Introduction
Biogeochemical reactions in aquatic and terrestrial ecosystems significantly influence the concentrations of dissolved oxygen (O₂) and carbon dioxide (CO₂). Variability of O₂ and CO₂ concentrations are thus indicative of various ecological processes and can provide valuable insights into the health and dynamics of these ecosystems. For example, under aerobic metabolism, O2 and CO2 are produced or consumed proportionally, and therefore paired measurements of these two gases are central in assessing aquatic metabolism and ecosystem functioning. However, relatively high-cost gas analyzers and data loggers can present barriers in terms of cost and functionality. Nowadays, studies measuring paired CO₂ and O₂ concentrations are very scare compared to the numerous studies that measure these gases separately.
To address these challenges, we developed an affordable multi-sensor system capable of continuously measuring dissolved O₂ and CO₂ in both terrestrial (i.e., soils) and aquatic environments (lakes, rivers or streams).
Hardware
The hardware section contains sensor design, build instructions, explanation of deployment scenarios and essential information regarding the sensor operation.
Multi-sensor overview
This multi-sensor is composed by the following parts encapsulated into a PTFE membrane (permeable to gases but impermeable to water):
Multi-sensor 3D view design

Multi-sensor design

Detailed circuit diagram

Components and supplies
A complete list of components and suppliers is provided below (in construction).
| Item | Price |
|---|---|
| Electronic boards | |
| Multisensor PCB | 22€ |
| Sensors | |
| Mixsen MIX8410 electrochemical oxygen gas sensor | 41.5€ |
| Ampehnol Telaire T6615-50k INIR CO2 sensor | 108€ |
| BME280 Combined temperature, humidity and pressure sensor | 9.1€ |
| Housing and cables | |
| Membrane | 160€ |
| PVC and others | 10€ |
| 2m Cable | 4.5€ |
| Weipu connector | 6.5€ |
| Sum | 361.6€ |
Build instructions
In construction
Software
https://github.com/toniw12/multisensor
Deployment
This section contains pictures of different field deployment examples in both aquatic and terrestrial ecosystems.

Calibration and maintenance
Under construction
Outcomes
Future developments
Coming soon
Resource List
Coming soon
References
Coming soon