An optode sensor array for long-term in situ oxygen measurements in soil and sediment

Area of Science:

• Environmental Science
• Ecosystem Dynamics
• Sensor Technology

Background:

• Long-term molecular oxygen (O) monitoring in wetlands is vital for assessing greenhouse gas budgets.
• Previous measurement limitations stemmed from a lack of appropriate in situ equipment.
• Understanding O dynamics is key to predicting ecosystem responses to environmental changes.

Purpose of the Study:

• To develop and validate a novel optode sensor array for long-term, in situ O measurements in wetland soils and sediments.
• To enable detailed in situ O profiling and analysis of its relationship with water level fluctuations.
• To provide a robust tool for investigating wetland ecosystem functions.

Main Methods:

• Construction of a 1.3-m spear-shaped rod equipped with 10 fiberoptic O optode sensor spots and thermocouples.
• Continuous data logging of O and temperature using a multichannel fiberoptic O meter and data logger.
• Development and application of a novel temperature compensation method for O optode readings.

Main Results:

• The sensor array successfully documented significant O variations in a peat bog over several months.
• Anoxic conditions were observed below the water table, with diel O variations in the upper soil layers.
• Rhizospheric oxidation by vegetation was identified as a likely driver of upper-layer O fluctuations.

Conclusions:

• The new sensor array provides unprecedented detailed insights into in situ O dynamics in wetlands.
• This technology is crucial for understanding how water level changes impact wetland O distribution and greenhouse gas cycling.
• The developed instrument overcomes previous limitations, facilitating more accurate ecosystem process studies.