CLIMER

Mercury (Hg) is an element that can undergo long-range transport in the atmosphere, and is historically accumulated even in catchment soils of remote locations. Inorganic Hg can be methylated into the toxic and bioaccumulative organic form methyl-Hg (MeHg), which is biomagnified in aquatic food webs with potential harmful effects on organisms. In recent decades, increasing concentrations of MeHg in freshwater fish has been documented, leading to increased risk of Hg exposure for fish consumers (including wildlife and humans). Today, the provision of healthy and uncontaminated fish for humans and wildlife by surface waters is under pressure.

Although awareness was raised concerning Hg as an environmental concern almost six decades ago, the complexity of the mechanisms controlling accumulation of MeHg in freshwater food webs are still largely unknown. Outstanding key questions regarding Hg concentrations in biota relate to; identification of driving factors of Hg in surface waters (including catchment Hg export); factors stimulating or limiting MeHg production; degradation of MeHg; transfer of MeHg into the food web; and trophic magnification of MeHg. Additionally, current trends of climate change, reduced sulphur deposition and surface water browning may have direct and indirect impacts on food web Hg exposure and bioaccumulation.

With these key drivers and mechanisms in mind, the present project propose to investigate spatial patterns and temporal trends of Hg in freshwater food webs by; 1) sampling food web gradients across boreal and subarctic lakes (including fish and lower trophic levels); 2) analysing temporal trends of Hg in fish in existing time-series (and adding to those time-series by targeted sampling) in relation to environmental drivers (including climate, deposition and water chemistry); 3) studying key processes in catchments, lakes and food webs in greater detail and transferring obtained insights to process-based modelling of catchment and lake Hg cycling and trophic transfer of Hg; and 4) building on expertise and existing data within the project international project consortium in order to improve the quality and reliability of predictions of food web exposure to Hg and food web Hg levels in boreal lakes.

The overarching aim of the project is to better assess present and future risk of Hg levels in biota and associated changes in ecosystem value from a toxicological and fisheries perspective. In particular, a better understanding of factors that drive aqueous MeHg concentrations and bioavailability will be assessed to improve future predictions of bioaccumulation of Hg in northern ecosystems food webs.