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The pile foundations of offshore wind turbines face serious problems from scour damage. This study takes offshore wind turbine monopile foundations as the research object and proposes an innovative anti-scour device for the protection net. A numerical simulation research method based on CFD-DEM was used to model the local scour of the pile foundation and protection net. The validity of the numerical model was verified by comparing the simulation results of the local scour of the pile foundation under the condition of clear water scour and the results of the flume test. The permeability rate was defined to characterize the overwatering of the protection net, and numerical simulations were performed for protection nets with permeability in the range of 0.681 to 0.802. The flow field perturbations, changes in washout pit morphology, and changes in washout depth development due to the protective netting were also analyzed. It was found that the protection net can effectively reduce the flow velocity around the pile, cut down the intensity of the submerged water in front of the pile, and provide scouring protection. Finally, the analysis and summary of the protection efficiency of the different protection nets revealed that the protection efficiency within the nets was consistently the highest. On the outside of the net, the protection efficiency is poor at a small permeability rate but increases with an increasing permeability rate. [ABSTRACT FROM AUTHOR]

Carbon (C) and nitrogen (N) coupling regulated by intensified microbial activity and turnover in the rhizosphere hotspots are essential for balancing C-N budgets, sustaining agroecosystem productivity and mitigating global climate changes. However, it remains unclear whether and how the (different) spatial distribution of root-derived C from rhizosphere to non-rhizosphere will regulate N transport and transformation. To address this, a rhizobox (100 × 80 × 80 cm) experiment was conducted on soils from the same site using 13C-CO2 (for 2 weeks) and 15 N-urea labelling for two cultivation systems, upland wheat and paddy rice. The paddy system showed larger proportion (43.5 versus 10.1%) of root-derived 13C retained into bulk soil, wider spatial transportation of both C and N (> 40 mm versus < 6.7 mm), higher proportion of plant-N uptake from soil pool (86.4 versus 62.3%), and higher loss of N derived from fertilizer pool (29.7 versus 13.2%), compared to the upland system. We identified that in paddy rice, larger amounts of N can be horizontally transported from bulk soil to the rhizosphere; the effects of root-derived C on N transformation mediated by soil microorganisms are more profound; higher plant uptake of soil-N as well as higher loss of fertilizer-N than those of upland wheat. Our results suggest that the transport and transformation of N are under the regulation of the spatial distribution of root-derived C and the associated microbial activities. This paves a new path towards proper management for weighing nutrient availability against fertilization reduction and balancing productivity with sustainability. [ABSTRACT FROM AUTHOR]