| 03 Nov 2025
Benchmarking the reactive transport code SCEPTER v1.0.2
Abstract. One-dimensional reactive transport codes are powerful tools for examining a range of geologic, biogeochemical, and agronomic phenomena. The reactive transport code SCEPTER (Soil Cycles of Elements simulator for Predicting TERrestrial regulation of greenhouse gases) has been recently developed for simulating a range of processes controlling soil biogeochemistry in managed lands, with a particular emphasis on soil pH management and enhanced weathering as a carbon sequestration strategy. While much of the basic framework implemented in SCEPTER is structurally and parametrically akin to existing reactive transport codes, its behavior has not been systematically benchmarked against other longstanding reactive transport models. Here, we quantitatively evaluate the performance of SCEPTER relative to a range of other reactive-transport models through a series of benchmarking experiments designed to assess the capacity of the code to simulate: (1) soil hydrology and fluid transport; (2) charge balance during cation exchange; and (3) mineral dissolution/precipitation, with (2) and (3) accompanied by diffusive/advective fluid transport and equilibria for aqueous speciation and gas dissolution into pore fluids. We show that the performance of SCEPTER is functionally identical to all other hydrological and reactive transport codes across the simulated benchmark conditions and discuss the emerging need for a reactive transport model benchmarking procedure that is fit for the purpose of predictive modeling of soil pH management in agricultural lands.
This manuscript conducts a systematic benchmarking of the core reactive transport capabilities of SCEPTER v1.0.2 across three classical benchmark tasks—soil hydrology via the Richards equation, cation exchange and charge balance on the soil exchange complex, and multi-mineral dissolution–precipitation under an acid rock drainage scenario—and compares the model performance against established codes including Hydrus-1D, openRE, PHREEQC, OpenGeoSys, CrunchFlow, MIN3P, Flotran, and HP1. The results demonstrate that SCEPTER is able to reproduce consistent trends in key profiles, fluxes, and time-series variables, supporting the model’s reliability and reproducibility across the core reactive transport processes. Suggested revisions are as follows: 1. The manuscript would benefit from a clearer articulation of the incremental contribution relative to previous SCEPTER publications, especially regarding the level of verification achieved or the advancement of benchmarking toward enhanced weathering applications; 2. In addition to visual comparison, consider including quantitative agreement metrics (e.g., RMSE, relative deviation, or integrated flux differences) to strengthen the rigor of the consistency assessment; 3. The discussion on the lack of dedicated benchmarking frameworks for enhanced weathering simulation could be expanded with more actionable directions, such as benchmarking for solid-phase transport, reactive surface area evolution, inversion for agronomic measurements, or greenhouse gas flux modules; 4. Clarify the representativeness and limitations of the selected benchmark cases with respect to enhanced weathering scenarios, to help readers understand the boundary of applicability; 5. Figures and parameter descriptions could be further optimized, including clearer indication of overlain versus differential plots and consolidation of key parameter tables to improve reproducibility; overall, moderate revision is recommended before the manuscript can be considered for publication.