| Autor: |
Rajyaguru A; Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 7610001, Israel., Metzler R; Institute for Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany.; Asia Pacific Centre for Theoretical Physics, Pohang 37673, Republic of Korea., Dror I; Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 7610001, Israel., Grolimund D; Paul Scherrer Institut, 5232 Villigen, Switzerland., Berkowitz B; Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 7610001, Israel. |
| Abstrakt: |
Molecular diffusion of chemical species in subsurface environments─rock formations, soil sediments, marine, river, and lake sediments─plays a critical role in a variety of dynamic processes, many of which affect water chemistry. We investigate and demonstrate the occurrence of anomalous (non-Fickian) diffusion behavior, distinct from classically assumed Fickian diffusion. We measured molecular diffusion through a series of five chalk and dolomite rock samples over a period of about two months. We demonstrate that in all cases, diffusion behavior is significantly different than Fickian. We then analyze the results using a continuous time random walk framework that can describe anomalous diffusion in heterogeneous porous materials such as rock. This methodology shows extreme long-time tailing of tracer advance as compared to conventional Fickian diffusion processes. The finding that distinct anomalous diffusion occurs ubiquitously implies that diffusion-driven processes in subsurface zones should be analyzed using tools that account for non-Fickian diffusion. |
