Changes in water quality of treated sewage effluents by their receiving environments in Tablas de Daimiel National Park, Spain.

The Tablas de Daimiel National Park (TDNP), a floodplain wetland located in the Upper Guadiana Basin (central Spain), receives pollution from wastewater treatment plants (WWTPs) discharging their treated sewage effluents (TSEs) to tributary channels to the wetland. The TSEs suffer transformations on their way to the TDNP, but the water quality is controlled only at the point of discharge. In this work, we analyse the change in water quality of the TSE from four urban WWTPs in the surroundings of the TDNP (Alcázar de San Juan, Daimiel, Manzanares and Villarrubia de los Ojos towns). The water samples were taken at the outlet of the plants and in the receiving environments, to analyse the water quality transformation of the TSE. The different discharge configurations of each WWTP have been related with the water quality transformation of their TSE, to interpret the influence of the hydro-geomorphology in the improvement or deterioration of the water quality of TSE. We found that the discharge of TSE into slow flow channels with macrophyte vegetation facilitates water self-purification but, with time, the accumulation of sludge in the beds of the effluents tends to be the cause of the deterioration of the water quality.