Adapting an Open-source Carbon Dioxide Sensor for Streams and Rivers

This research was published in the INSPIRED: A Publication of the New Hampshire Agricultural Experiment Station (Spring 2024)

Researchers: A. K. Robison, L. E. Koenig, J. D. Potter, L. E. Snyder, C. W. Hunt, W. H. McDowell & W. M. Wollheim

Rivers and streams play a pivotal role in the global carbon cycle, acting as significant sources of carbon dioxide (CO2) emitters to the atmosphere. Recent technological advancements have enabled high-frequency monitoring of dissolved CO2 in aquatic environments, particularly marine and freshwater bodies like lakes and ponds. However, due to their dynamic flow conditions in response to storms, moving freshwater ecosystems, such as rivers and streams, have proved difficult for measuring CO2 accurately. This research assesses whether accurate high-frequency measurements can be achieved by adapting an affordable and existing CO2 sensor to moving freshwater systems.

Fig. 1. Map of 10 monitoring locations in streams and rivers in New Hampshire and Massachusetts.

Methodology

This study adapted the SIPCO2 high-frequency sensor for use in fast-moving and variable waters by adding features to enhance its durability and accuracy. Modifications included adding a mechanism allowing the sensor to rise and fall with flow conditions, a protective housing to withstand dynamic flow conditions, and the use of materials that would resist microorganism damage. This approach allowed for more frequent and reliable CO2 measurements, especially during extreme weather events that disrupt normal water flow patterns.

For this study, the adapted SIPCO2 sensor was tested across 10 streams, covering a broad spectrum of land cover and basin sizes (Fig. 1.). The modified design included mechanisms to prevent biofouling, adapt to fluctuating water levels, and shorten the time needed for gas equilibration—the process used to calculate CO2 levels (Fig. 2). By assessing the impact of various factors on the uncertainty of CO2 emission estimates, the study highlights the importance of gas exchange velocity and sensor accuracy, especially when CO2 levels are near the point at which the water has absorbed as much CO2 as it can hold at a given temperature and pressure.

Results and Impacts

The adapted sensors demonstrated high reliability in measuring CO2 levels across various streams and identifying significant differences in emission magnitudes. The capability to monitor CO2 fluctuations continuously provides valuable insights into how land use changes, such as deforestation or urban development, can impact carbon emissions. For example, this information can aid scientists in identifying how land use changes and land management practices correlate with increases or decreases in CO2 emissions while also supporting the accuracy of climate modeling and informing policy decisions. Furthermore, the research sheds light on the underlying mechanisms driving these changes, such as alterations in stream metabolism and runoff dynamics.