During the first period of the project, the ReactiveFronts team has obtained significant modelling and experimental breakthroughs at the interface of fluid mechanics, geophysics, biogeochemistry and microbiology. Concerning the modelling of coupled mixing and reaction processes in porous, we have demonstrated the existence and origin of chaotic stretching in 3D granular media (Turuban et al. PRL 2018) and quantified its consequences on pore scale mixing dynamics through the lamella mixing theory (Lester et al. JFM 2016). Using this theory, we have shown how fluid stretching processes control the statistics of concentration gradients in porous media (Le Borgne et al. JFM 2017) and may be detected through geoelectrical measurements (Gosh et al. GRL 2018). These results open a range of perspectives, which will be explored by the team during the next part of the project, to investigate the interactions between mixing and biogeochemical processes. In particular, a novel experimental setup, based on optical index matching and laser-induced fluorescence, has been developed to provide an experimental demonstration of the chaotic nature of mixing in 3D porous media (Heyman et al. in preparation, Souzy et al. in preparation). A full experimental validation of the lamella theory has been obtained through a shear flow experiment developed at Aix-Marseille university (Souzy et al. JFM 2018). Finally, the exploration of reactive mixing processes in the field, using coupled hydrogeological and genomics technics, has led us to the discovery of deep microbial hot spots triggered by mixing in fractures (Bochet et al., under review in Nature Geoscience). Based on this observation, a new microfluidic experiment has been set up to investigate the link between mixing and microbiological processes.
