Public perception vs ecological quality status: Examining the ecological restoration of the Congost River's Environment.

This study examines the public's perceptions of the ecological restoration of the Congost River over the past thirty years, focusing on the period between 2010 and 2022. We conducted a survey of 112 river users across five key zones identified through a pilot study for their high pedestrian density, aiming to analyse how different sociodemographic groups perceive the river's ecological state. A structured questionnaire was distributed along both sides of the river to engage a diverse range of individuals typically utilizing the river environment. The collected data were analysed using regression models and Mann-Whitney U tests to assess differences between groups, with Bonferroni adjustments applied to control for multiple comparisons. The results reveal a broad increase in appreciation for the river since 2010, alongside measurable ecological improvements supported by scientific data. Despite these positive changes, a majority of surveyed users remain sceptical about the river's recovery, with less pronounced scepticism among older respondents, those with higher education, and environmental volunteers. These groups' perceptions align more closely with empirical evidence, highlighting the influence of sociodemographic factors on environmental awareness. Individuals living closer to natural settings and frequent river visitors were found to be more attuned to changes in the river's environment, particularly in aesthetic and sensory aspects. The study underscores the persistence of a perceptual gap between scientific assessments of ecological health and public sentiment, emphasizing the complex relationship between community perceptions and objective environmental indicators. These insights underline the complex relationship between community perceptions and objective environmental indicators, reflecting a broader trend in environmental awareness and the importance of factual communication in ecological issues.

The role of helophyte species on nitrogen and phosphorus retention from wastewater treatment plant effluents.

In the Mediterranean region, water scarcity compromises stream water quality particularly downstream of wastewater treatment plants (WWTP). We tested the potential of four helophyte species to reduce dissolved inorganic nitrogen (N) and phosphorus (P) from WWTP effluents. We conducted an 11-month mesocosm experiment to assess differences in N and P content among plant compartments and among species. Moreover, we quantified the relative contribution of above and belowground parts of the plants to N and P retention. The experiment was conducted at the Urban River Laboratory (www.urbanriverlab.com) in artificial channels (12 m long x 0.6 m wide x 0.4 m deep) planted with monospecific stands of Iris pseudoacorus, Typha angustifolia, Phragmites australis and Scirpus lacustris. Channels (three replicates per species) received water from the WWTP effluent, which flowed at a constant rate of 5 L min-1 through the sub-surface. The helophytes were planted in November 2014 and biomass standing stocks of carbon (C), N and P were measured in October 2015 at the time of maximum plant biomass. Differences in the concentration of N and P were larger among plant compartments than among species. The highest N concentration was measured in leaves while rhizomes showed the highest P concentration. The total plant biomass varied greatly among species from 11.4 to 4.6 Kg DW m-2 for Iris and Scirpus, respectively. Iris accumulated the highest amount of N (256 g N m-2) and P (27 g P m-2) in biomass. Plants retained from 8% (Scirpus) to 19% (Iris) of total dissolved inorganic N inputs to the channels (10.4 kg N) during the experiment, and from 6% (Phragmites) to 14% (Iris) of total dissolved inorganic P inputs (1.3 kg P). This study provides quantitative evidence to water managers of the potential role of helophytes to improve water quality in freshwater ecosystems receiving water from WWTP effluents.

Enhancement of carbon and nitrogen removal by helophytes along subsurface water flowpaths receiving treated wastewater.

Wastewater treatment plant (WWTP) effluents are sources of dissolved organic carbon (DOC) and inorganic nitrogen (DIN) to receiving streams, which can eventually become saturated by excess of DIN. Aquatic plants (i.e., helophytes) can modify subsurface water flowpaths as well as assimilate nutrients and enhance microbial activity in the rhizosphere, yet their ability to increase DIN transformation and removal in WWTP-influenced streams is poorly understood. We examined the influence of helophytes on DIN removal along subsurface water flowpaths and how this was associated with DOC removal and labile C availability. To do so, we used a set of 12 flow-through flumes fed with water from a WWTP effluent. The flumes contained solely sediments or sediments with helophytes. Presence of helophytes in the flumes enhanced both DIN and DOC removal. Experimental addition of a labile C source into the flumes resulted in a high removal of the added C within the first meter of the flumes. Yet, no concomitant increases in DIN removal were observed. Moreover, results from laboratory assays showed significant increases in the potential denitrifying enzyme activity of sediment biofilms from the flumes when labile C was added; suggesting denitrification was limited by C quality. Together these results suggest that lack of DIN removal response to the labile C addition in flumes was likely because potential increases in denitrification by biofilms from sediments were counterbalanced by high rates of mineralization of dissolved organic matter. Our results highlight that helophytes can enhance DIN removal in streams receiving inputs from WWTP effluents; and thus, they can become a relevant bioremediation tool in WWTP-influenced streams. However, results also suggest that the quality of DOC from the WWTP effluent can influence the N removal capacity of these systems.