Temporal trends in mercury concentrations in eggs of Tawny owl (Strix aluco) from Central Norway between 1986-2019: influence of dietary ecological parameters and climate variables

Abstract

Mercury (Hg) is considered as a global threat which is emitted in the environment through natural sources or anthropogenic activities. Emissions of mercury decreased during the last decades because of the implementation of mitigation measures. However, with the ongoing climate change, ecosystems are directly (e.g., rising temperature) or indirectly impacted (i.e., altered ecosystem by e.g., invasive species and over-harvesting). Therefore, climate variables should be integrated in assessing pollutant temporal trends. In the current study, we investigated the temporal trends of Hg concentrations over a 33-year period (1986-2019). The potential influence of climate variables (i.e., air temperature, maximum snow depth, and the North Atlantic Oscillation) and dietary ecological parameters (i.e., carbon and nitrogen stable isotopes, ∂13C and ∂15N) on the Hg concentrations in tawny owl eggs were also investigated. Mercury and stable isotope values were analyzed in eggs and the data for the air temperature and the maximum snow depth for the winter period (December-March) were retrieved from several stations surrounding Trondheim. The average values for the three climate variables (i.e., temperature, max snow depth, and North Atlantic Oscillation (NAO)) were calculated for the entire winter period (December-March). A sudden shift in Hg concentrations was observed between 2000 and 2005 while exploring the dataset, two periods (1986-2005 and 2006-2019) were therefore investigated. A significant difference (p < 0.01) was observed between the two periods (0.12 ± 0.07 μg.g-1 and 0.074 ± 0.039 μg.g-1, respectively). A significant annual decrease of 0.002 μg.g-1 in mercury concentration was observed throughout the entire studied period (t = -5.42, p < 0.001). Among the different models selected to investigate the influence of dietary ecology and the climate variables on temporal trends of Hg, the most parsimonious model included the influence of the temperature and the ∂13C. Therefore, temperature and feeding habitat (∂13C) were found to have a higher influence on egg Hg than trophic level (∂15N), precipitations (snow), and larger scale climate variable (NAO).