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

Martti Rask,Jukka Ruuhijärvi,Kimmo K Kahilainen,Tarja-Riitta Blauberg,Matti Verta,Tommi Malinen,Mikko Olin,Lauri Arvola,Jussi Vuorenmaa,Kari Nyberg

doi:10.1007/s11270-021-05303-z

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.

Highlights

Acidification of poorly buffered boreal and alpine lakes in the 1900s due to air pollutants resulted in population declines of several sensitive fish species in northern Europe, the USA and Canada (Almer et al, 1974; Baker et al, 1993; Hesthagen et al, 1999). Tammi et al (2003) estimated with a postal survey based on the Fennoscandian water chemistry data (Henriksen et al, 1998) that acidification-induced1 3 Vol.:(0123456789)382 Page 2 of 15 reproduction failures and subsequent declines and extinctions of fish populations occurred in more than 10,000 Nordic lakes (Finland, Norway, Sweden)
Relating the length-corrected average THg concentrations of perch to lake water quality parameters resulted in significant correlation with pH (Fig. 1a) and alkalinity, but not with water colour, dissolved organic carbon (DOC) (Fig. 1b), total nutrients or calcium (Table 3)
Among the 16 lakes with known fish population responses to acidification, the highest perch THg concentrations were recorded in the lakes that had suffered from severe fish population damage in the 1980s, including reproduction failures and changes in population structure and growth of perch and/or disappearance of roach (Rutilus rutilus L.)

Summary

Introduction

Acidification of poorly buffered boreal and alpine lakes in the 1900s due to air pollutants resulted in population declines of several sensitive fish species in northern Europe, the USA and Canada (Almer et al, 1974; Baker et al, 1993; Hesthagen et al, 1999). Tammi et al (2003) estimated with a postal survey based on the Fennoscandian water chemistry data (Henriksen et al, 1998) that acidification-induced1 3 Vol.:(0123456789)382 Page 2 of 15 reproduction failures and subsequent declines and extinctions of fish populations occurred in more than 10,000 Nordic lakes (Finland, Norway, Sweden). The estimate for Finland was 1850 fish populations, out of which 410 were affected perch populations This is in line with estimates of critical levels of acidification for common fish species and modelled number of lakes that acidified over those levels in Finland (Rask et al, 1995). A gillnet survey of 80 lakes indicated low fish status in strongly acidified lakes of southern Finland (Rask & Tuunainen, 1990). These observations were ascertained with more detailed studies, including mark and recapture studies of perch populations in lakes in different degree of acidification (Lappalainen et al, 1988) and field and laboratory experiments on survival of perch embryos in acidic waters (Rask et al, 1990; Vuorinen et al, 1992). High mercury concentrations have been often reported in fish from acidified lakes (Greenfield et al, 2001; Richman et al, 1988), but several studies have shown that the impacts of acidification or sulphate deposition on the dynamics of mercury are complex (Bloom et al, 1991; Wyn et al, 2010; Braaten et al, 2020; Watras et al, 2020)

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Conclusion