Anthropogenic changes in the fluxes to estuaries: wastewater discharges compared with river loads in small rias

The modification of chemical inputs into estuaries/rias by wastewater discharges is poorly documented. Concentrations and fluxes of nutrient salts, organic matter and trace metals in rivers and wastewaters to the mesotrophic Rias of Ortigueira (38 km2) and Viveiro (27 km2), located on the western Cantabrian coast (Bay of Biscay), were evaluated to assess changes in the land-sea fluxes. Water was sampled monthly during a year in the Mera (6.0 m3·s-1) and Landro (9.4 m3·s-1) rivers flowing into the Rias of Ortigueira and Viveiro, respectively. The urban effluents of Ortigueira (1,800 inhabitants; treated sewage) and the Viveiro (7,100 inhabitants; municipal treated sewage and untreated industrial wastewaters) were also monitored. Concentrations of chemical compounds and their fluxes were quite similar and close to pristine conditions in both rivers. Nitrate (98% of DIN), the limiting nutrient of ria primary production, was controlled by river flow while phosphate by wastewater discharge. Sewage discharges should not disturb the Ria of Ortigueira. Wastewaters fluxes of phosphate, POC, PON, dissolved Cu and particulate Cd, Cu and Zn into the Ria of Viveiro exceeded those of the Landro River, mainly during summer. Also, untreated wastewater effluents from fish food processing in such small fishing ports can be a source of contamination. The Rias of Ortigueira and Vivieiro are a reference point to evaluate fluvial pristine conditions and wastewater discharges on small estuary-ria receptor systems.Álvarez-Vázquez, M.A., Prego, R., Ospina-Alvarez, N., Caetano, M., Bernárdez, P., Doval, M., Filgueiras, A.V., Vale, C., Anthropogenic changes in the fluxes to estuaries: wastewater discharges compared with river loads in small rias, Estuarine, Coastal and Shelf Science (2015), doi: 10.1016/j.ecss.2015.08.02