Performance of surface and subsurface flow constructed wetlands treating eutrophic waters

Three medium size constructed wetlands (CWs) with a total surface of 90 ha are working since 2009 in the Albufera de Valencia Natural Park (Spain). Two of them are fed with eutrophic waters from l'Albufera Lake. Their objectives are both reduce the phytoplankton biomass and increase the biodiversity; consequently, improved water quality is returned to the lake. A science based governance of these CWs is ongoing inside the LIFE + 12 Albufera Project to demonstrate the environmental benefits of these features. In this paper, results and relationships among hydraulic operation, physicochemical variables and plankton in two different CWs typologies, five free water surface CW (FWSCW) and one horizontal subsurface flow CW(HSSFCW), were analysed showing that CWs were capable of improving the water quality and biodiversity but showing clear differences depending on the CW type. The CWs worked under different hydraulic load rates (HLR) from <0.12 to 54.75 m yr(-1). Inflow water quality was typical from eutrophic waters with mean values of chlorophyll a (Chl a) about 22-90 mu g Chl a l(-1) and mean total phosphorus (TP) between 0.122 and 0.337 mg l(-1). The main conclusion is that HSSFCW was much more efficient than FWSCW in the removal of organic matter, suspended solids and nutrients. The biological role of several shallow lagoons located at the end of the CWs has also been evaluated, showing that they contribute to increase the zooplankton biomass, a key factor to control the phytoplankton blooms. (C) 2017 Elsevier B.V. All rights reserved.