Anthropogenic nutrient and trace element loadings of marine environments significantly impact ecosystem structure and functioning, leading to increased productivity, eutrophication, changes in microbial abundance and in both producer and consumer community composition, accumulation of contaminants in biomasses and their transfer along food chains. In turn, this can result in algal blooms (including toxic algae), hypoxia and anoxia events, biodiversity loss, fish kills and trophic disruption, with important implications for water body-related economic activities and public health.
Anthropogenic organic nitrogen is relatively enriched in 15N with respect to synthetic-derived nitrogen, and both of them can be distinguished from atmospheric-derived (i.e. natural) nitrogen on the basis of their δ15N signatures. According to this, stable isotopes of nitrogen have been shown to be a powerful tool to track the origin of nutrient loadings in aquatic systems. In addition, isotopic signatures of carbon and sulfur can discriminate the relative contribution of different sources to nutrients accumulated in sediments or assimilated by consumers, making it possible to describe trophic pathways and food web structure across multiple spatial and temporal scales. Isotopic signatures will be determined in primary producers, sediments and consumers collected in multiple sampling sites and occasions within each study sites. Isotopic gradients will be described and isotopic variations compared along gradients of anthropogenic pressure and with respect to reference sites.