Beyond flood protection to prevent severe damage, the restored floodplain grassland in Austria provides ecosystem services in terms of carbon balance. Net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (Reco) were quantified by the eddy covariance (EC) method before, during and after a severe flooding event. Our results show that the carbon balance is heavily influenced by water level in the study site. The diurnal variations influenced by various degree from the flood are analysed, showing the average daily GPP of the floodplain grassland in Marchegg dropping from 1.048 g C m-2 day-1 before the flood, down to 0.470 g C m-2 day-1 during the flood. The study demonstrates that the restored floodplain grassland in Marchegg functions as a robust CO2 sink with a cumulative NEE of 38.8 g carbon per m2 over the three-month study period, despite temporary disruptions caused by flooding events. The findings emphasise the considerable potential of floodplain grassland restoration for carbon storage and climate change mitigation, with the new data from the EC station offering valuable insights for future restoration projects. Finally, this supports the adoption of the new EU Nature Restoration Law and the need for restoring wetlands, floodplains and rivers to secure water availability and biodiversity in these unique ecosystems. NBS and more specifically as Soil and Water Bioengineering (SWBE) are methods with ecological advantages and a huge potential for sustainable recreation of nearnatural ecosystems. It is of crucial importance to prove these beneficial effects, and to quantify them transparently in terms of quality assurance and use of resources in a sustainable and eco-friendly way.

As Nature-Based and Bio-based Solutions, soil and water bioengineering (SWB) provides several benefits to humans and nature. It has been widely used for erosion control, vegetation recovery and ecosystem restoration in riparian zones. Nevertheless, studies on riparian restoration in sandy zones with alfalfa as pioneer plant in initial stage of SWB are still rare, which are important for understanding the role of pioneer plants during the initial stage of SWB and also for choice of the appropriate measures. Here, three commonly applied SWB measures (vegetation geobag / VGB, grass-planting concrete block / GCB, and untreated flat area / NTF) are established in sandy riparian zones to explore the growth characteristics structural mechanics and reinforcement of pioneer plant (alfalfa) root, and also the factors influencing biomechanical properties in initial stage of SBE. Our results show that: (1)NTF demonstrated superior overall growth compared to GCB and VGB, underscoring the limitations that geobags and steep slopes impose on initial SWB vegetation establishment. In all treatments, alfalfa roots were able to penetrate soil layers below 60 cm, with NTF exhibiting the highest root biomass and diameter (NTF > GCB > VGB). GCB's higher root-to-shoot ratio may reflect a drought-resistant strategy. In contrast, VGB showed greater root length, maximum rooting depth, and a smaller crown width, indicating a focus on root growth to overcome geobag constraints (2) Differences in root growth distribution among the three treatments resulted in varying biomechanical impacts. Specifically, NTF exhibited significantly lower soil-root bond strength than GCB, while both NTF and GCB had higher maximum pull-out forces compared to VGB. Root diameter showed a significant negative correlation with Young's modulus and root tensile strength, but a positive correlation with root tensile force (p GCB > NTF. Result of this study could provide valuable insights into the practical applications of SWB in sandy riparian restoration. Furthermore, it underscores the importance of pioneer plants in the fragile and critical initial stages of SWB, and also benefit both researchers and practitioners in effectively transitioning from the scientific research to practical solutions for riparian restoration.