Epsilon Archive for Student Projects

Abstract

Previous studies done on water chemistry found that clear-cutting forests increases methylmercury (MeHg) concentrations. In recent years, few studies have been conducted on what effect forestry operations have on mercury (Hg) concentrations in biota, more specifically on fish. Predictions were made that Hg concentrations would increase by 10-25% in fish after clear-cutting. In order to determine if the predictions were accurate, a study was
done on the effects of Hg in perch after clear-cutting around six study lakes throughout Sweden between the years 2010-2013. Fish samples were taken before (2010) and after (2011 and 2013) the clear-cutting took place. There was a significant increase in Hg concentration in relation to fish size. There was an increase of 10% in fish Hg overall post-harvest, when length, weight, and age were used as covariates in the analysis of clear-cut effects. The lakes
with higher clear-cut areas within their catchments were also higher in mean Hg concentration ([Hg]) post-harvest, whereas the lakes with the lowest clear-cut areas were found lower in mean [Hg] post-harvest. These results are consistent with previous studies done on biota,water, and soil in boreal lake catchments. These findings give insight on how forest harvest can have a negative impact on the surrounding catchments and on the lake fish Hg concentrations. Further studies should be conducted on the role of the bacteria, zooplankton, and nitrogen isotopes within these catchments to better explain how Hg is released and methylated after forest harvest, moving from the water into the aquatic food web.