Microbiological monitoring of bivalves from the Ria Formosa Lagoon (south coast of Portugal): A 20Â years of sanitary survey

The microbiological pollution of coastal waters is a major problem, especially in shellfish areas. This article shows the faecal contamination in bivalves from the Ria Formosa Lagoon (south coast of Portugal) along 20 years (1990-2009). The highest values of Escherichia coli in bivalves were obtained during the 90s, related with the discharge of untreated wastewaters and agricultural runoff. In the 2000s contamination levels decreased, with 83% of the population already served by new or remodelled sewage treatment plants. The highest levels were found in bivalves close to the largest city, where punctual and diffuse contamination sources still exist. Bivalves from the less impacted site showed the lowest contamination, an area with more water renewal. Seasonally, the highest levels were in autumn and winter, due to the runoff of waters from rainfall. These were opposite to those in spring and summer, when the highest temperatures and salinity showed a bactericidal effect.

► Escherichia coli levels in bivalves from the Ria Formosa Lagoon between 1990 and 2009. ► Highest in the 90s due to untreated wastewaters and agricultural runoff. ► In the 2000s decreased with new/remodelled STPs. ► Highest in autumn and winter due to water runoff. ► Lowest in spring and summer due to bactericidal effect of temperature and salinity.