Resumen de The functional role of emergent macrophytes in nature-based solutions (nbs) aiming to mitigate nutrient loading in freshwaterecosystems
Freshwater degradation has been largely attributed to excess nutrient concentrations of anthropogenic origin.Freshwater degradation in combination with water scarcity are the reason of severe stress on water resources globally. As one third of the world’s population does not have access to clean drinking water,nutrientpollution is imperative to be addressed.Nature-based solutions (NBS) is a recent concept to address several societal challenges, using techniques inspired by nature, or by nature itself, while preserving ecosystem sustainability. Water security is among the essential societal challenges that NBS can address, with nutrient pollution of freshwater systems being one of its primary aspects. While NBS projects aiming to addressnutrient loading in freshwater systems, conspicuously includeemergent macrophytes in their design, there is a lack in mechanistic understanding of how these aquatic plants enhance water treatment performance.In the present doctoral thesis, we focused onbridging this knowledge gap by investigating the plants’ physical, chemical and biological influence on the subsurface aquatic environment and the implications for nutrient mitigation. Specifically, we examined subsurface solute transport and nutrient retention under the presence of three emergent macrophyte species; Iris pseudacorusL., Phragmites australisL., and Scirpus lacustrisL., while we also explored the influence of dissolved organic carbon (DOC) quality on nitrogen cycling. To this aim, we performed a series of three studies in a setup of 12 artificial flumes, where we used traditional methods of stream ecology (i.e. pulse additions of conservative and reactive tracers) to characterize subsurface solute transport and to estimate nutrient spiraling metrics. Likewise, we experimentally modified DOClability in the flumes, and we characterized root system architecture of the used emergent macrophytes. Regarding the physical effect of macrophytes, our results showed that macrophytes root architecture can substantially influence subsurface solute transport. Specifically, a dense root system of fine roots results in increased hydraulic retention, while an architecture of thicker roots leads to inverse results, facilitating infiltration. Further, we found that the chemical and biological influence of emergent macrophytes on the subsurface aquatic environment is species specific, and dependson physiological differences between the species, and on the plants’ capacity to create long residence times in thesubsurface. Additionally, the presence of emergent macrophytes was found to facilitate N removal, while the availability of a labile C source mostly increased microbial respiration, rather than denitrification.Finally, in the general discussion of the thesis, we discuss the above results and Página 4de 4Horari d’atenció al públic / horario de atención al público:Consulteu la pàgina web de la Facultat o truqueu a la Secretaria d’Estudiants i Docència. Consultar la página webde la Facultad o llamar a la Secretaría de Estudiantes y Docencia.Secretaria d’Estudiants i Docència Av. Diagonal, 643. 08028 -BarcelonaFacultat de Biologiadoctorat.biologia@ub.eduTel.: 93 402 11 32further synthesized them with information from the literature, within the context of NBS. Overall, the present doctoral thesis elucidates some unclear aspectsof the functional role of emergent macrophytes in NBS aiming nutrient mitigation, highlight the importance of suitable macrophyte species selection in NBS systems to optimizetreatment performance,and provides valuable guidelines to NBS practitioners forsuccessful macrophyte species identification.
