HYDROGEOLOGIC CONTROLS ON SUBSURFACE BIOGEOCHEMISTRY: FIELD-SCALE EFFECTS OF HETEROGENEOUS COUPLED PHYSICAL AND BIOGEOCHEMICAL PROCESSES

Much knowledge has been developed in the past few decades regarding fundamental biogeochemical processes of importance to environmental issues such as contaminant remediation. Quantitative models of biogeochemical reaction systems are based on constituent concentration as the primary dependent variable, which requires assumptions involving scales of averaging and mixing. At laboratory scales, complete mixing and homogeneity conditions can be (and usually are) enforced and resulting theories are conditioned on those assumptions. However, at field scales physical, chemical and biological heterogeneity and incomplete mixing are the rule rather than the exception. Several examples from recent research, including experiments and simulations ranging from pore to field scales, will be presented to illustrate these issues and identify possible solutions. These examples include a combined field- and laboratory-scale study of bacterial transport, a field study of metals bioremediation in a highly heterogeneous aquifer, and pore- to continuum-scale simulations of coupled flow and mineral precipitation reactions.