Catchment area composition and water chemistry heavily affects mercury levels in perch (Perca fluviatilis L.) in circumneutral lakes

The environmental impact on the mercury level in perch (Perca fluviatilis L.) is examined using Partial Least Square regression (PLS) on 48 environmental descriptors assessing land use, various catchment area and lake characteristics, lake water chemistry, and fish stock. The lake specific intercepts of Hg content vs. fish length regressions are used to describe the Hg level in the fish. The Hg levels in perch from 78 circumneutral lakes were largely influenced by land use in the surroundings. Boreal forest lakes had the highest Hg burden in the fish, while fish from lakes heavily influenced by arable land possessed lower contents. The Hg levels also showed a negative relationship to the concentrations of dissolved ions and total nutrients in lake water, and to the perch growth rate, whereas the relationship was positive to the concentration of TOC/humic matter. Lake pH did not have any significant influence on the Hg content in perch in these circumneutral lakes. The Hg levels in perch from lakes surrounded by large amounts of wetland were less satisfactorily explained by the presently examined environmental descriptors, which suggests that the Hg burden in fish from these lakes are influenced by other factors.