Search

The Water Framework Directive (WFD) requires member states to implement a strategy to meet the environmental quality standards (EQS) set by the WFD for a number of priority substances. Since the EQSs listed in the WFD are derived to protect the most sensitive species in the ecosystem, often top predators or humans, it has been decided that for certain priority substances the quality standards should be compared to a monitoring species with a trophic position (TP) similar to the diet of the most sensitive species. To enable such adjustment require both knowledge about the monitoring species TP in the food web as well as the relationship between contaminant concentration and trophic position. In this study, we focus on finding a suitable method for TP estimates of perch in Swedish lakes by evaluating both traditional stable isotope analysis in bulk samples (BSIA) using different baseline matrices and the more recent development of compound-specific stable isotope analysis in amino acids (CSIA-AA). For this, three representative monitoring lakes were selected in which perch together with potential baseline matrices (bivalves, gastropods and sediment) were sampled. We applied triple-isotope analyses, d15N, d13C and d34S, of bulk material of all sampled matrices, and in addition d15N in perch using CSIA-AA. Results showed that TP estimates derived from CSIA-AA were significantly (p<0.001) lower compared to all the BSIA-derived methods and further that the BSIA-derived TP estimates using gastropods as a baseline were significantly higher (p<0.001) than all other TP estimates. Since no statistical differences could be detected between TP estimates based on bivalves, sediment or a ‘mixture’ baseline these were assumed to produce similar results and therefore all valid baseline matrices for TP estimates of perch in these three lakes. In the present study we also attempted to adjust mercury contaminant data to a specific TP of 3.5 according to the WFD. The adjustment re

Within the Swedish National Monitoring Programme for Contaminants in Freshwater Biota, perch, pike and Arctic char are being analysed from 32 lakes distributed all over Sweden. One of the main objectives of the monitoring has been to detect temporal trends in different areas and for different contaminants. However, the measured concentrations in biota can be affected by biological factors such as age, length, trophic position (TP), fat or dry weight content. A change in one or several of these variables over time, or even among specimens taken within the same year, is likely to result in an increased variation of the measured concentrations and hence in a lower chance of detecting a trend. The purpose of this study was to evaluate if an adjustment of contaminant time trends by primarily stable isotopes, but also other confounding factors can: A) reduce the individual and between-year variation and hence B) improve the likelihood of detecting temporal trends in time series for metals and organic contaminants. The study revealed an improvement in the likelihood of detecting a contaminant trend after adjustment of the data for almost all lakes and for all tested substances. For some lakes and substances, this improvement was substantial. Age seems to be an important confounding factor for metals and per- and polyfluoroalkyl substances. For lipophilic substances, fat content also appears to be an important factor in some lakes together with adjustments for carbon and nitrogen isotope ratios (d13C and d15N), which all reduced the variation in contaminant data. This suggests that there is a benefit of adjusting data on a regular basis in contaminant monitoring programmes in the future.