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The rate of carbon dioxide exchange between soil and the atmosphere, called soil carbon flux, is important in modeling how carbon cycles through an ecosystem. This flux can be influenced by various factors, including soil moisture, temperature, land use practices, and the presence of microorganisms. Understanding soil carbon flux is crucial for assessing the overall health and productivity of ecosystems, as well as for predicting future climate patterns and developing sustainable land management strategies.

Accordingly, measuring soil carbon flux is crucial to many research projects. Existing tools generally are chamber-based devices that are placed on the surface of the soil. Detection mechanisms enclosed within these chambers monitor the rate at which carbon dioxide from the soil is emitted into the chamber. While these tools are both accurate and reliable, the data must be collected manually. For this reason, collecting measurements from a large geographical area, or over a long period of time, is extremely labor-intensive, and larger efforts quickly become impractical.

An automated and low-cost option would enable researchers to collect much more, and more useful, data about soil carbon flux. A new tool called Fluxbot 2.0, developed by a team at Yale University and the University of California Santa Barbara, seeks to do exactly that. This open source autonomous chamber costs under $500 and was designed to make real-time data collection possible. Using Fluxbot 2.0, the deployment of large sensor arrays for high-resolution monitoring of soil carbon flux over broad spatial and temporal scales is made practical.

Fluxbot 2.0 utilizes a commercially available PVC sewer cap with a hinged lid that serves as the chamber, offering a durable, airtight environment for carbon dioxide measurements. The lid is actuated by a servo motor that opens and closes the chamber on a preset schedule, minimizing power consumption. The electronics consist of a Particle Boron microcontroller with an onboard LTE modem for real-time wireless data transmission, which enables remote monitoring and data collection via cellular networks. The sensors include a Senseair K30 non-dispersive infrared carbon dioxide sensor, along with temperature, humidity, and pressure sensors, all of which are mounted on a custom 3D-printed bracket inside the chamber. A rechargeable battery pack enables the system to run for 317 hours on a single charge.

The evaluation and validation of Fluxbot 2.0 included stress testing, lab comparisons, and field deployment. Stress tests identified issues with moisture affecting the carbon dioxide sensors and inadequate servo motors, which were fixed by adding a PTFE envelope and upgrading the motors. Lab testing involved comparing Fluxbot 2.0 against a high-precision commercial gas analyzer, showing strong agreement in carbon dioxide flux measurements. For real-world validation, an array of 16 Fluxbots was deployed in a forest. The devices performed well, demonstrating reliable data transmission and excellent battery life.

Looking ahead, the team intends to look for better ways to keep moisture from entering the device’s chamber and interacting with the sensors. They will also attempt to extend the battery life of Fluxbot 2.0 so that it can, ideally, operate for a full month between charges. With refinements such as these, this tool could provide researchers with the raw data they need to better manage ecosystems and natural resources.