01 Feb Presented the first PhD thesis fully conducted at URL
On January the 29th, Myrto Nikolakopoulou successfully presented her doctoral dissertation entitled “The functional role of emerging macrophytes in nature-based solutions (NBS) aiming to mitigate nutrient loading in freshwater ecosystems”. This research was fully conducted at the URL.
Abstract: 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, nutrient pollution 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 address nutrient loading in freshwater systems, conspicuously include emergent 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 on bridging 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 pseudacorus L., Phragmites australis L., and Scirpus lacustris L., 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 DOC lability 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 depends on physiological differences between the species, and on the plants’ capacity to create long residence times in the subsurface. 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 further synthesized them with information from the literature, within the context of NBS.
Overall, the present doctoral thesis elucidates some unclear aspects of the functional role of emergent macrophytes in NBS aiming nutrient mitigation, highlight the importance of suitable macrophyte species selection in NBS systems to optimize treatment performance, and provides valuable guidelines to NBS practitioners for successful macrophyte species identification.