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Stable Isotope Composition in Daphnia Is Modulated by Growth, Temperature, and Toxic Exposure: Implications for Trophic Magnification Factor Assessment
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
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Number of Authors: 5
2015 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 49, no 11, 6934-6942 p.Article in journal (Refereed) Published
Abstract [en]

The potential for using stable isotope analysis in risk assessment of environmental contaminants is crucially dependent on the predictability of the trophic transfer of isotopes in food webs. The relationship between contaminant levels and trophic position of consumers is widely used to assess biomagnification properties of various pollutants by establishing trophic magnification factors (TMF). However, contaminant-induced variability of the isotopic composition in biota is poorly understood. Here, we investigated effects of toxic exposure on delta N-15 and delta C-13 values in a consumer, with a main hypothesis that these effects would be largely mediated via growth rate and metabolic turnover of the test animals. The cladoceran Daphnia magna was used in two experiments that were conducted to manipulate growth and body condition (assayed as C:N ratio) by food availability and temperature (Experiment 1) and by toxic exposure to the pesticide lindane (Experiment 2). We found a significant negative effect of growth rate and a positive effect of temperature on the consumer-diet discrimination factor for delta N-15 and delta C-13, with no effects on the C:N ratio (Experiment 1). In lindane-exposed daphnids, a significant growth inhibition was observed, with concomitant increase in metabolic costs and significantly elevated size-specific delta N-15 and delta C-13 values. Moreover, a significantly higher incorporation of carbon relative to nitrogen, yet a concomitant decrease in C:N ratio was observed in the exposed animals. Together, these results have methodological implications for determining trophic positions and TMF in polluted environments, where elevated delta N-15 values would translate into overestimated trophic positions and underestimated TMF. Furthermore, altered delta C-13 values may lead to erroneous food-chain assignment of the consumer in question.

Place, publisher, year, edition, pages
2015. Vol. 49, no 11, 6934-6942 p.
National Category
Environmental Engineering Earth and Related Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-119157DOI: 10.1021/acs.est.5b00270ISI: 000355779100068OAI: oai:DiVA.org:su-119157DiVA: diva2:845523
Available from: 2015-08-12 Created: 2015-07-29 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Towards understanding stable isotope signatures in stressed systems
Open this publication in new window or tab >>Towards understanding stable isotope signatures in stressed systems
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Stable isotope analysis (SIA) is a valuable tool in ecotoxicology because δ13C and δ15N may provide insights into the trophic transfer of contaminants in a food web. The relationship between a species’ trophic position (TP, determined from δ15N) and internal concentration of biomagnifying contaminants can be established and used for regulatory purposes. However, the exposure of organisms to xenobiotics incurs physiological costs, and the stable isotope signature of a consumer reflects not only diet but also a physiological state. The latter raises questions regarding the interpretation of stable isotope signatures in contaminated areas. Therefore, the aim of this Thesis was to evaluate the behaviour of consumers’ stable isotope signatures in stressed systems, with a primary focus on the effects of environmental contaminants.

In paper I, the physiological costs of chemical exposure were found to alter incorporation rates of dietary nitrogen and carbon in a consumer by influencing both growth and metabolic turnover, with resulting changes in isotope signatures relative to a control system. In paper II, the diet-consumer discrimination factors for 15N and 13C were confirmed to increase under chemical exposure mediated via increased metabolic costs. However, the physiological response was low and translated into only minor shifts in the δ13C and δ15N. The predictability of exposure effects on the stable isotope signature was demonstrated in paper III, in which animals exposed to a chemical with a known mode of action presented expected effects on elemental composition, body size, biomarkers of oxidative stress and the stable isotope signatures. Moreover, consumers’ oxidative balance was found to be related to their δ15N values, thus providing evidence of the kinetic isotope effect on the oxidative status. However, despite the alterations in stable isotope signatures observed in laboratory settings (papers I-III), the effect of xenobiotics on the TP estimates was nil or minor in the field-collected animals. Moreover, the TP values were not significantly different between the animals in the contaminated and the reference habitats because of the high overall uncertainties in the TP estimates (paper IV). Also, the TP estimates based on δ15N in bulk material were more similar between the contaminated and the reference systems than TP estimates based on δ15N values in amino acids. Therefore, the latter method appears more sensitive towards xenobiotics (and, possibly, other environmental stressors) and thus less suitable for TP assessment in contaminated areas.

This Thesis improved the overall understanding of the applicability of SIA in stressed systems by establishing relationships between various exposure regimes, physiological responses and the stable isotope signatures in consumers. In model species at low trophic levels, the exposure to xenobiotics was found to significantly affect δ13C and δ15N values, which can be expected whenever physiological responses are detected. However, because of the overall high uncertainty in TP estimates, no significant differences between contaminated and control systems were detected, although the estimated TP were consistently higher in the contaminated systems. Future research should focus on higher trophic levels, in which effects of a greater magnitude can be expected. Moreover, the effects in entire food webs should be addressed rather than single prey–consumer relationships as well as other environmental variables that may contribute to the stable isotope variability in and among systems under various environmental pressures.

Place, publisher, year, edition, pages
Stockholm: Department of Environmental Science and Analytical Chemistry, Stockholm University, 2016. 38 p.
Keyword
Stable isotope analysis, trophic position, chemical exposure, oxidative stress, Daphnia magna, Gammarus spp., Limecola balthica
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-134967 (URN)978-91-7649-523-0 (ISBN)978-91-7649-524-7 (ISBN)
Public defence
2016-12-15, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 09:30 (English)
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Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2016-11-22 Created: 2016-10-27 Last updated: 2016-11-14Bibliographically approved

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Ek, CarolineKarlson, Agnes M. L.Hansson, StureGorokhova, Elena
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