Using isotope markers to break down food webs and track changes in them, as well as tracing the pathways and accumulation of pollutants in aquatic organisms – the Otto Jaag Water Protection Prize was awarded in 2025 for two exciting and highly topical doctoral theses.
Thanks to an increase in the Otto Jaag Water Protection Prize by former Eawag Director Janet Hering, two prizes for outstanding doctoral theses were awarded in 2025. They went to environmental chemist Johannes Raths and evolutionary biologist Grégoire Saboret.
Food chain reconstructed thanks to isotope analysis
Grégoire Saboret conducted his research at Eawag in Kastanienbaum under the supervision of Prof. Carsten Schubert (Surface Water Department). Under the joint supervision of Dr Jakob Brodersen and Dr Blake Matthews (Fish Ecology and Evolution Department), he further developed isotope analyses of amino acids and applied them specifically to fish. This enabled him to expand our understanding of food webs, as the markers provide information about primary producers (algae and bacteria) and all intermediate consumers on which they fed. Among other things, Saboret has shown how eutrophication of lakes affects production sources in the food webs of Swiss lakes and how the current melting of glaciers in Greenland is changing the diet of fish.
Fish eyes with annual rings
Grégoire Saboret has received a mobility grant from the Swiss National Science Foundation and is currently at the University of California in Santa Cruz. However, he continues to conduct research and publish articles together with colleagues at Eawag. A publication is currently in preparation that analyses carbon and nitrogen isotopes from the lenses of fish eyes. As the lenses grow in rings, these rings, similar to the annual rings of a tree, form an archive that provides information about the entire life cycle of the fish.
How aquatic invertebrates absorb pollutants
Johannes Raths conducted research for his dissertation in the Environmental Chemistry Department under the supervision of Prof. Juliane Hollender. The work examined toxicokinetic processes in aquatic organisms, i.e. how pesticides and pharmaceuticals are absorbed, accumulate, change in the organism and, eventually, are excreted again. These mechanisms form a bridge between water pollution on the one hand and its effect on aquatic communities and ecosystems on the other. "Effective protection of water bodies is really only possible if we understand these processes and how they change in the context of global environmental change," says supervisor Prof. Juliane Hollender. She is convinced that Rath's interdisciplinary research will find its way into both textbooks and practice.
Unfortunately, neither of the two award-winning researchers was able to attend the ceremony on ETH Day last November. When asked, both Raths and Saboret said they considered the award a great honour and emphasised the support they had received at Eawag. Saboret emphasised that the prize was also recognition for work that honours the protection of aquatic ecosystems. Raths, meanwhile, focuses on the interaction between climate change and environmental pollution in his work: this will continue to occupy us intensively in the future.
New candidates wanted
The Otto Jaag Water Protection Prize is awarded to the best dissertation, and in special cases also the best master's thesis, at ETH Zurich in the field of water protection and hydrology. Members of the teaching staff at ETH Zurich are eligible to nominate candidates for the prize. The prize money is CHF 5,000. Nominations for the 2026 prize can be submitted until 1 June.
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title => protected'Trophic dynamics in meta-ecosystems: insights from compound-specific stable isotopes' (84 chars)
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description => protected'Food webs are crucial for understanding how carbon and nutrients flow within ecosystems, influencing sustainability and carbon fluxes. Ecosystems are in terconnected, exchanging energy, nutrients, and organic matter—a concept c aptured by meta-ecosystem theory. Consequently, changes in one ecosystem can have cascading effects on others. This interconnectedness becomes increasin gly important as global change drives significant alterations in food webs. Therefore, there is a pressing need to characterize food web functioning in complex settings, such as meta-ecosystems, and to study how these webs are i mpacted by global change. [...]' (639 chars)
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Bioaccumulation of polar organic contaminants in aquatic invertebrates: impact of climate, uptake pathways and spatial distribution
Global freshwater resources are threatened by a range of human activities including pollution and accelerating global climate change. Environmental contaminants are numerous and can form complex contamination patterns and mixtures in aquatic systems. The vast majority of organic contaminants originates from human use and enters aquatic environments from agricultural, industrial and household emissions. Pharmaceuticals and pesticides are contaminants of particular concern as they are specifically designed to be biologically active and thus cause adverse effects on non-target organisms such as aquatic invertebrates. Aquatic invertebrates, including amphipods, provide important ecological functions such as detritus processing and transfer of energy to higher trophic levels that maintain the functionality and diversity of aquatic ecosystems. [...]
Raths, J. (2023) Bioaccumulation of polar organic contaminants in aquatic invertebrates: impact of climate, uptake pathways and spatial distribution, 288 p, doi:10.3929/ethz-b-000641995, Institutional Repository
Trophic dynamics in meta-ecosystems: insights from compound-specific stable isotopes
Food webs are crucial for understanding how carbon and nutrients flow within ecosystems, influencing sustainability and carbon fluxes. Ecosystems are interconnected, exchanging energy, nutrients, and organic matter—a concept captured by meta-ecosystem theory. Consequently, changes in one ecosystem can have cascading effects on others. This interconnectedness becomes increasingly important as global change drives significant alterations in food webs. Therefore, there is a pressing need to characterize food web functioning in complex settings, such as meta-ecosystems, and to study how these webs are impacted by global change. [...]
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categories => protected'amino acid isotope; arctic char; fjord; food web; glacier; Greenland; polyun saturated fatty acid; trophic position' (114 chars)
description => protected'The primary production of fjords across the Arctic and Subarctic is undergoi ng significant transformations due to the climatically driven retreat of gla ciers and ice sheets. However, the implications of these changes for upper t rophic levels remain largely unknown. In this study, we employ both bulk and compound-specific stable isotope analyses to investigate how shifts at the base of fjord food webs impact the carbon and energy sources of consumers. F ocusing on two rapidly changing fjords in Southern Greenland, we used the mi gratory Arctic char as an indicator species, sampling populations along envi ronmental gradients within the fjords, building upon the assumption that cha r populations feed primarily close to their natal stream, thereby integratin g a dietary gradient. Our analysis of bulk stable isotopes in Arctic char ti ssue confirmed this premise, revealing a consistent change in resource use f rom the outer to the inner fjord, which nonetheless served as preferred feed ing grounds. Essential amino acid analysis further indicated shifts in carbo n and nitrogen sources, consistent with changes in nutrient use near glacier inputs characterized by low turbidity and high iron levels. Notably, these changes in the source of primary production were associated with shifts in t rophic positions and the transfer of polyunsaturated fatty acids, with Arcti c char in glacier-influenced inner fjords feeding at lower trophic level (si ze-corrected) and accumulating higher levels of high-quality docosahexaenoic acid (DHA). These findings highlight the usefulness of new analytical tools in revealing that glacial retreat can substantially alter food web dynamics , enhancing both carbon flow and the nutritional quality of fish in fjord ec osystems. The two Southern Greenland fjords studied could represent the futu re of other fjords, where retreating glaciers become land-terminating and gl acial inputs decrease. Our study underscores the critical role of glacier dy namics in affecting high...' (2075 chars)
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title => protected'Quantifying the utilisation of blue, green and brown resources by riparian p redators: a combined use of amino acid isotopes and fatty acids' (139 chars)
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categories => protected'amino acids; CSIA; food webs; MixSIAR; nutrient fluxes; polyunsaturated fatt y acids; spiders; stable isotopes' (109 chars)
description => protected'1. Global change drives multiple facets of biodiversity including interactio n diversity, which is fundamental for ecosystem functioning. However, studyi ng trophic interactions is challenging in meta-ecosystems, that is ecosystem s connected by spatial flows of energy, materials and organisms across ecosy stem boundaries. While analytical methods based on abundances of polyunsatur ated fatty acids (PUFAs) and stable isotopes of amino acids (AAs) are being increasingly used, it has never been explored if both approaches could be: ( i) combined in mixing models to enhance precision in dietary inference (ii) compared to disentangle transfers of various PUFAs and proteins in food webs in the wild.<br />2. We explore the utility of analytical approaches based on PUFA abundances and AA isotopes to resolve resource transfers in a natura l riparian food web. We focus on spiders and their potential prey from blue, green and brown sources to address three important and persisting methodolo gical issues in food-web ecology, namely whether (i) essential AA carbon iso topes can resolve protein origin from blue, green and brown resources, (ii) PUFA relative abundance and AA isotopes can be combined in a mixing model to provide higher precision estimates (i.e. narrower intervals) and (iii) comb ining the two approaches can unveil the coupling of protein and PUFA transfe rs in food webs. 3. Our research demonstrates the power of AA isotopes and P UFAs to distinguish blue, green, and brown sources and their transfer up to consumers. We show that combining PUFA relative abundance and AA isotopes in a mixing model provides overall estimates similar to the individual estimat es but significantly increases precision. In addition, we showcase how combi ning approaches unveil the coupling of protein and PUFA transfers. For insta nce, we show that most PUFAs are less concentrated from prey to predators, r elative to proteins, highlighting uncoupling of PUFAs and protein transfer a long food chains.<br />4...' (2301 chars)
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title => protected'Elimination resistance: characterizing multi-compartment toxicokinetics of t he neonicotinoid thiacloprid in the amphipod <em>Gammarus pulex</em> using b ioconcentration and receptor-binding assays' (195 chars)
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description => protected'Delayed toxicity is a phenomenon observed for aquatic invertebrates exposed to nicotinic acetylcholine receptor (nAChR) agonists, such as neonicotinoids . Furthermore, recent studies have described an incomplete elimination of ne onicotinoids by exposed amphipods. However, a mechanistic link between recep tor binding and toxicokinetic modeling has not been demonstrated yet. The el imination of the neonicotinoid thiacloprid in the freshwater amphipod <em>Ga mmarus pulex</em> was studied in several toxicokinetic exposure experiments, complemented with in vitro and in vivo receptor-binding assays. Based on th e results, a two-compartment model was developed to predict the uptake and e limination kinetics of thiacloprid in <em>G. pulex</em>. An incomplete elimi nation of thiacloprid, independent of elimination phase duration, exposure c oncentrations, and pulses, was observed. Additionally, the receptor-binding assays indicated irreversible binding of thiacloprid to the nAChRs. Accordin gly, a toxicokinetic-receptor model consisting of a structural and a membran e protein (including nAChRs) compartment was developed. The model successful ly predicted internal thiacloprid concentrations across various experiments. Our results help in understanding the delayed toxic and receptor-mediated e ffects toward arthropods caused by neonicotinoids. Furthermore, the results suggest that more awareness toward long-term toxic effects of irreversible r eceptor binding is needed in a regulatory context. The developed model suppo rts the future toxicokinetic assessment of receptor-binding contaminants.' (1593 chars)
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Impact of glaciers on trophic dynamics and polyunsaturated fat accumulation in Southern Greenland Fjord ecosystems
The primary production of fjords across the Arctic and Subarctic is undergoing significant transformations due to the climatically driven retreat of glaciers and ice sheets. However, the implications of these changes for upper trophic levels remain largely unknown. In this study, we employ both bulk and compound-specific stable isotope analyses to investigate how shifts at the base of fjord food webs impact the carbon and energy sources of consumers. Focusing on two rapidly changing fjords in Southern Greenland, we used the migratory Arctic char as an indicator species, sampling populations along environmental gradients within the fjords, building upon the assumption that char populations feed primarily close to their natal stream, thereby integrating a dietary gradient. Our analysis of bulk stable isotopes in Arctic char tissue confirmed this premise, revealing a consistent change in resource use from the outer to the inner fjord, which nonetheless served as preferred feeding grounds. Essential amino acid analysis further indicated shifts in carbon and nitrogen sources, consistent with changes in nutrient use near glacier inputs characterized by low turbidity and high iron levels. Notably, these changes in the source of primary production were associated with shifts in trophic positions and the transfer of polyunsaturated fatty acids, with Arctic char in glacier-influenced inner fjords feeding at lower trophic level (size-corrected) and accumulating higher levels of high-quality docosahexaenoic acid (DHA). These findings highlight the usefulness of new analytical tools in revealing that glacial retreat can substantially alter food web dynamics, enhancing both carbon flow and the nutritional quality of fish in fjord ecosystems. The two Southern Greenland fjords studied could represent the future of other fjords, where retreating glaciers become land-terminating and glacial inputs decrease. Our study underscores the critical role of glacier dynamics in affecting high-level consumers, such as salmonids, with implications for fjords globally.
Saboret, G.; Moccetti, C.; Wassenaar, L. I.; Matthews, B.; Aquino, N. J.; Janssen, D. J.; Brodersen, J.; Schubert, C. J. (2025) Impact of glaciers on trophic dynamics and polyunsaturated fat accumulation in Southern Greenland Fjord ecosystems, Global Change Biology, 31(1), e70044 (19 pp.), doi:10.1111/gcb.70044, Institutional Repository
Quantifying the utilisation of blue, green and brown resources by riparian predators: a combined use of amino acid isotopes and fatty acids
1. Global change drives multiple facets of biodiversity including interaction diversity, which is fundamental for ecosystem functioning. However, studying trophic interactions is challenging in meta-ecosystems, that is ecosystems connected by spatial flows of energy, materials and organisms across ecosystem boundaries. While analytical methods based on abundances of polyunsaturated fatty acids (PUFAs) and stable isotopes of amino acids (AAs) are being increasingly used, it has never been explored if both approaches could be: (i) combined in mixing models to enhance precision in dietary inference (ii) compared to disentangle transfers of various PUFAs and proteins in food webs in the wild. 2. We explore the utility of analytical approaches based on PUFA abundances and AA isotopes to resolve resource transfers in a natural riparian food web. We focus on spiders and their potential prey from blue, green and brown sources to address three important and persisting methodological issues in food-web ecology, namely whether (i) essential AA carbon isotopes can resolve protein origin from blue, green and brown resources, (ii) PUFA relative abundance and AA isotopes can be combined in a mixing model to provide higher precision estimates (i.e. narrower intervals) and (iii) combining the two approaches can unveil the coupling of protein and PUFA transfers in food webs. 3. Our research demonstrates the power of AA isotopes and PUFAs to distinguish blue, green, and brown sources and their transfer up to consumers. We show that combining PUFA relative abundance and AA isotopes in a mixing model provides overall estimates similar to the individual estimates but significantly increases precision. In addition, we showcase how combining approaches unveil the coupling of protein and PUFA transfers. For instance, we show that most PUFAs are less concentrated from prey to predators, relative to proteins, highlighting uncoupling of PUFAs and protein transfer along food chains. 4. We show for the first time the effectiveness of combining AA isotopes and PUFA abundances, particularly relevant for complex trophic interactions in a meta-ecosystem context. Our study illustrates the trophic uncoupling of proteins and PUFAs, highlighting the necessity in combining both approaches.
Saboret, G.; Drost, B. J. W.; Kowarik, C.; Schubert, C. J.; Gossner, M. M.; Ilić, M. (2024) Quantifying the utilisation of blue, green and brown resources by riparian predators: a combined use of amino acid isotopes and fatty acids, Methods in Ecology and Evolution, 15(8), 1450-1462, doi:10.1111/2041-210X.14371, Institutional Repository
Bioaccumulation of polar organic contaminants in aquatic invertebrates: impact of climate, uptake pathways and spatial distribution
Global freshwater resources are threatened by a range of human activities including pollution and accelerating global climate change. Environmental contaminants are numerous and can form complex contamination patterns and mixtures in aquatic systems. The vast majority of organic contaminants originates from human use and enters aquatic environments from agricultural, industrial and household emissions. Pharmaceuticals and pesticides are contaminants of particular concern as they are specifically designed to be biologically active and thus cause adverse effects on non-target organisms such as aquatic invertebrates. Aquatic invertebrates, including amphipods, provide important ecological functions such as detritus processing and transfer of energy to higher trophic levels that maintain the functionality and diversity of aquatic ecosystems. [...]
Raths, J. (2023) Bioaccumulation of polar organic contaminants in aquatic invertebrates: impact of climate, uptake pathways and spatial distribution, 288 p, doi:10.3929/ethz-b-000641995, Institutional Repository
Elimination resistance: characterizing multi-compartment toxicokinetics of the neonicotinoid thiacloprid in the amphipod Gammarus pulex using bioconcentration and receptor-binding assays
Delayed toxicity is a phenomenon observed for aquatic invertebrates exposed to nicotinic acetylcholine receptor (nAChR) agonists, such as neonicotinoids. Furthermore, recent studies have described an incomplete elimination of neonicotinoids by exposed amphipods. However, a mechanistic link between receptor binding and toxicokinetic modeling has not been demonstrated yet. The elimination of the neonicotinoid thiacloprid in the freshwater amphipod Gammarus pulex was studied in several toxicokinetic exposure experiments, complemented with in vitro and in vivo receptor-binding assays. Based on the results, a two-compartment model was developed to predict the uptake and elimination kinetics of thiacloprid in G. pulex. An incomplete elimination of thiacloprid, independent of elimination phase duration, exposure concentrations, and pulses, was observed. Additionally, the receptor-binding assays indicated irreversible binding of thiacloprid to the nAChRs. Accordingly, a toxicokinetic-receptor model consisting of a structural and a membrane protein (including nAChRs) compartment was developed. The model successfully predicted internal thiacloprid concentrations across various experiments. Our results help in understanding the delayed toxic and receptor-mediated effects toward arthropods caused by neonicotinoids. Furthermore, the results suggest that more awareness toward long-term toxic effects of irreversible receptor binding is needed in a regulatory context. The developed model supports the future toxicokinetic assessment of receptor-binding contaminants.
Raths, J.; Schinz, L.; Mangold-Döring, A.; Hollender, J. (2023) Elimination resistance: characterizing multi-compartment toxicokinetics of the neonicotinoid thiacloprid in the amphipod Gammarus pulex using bioconcentration and receptor-binding assays, Environmental Science and Technology, 57(24), 8890-8901, doi:10.1021/acs.est.3c01891, Institutional Repository
Cover picture: The melting of glaciers is changing food webs in aquatic environments, as seen here in Greenland, but also in alpine regions. (Foto: Coralie Moccetti)
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