supporting data on isotope composition and physiological status in Monoporeia affinis in both experiments

supporting data on isotope composition and physiological status in Monoporeia affinis in both experiments. see sheet "read me" for instruction

Supplementary tables and figures from Isotopic niche reflects stress-induced variability in physiological status

Tables S1-S7 and Figures S1-S1

The datasets supporting are uploaded at DRYAD and will be available if the manuscript is accepted (doi:10.5061/dryad.8h439). from Isotopic niche reflects stress-induced variability in physiological status

Excel work book containing five excel sheets with data on all individuals used in the two experiments. see sheet "read me" for instructions

Growth Retardation and Altered Isotope Composition As Delayed Effects of PCB Exposure in <i>Daphnia magna</i>

Trophic magnification factor (TMF) analysis employs stable isotope signatures to derive biomagnification potential for environmental contaminants. This approach relies on species δ¹⁵N values aligning with their trophic position (TP). This, however, may not always be true, because toxic exposure can alter growth and isotope allocation patterns. Here, effects of PCB exposure (mixture of PCB18, PCB40, PCB128, and PCB209) on δ¹⁵N and δ¹³C as well as processes driving these effects were explored using the cladoceran <i>Daphnia magna.</i> A two-part experiment assessed effects of toxic exposure during and after exposure; juvenile daphnids were exposed during 3 days (accumulation phase) and then allowed to depurate for 4 days (depuration phase). No effects on survival, growth, carbon and nitrogen content, and stable isotope composition were observed after the accumulation phase, whereas significant changes were detected in adults after the depuration phase. In particular, a significantly lower nitrogen content and a growth inhibition were observed, with a concomitant increase in δ¹⁵N (+0.1 ‰) and decrease in δ¹³C (−0.1 ‰). Although of low magnitude, these changes followed the predicted direction indicating that sublethal effects of contaminant exposure can lead to overestimation of TP and hence underestimated TMF

Stable Isotope Composition in <i>Daphnia</i> Is Modulated by Growth, Temperature, and Toxic Exposure: Implications for Trophic Magnification Factor Assessment

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 δ¹⁵N and δ¹³C 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 δ¹⁵N and δ¹³C, 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 δ¹⁵N and δ¹³C 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 δ¹⁵N values would translate into overestimated trophic positions and underestimated TMF. Furthermore, altered δ¹³C values may lead to erroneous food-chain assignment of the consumer in question

Using Compound-Specific and Bulk Stable Isotope Analysis for Trophic Positioning of Bivalves in Contaminated Baltic Sea Sediments

Stable nitrogen isotopes (δ¹⁵N) are used as indicators of trophic position (TP) of consumers. Deriving TP from δ¹⁵N of individual amino acids (AAs) is becoming popular in ecological studies, because of lower uncertainty than TP based on bulk δ¹⁵N (TP_bulk). This method would also facilitate biomagnification studies provided that isotope fractionation is unaffected by toxic exposure. We compared TP_AA and TP_bulk estimates for a sediment-dwelling bivalve from two coastal sites, a pristine and a contaminated. Chemical analysis of PCB levels in mussels, sediments, and pore water confirmed the expected difference between sites. Both methods, but in particular the TP_AA underestimated the actual TP of bivalves. Using error propagation, the total uncertainty related to the analytical precision and assumptions in the TP calculations was found to be similar between the two methods. Interestingly, the significantly higher intercept for the regression between TP_AA and TP_bulk in the contaminated site compared to the pristine site indicates a higher deamination rate due to detoxification as a result of chronic exposure and a higher ¹⁵N fractionation. Hence, there is a need for controlled experiments on assumptions underlying amino acid-specific stable isotope methods in food web and bimagnification studies

CO₂ flow intensity signal measured by TCD (black line) and cps spectra of samples No. 3 (green), No. 6 (blue) and background (red) as determined with the semiconductor detector.

<p>In total, three combustion cycles (400 s each) were used to completely combust the non-ground graphite sample.</p

An example spectrum of ¹⁴C measured using semiconductor detectors.

<p>The green color denotes the spectrum of sample No. 3 and the black color denotes a typical background spectrum. Both spectra were collected over 100 s time intervals.</p

CO₂ gas flow in the TCD and the β counter chamber during the first cycle of combustion of sample No. 6.

<p>CO₂ gas flow in the TCD and the β counter chamber during the first cycle of combustion of sample No. 6.</p

The correlation of the graphite sample mass as determined by two independent methods: Weighing and combustion in the elemental analyzer.

<p>Graphite sample mass in the same sample was determined by weighing with balances (horizontal axis) and by combustion in the elemental analyzer, measured from the resulting CO₂ (vertical axis). The parameters of linear approximation (y = a + bx) are: a = 3 ± 10, b = 0.96 ± 0.06, R = 0.97.</p