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- Impacts of decommissioning and upgrading urban wastewater treatment plants on the water quality in a shellfish farming coastal lagoon (Ria Formosa, South Portugal)Publication . Jacob, J.; Correia, Cátia; Torres, Ana Flor; Xufre, Gustavo; Matos, André Filipe; Ferreira, Cristina; Reis, Margarida; Caetano, Sandra; Freitas, Carla; Barbosa, Ana B.; Cravo, AlexandraRia Formosa is a productive coastal lagoon, located on the south coast of Portugal, and represents the largest national producer of shellfish bivalves (ca. 90% production). This ecosystem is subjected to various anthropogenic pressures, including the discharge of urban wastewater treatment plants (UWWTP), which impacts the lagoon water quality. This study aimed to assess the impact of alterations in the functioning of two UWWTP on the water quality of Ria Formosa, based on chemical variables, phytoplankton composition ( including potential harmful species) and faecal contamination. During the period September 2018 - October 2019, water sampling was conducted along dominant longitudinal gradients of the effluent dispersion from the discharge point (1-2 km), for two sites: a decommissioned (OP) and a modified (FO) UWWTP. After modification, the later started receiving a higher influent volume (ca. 40%), under an innovative technology system (biological treatment in aerobic granular sludge). Based on chemical water quality variables, phytoplankton and indicators of faecal contamination, a significant improvement along the longitudinal gradient from the discharge point was observed after OP decommissioning. This improvement was fast, being detected two months after decommissioning, positively affecting areas used as shellfish farming grounds. However, distribution patterns of bacteriological indicators and regular shellfish harvesting interdictions suggested an alternative source of faecal contamination after OP decommissioning. At FO, both chemical variables and bacteriological indicators of faecal contamination revealed a slower improvement, only six-months after the UWWTP alteration. Before that, increased and highly variable ammonium, chlorophyll a concentration, phytoplankton abundances and Escherichia coli densities, revealed an unstable phase. Overall, a lower water quality at FO in respect to OP reflected not only a higher effluent volume but also more restricted water circulation for the former.
- Unravelling the effects of treated wastewater discharges on the water quality in a coastal lagoon system (Ria Formosa, South Portugal): Relevance of hydrodynamic conditionsPublication . Cravo, Alexandra; Barbosa, A.B.; Correia, C.; Matos, A.; Caetano, S.; Lima, M.J.; Jacob, J.This study aimed to assess the influence of treated wastewater disposal on Ria Formosa coastal lagoon (South Portugal), the largest national producer of bivalve mollusks. Water quality was evaluated at two areas under different wastewater loads and hydrodynamic conditions, using physico-chemical variables, bacterial indicators of contamination, chlorophyll-a concentration, phytoplankton abundance and composition. Samples were collected monthly, between October 2018 and September 2019. Minor influence of effluent discharge was detected at the eastern Olhao ˜ area, exposed to stronger hydrodynamics and higher wastewater load than the northwestern Faro area (ca. 2–4-fold total nitrogen and phosphorus). The lower load weakly flushed area showed a poorer water quality, up to 500 m from the discharge point, more marked during the spring-summer period. The intensity, persistence, and spatial extent of the wastewater footprint, lower for the highest-loading area, reflected the role of local hydrodynamic conditions, modulating the influence of wastewater discharge on lagoonal water quality.
- Water quality for bivalve molluscs and consumer safety: application of novel and adapted multimetric indices in a coastal lagoon system exposed to wastewater dischargesPublication . Cravo, Alexandra; Barbosa, Ana; BORLIDO OLIVEIRA LIMA, MARIA JOÃO; Ferreira, Cristina; Correia, Cátia; Matos, André Filipe; Jacob, José; Caetano, SandraWater quality degradation associated with wastewater discharges compromises the production of marine living resources. Water quality indices (WQIs) are relevant tools for water quality management, but most applications are limited to the suitability of freshwater for drinking. In this study, a novel WQI was developed to assess the effects of urban wastewater treatment plant (WWTP) discharges on the water quality in Ria Formosa coastal lagoon, targeting the condition of bivalve molluscs and consumer food safety (WQIB). The application of WQIB was compared with an adapted version of the Canadian Council of Ministers of the Environment Water Quality Index, using similar parameters (CCME-WQIB). WQIB and CCME-WQIB were applied to four areas next to WWTPs, over a 2-year period. WQIB integrated seven sub-indices (salinity, unionized ammonia, dissolved oxygen, suspended solids, chlorophyll-a, Escherichia coli and toxigenic phytoplankton), using a weighted additive aggregation function. Water quality ranged from very poor to very good and generally improved with distance from the effluent discharge points, and during the cold period. Highest influence of WWTP discharges was detected in areas under weak hydrodynamics. In areas under strong hydrodynamics, poor water quality was caused by the advection of toxigenic phytoplankton from adjacent coastal waters during the warm period. Although correlated, the use of WQIB should be preferred over CCME-WQIB due its greater sensitivity, use of weighted parameters and application at the sampling event scale. Our novel index extends the limited number of WQIs applied to marine systems and can be adapted to other systems and water use purposes.