RESUMEN
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.
Asunto(s)
Cianobacterias , Humedales , Animales , Fitoplancton , Plancton , ZooplanctonRESUMEN
Microcystins (MCs) are produced by cyanobacteria in aquatic environments and adversely affect macrophytes at very high concentrations. However, the effects of MC on macrophytes at concentrations of environmental relevance are largely unknown. The main objective of this study was to analyze the allelopathic effects of MC-LR at natural concentrations (1, 8 and 16 µg MC-LR/L) on five charophyte species (Chara aspera, C. baltica, C. hispida, C. vulgaris and Nitella hyalina) and the angiosperm Myriophyllum spicatum. Macrophyte specimens were obtained from a restored area located in Albufera de València Natural Park, a protected coastal Mediterranean wetland. Two different experiments were conducted involving (i) the addition of MC-LR to natural sediment to evaluate its effects on seed germination and (ii) the addition of MC-LR to water cultures of macrophytes to evaluate its effects on growth and metabolic functions. In water, the MC-LR concentration decreased by 84% in two weeks; the loss was not significant in sediment. The first seedlings (all C. hispida) emerged from the wetland sediment following a delay of a few days in the presence of MC-LR. The germination rates in 8 and 16 µg MC-LR/L treatments were 44% and 11% of that occurring in the absence of MC, but these differences disappeared over time. The final density was 6-7 germlings/dm(3). Final germling length was unaffected by MC-LR. Rotifers (Lecane spp.) emerging from the natural sediment during the experiment were favored by MC-LR; the opposite pattern was observed in the cladoceran Daphnia magna. The growth rates of C. vulgaris, C. baltica and N. hyalina were unaffected by MC exposure, whereas those of C. hispida and C. aspera were reduced in the MC treatments relative to the control treatment. The concentration of chlorophyll-a and the in vivo net photosynthetic rate were lower in the presence of MC-LR, even at the lowest concentration, for all of the characeans tested. M. spicatum was sensitive to the presence of MC-LR in the culture medium; the growth and chlorophyll-a concentrations were reduced. Therefore, environmentally relevant concentrations of MC might induce important changes in macrophyte meadows and the structure of the associated plankton community. Synchrony or delay in the processes evaluated here in response to environmentally relevant concentrations of cyanobacteria MC exudates can enhance understanding of the turning point to alternative states and the point of no return in eutrophicated shallow lakes.