Reactive Transport at the Crossroads

Reactive transport in the Earth and Environmental Sciences is at a crossroads today. The discipline has reached a level of maturity well beyond what could be demonstrated even 15 years ago. This is shown now by the successes with which complex and in many cases coupled behavior have been described in a number of natural Earth environments, ranging from corroding storage tanks leaking radioactive Cs into the vadose zone (Zachara et al. 2002; Steefel et al. 2003; Lichtner et al. 2004), to field scale sorption behavior of uranium (Davis et al. 2004; Li et al. 2011; Yabusaki et al. 2017) to the successful prediction of mineral and pore solution profiles in a 226 ka chemical weathering profile (Maher et al. 2009), to the prediction of ion transport in compacted bentonite and clay rocks (Tournassat and Steefel 2015; Soler et al. 2019; Tournassat and Steefel 2019, this volume). Yet for those thinking deeply about Earth and Environmental Science problems impacted by reactive transport processes, it is clear that many challenges remain.