scholarly journals Stable Isotope Mixing Models Are Biased by the Choice of Sample Preservation and Pre-treatment: Implications for Studies of Aquatic Food Webs

2021 ◽  
Vol 7 ◽  
Author(s):  
Marc J. Silberberger ◽  
Katarzyna Koziorowska-Makuch ◽  
Karol Kuliński ◽  
Monika Kędra
Keyword(s):  
Organic Matter ◽  
Stable Isotope ◽  
Food Webs ◽  
Benthic Invertebrate ◽  
Mixing Models ◽  
Sample Preservation ◽  
Bayesian Mixing Models ◽  
Aquatic Food ◽  
Pre Treatment ◽  
Isotope Mixing Models

Stable isotope analysis has become one of the most widely used techniques in ecological studies. However, there are still uncertainties about the effects of sample preservation and pre-treatment on the ecological interpretation of stable isotope data and especially on Bayesian stable isotope mixing models. Here, Bayesian mixing models were used to study how three different preservation methods (drying, freezing, formalin) and two pre-treatments (acidification, lipid removal) affect the estimation of the utilized organic matter sources for two benthic invertebrate species (Limecola balthica, Crangon crangon) collected in the Baltic Sea. Furthermore, commonly used mathematical lipid normalization and formalin correction were applied to check if they were able to adjust the model results correctly. Preservation effects were strong on model outcomes for frozen as well as formalin preserved L. balthica samples, but not for C. crangon. Pre-treatment effects varied with species and preservation method and neither lipid normalization nor mathematical formalin correction consistently resulted in the desired model outcomes. Our analysis highlights that particularly small, not significant changes in stable isotope ratios introduced by different preservation and pre-treatments display a so far unrecognized source of error in stable isotope mixing models. We conclude that mathematical correction of benthic invertebrate stable isotopes data should be avoided for Bayesian mixing models and that previously unaddressed effects of sample preservation (especially those arising from preservation by freezing) have potentially biased our understanding of the utilization of organic matter in aquatic food webs.

scholarly journals Sample preservation and pre-treatment in stable isotope analysis: Implications for the study of aquatic food webs

2020 ◽  
Author(s):  
Marc Jürgen Silberberger ◽  
Katarzyna Koziorowska-Makuch ◽  
Karol Kuliński ◽  
Monika Kędra
Keyword(s):  
Stable Isotope ◽  
Food Webs ◽  
Stable Isotope Analysis ◽  
Isotope Analysis ◽  
Mixing Models ◽  
Sample Preservation ◽  
Aquatic Food Webs ◽  
Bayesian Mixing Models ◽  
Aquatic Food ◽  
Pre Treatment

Abstract. Stable isotope analysis has become one of the most widely used techniques in ecology. However, uncertainties about the effects of sample preservation and pre-treatment on the ecological interpretation of stable isotope data and especially on Bayesian stable isotope mixing models remain. Here, Bayesian mixing models were used to study how three different preservation methods (drying, freezing, formalin) and two pre-treatments (acidification, lipid removal) affect the estimation of diet composition for two benthic invertebrate species (Limecola balthica, Crangon crangon). Furthermore, commonly used mathematical lipid normalization and formalin correction were applied to check if they improve the model results. Preservation effects were strong on model outcomes for frozen as well as formalin preserved L. balthica samples, but not for C. crangon. Pre-treatment effects varied with species and preservation method and neither lipid normalization nor mathematical formalin correction consistently resulted in improved model outcomes. Our analysis highlights that particularly small changes in δ15N introduced by different preservation and pre-treatments display a so far unrecognized source of error in stable isotope studies. We conclude that mathematical correction of stable isotopes data should be avoided for Bayesian mixing models and that previously unaddressed effects of sample preservation (especially those arising from preservation by freezing) have potentially biased our understanding of the utilization of organic matter in aquatic food webs.

scholarly journals Elevated temperature and browning increase dietary methylmercury, but decrease essential fatty acids at the base of lake food webs

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Pianpian Wu ◽  
Martin J. Kainz ◽  
Fernando Valdés ◽  
Siwen Zheng ◽  
Katharina Winter ◽  
...  
Keyword(s):  
Climate Change ◽  
Fatty Acids ◽  
Organic Matter ◽  
Food Webs ◽  
Essential Fatty Acids ◽  
Trophic Levels ◽  
Climate Change Scenarios ◽  
Essential Nutrients ◽  
Aquatic Food Webs ◽  
Aquatic Food

AbstractClimate change scenarios predict increases in temperature and organic matter supply from land to water, which affect trophic transfer of nutrients and contaminants in aquatic food webs. How essential nutrients, such as polyunsaturated fatty acids (PUFA), and potentially toxic contaminants, such as methylmercury (MeHg), at the base of aquatic food webs will be affected under climate change scenarios, remains unclear. The objective of this outdoor mesocosm study was to examine how increased water temperature and terrestrially-derived dissolved organic matter supply (tDOM; i.e., lake browning), and the interaction of both, will influence MeHg and PUFA in organisms at the base of food webs (i.e. seston; the most edible plankton size for zooplankton) in subalpine lake ecosystems. The interaction of higher temperature and tDOM increased the burden of MeHg in seston (< 40 μm) and larger sized plankton (microplankton; 40–200 μm), while the MeHg content per unit biomass remained stable. However, PUFA decreased in seston, but increased in microplankton, consisting mainly of filamentous algae, which are less readily bioavailable to zooplankton. We revealed elevated dietary exposure to MeHg, yet decreased supply of dietary PUFA to aquatic consumers with increasing temperature and tDOM supply. This experimental study provides evidence that the overall food quality at the base of aquatic food webs deteriorates during ongoing climate change scenarios by increasing the supply of toxic MeHg and lowering the dietary access to essential nutrients of consumers at higher trophic levels.

scholarly journals Bayesian stable isotope mixing models

2013 ◽  
pp. n/a-n/a ◽  
Author(s):  
Andrew C. Parnell ◽  
Donald L. Phillips ◽  
Stuart Bearhop ◽  
Brice X. Semmens ◽  
Eric J. Ward ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Mixing Models ◽  
Isotope Mixing Models

scholarly journals Application of stable isotope mixing models for defining trophic biomagnification pathways of mercury and selenium

2014 ◽  
Vol 59 (4) ◽  
pp. 1181-1192 ◽  
Author(s):  
H. J. Jones ◽  
K. M. Swadling ◽  
E. C. V. Butler ◽  
L. A. Barry ◽  
C. K. Macleod
Keyword(s):  
Stable Isotope ◽  
Mixing Models ◽  
Isotope Mixing Models

Incorporating concentration dependence in stable isotope mixing models

Oecologia ◽  
2002 ◽  
Vol 130 (1) ◽  
pp. 114-125 ◽  
Author(s):  
Donald L. Phillips ◽  
Paul L. Koch
Keyword(s):  
Stable Isotope ◽  
Concentration Dependence ◽  
Mixing Models ◽  
Isotope Mixing Models

scholarly journals Tracking Dissolved Organic Matter in Coastal Ecosystems

Eos ◽  
2019 ◽  
Vol 100 ◽  
Author(s):  
Elizabeth Thompson
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Food Webs ◽  
Coastal Ecosystems ◽  
Coastal Systems ◽  
Aquatic Food Webs ◽  
Aquatic Food

Dissolved organic matter supports aquatic food webs and holds as much carbon as the atmosphere. A new study tracks which sources and processes play the biggest role in coastal systems.

scholarly journals Statistical basis and outputs of stable isotope mixing models: Comment on Fry (2013)

2013 ◽  
Vol 490 ◽  
pp. 285-289 ◽  
Author(s):  
BX Semmens ◽  
EJ Ward ◽  
AC Parnell ◽  
DL Phillips ◽  
S Bearhop ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Mixing Models ◽  
Isotope Mixing Models

scholarly journals Large herbivorous wildlife and livestock differentially influence the relative importance of different sources of carbon for riverine food webs

2021 ◽  
Author(s):  
Frank O. Masese ◽  
Thomas Fuss ◽  
Lukas Bistarelli ◽  
Caroline Buchen-Tschiskale ◽  
Gabriel Singer
Keyword(s):  
Organic Matter ◽  
Food Webs ◽  
Aquatic Ecosystems ◽  
Carbon Sources ◽  
Large River ◽  
Livestock Grazing ◽  
Relative Importance ◽  
River Continuum ◽  
Aquatic Food ◽  
Different Sources

In many regions around the world, large populations of native wildlife have declined or been replaced by livestock grazing areas and farmlands, with consequences on terrestrial-aquatic ecosystems connectivity and trophic resources supporting food webs in aquatic ecosystems. The river continuum concept (RCC) and the riverine productivity model (RPM) predict a shift of carbon supplying aquatic food webs along the river: from terrestrial inputs in low-order streams to autochthonous production in mid-sized rivers. Here, we studied the influence of replacing large wildlife (mainly hippos) with livestock on the relative importance of C3 vegetation, C4 grasses and periphyton on macroinvertebrates in the Mara River, which is an African montane-savanna river known to receive large subsidy fluxes of terrestrial carbon and nutrients mediated by LMH, both wildlife and livestock. Using stable carbon (δ13C) and nitrogen (δ15N) isotopes, we identified spatial patterns of the relative importance of allochthonous carbon from C3 and C4 plants (woody vegetation and grasses, respectively) and autochthonous carbon from periphyton for macroinvertebrates at various sites of the Mara River and its tributaries. Potential organic carbon sources and invertebrates were sampled at 80 sites spanning stream orders 1 to 7, various catchment land uses (forest, agriculture and grasslands) and different loading rates of organic matter and nutrients by LMH (livestock and wildlife, i.e., hippopotamus). The importance of different sources of carbon along the river did not follow predictions of RCC and RPM. First, the importance of C3 and C4 carbon was not related to river order or location along the fluvial continuum but to the loading of organic matter (dung) by both wildlife and livestock. Notably, C4 carbon was important for macroinvertebrates even in large river sections inhabited by hippos. Second, even in small 1st -3rd order forested streams, autochthonous carbon was a major source of energy for macroinvertebrates, and this was fostered by livestock inputs fuelling aquatic primary production throughout the river network. Importantly, our results show that replacing wildlife (hippos) with livestock shifts river systems towards greater reliance on autochthonous carbon through an algae-grazer pathway as opposed to reliance on allochthonous inputs of C4 carbon through a detrital pathway.

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