Influence of wildfires on solute mobilization through the critical zone

R. Andrés Sánchez, Thomas Meixner, Jennifer McIntosh, and Jon Chorover1
Department of Hydrology and Atmospheric Sciences
The University of Arizona

The increasing number, size and severity of wildfires in forested water-stressed catchments in the western Unites States may affect their hydrology and the hydrochemical signature in the surface water that may prevail for extended periods of time. In 2013, the Thompson Ridge wildfire burned headwater catchments in the Jemez River Basin Critical Zone Observatory (JRB-CZO) within the Valles Caldera in northern New Mexico. This study investigates the impact of the wildfire on solute fluxes to the surface water, specifically we aim to understand what hydrologic and biogeochemical processes control these post-fire solute concentrations within the critical zone. Comparison of pre-and post-fire surface water solute chemistry and annual fluxes show increases in major cations (K+, Ca2+, andMg2+) and Si following fire. Furthermore, hydrolyzing metals, such as Al, show depleted concentrations after the fire.  While pre-fire Al concentrations in stream flow increased significantly during the wet seasons (snowmelt and monsoons), the post-fire observations do not show significant changes with increase in discharge. Research conducted in the JRB-CZO has provided a better understanding of the architecture of the CZ and its connection to the seasonal variability of groundwater contribution to the streams.  Understanding structure and dynamics in the deep CZ provided new insights to assess wildfire effects on CZ processes, e.g. mineral weathering, that drive solute transfer through regolith and fractures of the vadose and deep saturated zones.

1Joint Professor, Department of Soil, Water, and Environmental Sciences, The University of Arizona

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