Fate of microbial contamination in a South European Coastal Lagoon (Ria Formosa) under the influence of treated effluents dispersal

Abstract

Aim Assessment of the fate of microbial contamination driven from treated wastewater disposal at a highly productive zone on a South European coastal lagoon (Ria Formosa). Methods and results Microbial indicators of contamination (Total coliforms, Escherichia coli and Enterococci) were evaluated monthly during September 2018-September 2020, at three study areas (Faro, Olhão, Tavira) under different wastewater discharge flows and hydrodynamic conditions. Additional data on E. coli monitoring in bivalves, available from the national institution responsible for their surveillance was also considered. The maximum microbial contamination was found at Faro, the highest-load and less-flushed study area, contrasting the lowest contamination at Olhão, a lower-load and strongly flushed area. The wastewater impact decreased along the spatial dispersal gradients and during high water, particularly at Faro and Tavira study areas, due to a considerable dilution effect. Microbial contamination at Olhão increased during the summer while at the other study areas seasonal evidence was not clear. Data also indicate that E. coli in bivalves from BPZ next to the three study areas reflected the differentiated impact of the wastewater treatment plants effluents on the water quality of those areas. Conclusions Effluent loads together with local hydrodynamics, water temperature, solar radiation, precipitation and land runoff as well as seabirds populations and environmentally adapted faecal or renaturelized bacterial communities, contributed to microbial contamination of the study areas.

Patterns and Predictors of Phytoplankton Assemblage Structure in a Coastal Lagoon: Species-Specific Analysis Needed to Disentangle Anthropogenic Pressures from Ocean Processes

“…The relatively restricted hydrodynamics over the two innermost stations [48], together with sampling during neap low tides (see [30]), can explain this water quality gradient. The distribution of the microbial indicators of faecal contamination assessed concurrently with our study also showed a reduction along the 1.5 km longitudinal transect, with a strong dilution effect during high tide [118]. However, regardless of the WWTP influence, increased agricultural nutrient runoff, confinement, shallowness, sediment resuspension, and biological activity could partially justify the higher nutrient concentrations in the inner compared to outer coastal lagoon areas (e.g., [42,46]).…”