The Critical Zone: Environmental research at the intersection of atmosphere, hydrosphere, geosphere and biosphere
Dr. Fereidoun Rezanezhad
Earth and Environmental Sciences
University of Waterloo
The Critical Zone is the Earth's permeable layer that extends from the top of the vegetation to the bottom of the fresh groundwater zone. The biogeochemical functioning of the Critical Zone results from intricately linked physical, chemical and biological processes. These processes respond dynamically to variations in hydrological and climatic conditions, such as wet-dry cycles, flooding events, groundwater extraction, and freezing and thawing, as well as to changes in land use. The ensuing spatial and temporal variations in chemical properties, texture, temperature and water content modulate the turnover of carbon, nutrients and redox-active elements, in some cases resulting in highly variable emissions of greenhouse gases produced by microbial respiration and fermentation processes. My research focuses on the vadose zone and the underlying shallow groundwater that, together, form the most reactive portion of the Critical Zone. I aim to unravel the mechanisms that control soil microbial respiration, water flow regime, and the biogeochemical transformations of nutrients and pollutants, in order to develop a predictive understanding of how Critical Zone processes modulate gas exchanges with the atmosphere and groundwater quality. I will present novel experimental approaches I use to acquire integrated physical, chemical and microbial data series, coupled to model simulations. In addition to providing examples of past and current research projects, I will highlight emerging and future directions in Critical Zone research, with an emphasis on the response of soil biogeochemistry to human-driven environmental changes.