High Mercury Concentrations of European Perch (Perca fluviatilis) in Boreal Headwater Lakes with Variable History of Acidification and Recovery

Abstract

High dissolved organic carbon and low pH are often associated with elevated mercury content of fish in boreal lakes, but less is known about the fish mercury dynamics in lakes recovering from acidification stress. We measured total mercury concentration (THg) in muscle of European perch (Perca fluviatilis) and evaluated the overall correlation with environmental and growth variables in 24 boreal headwater lakes in the 2010s. We found negative correlations of length-corrected perch THg with lake pH and perch growth, but no correlation with dissolved organic carbon. The main emphasis in the present study was focused to a subset of ten lakes in southern Finland with known perch THg during severe acidification in the 1980–1990s. The comparison of perch THg concentrations in the 2010s with values determined in the 1980–1990s showed a sharp increase in most acidic lakes where the perch populations suffered from severe acid stress in the 1980s. This increase was attributed to growth condensation caused by sharp decrease in perch growth during recovery of reproduction capacity and the consequent increases in population densities of perch. Our results highlight the importance of perch growth rate and population density for understanding the variability of fish Hg in boreal headwater lakes, where recovery from acidification can lead to higher mercury concentration of fish in certain cases.

Mercury and Amino Acid Content Relations in Northern Pike (Esox Lucius) in Subarctic Lakes Along a Climate-Productivity Gradient

“…Furthermore, low pH in catchment and lake could enhance mercury methylation and increase THg content in fish (Compeau and Bartha, 1984;Gilmour and Henry, 1991;Wyn et al, 2009;Rask et al, 2021). Many studies show dilution of mercury due to high growth rate (Simoneau et al, 2005;Karimi et al, 2007;Rask et al, 2021;Moslemi-Aqdam et al, 2022), but in this study pike growth rate showed a positive relationship with THg content in the model. Positive relationship between total mercury and growth rate could be related on faster growing individuals feeding on higher trophic level.…”

“…Increased catchment properties could enhance higher THg content in pike, however, nutrient enrichment from larger catchment area could have an inhibiting effect through biodilution of THg in lake biomass (Todorova et al, 2015). Furthermore, low pH in catchment and lake could enhance mercury methylation and increase THg content in fish (Compeau and Bartha, 1984;Gilmour and Henry, 1991;Wyn et al, 2009;Rask et al, 2021). Many studies show dilution of mercury due to high growth rate (Simoneau et al, 2005;Karimi et al, 2007;Rask et al, 2021;Moslemi-Aqdam et al, 2022), but in this study pike growth rate showed a positive relationship with THg content in the model.…”

Ecological Drivers of Mercury Bioaccumulation in Fish of a Subarctic Watercourse

“…Perch had high THg concentrations too, which was somewhat surprising considering that their δ 15 N isotope signatures positioned them at a trophic level that was lower than the other piscivores and similar to large sparsely rakered whitefish. A plausible reason for this comparative difference is the slow somatic growth rate and high longevity of perch in the Pasvik watercourse, which may have resulted in inverse growth dilution of Hg, as has been reported for other European perch populations (Rask et al, 2021).…”