REWTCrunch: A Modeling Framework for Vegetation Induced Reactive Zone Processes in the Critical Zone

Vegetation optimizes its geochemical environment for resource management via root exudation. We refer to the soil zone where biogeochemical behavior is significantly influenced, directly or indirectly, by root processes as the vegetation induced reactive zone (VIRZ). Root exudates react with VIRZ soil substrates creating temporally variable chemical environments through depth that extend below the rooting zone, impacting weathering, and releasing solutes and gases. We present a new framework, REWTCrunch, to capture VIRZ dynamics by integrating three modeling advances: the multicomponent reactive transport model CrunchFlow, the root exudation model REWT, and the multilayer canopy-root ecohydrologic model MLCan. REWTCrunch's high-resolution, process-based simulation of root exudation, and the transport and transformation of carbon (C) and nutrients according to mass-balanced and charge-balanced reaction networks gives new insight into vertically resolved root-soil-microbe-water interactions and their influence on solute fluxes at a daily timescale. We benchmark REWT and CrunchFlow, illustrate coupling mechanisms, and present REWTCrunch simulations for an agricultural site in the US Midwest. Results demonstrate root-sourced reactive C can augment or reduce solute concentrations in the soil by several orders of magnitude. Silicate weathering products illustrate after-harvest effects of plant C inputs in leaching patterns. Calcium simulations reveal the development of a stable weathering front. Aluminum concentrations are particularly responsive to root-sourced reactivity, and analysis of leaching concentration versus leaching flux indicates hysteresis behavior. REWTCrunch significant improves our ability to simulate the link between root processes and soil biogeochemistry, thereby filling an important gap in the numerical simulation of root processes, weathering, and long-term soil health.