Coupled hydrologic and biogeochemical processes often shape environmental systems, yet linking observations to underlying mechanisms remains a central challenge. Despite substantial advances in both hydrologic and biogeochemical theory, the absence of integrated, process-based frameworks limits our ability to quantitatively predict system responses to environmental change. Advances in reactive transport models (RTMs) are helping to unfold the black box of coupled hydro-biogeochemical interactions that drive fluxes in the critical zone and regulate system responses to environmental change. We seek abstracts that apply RTMs and related analyses to test hypotheses, constrain processes, advance theories, and evaluate system behavior across soils, hillslopes, watersheds, and coastal environments. We particularly encourage studies that leverage field observations, tracers, or experimental systems to inform or evaluate reactive transport and its role in Earth system processes, including biogeochemical cycling, water–rock interactions, ecosystem responses, and natural or anthropogenic perturbations.

• B - Biogeosciences
• GC - Global Environmental Change