18 research outputs found
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 δ<sup>15</sup>N 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 δ<sup>15</sup>N and
δ<sup>13</sup>C 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 δ<sup>15</sup>N (+0.1
‰) and decrease in δ<sup>13</sup>C (−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 δ<sup>15</sup>N and δ<sup>13</sup>C 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 δ<sup>15</sup>N and
δ<sup>13</sup>C, 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 δ<sup>15</sup>N and δ<sup>13</sup>C 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 δ<sup>15</sup>N values would translate
into overestimated trophic positions and underestimated TMF. Furthermore,
altered δ<sup>13</sup>C 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 (δ<sup>15</sup>N) are used as indicators
of trophic position (TP) of consumers. Deriving TP from δ<sup>15</sup>N of individual amino acids (AAs) is becoming popular in
ecological studies, because of lower uncertainty than TP based on
bulk δ<sup>15</sup>N (TP<sub>bulk</sub>). This method would
also facilitate biomagnification studies provided that isotope fractionation
is unaffected by toxic exposure. We compared TP<sub>AA</sub> and TP<sub>bulk</sub> 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<sub>AA</sub> 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<sub>AA</sub> and TP<sub>bulk</sub> 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 <sup>15</sup>N fractionation. Hence, there is a need for controlled experiments
on assumptions underlying amino acid-specific stable isotope methods
in food web and bimagnification studies
CO<sub>2</sub> 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 <sup>14</sup>C 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
CO<sub>2</sub> gas flow in the TCD and the β counter chamber during the first cycle of combustion of sample No. 6.
<p>CO<sub>2</sub> 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 CO<sub>2</sub> (vertical axis). The parameters of linear approximation (y = a + bx) are: a = 3 ± 10, b = 0.96 ± 0.06, R = 0.97.</p