of the Baltic Sea. The recent decades have brought significant changes in the Baltic Sea. First, the rising nutrient loads from land in the second half of the 20th century led to eutrophication and spreading of hypoxic and anoxic areas, for which permanent stratification of the water column and limited ventilation of deep-water layers made favourable conditions. Since the 1980s the nutrient loads to the Baltic Sea have been continuously decreasing. This, however, has so far not resulted in significant improvements in oxygen availability in the deep regions, which has revealed a slow response time of the system to the reduction of the land-derived nutrient loads. Responsible for that is the low burial efficiency of phosphorus at anoxic conditions and its remobilization from sediments when conditions change from oxic to anoxic. This results in a stoichiometric excess of phosphorus available for organic-matter production, which promotes the growth of N2-fixing cyanobacteria and in turn supports eutrophication.

This assessment reviews the available and published knowledge on the biogeochemical functioning of the Baltic Sea. In its content, the paper covers the aspects related to changes in carbon, nitrogen, and phosphorus (C, N, and P) external loads, their transformations in the coastal zone, changes in organic-matter production (eutrophication) and remineralization (oxygen availability), and the role of sediments in burial and turnover of C, N, and P. In addition to that, this paper focuses also on changes in the marine CO2 system, the structure and functioning of the microbial community, and the role of contaminants for biogeochemical processes. This comprehensive assessment allowed also for identifying knowledge gaps and future research needs in the field of marine biogeochemistry in the Baltic Sea.

National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-204048 (URN)10.5194/esd-13-633-2022 (DOI)000776233300001 ()
Available from: 2022-04-20 Created: 2022-04-20 Last updated: 2022-04-20Bibliographically approved
Ehrnsten, E., Pavlovitch Savchuk, O. & Gustafsson, B. (2022). Modelling the effects of benthic fauna on carbon, nitrogen and phosphorus dynamics in the Baltic Sea. Biogeosciences, 19(13), 3337-3367
Open this publication in new window or tab >>Modelling the effects of benthic fauna on carbon, nitrogen and phosphorus dynamics in the Baltic Sea
2022 (English)In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 19, no 13, p. 3337-3367Article in journal (Refereed) Published
Abstract [en]

Even though the effects of benthic fauna on aquatic biogeochemistry have been long recognized, few studies have addressed the combined effects of animal bioturbation and metabolism on ecosystem–level carbon and nutrient dynamics. Here we merge a model of benthic fauna (BMM) into a physical–biogeochemical ecosystem model (BALTSEM) to study the long-term and large-scale effects of benthic fauna on nutrient and carbon cycling in the Baltic Sea. We include both the direct effects of faunal growth and metabolism and the indirect effects of its bioturbating activities on biogeochemical fluxes of and transformations between organic and inorganic forms of carbon (C), nitrogen (N), phosphorus (P) and oxygen (O). Analyses of simulation results from the Baltic Proper and Gulf of Riga indicate that benthic fauna makes up a small portion of seafloor active organic stocks (on average 1 %–4 % in 2000–2020) but contributes considerably to benthic–pelagic fluxes of inorganic C (23 %–31 %), N (42 %–51 %) and P (25 %–34 %) through its metabolism. Results also suggest that the relative contribution of fauna to the mineralization of sediment organic matter increases with increasing nutrient loads. Further, through enhanced sediment oxygenation, bioturbation decreases benthic denitrification and increases P retention, the latter having far-reaching consequences throughout the ecosystem. Reduced benthic–pelagic P fluxes lead to a reduction in N fixation and primary production, lower organic matter sedimentation fluxes, and thereby generally lower benthic stocks and fluxes of C, N and P. This chain of effects through the ecosystem overrides the local effects of faunal respiration, excretion and bioturbation. Due to large uncertainties related to the parameterization of benthic processes, we consider this modelling study a first step towards disentangling the complex ecosystem-scale effects of benthic fauna on biogeochemical cycling.

National Category
Biological Sciences Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-207914 (URN)10.5194/bg-19-3337-2022 (DOI)000825472600001 ()2-s2.0-85134424750 (Scopus ID)
Available from: 2022-08-22 Created: 2022-08-22 Last updated: 2022-08-22Bibliographically approved
Svedäng, H., Savchuk, O., Villnäs, A., Norkko, A., Gustafsson, B., Wikström, S. & Humborg, C. (2022). On the decline of eastern Baltic cod: we need to take more holistic views into account. Reply to Brander (2022) comment on Svedäng et al. (2022). ICES Journal of Marine Science, 79(7), 2157-2158
Open this publication in new window or tab >>On the decline of eastern Baltic cod: we need to take more holistic views into account. Reply to Brander (2022) comment on Svedäng et al. (2022)
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2022 (English)In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 79, no 7, p. 2157-2158Article in journal (Refereed) Published
Abstract [en]

Explaining the recent decline of eastern Baltic cod (EBC) remains scientifically challenging. Brander proposes in a comment to Svedäng et al.that the observed trend in oxygen in SD 25 supports the idea that juvenile cod are balancing the physiological cost of living under mild hypoxiaby offsetting the risk of being eaten by diving seals and cormorants in shallower water with more oxygen. There are a number of objections tothis conjecture, besides the fact that supporting observations are missing. Hence, it is difficult to reconcile the long-term development of EBCunder varying oxygen conditions with the hypothesis that a small reduction in oxygen content can explain the current strong and uniform declinein growth observed in the entire southern Baltic Sea.

Keywords
Eastern Baltic cod, Gadus morhua, Holistic view, Decline in productivity
National Category
Natural Sciences
Research subject
Ecology and Evolution
Identifiers
urn:nbn:se:su:diva-214629 (URN)10.1093/icesjms/fsac071 (DOI)000784515600001 ()2-s2.0-85146880834 (Scopus ID)
Available from: 2023-02-07 Created: 2023-02-07 Last updated: 2023-04-20Bibliographically approved
Tomczak, M. T., Müller-Karulis, B., Blenckner, T., Ehrnstén, E., Eero, M., Gustafsson, B., . . . Humborg, C. (2022). Reference state, structure, regime shifts, and regulatory drivers in a coastal sea over the last century: The Central Baltic Sea case. Limnology and Oceanography, 67(S1), S266-S284
Open this publication in new window or tab >>Reference state, structure, regime shifts, and regulatory drivers in a coastal sea over the last century: The Central Baltic Sea case
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2022 (English)In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 67, no S1, p. S266-S284Article in journal (Refereed) Published
Abstract [en]

The occurrence of regime shifts in marine ecosystems has important implications for environmental legislation that requires setting reference levels and targets of quantitative restoration outcomes. The Baltic Sea ecosystem has undergone large changes in the 20(th) century related to anthropogenic pressures and climate variability, which have caused ecosystem reorganization. Here, we compiled historical information and identified relationships in our dataset using multivariate statistics and modeling across 31 biotic and abiotic variables from 1925 to 2005 in the Central Baltic Sea. We identified a series of ecosystem regime shifts in the 1930s, 1970s, and at the end of the 1980s/beginning of the 1990s. In the long term, the Central Baltic Sea showed a regime shift from a benthic to pelagic-dominated state. Historically, benthic components played a significant role in trophic transfer, while in the more recent productive system pelagic-benthic coupling was weak and pelagic components dominated. Our analysis shows that for the entire time period, productivity, climate, and hydrography mainly affected the functioning of the food web, whereas fishing became important more recently. Eutrophication had far-reaching direct and indirect impacts from a long-term perspective and changed not only the trophic state of the system but also affected higher trophic levels. Our study also suggests a switch in regulatory drivers from salinity to oxygen. The reference ecosystem identified in our analysis may guide the establishment of an ecosystem state baseline and threshold values for ecosystem state indicators of the Central Baltic Sea.

National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-199999 (URN)10.1002/lno.11975 (DOI)000720319000001 ()2-s2.0-85119335563 (Scopus ID)
Available from: 2021-12-27 Created: 2021-12-27 Last updated: 2022-06-03Bibliographically approved
Svedäng, H., Savchuk, O., Villnäs, A., Norkko, A., Gustafsson, B. G., Wikström, S. A. & Humborg, C. (2022). Re-thinking the “ecological envelope” of Eastern Baltic cod (Gadus morhua): conditions for productivity, reproduction, and feeding over time. ICES Journal of Marine Science, 79(3), 689-708
Open this publication in new window or tab >>Re-thinking the “ecological envelope” of Eastern Baltic cod (Gadus morhua): conditions for productivity, reproduction, and feeding over time
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2022 (English)In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 79, no 3, p. 689-708Article in journal (Refereed) Published
Abstract [en]

Hypoxia is presently seen as the principal driver behind the decline of the former dominating Eastern Baltic cod stock (EBC; Gadus morhua). It has been proposed that both worsening conditions for reproduction and lower individual growth, condition, and survival are linked to hypoxia. Here, we elucidate the ecological envelope of EBC in terms of salinity stratification, oxygen content, and benthic animal biomasses, and how it has affected EBC productivity over time. The spawning conditions started deteriorating in the Gotland Deep in the 1950s due to oxygen depletion. In contrast, in the Bornholm Basin, hydrographic conditions have remained unchanged over the last 60 years. Indeed, the current extent of both well-oxygenated areas and the frequency of hypoxia events do not differ substantially from periods with high EBC productivity in the 1970s–1980s. Furthermore, oxygenated and therefore potentially suitable feeding areas are abundant in all parts of the Baltic Sea, and our novel analysis provides no evidence of a reduction in benthic food sources for EBC over the last 30 years. We find that while reproduction failure is intricately linked to hydrographic dynamics, a relationship between the spread of hypoxia and the decline in EBC productivity during the last decades cannot be substantiated. 

Keywords
benthic biomass, Eastern Baltic cod, hypoxia, productivity, reproduction volume, spatial scales
National Category
Biological Sciences Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-202749 (URN)10.1093/icesjms/fsac017 (DOI)000757533800001 ()
Available from: 2022-03-11 Created: 2022-03-11 Last updated: 2022-06-03Bibliographically approved
Friedland, R., Macias, D., Cossarini, G., Daewel, U., Estournel, C., Garcia-Gorriz, E., . . . Vandenbulcke, L. (2021). Effects of Nutrient Management Scenarios on Marine Eutrophication Indicators: A Pan-European, Multi-Model Assessment in Support of the Marine Strategy Framework Directive. Frontiers in Marine Science, 8, Article ID 596126.
Open this publication in new window or tab >>Effects of Nutrient Management Scenarios on Marine Eutrophication Indicators: A Pan-European, Multi-Model Assessment in Support of the Marine Strategy Framework Directive
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2021 (English)In: Frontiers in Marine Science, E-ISSN 2296-7745, Vol. 8, article id 596126Article in journal (Refereed) Published
Abstract [en]

A novel pan-European marine model ensemble was established, covering nearly all seas under the regulation of the Marine Strategy Framework Directive (MSFD), with the aim of providing a consistent assessment of the potential impacts of riverine nutrient reduction scenarios on marine eutrophication indicators. For each sea region, up to five coupled biogeochemical models from institutes all over Europe were brought together for the first time. All model systems followed a harmonised scenario approach and ran two simulations, which varied only in the riverine nutrient inputs. The load reductions were evaluated with the catchment model GREEN and represented the impacts due to improved management of agriculture and wastewater treatment in all European river systems. The model ensemble, comprising 15 members, was used to assess changes to the core eutrophication indicators as defined within MSFD Descriptor 5. In nearly all marine regions, riverine load reductions led to reduced nutrient concentrations in the marine environment. However, regionally the nutrient input reductions led to an increase in the non-limiting nutrient in the water, especially in the case of phosphate concentrations in the Black Sea. Further core eutrophication indicators, such as chlorophyll-a, bottom oxygen and the Trophic Index TRIX, improved nearly everywhere, but the changes were less pronounced than for the inorganic nutrients. The model ensemble displayed strong consistency and robustness, as most if not all models indicated improvements in the same areas. There were substantial differences between the individual seas in the speed of response to the reduced nutrient loads. In the North Sea ensemble, a stable plateau was reached after only three years, while the simulation period of eight years was too short to obtain steady model results in the Baltic Sea. The ensemble exercise confirmed the importance of improved management of agriculture and wastewater treatments in the river catchments to reduce marine eutrophication. Several shortcomings were identified, the outcome of different approaches to compute the mean change was estimated and potential improvements are discussed to enhance policy support. Applying a model ensemble enabled us to obtain highly robust and consistent model results, substantially decreasing uncertainties in the scenario outcome. ABSTRACT A novel pan-European marine model ensemble was established, covering nearly all seas under the regulation of the Marine Strategy Framework Directive (MSFD), with the aim of providing a consistent assessment of the potential impacts of riverine nutrient reduction scenarios on marine eutrophication indicators. For each sea region, up to five coupled biogeochemical models from institutes all over Europe were brought together for the first time. All model systems followed a harmonised scenario approach and ran two simulations, which varied only in the riverine nutrient inputs. The load reductions were evaluated with the catchment model GREEN and represented the impacts due to improved management of agriculture and wastewater treatment in all European river

Keywords
MSFD, eutrophication, water quality indicators, lower trophic level models, model ensemble, pan-European river management impacts
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-193131 (URN)10.3389/fmars.2021.596126 (DOI)000635494100001 ()
Available from: 2021-05-14 Created: 2021-05-14 Last updated: 2022-02-25Bibliographically approved
Jilbert, T., Gustafsson, B. G., Veldhuijzen, S., Reed, D. C., Helmond, N. A. G., Hermans, M. & Slomp, C. P. (2021). Iron-Phosphorus Feedbacks Drive Multidecadal Oscillations in Baltic Sea Hypoxia. Geophysical Research Letters, 48(24), Article ID e2021GL095908.
Open this publication in new window or tab >>Iron-Phosphorus Feedbacks Drive Multidecadal Oscillations in Baltic Sea Hypoxia
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2021 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 48, no 24, article id e2021GL095908Article in journal (Refereed) Published
Abstract [en]

Hypoxia has occurred intermittently in the Baltic Sea since the establishment of brackish-water conditions at ∼8,000 years B.P., principally as recurrent hypoxic events during the Holocene Thermal Maximum (HTM) and the Medieval Climate Anomaly (MCA). Sedimentary phosphorus release has been implicated as a key driver of these events, but previous paleoenvironmental reconstructions have lacked the sampling resolution to investigate feedbacks in past iron-phosphorus cycling on short timescales. Here we employ Laser Ablation (LA)-ICP-MS scanning of sediment cores to generate ultra-high resolution geochemical records of past hypoxic events. We show that in-phase multidecadal oscillations in hypoxia intensity and iron-phosphorus cycling occurred throughout these events. Using a box model, we demonstrate that such oscillations were likely driven by instabilities in the dynamics of iron-phosphorus cycling under preindustrial phosphorus loads, and modulated by external climate forcing. Oscillatory behavior could complicate the recovery from hypoxia during future trajectories of external loading reductions.

National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-201137 (URN)10.1029/2021gl095908 (DOI)000735897000023 ()
Funder
Academy of Finland, 317684
Available from: 2022-01-19 Created: 2022-01-19 Last updated: 2023-03-20Bibliographically approved
Gustafsson, E., Gustafsson, B., Carstensen, J., Rehder, G. & Fleming, V. (2021). OMAI – Assessing acidification in the Baltic Sea, monitoring and scientific basis. Copenhagen: Nordisk Ministerråd
Open this publication in new window or tab >>OMAI – Assessing acidification in the Baltic Sea, monitoring and scientific basis
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2021 (English)Report (Other academic)
Abstract [en]

In marine and brackish waters, the acidity of the water is mainly controlled by the inorganic carbon system. Anthropogenic CO2 emissions will – unless reduced – gradually move the Baltic Sea towards a state where acidification becomes harmful for some organisms. The effect is caused by the uptake of CO2 in the water, but can be further enhanced by other climate effects, such as increased water temperature and a possible freshening of the sea water. This is expected to lead to changes in species composition, both directly (competitive advantages/disadvantages) and indirectly (altered food availability), potentially influencing ecosystem functioning.

Coastal seas, such as the Baltic Sea, are highly influenced by their catchment areas, which means that pH dynamics is generally more complex than in the open ocean. The reason is that pH, in addition to the response to increasing CO2, is also influenced by changes in hydrology and changes in the supply of carbon and nutrients. High-productive waters typically experience larger seasonal pH variations than low-productive waters, with higher pH peaks in spring/summer and also a more pronounced pH decline in winter. The comparatively weak long-term acidification trend can be masked behind much larger short-term variations. Furthermore, since acidification is a slow process, organisms can to varying degrees adapt to the changes.

Model simulations performed as a part of the OMAI (Operational Marine Acidification Indicator) project indicate that the expected acidification in the Baltic Sea generally follows the same trajectory as the open oceans, with a pH decline of almost 0.4 by year 2100 and a further decline of 0.3 by year 2300 in the worst-case scenario. Due to large regional differences in the area, the annual mean pH in the Bothnian Bay might decline from present-day 7.8 to 7.4 by year 2100, whereas in the Gotland Sea and Southern Kattegat mean pH could decline from present-day 8.1 to 7.7. The degree of eutrophication has a comparatively small effect on the annual mean pH, but on the other hand a considerable impact on the seasonal amplitude and thus minimum and maximum values.

The complex situation in the Baltic Sea gives a strong incentive to improve the temporal and spatial coverage of acidification monitoring. This would broaden the understanding of current acidification trends and also improve the capacity to predict future changes. An indicator for acidification in the Baltic Sea is currently under development. Monitoring of parameters relevant for acidification, i.e., the inorganic carbon system parameters, would as an added value also provide an additional handle in terms of assessing changes in primary production and eutrophication trends.

Place, publisher, year, edition, pages
Copenhagen: Nordisk Ministerråd, 2021. p. 25
Series
TemaNord, ISSN 0908-6692 ; 2021:512
National Category
Oceanography, Hydrology and Water Resources
Research subject
Oceanography
Identifiers
urn:nbn:se:su:diva-203194 (URN)10.6027/temanord2021-512 (DOI)978-92-893-6981-7 (ISBN)978-92-893-6980-0 (ISBN)
Funder
Nordic Council of Ministers, 190009
Available from: 2022-03-24 Created: 2022-03-24 Last updated: 2022-03-25Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1048-8452

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