Analysis of the phytoplankton community in the vicinity of domestic sewage outflow during stratified conditions

The response of phytoplankton community structure to anthropogenically-derived nutrients from the submarine sewage outflow was analysed in a shallow coastal area of the middle Adriatic Sea. The study was conducted during an eight-year period (2002-2010) at six stations in the Brač Channel, aiming to assess the potential change in the state of biological and environmental parameters before and after commissioning of the sewage plant. Research was focused on phytoplankton producers in particular, during the summer, which is considered to be critical due to water stratification and low water dynamics. The results show an increase in phytoplankton biomass in the deep layer after discharge activation that was significant (M-W test; U=584.5, p<0.01), but not related to any intense phytoplankton bloom or oxygen deficiency. Temporal variability of total phytoplankton abundances throughout the research period indicated a significant increase in 2005, the year following sewage outflow activation. The Pairwise Dunn’s multiple comparison test emphasised the difference in the years before sewage activation (2002, 2003) compared t