Ecological characteristics of seawater in the vicinity of submarine outfalls

摘要

To study the impact of sewage discharged from a mechanical treatment plant into a shallow coastal sea (Gulf of Trieste, Adriatic Sea), two submarine outfalls were chosen as the area for extensive research. Sampling was carried out at a station located above the two outfalls and at a reference station during periods of different stratification conditions of the water column. The spreading of the sewage in the seawater was detected through observing small vertical salinity oscillations (～0.1 PSU), and by the presence of faecal coliforms. The main nutrient load was traced in the form of ammonium and total phosphorus. Microscopic and HPLC analyses were used to identify the taxonomic composition and ratios among major phytoplanktonic taxa. Both methods indicated small changes in taxonomic composition and phytoplankton biomass in a locally enriched environment, which would be difficult to follow without a small-scale vertical sampling strategy.