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

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.Peer reviewe

Pollution stress of Siberian forests

Many articles in the popular press and western scientific literature stress the severe environmental conditions in Russia and Siberia. The general pollution problem is described in many cases to be close to a disaster. The availability of consistent data for anthropogenic stress factors to the Siberian forests is limited, both from a registration point of view, and from a methodological one. The objective of the overall study has been to attempt to estimate the extent of anthropogenic stress factors to the Siberian forests, based on existing data and studies in Russia. The following activities have been carried out and are summarized in this paper; estimations of emissions and depositions of major pollutants, estimations of the radio nuclide contamination, analyses of the current forest decline in Siberia, and estimates on the areas and growing stock under risk of future forest decline. From these results the following can be identified. The highest depositions of heavy metals are in Norilsk,the Irkutsk region, and the southern part of the Far East. Based on Russian estimates of the critical loads for heavy metals and forests, it can be concluded that even the highest depositions of heavy metals (30–41 kg km-2yf-1) are below the critical loads. However, in the vicinity of the emitters, the critical loads are substantially exceeded. Based on the current critical load calculations for ecosystems, it can be seen that critical loads for sulfur are seriously exceeded in the Urals and Altai Mountains, West Siberia, western East Siberia, in the boundary regions of Kazakhstan, the Norilsk region, southern Far East, Sakhalin, and the southern Kurilean islands. The exceedance of critical loads for nitrogen are most serious in the Urals, West Siberia, in the boundaries to Kazakhstan, Norilsk, and in the Far East. Based on the existing data for radioactivity, we can tentatively conclude that soil contamination and contaminated forest ecosystems do not seem to be a dramatic problem from an area point of view. However,there are concerns which must be resolved for the Irkutsk region and the Yenisey river basin. The storage of nuclear waste is a high potential risk for future large-scale radioactive contamination. This high risk condition requires further investigation

Pike Mercury Concentration in Small Boreal Headwater Lakes During Four Decades of Regional and Local Changes

We measured the total mercury (THg) concentration in the muscle of northern pike (Esox lucius L.) from 12 boreal headwater lakes once per decade during the 1980s to 2010s. Relations of pike THg to regional environmental changes, such as reduction of acid deposition and increase in water colour (i.e. browning), were examined as well as the effects of local lake-specific changes caused by introduced beavers (Castor canadensis) and intensive fishing of pike. No consistent decrease in pike THg took place during 1983–2013 despite the reductions in mercury emissions from European sources since the 1990s and the associated decreased mercury deposition in Finland. In most of the lakes, individual pike exceeded the recommended limit for human consumption (1 mg kg−1, wet weight). The highest THg levels were recorded in 2002 following intensive browning of the lakes in the 1990s in connection with decreased sulphate deposition. The effects of acid deposition were only seen as the highest pike THg in the two most acidic lakes in the early 1980s. After taking length effects into account, pike THg had a negative relationship with growth (i.e. growth dilution), but a positive relationship with water colour, iron, nutrients and maximum lake depth. Females grew faster and had lower THg than males. Pike THg was elevated in beaver-impacted lakes. Experimental removal of pike from three study lakes during 2005–2013 resulted in a decrease of pike THg. These findings emphasize the significance of local abiotic and biotic drivers when interpreting the regional long-term trends in pike THg.Peer reviewe