Abstract
Forest vegetation plays a key role in the cycling of mercury (Hg) and organic matter (OM) in terrestrial ecosystems. Litterfall has been indicated as the major transport vector of atmospheric Hg to forest soils, which is eventually transported and stored in the sediments of forest lakes. Hence, it is important to understand how changes in forest vegetation affect Hg in soil and its biogeochemical cycling in lake systems. We investigated the pollen records and the geochemical compositions of sediments from two lakes (Schurmsee and Glaswaldsee) in the Black Forest (Germany) to evaluate whether long-term shifts in forest vegetation induced by climate or land use influenced Hg accumulation in the lakes. We were particularly interested to determine whether coniferous forests were associated with a larger export of Hg to aquatic systems than deciduous forests. Principal components analysis followed by principal component regression enabled us to describe the evolution of the weight of the latent processes determining the accumulation of Hg over time. Our results emphasize that the in-lake uptake of Hg during warm climate periods, soil erosion after deforestation and emissions from mining and other human activities triggered changes in Hg accumulation during the Holocene stronger than the changes caused by forest vegetation alone.
Highlights
Mercury is a pollutant of concern due to its toxicity and high bio-magnification potential in aquatic systems; because Hg is organophilic, organic matter (OM) is a key component to determine the retention and transport of Hg in the environment [1,2]
Observed increases in Hg concentrations and accumulation rates in lake sediments deposited during the past century are commonly accepted as records of increasing anthropogenic input of Hg to the atmosphere and atmospheric deposition of Hg to lake sediments [3,4,5,6]
Considering the the altitude altitude of of the the lakes, lakes, this this mixed forest was likely dominated by Abies alba, but Fagus sylvatica was present in the catchment
Summary
Mercury is a pollutant of concern due to its toxicity and high bio-magnification potential in aquatic systems; because Hg is organophilic, OM is a key component to determine the retention and transport of Hg in the environment [1,2]. Lake sediments accumulate material from the entire catchment and can be understood as a record of OM and many major and trace elements, including Hg [7,8]. Because new material is deposited on top of older deposits, these sediments are natural archives for temporal changes in trace element loadings [9,10,11]. Most studies of Hg in lake sediments have focused on correcting Hg accumulation in sediments for catchment effects to convert Hg accumulation rates into atmospheric deposition rates [5,12,13]. The effects of the evolution of landscapes on Hg transport and the accumulation of this element to and within aquatic systems have been considered to a much lesser extent. It is well established that the vegetation type influences the cycling of OM
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