Use of stable isotope composition variability of particulate organic matter to assess the anthropogenic organic matter in coastal environment (Istra Peninsula, Northern Adriatic)

Nitrogen and carbon stable isotope analysis of particulate organic matter (POM) was used to assess the impact of anthropogenically derived organic matter in coastal parts of the Istra Peninsula (Northern Adriatic). The investigation was conducted in areas potentially impacted and enriched with different amounts of organic matter. Elevated δ15N values in POM reflect enrichment of organic matter near the coast due to inadequate municipal infrastructure in cities and local septic systems as well as inputs from riverine terrestrial material. On the contrary, negative δ15N values reflect the depleting effect of purification plants. Significant differences in nitrogen stable isotope ratios were observed between western and southeastern coasts. The δ13C values show small depletion at sites with potentially greater anthropogenic impact. A weak temporal increase of δ15N from spring to late summer was observed. The results for nitrogen and carbon isotope ratios of POM and their comparisons with other areas suggest diverse amounts and sources of organic matter as well as differences in movement of floating POM within the water column. The δ15N and δ13C values reflect the ratios of marine and terrigenous organic matter, the latter being mainly anthropogenically influenced. The results finally suggest precaution in applicability of POM as tracers for detecting anthropogenic organic matter in marine coastal ecosystem.