The water concentrations of 12 heavy and other metals/metalloids were analysed seasonally along two horizontal-flow constructed wetlands -CWs- (Tancat Mília -TM- and Tancat l’Illa -TLI) located within the Mediterranean Albufera de València Natural Park during 2020-2021. A wide-scope screening of pesticides present in waters was also performed. The two CWs were created to improve water quality and increase biodiversity. They currently receive effluent waters from two different tertiary-treatment wastewater plants, and the water flows along the CWs before being discharged into the main lagoon and a smaller lagoon in TM and TLI, respectively. TLI manages to reduce (Mn) or maintain the concentration of most of the studied elements (Zn, Ni, Hg, Cr, Fe Cd, Cu) at the same level as outside (67%). Only Al, Pb, B and As remain at a higher concentration. TM also reduces Zn and Cu and keeps the concentration of Cr, Cd and Hg (representing 42%). Al, Pb, B and As remain at higher concentrations, as in TLI, but Ni, Fe and Mn are also at higher concentrations. Although both CWs vary in their ability to remove elements, no risks to human health or the environment have been detected due to the low metal concentration in their outlets, all of them (except Hg) below the legal limits for environmental quality in the European Union. With the detection of 71 compounds in water in each CW area (26 herbicides, 26 insecticides and 19 fungicides in TLI, and 29 herbicides, 23 insecticides and 19 fungicides in TM), we also provide evidence of the impact of pesticides, which depends on the application method (helicopter, tractor), originated from areas with high agricultural pressure (chiefly rice crops) on systems (mainly TM) created to preserve biodiversity. Nevertheless, both systems provide crucial environmental services in water quality in this agrolandscape.
Constructed wetlands (CWs) are created to enhance wildlife and improve water quality. These services are especially relevant when the CWs are linked to a natural wetland. The CWs effectiveness in improving water quality has been demonstrated, but their role in enhancing the plankton biodiversity discharged into the wetland has not. To assess this, we analysed the plankton community of three structurally different CWs created within a protected Mediterranean wetland (Albufera de València Natural Park) over two years (2014–2015). We hypothesize that alpha-diversity in the inlet communities (a species mix from anthropically disturbed environments) will be higher than those from inner and outlet sites where natural assembly processes occur, and the beta-diversity of the Natural Park will increase due to the different communities found within and between the CWs. The first hypothesis was only partially supported: in two CWs the diversity decreased due to the loss of chlorophytes and cyanobacteria, or the dominance of large copepods or cladocerans. However, when organisms in the inlet bloomed, the emerging assemblages within the CW increased the diversity, as occurred in the third CW. The species of the resulting communities were indicative of improved water quality. The second hypothesis was also proved: the CWs contributed to beta-diversity as they functioned as generators of communities. Within the CWs, vegetation and sediment supplied benthic species to the water column. Communities being discharged into the wetland were much more dissimilar than those arriving in the CWs. Therefore, the wetland assemblage beta-diversity increased thanks to the diversity of CWs.
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