Partitioning and sources of microbial pollution in the Venice Lagoon

Microbial pollutants are a serious threat to human and environmental health in coastal areas. Based on the hypothesis that pollution from multiple sources may produce a distinct microbial signature and that microbial pollutants seem to distribute between a free-living and a particle-attached fraction, we investigated the occurrence, partitioning and sources of microbial pollutants in water samples collected in the Venice Lagoon (Italy). The area was taken as a case study of an environment characterized by a long history of industrial pollution and by growing human pressure. We found a variety of pollutants from several sources, with sewage-associated and faecal bacteria accounting for up to 5.98% of microbial communities. Sewage-associated pollutants were most abundant close to the city centre. Faecal pollution was highest in the area of the industrial port and was dominated by human inputs, whereas contamination from animal faeces was mainly detected at the interface with the mainland. Microbial pollutants were almost exclusively associated with the particle-attached fraction. The samples also contained other potential pathogens. Our findings stress the need for monitoring and managing microbial pollution in highly urbanized lagoon and semi-enclosed systems and suggest that management plans to reduce microbial inputs to the waterways should include measures to reduce particulate matter inputs to the lagoon. Finally, High-Throughput Sequencing combined with computational approaches proved critical to assess water quality and appears to be a valuable tool to support the monitoring of waterborne diseases.