Challenges in measuring nitrogen isotope signatures in inorganic nitrogen forms: An interlaboratory comparison of three common measurement approaches

Rationale Stable isotope approaches are increasingly applied to better understand the cycling of inorganic nitrogen (Ni) forms, key limiting nutrients in terrestrial and aquatic ecosystems. A systematic comparison of the accuracy and precision of the most commonly used methods to analyze δ15N in NO3− and NH4+ and interlaboratory comparison tests to evaluate the comparability of isotope results between laboratories are, however, still lacking. Methods Here, we conducted an interlaboratory comparison involving 10 European laboratories to compare different methods and laboratory performance to measure δ15N in NO3− and NH4+. The approaches tested were (a) microdiffusion (MD), (b) chemical conversion (CM), which transforms Ni to either N2O (CM-N2O) or N2 (CM-N2), and (c) the denitrifier (DN) methods. Results The study showed that standards in their single forms were reasonably replicated by the different methods and laboratories, with laboratories applying CM-N2O performing superior for both NO3− and NH4+, followed by DN. Laboratories using MD significantly underestimated the “true” values due to incomplete recovery and also those using CM-N2 showed issues with isotope fractionation. Most methods and laboratories underestimated the at%15N of Ni of labeled standards in their single forms, but relative errors were within maximal 6% deviation from the real value and therefore acceptable. The results showed further that MD is strongly biased by nonspecificity. The results of the environmental samples were generally highly variable, with standard deviations (SD) of up to ± 8.4‰ for NO3− and ± 32.9‰ for NH4+; SDs within laboratories were found to be considerably lower (on average 3.1‰). The variability could not be connected to any single factor but next to errors due to blank contamination, isotope normalization, and fractionation, and also matrix effects and analytical errors have to be considered

Urban geoarchaeology in Belgium: Experiences and innovations

Geoarchaeological research in urban contexts is a relatively recent development in Belgian geoarchaeology, with pioneering studies dating back to the 1990s. In the beginning of the 21st century, a specific research protocol was developed in Brussels, and in the last years, there have been several attempts to apply a similar approach to urban contexts in Flanders and occasionally in Wallonia. Current debates in urban geoarchaeology mainly focus on: – The study of site stratigraphy (microstratified layers and Dark Earths) – The impact of urbanization on the soil – Rivers in towns – Reconstruction of the ancient relief and its modifications through time – Soil erosion and soil protection – Ancient soil pollution – The integration of geoarchaeology with other archaeo-environmental studies (archaeobotany, archaeozoology, etc.). Key themes for the future development of Belgian urban geoarchaeology include the in situ preservation of sites; a further integration with other methods and method development; systematic studies producing topographical insight and mapping; and synthesis work on critical issues.SCOPUS: re.jDecretOANoAutActifinfo:eu-repo/semantics/publishe