The Importance of Advection for Carbon Dioxide Dynamics and Weathering Patterns within the Karst Critical Zone

Abstract:

Models of carbon dioxide (CO₂) dynamics within the vadose zone frequently assume that transport is dominated by diffive processes. Here, we develop a simple physics-based model of vertical CO₂ transport within the vadose zone of a karst or fissured aquifer. Dimensional analysis of this model suggests that advective processes frequently dominate, effectively controlling the vertical distribution of CO₂ concentrations in a variety of common settings. Buoyantly driven flow of gases through open fractures and vertical film flow of water are both important advective processes. We also consider the presence of a soil cover and its potential control on buoyant flow of gases. Ultimately, advective processes influence the distribution of chemical weathering within the vadose zone and may play an important role in the rates and patterns of further karst flow path development. Consequently, models of Critical Zone dynamics within karst and fissured aquifers need to consider the function of such advective processes and their influence on weathering patterns and resulting aquifer and landscape evolution.