The effect of forest vegetation on the formation of mercury accumulation signals in lake sediments

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The aim of the proposed project is to study how changes in forest vegetation will affect the accumulation of mercury in lake sediments. This approach builds on the hypothesis that different forest vegetation in lake catchments causes different Hg accumulation rates to forest soils. Moreover, forest type affects production, degradation and release of organic matter (OM) from forest soils, and thus also the transport of mercury to lakes. The proposed project will combine the investigation of long (several millennia) sediment records with known vegetation histories (from pollen analyses) taken from four catchment-lake systems, one with deciduous and three with coniferous vegetation. In addition we will investigate the contemporary relation between OM quality and quantity and Hg sedimentation in the study lakes through POM and DOM analyses. As chemical characteristics of organic matter in soils and assumingly also in sediments are strongly influenced by forest vegetation, we will use a qualitative approach where the OM quality (as defined by Fourier-transform infrared spectroscopy and Pyrolysis-GC-MS) will be related to changes in forest vegetation as derived from the tree pollen distribution in the sediments. Moreover, we will use multivariate statistical approaches to disentangle to which extent the influence of changes in forest vegetation on Hg accumulation in the lake sediments can be distinguished from other processes affecting the Hg load. A deeper understanding of this relationship is seen as the basis to predict the release auf Hg from the widely contaminated surface soils in the Northern Hemisphere to aquatic systems under changing land use or climatic conditions.