Microbial Transport and Fate in the Subsurface Environment: Introduction to the Special Section.

Microorganisms constitute an almost exclusive form of life in the earth's subsurface environment (not including caves), particularly at depths exceeding the soil horizon. While of broad interest to ecology and geology, scientific interest in the fate and transport of microorganisms, particularly those introduced through the anthropogenic environment, has focused on understanding the subsurface environment as a pathway for human pathogens and on optimizing the use of microbial organisms for remediation of potable groundwater. This special section, inspired by the 2014 Ninth International Symposium for Subsurface Microbiology, brings together recent efforts to better understand the spatiotemporal occurrence of anthropogenic microbial groundwater contamination and the fate and transport of microbes in the subsurface environment: in soils, deep unsaturated zones, and within aquifer systems. Work includes field reconnaissance, controlled laboratory studies to improve our understanding of specific fate and transport processes, and the development and application of improved mechanistic understanding of microbial fate and transport processes in the subsurface environment. The findings confirm and also challenge the limitations of our current understanding of highly complex microbial fate and transport processes across spatiotemporal scales in the subsurface environment; they also add to the increasing knowledge base to improve our ability to protect drinking water resources and perform in situ environmental remediation.