Plankton participation in the performance of three constructed wetlands within a Mediterranean natural park

The contribution of plankton in the performance of three constructed wetlands (CWs) within the Albufera de València Natural Park has been analyzed, taxonomic group by group, over a two-year operation period in the different sectors of each CW: horizontal subsurface-flow -A-, free-water surface flow -B- and lagoons -C-. Tancat de la Pipa CW (TPCW) only contains B-C sectors, while the others have all three types. Treatment efficiency of each sector type on the taxonomic groups was evaluated by calculating frequency of phytoplankton reduction (or zooplankton production), mass removal (or production) efficiencies and rates, and accumulated removed phytoplankton mass (or produced zooplankton mass). The phytoplankton biomass entering Tancat de Mília CW (TMCW) was significantly higher (47 ± 22 mm³·L^-1) than in the other CWs (10 ± 11, 6 ± 5 mm³·L^-1), but the outlets did not show significant differences. 7574 and 180 kg DW were eliminated during the two-year period in TMCW and Tancat de L'Illa CW (TLICW), from which 72% and 91% were removed cyanobacteria. Conversely, 470 kg DW of phytoplankton were produced in TPCW, but 99 kg of cyanobacteria eliminated. Mean efficiencies in zooplankton production were 682%, 157% and 112% in TLICW, TMCW and TPCW. There were evident spring production peaks of cladocerans in all CWs. Ostracods were much more abundant in the B sectors (related to the high density of emergent vegetation). In TMCW, the removal efficiencies were significantly higher during the second operation year. These CWs have undergone changes in the composition of phytoplankton and zooplankton communities, both spatially and temporally, which represent an improvement in the water quality which is returned to the eutrophic main lagoon within the Natural Park. We do not recommend using only chlorophyll and phycocyanin measurements as a surrogate of phytoplankton and cyanobacterial biomass. Instead, this can be considered only as a complement to the traditional analyses of microalgae and cyanobacterial presence.