Espen Lund

Seasonal and year‐to‐year variation of mercury concentration in perch (Perca fluviatilis) in boreal lakes

The authors examined the seasonal and year-to-year variations of mercury (Hg) concentrations in populations of perch (Perca fluviatilis) from 2 boreal freshwater lakes in southeast Norway. Fish Hg concentrations were determined seasonally (spring, summer, and autumn) over 3 yr (2010, 2011, and 2012) to test the hypothesis that there are substantial changes in fish Hg concentrations during the year (seasonal variation) as well as annually. Concentrations were significantly (p < 0.0001) different in the 2 study lakes, with mean seasonal concentrations varying from 0.24 mg/kg to 0.36 mg/kg and from 0.29 mg/kg to 0.37 mg/kg, respectively. The Hg concentrations of both perch populations showed significant year-to-year (p < 0.0001) and seasonal variation (p < 0.01). The changing fish Hg concentrations were 25% and 28% (2010-2011) and 17% and 0% (2011-2012) in the 2 lakes over the 3 yr, respectively. The results demonstrate how the significant year-to-year increase is, among other variables, related to changes in trophic position, shown through stable nitrogen (δ(15)N) isotope data. The seasonal variation is related to summer growth dilution. The results highlight the clear need for yearly studies of fish Hg concentrations, rather than the 3-yr cycle suggested by current European policy through the Water Framework Directive. The lack of yearly sampling may result in erroneous conclusions regarding fish Hg concentration time trends.

Modeling Future Acidification and Fish Populations in Norwegian Surface Waters

Despite great progress made in the past 25 years, acid deposition continues to cause widespread damage to the environment in Europe and eastern North America. Legislation to limit emissions of sulfur and nitrogen compounds in Europe is now under revision. The most recent protocol was based in part on the critical loads concept. The new protocol may also take into consideration the time delays between dose and response inherent in natural ecosystems. Policy decisions to reduce adverse effects on ecosystems entail a trade-off: quick response will require deeper cuts in emissions and thus higher costs, whereas lower costs with lesser cuts in emissions will give slower response. Acidification of lakes and damage to fish populations in Norway is used as an example. Under current legislation for emission reductions, surface waters will continue to slowly recover, but for many decades lakes in about 18% of Norway will continue to have water quality insufficient to support healthy populations of brown trout and other indicator organisms. Additional emission reductions can speed up the rate and degree of recovery.

National-Scale Dynamic Model Applications for Nordic Lake Catchments

This chapter presents an overview of national-scale dynamic hydro-geochemical model applications to lake catchments in Norway, Sweden and Finland. Model simulations have been used to predict the recovery of soil and surface water chemistry in response to (1) decreased deposition of acidifying compounds, (2) the combined impacts of acidifying and climate change processes, and (3) the impacts of increased removal of forest harvesting residues for bioenergy production.