A Modular, Field‐Ready System for Measuring In Situ Depth‐Resolved Soil Dissolved Oxygen Time Series

Oxygen plays a central role in regulating biogeochemical processes across terrestrial and aquatic ecosystems. However, its dynamics in hydrologically and redox‐dynamic ecosystems remain poorly characterized due to high spatiotemporal variability and the lack of field‐ready instrumentation capable of long‐term, depth‐resolved deployments required to capture these dynamics. Here, we present a practical, modular system for measuring high‐frequency in situ dissolved oxygen time series across multiple soil depths in both unsaturated and saturated conditions. The platform integrates commercially available optical oxygen sensors with a portable logging and power system housed in a weatherproof enclosure. This system is cost‐effective and designed for rapid assembly, flexible deployment, and robust operation under harsh field conditions. We demonstrate system performance across contrasting environmental settings, including an experimental flooding event in an upland forest and king tide‐driven inundation in a coastal marsh, capturing rapid transitions between oxic and anoxic states and revealing depth‐dependent oxygen dynamics. To support broader adoption, we provide open‐source code for data processing and visualization, and outline pathways for future development, including integration with commercial dataloggers. By lowering technical and logistical barriers to depth‐resolved in situ soil oxygen monitoring, this approach facilitates improved characterization of short‐term oxygen dynamics and associated biogeochemical processes across a wide range of fundamental and applied research settings.