Impacts of Decommissioning and Upgrading Urban Wastewater Treatment Plants on the Water Quality in a Shellfish Farming Coastal Lagoon (Ria Formosa, South Portugal)

Abstract

Impacts of decommissioning and upgrading urban wastewater treatment plants on the water quality in a shellfish farming coastal lagoon (Ria Formosa, South Portugal).

Unravelling the effects of treated wastewater discharges on the water quality in a coastal lagoon system (Ria Formosa, South Portugal): Relevance of hydrodynamic conditions

“…2). Relatively similar spatial patterns for salinity, nutrients, faecal indicators, Chl-a, and chlorophytes were recently reported for other main WWTP (Faro-Olhão) discharging effluents into a relatively confined RF location (Jacob et al, 2020). However, the effects associated with this WWTP were more intense, affecting areas furthest from the discharge point (up to 750 m), probably due to a 3.5-fold higher effluent discharge rate, in respect with FNW (Jacob et al, 2020).…”

“…These discharges represent a relevant nutrient source (Malta et al, 2017), and have impaired water quality (Bebianno, 1995;Newton et al, 2003;Cravo et al, 2015) and bivalve microbiological quality in specific areas of this lagoon (Martins et al, 2006;Almeida and Soares, 2012;Botelho et al, 2015;Cravo et al, 2015). More recently, some WWTPs discharging into the RF have upgraded their treatment technologies (Cravo et al, 2018), but the impact of these alterations was not yet fully assessed (see Jacob et al, 2020). This information is crucial for improving wastewater management strategies (e.g., Biancani et al, 2012;Machado and Imberger, 2012), promoting the condition of shellfish farming grounds, that intrinsically depend on water quality.…”

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

“…1.5 km from the Tavira inlet. The three stations used in our study were selected based on previous studies in Ria Formosa, which reported the WWTP influence up to 750 m from the discharge points, followed by reference lagoon conditions for the furthest stations [30,47,56]. The distance between stations increased from those closer to the discharge point (500 m, ALM 250-ALM 750) to the outer stations (1000 m, ALM 750-ALM 1750) due to the occurrence of stronger water quality gradients in areas closer to the WWTP discharge points [30,47,56].…”

“…However, RF is exposed to various anthropogenic stressors [45,46], including discharges from wastewater treatment plants [30,47,48], and is located in an area particularly vulnerable to climate change [49]. Previous studies of phytoplankton in the RF lagoon, focusing on the western sector of the lagoon, have addressed the spatial-temporal dynamics of chlorophyll-a (e.g., [42,50,51]), assemblage structure [30,[52][53][54][55][56], production [57,58], specific HAB-forming taxa [59][60][61], and the effects of physico-chemical variables (temperature, light, CO 2 , nutrients, ultraviolet radiation) on phytoplankton growth and composition (e.g., [62][63][64][65][66][67]). However, no information on phytoplankton is currently available for the eastern sector of the lagoon, which is more affected by freshwater discharges [47] and where water quality is worst [46,51].…”

“…and (iii) What are the physico-chemical conditions most closely associated with the spatial-temporal variability in the phytoplankton assemblage structure? Based on previous studies (e.g., [3,30,56,68]), we hypothesized that the phytoplankton assemblage structure varied between sites, with a higher prevalence of chlorophytes and lower taxonomic diversity at the site closest to the WWTP. We also expected to find strong intraannual patterns, but variable between sites, that could be interpreted in terms of the underlying environmental conditions.…”