Organic pollutants and functional properties of benthic microbial communities in coastal lagoons (River Po delta )

The sediment is a compartment of fundamental importance in the aquatic ecosystem by acting as a sink or source of organic matter, including pollutants, and nutrients. The sediment hosts diverse biological communities where heterotrophic microorganisms, posed at the base of the heterotrophic food chain, play an important role in the biodegradation processes and ecosystem functions. Information regarding possible links between organic pollutants contamination and the processes mediated by microbial communities are still lacking. Moreover for the establishment of environmental quality standards (EQS) the sediment compartment is not necessarily monitored although threshold values are given for priority organic substances by the European water Framework Directive (2013/39/UE). In the framework of the project RITMARE, funded by the Italian Ministry of University and Scientific Research, a survey was conducted in five coastal lagoons sited at the confluence of the Po river in the northern Adriatic Sea. This fragile system receives nutrients and contaminants transported by the Po river, one of the most important contributor of organic matter and nutrients to the Mediterranean sea. Such high loads may pose a substantial ecotoxicological risk, that is of particular concern considering their exploitation for clam farming. In this survey were selected 12 stations sited in the Caleri, Marinetta, Vallona, Canarin, Scardovari lagoons. Surface sediments were analyzed for the concentrations of the organic matter (Element analyzer R.ZONTA), proteins, lipids and carbohydrates (metodo T.Cibic) along with stable isotope of organic carbon (?13C), by mass spectrometer and CHN analyzer ZONTA. The quality of sediments were then described by the analysis of organic contaminants of environmental concern (Polycyclic Aromatic Hydrocarbons, PAHs, nonylphenol, NP, and Bisphenol A, BPA, by RP-HPLC). Benthic microbial properties were described by bacterial cell abundances (DAPI stain), Bacterial C Production rate (BCP, 3H-leucine inc.), community respiration rates (CR, ETS), extracellular enzyme activities (lipase, aminopetidase, beta glucosidase activities, fluorimetric assay). Overall the lagoons showed moderate pollution by organic contaminants and different trophic profiles. The lagoon Canarin, that receives freshwater from the primary branch of the Po River, showed the highest values of organic contaminants (?PAHs 100±9.9ng/g; BPA 29.9±13ng/g; NP95.58±15ng/g). Overall no concentrations of PAH congeners exceeded the limits of the quality standards, whereas NP concentration exceeded the Predicted No-Effect Concentration (PNEC) for sediment (39 ng/g), suggested by the European Directives, in the Marinetta, Canarin and Scardovari lagoons. The analysis of the Principal Components (PCA) based on the correlation matrix of the variables, showed the highest trophic level of the Canarin lagoon with the highest values of bacterial abundances (mean 6.01±1.8 x10^8 cell/g), bacterial C production rates (BCP mean 0.45±071 nmolC h-1g-1) and higher BCP/CR ratio values. In conclusion the change observed in the sediment quality implies changes in the metabolic properties of the microbial communities with potential repercussions in the fate of the organic matter (energy transfer to trophic chain or oxidative processes with CO2 emission). These results suggest a closer look into the microbial compartment to better describe the environmental quality.