Changes in water quality of the Calich Lagoon and in its adjacent marine area (NW Sardinia, Italy)

The Calich Lagoon is a shallow water body located on the north western coast of Sardinia, strictly connected with the town of Alghero, an important touristic place in the northern Sardinia. The lagoon is part of the Regional Park of Porto Conte. Since April 2009, it has been receiving waste water from a waste water treatment plant, throughout one of the main tributary. A study was carried out for more than three years (September 2008-May 2012) to provide an environmental frame for the ecosystem management. Subsequently, due the intense water discoloration events in the adjacent marine system, the study was also useful to assess the influence of the lagoon waters on this area. Data on chemical-physical parameters, nutrients, chlorophyll a and phytoplankton were collected monthly at three stations inside the lagoon and at one station in the adjacent marine area. Water samples were very enriched in nutrients, both at the lagoonal (about 5.4 μM for total phosphorus and 68.37 μM for dissolved inorganic nitrogen) and marine stations (1.72 μM and 29.71 μM respectively). In the lagoon, enrichment was more severe close to the main tributary, as well as in the confined shallow extremities. Therefore, substantial phytoplankton abundance was supported all year-round (about 14.25 μg l-1 and 4.87 μg l-1 as chlorophyll a respectively in the lagoon and in the marine area). Different guidelines of classification indicated the system is univocally highly eutrophic. Water quality deterioration of the Calich Lagoon seems to negatively affects also the marine environment. Management options for quality environmental improvement include, firstly, urban waste water diversion, and radical changes in land uses of watershed and, even in extreme a hydraulic reorganization, such as the opening of a supplementary inlet.