Mercury deposition in forest ecosystems

Background and Objective

Mercury (Hg) is one of the priority substances in the Geneva Air Pollution Control Convention (CLRTAP). In the Heavy Metals Protocol (Aarhus 1998, updated 2012) regulations for reducing the emission of cadmium (Cd), lead (Pb) and Hg into the atmosphere were agreed. The risk assessment with the methods developed within the CLRTAP for calculating and checking critical loads for Hg and their exceedances shows a widespread exceedance of the ecological load limits for terrestrial ecosystems, in particular forests, for Germany (and Europe). In the National Strategy on Biological Diversity, Germany has set itself the target of achieving by 2020 the Critical Loads u. a. for heavy metals. This goal is unlikely to be achieved.

The project aims to bridge existing knowledge gaps regarding atmospheric inputs of mercury and their distribution in forest ecosystems. It is intended to support the development of a methodology to measure wet mercury deposition under the canopy of forests, which nevertheless provides reliable, reproducible results when using the simplest possible technical means. This creates the prerequisites for recording the actual entry in forest soils, which up to now can only be quantified with great uncertainty with the help of existing models (e.g. land use-dependent Hg deposition calculation with the EMEP model). The measurement results should be evaluated together with measured Hg concentrations in leaves, needles and soils (from the intensive forest environmental monitoring) in order to obtain information on Hg flows in, and possibly also for reemission from forest ecosystems.