Physical Migration Rules of Pahs in Rice-Crab Co-Culture Paddy Sediment by Using Ex-Situ Ultraviolet Imaging-Fluorescent Sands Tracing Technique and Model Simulation

In this study, we constructed a rice-crab co-culture microcosm system and used ex-situ ultraviolet imaging-fluorescent sands tracing technique and reaction-diffusion models to qualitatively and quantitatively simulate the physical migration process of polycyclic aromatic hydrocarbons soil particles in paddy soil under crab bioturbation in order to reveal the migration rule of typical PAHs represented by phenanthrene in the RC system. The results demonstrated the promotional effect of increasing crab biomass/volume, density and bioturbation time on the migration of PAHs in the paddy soil. Furthermore, the bioturbation coefficient (Db) of Vertical bioturbation groups (V) Lateral bioturbation groups (L), and Mixed bioturbation migration groups (M) (Db-V=56.24*10-2cm-2/y-0.25*10-2cm-2/y, Db-L=88.12*10-2cm-2/y-0.21*10-2cm-2/y and Db-M=40.63*10-2cm-2/y-0.03*10-2cm-2/y), and biotransport coefficient (r=15.51%-0.23%) in the RC system were quantified. The correlation between Db, r, PHE and fluorescent sands concentration were further investigated. These results suggested that the different roles of crabs as "horizontal diffuser", "vertical transporters" and "regenerators" which contributed to the migration of superficial and historical deposition of PAHs in the RC paddy soil. Ultraviolet images qualitatively demonstrated the distribution of fluorescent sands in the sediment profile after crab bioturbation, especially proved the fact that PAHs in the paddy soil were migrated to the rice root system by crab bioturbation