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Sources of anthropogenic nutrients and their implications on nutrient chemistry and ecological conditions of Ria Formosa lagoon, Portugal

Publication . Oduor, Nancy A.; Cristina, Sónia; Goela, Priscila

Shallow coastal waters receive high anthropogenic nutrients (nitrogen-N and phosphorus-P) from land that can change their nutrient chemistry, algal composition, and food webs with serious effects on marine life, human health, and local livelihoods. Managing anthropogenic nutrient inputs is thus key to ensuring healthy and productive coastal ecosystems. This study conducted a bimonthly sampling for eight months between 2014 and 2015 to determine the influence of agriculture, sewage, and natural nutrient sources on nutrient chemistry, ecological status, and possible implications for aquaculture production in the western side of Ria Formosa lagoon. Ecological Quality Ratios (EQR) were calculated from nutrient ratios (N: P: Si) computed from nutrient concentrations with the Redfield ratio (N: P: Si =16:1:16) used as a reference for ecological status determination. A mean of 3.7, 1.0, and 4.6 mu mol/L; 6.7, 1.12, and 5.5 mu mol/L; and 4.6, 0.7, and 2.8 mu mol/L were recorded for dissolved inorganic nitrogen, phosphorus and silicates concentrations at sewage, agriculture, and natural sites respectively. The site mean EQR values ranged between 0.55 and 0.69. The overall ecological status of the west part of the lagoon was 'Moderate', with all the sites grouped under 'Good'/'Moderate' and 'Moderate'/'Poor' classes based on nutrient ratios. This study demonstrates that the western part of the lagoon's nutrient chemistry is highly influenced by the nutrient sources with agricultural run-off and sewage discharges associated with nitrates, and ammonia and phosphates respectively. The elevated ammonium and phosphates registered can transform the phytoplankton composition to non-diatomic species and affect the current ecological functions of the lagoon. We recommend further studies, including biological quality elements, to get more comprehensive results on the study area.(c) 2023 Elsevier B.V. All rights reserved.

2023-07Journal article

Restricted

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

Publication . Newton, Alice; Cañedo-Argüelles, Miguel; March, David; Goela, Priscila; Cristina, Sónia; Zacarias, Marta; Icely, John

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.

2022Journal article

Open Access