In an area that contains high concentrations of natural organic matter, it is expected that it plays an important role on the behavior of rare earth elements (REE), like europium, and of trivalent actinides. Competitive interactions with H + , inorganic species, major cations, e.g., Ca(II) or Mg(II), could influence these metals transport and bioavailability. Competitive experiments between cations, which can bind differently to humic substances and Eu 3+ , will bring an improved understanding of the competitive mechanisms. The aim of this study is to acquire data for Eu(III)/Cu(II) and Eu(III)/Ca(II) competitive binding to a sedimentary originated humic acid (Gorleben, Germany). The NICA-Donnan parameters for Ca 2+ , Cu 2+ , and Eu 3+ obtained from competitive binding experiments using Ca 2+ or Cu 2+ ion selective electrodes were used to model time-resolved laser fluorescence spectroscopy (TRLFS) measurements. Eu 3+ and Cu 2+ are in direct competition for the same type of sites, whereas Ca 2+ has an indirect influence through electrostatic binding.

Organochlorine molecules (Cl org ) are surprisingly abundant in soils and frequently exceed chloride (Cl − ) levels. Despite the widespread abundance of Cl org and the common ability of microorganisms to produce Cl org , we lack fundamental knowledge about how overall chlorine cycling is regulated in forested ecosystems. Here we present data from a long-term reforestation experiment where native forest was cleared and replaced with five different tree species. Our results show that the abundance and residence times of Cl − and Cl org after 30 years were highly dependent on which tree species were planted on the nearby plots. Average Cl − and Cl org content in soil humus were higher, at experimental plots with coniferous trees than in those with deciduous trees. Plots with Norway spruce had the highest net accumulation of Cl − and Cl org over the experiment period, and showed a 10 and 4 times higher Cl − and Cl org storage (kg ha −1 ) in the biomass, respectively, and 7 and 9 times higher storage of Cl − and Cl org in the soil humus layer, compared to plots with oak. The results can explain why local soil chlorine levels are frequently independent of atmospheric deposition, and provide opportunities for improved modeling of chlorine distribution and cycling in terrestrial ecosystems.