Determining the footprint of sewage discharges in a coastal lagoon in South-Western Europe

Hepatic transcriptome, transcriptional effects and antioxidant responses in Poecilia vivipara exposed to sanitary sewage

Aquatic environments are subject to threats from multiple human activities, particularly through the release of untreated sanitary sewage into the coastal environments. These effluents contain a large group of natural or synthetic compounds referred to as emerging contaminants. Monitoring the types and quantities of toxic substances in the environment, especially complex mixtures, is an exhausting and challenging task. Integrative effect-based tools, such as biomarkers, are recommended for environmental quality monitoring programs. In this study, fish Poecilia vivipara were exposed for 24 and 96 h to raw untreated sewage diluted 33 % (v/v) in order to identify hepatic genes to be used as molecular biomarkers. Through a de novo hepatic transcriptome assembly, using Illumina MiSeq, 54,285 sequences were assembled creating a reference transcriptome for this guppy species. Transcripts involved in biotransformation systems, antioxidant defenses, ABC transporters, nuclear and xenobiotic receptors were identified and evaluated by qPCR. Sanitary sewage induced transcriptional changes in AhR, PXR, CYP2K1, CYP3A30, NQO1, UGT1A1, GSTa3, GSTmu, ST1C1, SOD, ABCC1 and SOX9 genes from liver of fish, particularly after 96 h of exposure. Changes in hepatic enzyme activities were also observed. The enzymes showed differences in fish exposed to both periods, while in the gills there was a prevalence of significant results after 96 h. The observed differences were associated to gender and/or to sewage exposure. The obtained results support the use of P. vivipara as sentinel and model organism for ecotoxicological studies and evidence the importance of understanding the differential responses associated to gender.

Dynamics of CO2, CH4, and N2O in Ria Formosa coastal lagoon (southwestern Iberia) and export to the Gulf of Cadiz

A first characterization of greenhouse gases had been carried out to study their role and impact in a productive transitional coastal system of the southern Portugal - Ria Formosa lagoon. To this purpose, the partial pressure of CO2 (pCO2) and the concentration of dissolved CH4 and N2O have been measured. Two surveys were carried out during 2020, at low tide under typical conditions of Spring (March) and end of Summer (October). The samplings sites were distributed along the costal lagoon covering: i) inner areas with strong human impact (influence of different flows of treated wastewater discharges); and ii) main channels in connection with the main inlets to study the exchanges with the ocean. In general, the highest values of the three greenhouse gases were found at the inner studied areas, especially affected by the disposal of treated effluents from wastewater treatment plans, in October. The mean water - atmosphere fluxes of the CO2, CH4 and N2O are positive, showing that the study area acts as a source of these gases to the atmosphere. On the other hand, it was calculated a rough estimation of the three gases globally exported from Ria Formosa to the ocean, through the main six inlets to evaluate the magnitude of the supply of these gases from Ria Formosa to the adjacent ocean. The mean CO2, CH4 and N2O horizontal water fluxes exported from all the inlets of Ria Formosa to the Gulf of Cadiz for both seasons, during low water, are 8.7 ± 3.9 mmol m-2 s-1, 8.0 ± 3.5 μmol m-2 s-1 and 3.2 ± 1.5 μmol m-2 s-1, which corresponds to a mass transport through the inlets section of 0.7 ± 0.7 kg s-1, 0.2 ± 0.2 g s-1 and 0.2 ± 0.3 g s-1 respectively. From these estimates, as expected, the higher mass transport was found at the larger and deeper inlets (Faro-Olhão and Armona).

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

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, and 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 bivalve production zones 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.

Deoxygenation turns the coastal Red Sea lagoons into sources of nitrous oxide

Direct measurements of dissolved N₂O concentrations, fluxes and saturation percentages undertaken for the first time in two coastal lagoons - Al-Shabab and Al-Arbaeen, along the east coast of the Red Sea, revealed the region as a significant source of N₂O to the atmosphere. The exacerbated dissolved inorganic nitrogen (DIN) from various anthropogenic sources led to substantial oxygen depletion in both the lagoons, which turned to bottom anoxia at Al-Arbaeen lagoon during the spring season. We assume that the accumulation of N₂O is caused by nitrifier-denitrification in the hypoxic/anoxic boundaries. In fact, the results indicated that oxygen-depleted bottom waters favoured denitrification when the oxygenated surface waters recorded nitrification signals. Overall, the N₂O concentration ranged from 109.4 to 788.6 nM (40.6-325.6 nM) in spring and 58.7 to 209.8 nM (35.8-89.9 nM) in winter in the Al-Arbaeen (Al-Shabab) lagoon. The N₂O flux ranged from 647.1 to 1763.2 μmol m^-2 day^-1 (85.9 to 160.2 μmol m^-2 day^-1) and 112.5 to 150.8 μmol m^-2 day^-1 (76.1 to 88.7 μmol m^-2 day^-1) in the spring and winter respectively, in the Al-Arbaeen (Al-Shabab) lagoons. The ongoing developmental activities may worsen the current situation of hypoxia and associated biogeochemical feedbacks; therefore, the present results underline the need for continuous monitoring of both lagoons to restrict more severe oxygen depletion in future.

Seasonal and Spatial Variability of Phytoplankton Primary Production in a Shallow Temperate Coastal Lagoon (Ria Formosa, Portugal)

Coastal lagoons are among the most productive ecosystems in the world, and they provide a wide range of ecosystem services and resources. In the Ria Formosa (southern Portugal), phytoplankton production has rarely been addressed. The main goal of this study is thus to evaluate the variability of phytoplankton production and photosynthetic characteristics over the seasonal cycle and in different locations (landward, urban, intermediate, and seaward boundaries) of the Ria Formosa coastal lagoon, subjected to distinct natural and anthropogenic stressors. Primary production was evaluated using the ¹⁴C incorporation technique, and photosynthetic parameters were estimated by fitting photosynthesis-irradiance curves. Primary production showed significant seasonal variations, with higher values in the summer associated with lower euphotic depths, higher water temperatures, and higher nutrient concentrations. No spatial differences were found for primary production or photosynthetic parameters. Primary production values were lower than previous estimates, which reflects an improvement in water quality in the Ria Formosa, but values are higher than primary production estimates for other temperate coastal ecosystems, which reflects the highly productive nature of this coastal lagoon.

Assessing the effectiveness of management measures in the Ria Formosa coastal lagoon, Portugal

The Ria Formosa is an important transitional and coastal lagoon on the south coast of Portugal that provides valuable ecosystem services. The lagoon is a protected area under national and international conventions. There is a great potential for Blue Growth sectors, such as aquaculture and coastal tourism, but these rely on good water quality. European environmental legislation, such as the Water Framework Directive, requires member states, such as Portugal to implement management measures if a surface water body is not of good ecological status. This work addresses the effectiveness of management measures, such as wastewater treatment plant implementation and dredging, on the water quality of the Ria Formosa coastal lagoon system. This is an important social-ecological issue, since management measures can be very expensive. The ecological status of Ria Formosa was evaluated, according to the physico-chemical and biological quality elements of the Water Framework Directive. The main indicators were the physico-chemical quality elements of nutrient and oxygen condition, and the biological quality element chlorophyll a, as a proxy for phytoplankton biomass, under the Water Framework Directive. The data for these quality elements from the Ria Formosa were analyzed for consistency with the classification for the Water Framework Directive water bodies. The data after the implementation of management measures was compared with historical data to evaluate if these measures had been effective. The relation between nutrient pressures, meteorological and hydrological conditions was addressed, especially rainfall and runoff. Results showed a decrease in nutrient concentration after the management interventions, despite the increase of population and intensifying agriculture in the catchment. The Ecological Status is spatially variable with an overall moderate status, indicating the need for further management measures. There is a significant reduction in nutrient pressure on the lagoon during drought years. This indicates that climate change may alter the structure and function of the lagoon in the future.

Understanding the bioaccumulation of pharmaceutical active compounds by clams Ruditapes decussatus exposed to a UWWTP discharge

Twenty-four pharmaceutical active compounds (PhACs) were evaluated in the soft tissues of clams Ruditappes decussatus exposed along a 1.5-km dispersal gradient of the treated effluent from an urban wastewater treatment plant discharging in Ria Formosa, and compared with those in the marine waters and discharged effluents. The clams were exposed for 1 month, in June-July 2016, 2017 and 2018. PhACs were quantified by high performance liquid chromatography coupled to tandem mass spectrometry after the quick, easy, cheap, effective, rugged and safe (QuEChERS) method (clams) or solid-phase extraction (water samples). The most representative PhACs in the effluents and receiving waters (regardless of the tidal dilution effect) were diclofenac, carbamazepine and caffeine (on average ≤ 2 μg/L) and only caffeine exhibited significant inter-annual differences, with higher values in 2017. In turn, the most bioaccumulated PhACs in clams were caffeine (0.54-27 ng/g wet weight, significantly higher in 2016) and acetaminophen (0.37-3.7 ng/g wet weight, significant lower in 2016). A multivariate principal component analysis showed (i) PhAC bioaccumulation primarily depended on biotic factors (clams length and weight), (ii) PhAC physicochemical properties Log K_ow, pKa and water solubility interplaying with water abiotic variables were more relevant for explaining data variability in water than the physical dilution/tidal mixing, (iii) this process, reflected by the salinity gradient, had a tertiary role in data variation, responsible for spatial discrimination of marine waters. This study provides a better understanding of PhACs bioaccumulation by clams Ruditapes decussatus in real environmental conditions, under the influence of urban treated effluent dispersal in Ria Formosa coastal lagoon, a major producer of bivalves, ultimately disentangling key factors of PhAC bioaccumulation.

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

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 Olhão 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.

Effects of climate change and anthropogenic pressures in the water quality of a coastal lagoon (Ria Formosa, Portugal)

Understanding how climatic and anthropogenic drivers will influence coastal lagoons is fundamental to guarantee their preservation and sustainability. The Ria Formosa (coastal lagoon, South coast of Portugal) is a very important ecosystem that supports diverse economic activities in the region. The 3D coupled hydrodynamic-biogeochemical model SCHISM was validated and used to assess the influence of climate change and anthropogenic pressures on the water quality of the Ria Formosa. Five scenarios were simulated: reference scenario (S0), mean sea level rise (SLR) of 0.5 m (S1), increase of the air temperature of 1.68 °C (S2), increase of the outflow from the wastewater treatment plants (WWTP) by 50% (S3) and a combined scenario (S4). Results suggest that SLR of 0.5 m promotes an increase of 0.5-3 in the salinity near the area of influence of the WWTP. SLR decreases the inorganic nutrient concentrations in these areas by about 40-60%, due to an increase of the dilution. In contrast, the increase of the outflow from the WWTP by 50% increases the nutrients concentrations by about 20-40%. The increase of the air temperature alone by 1.68 °C increases the water temperature by 0-1 °C. The combined scenario suggests antagonist effects in the nutrient concentrations. Overall, the trophic index (TRIX) of the lagoon calculated for the scenarios exhibits only minor differences relative to the reference scenario, except in some areas near the WWTP discharges. In these areas, TRIX tends to increase with the increase of the outflow from the WWTP in scenario S3. These results provide further insight into the response of coastal lagoons, and the Ria Formosa in particular, to future changes and contribute to support their management.

Biomarker Responses of the Clam Ruditapes decussatus Exposed to a Complex Mixture of Environmental Stressors under the Influence of an Urban Wastewater-Treatment Plant

To evaluate the potential impact of an urban wastewater-treatment plant on Ria Formosa coastal lagoon, a sentinel species, the clam Ruditapes decussatus, was exposed along a gradient of the effluent's dispersal for 1 mo. Three exposure sites were selected to study the responses of 3 biomarkers: electron transport system, acetylcholinesterase, and lipid peroxidation. As complementary data, morphometric measurements, condition index, and lipid and protein content were considered together with in situ physicochemical characterization of the sites (temperature, salinity, pH, and dissolved oxygen). Electron transport system activity levels were between 35.7 and 50.5 nmol O₂ /min g protein, acetylcholinesterase activity levels ranged from 2.6 to 3.8 nmol/min g protein, and lipid peroxidation ranged from 174.7 to 246.4 nmol malondialdehyde/g protein. The exposure sites shaped the response not only of biomarkers but also of "health" parameters (protein, lipids, and condition index). Lipid peroxidation was the most responsive biomarker also associated with electron transport system, especially at the closest site to the urban wastewater-treatment plant. Because of the presence of complex mixtures of contaminants in urban effluents, biomarker responses can provide valuable information in environmental assessment. However, it is vital to identify all biological and ecological factors induced by the natural life cycle of clams. Abiotic factors can mask or overlap the response of biomarkers and should be considered in a multibiomarker approach. Environ Toxicol Chem 2021;40:272-283. © 2020 SETAC.

Evaluating the impact of sewage discharges on the marine environment with a lightweight AUV

Environmental studies that use small Autonomous Underwater Vehicles (AUVs) can survey wider and deeper areas, compared to traditional methods, at a reasonable cost. Thanks to the precise vehicle navigation systems, the data collected can be accurately geolocalized. Besides, lightweight vehicles can be deployed from the shore or from small boats and programmed by means of user-friendly graphical interfaces, thus reducing and simplifying the need of human resources and infrastructures. Based on such a technology, this paper presents a framework to assess the environmental impact of a marine sewage outfall set in the Bay of Palma (Mallorca, Spain). We report the results of the analysis of the images recorded in the course of six missions conducted with an AUV. The plan was designed after a microbiological analysis detected the presence of cyanobacteria in a sample of sand and water collected by scuba divers close to the sewer pipe mouth.