Robust optode-based method for measuring in situ oxygen profiles in gravelly streambeds

Area of Science:

• Environmental Science
• Analytical Chemistry
• Geochemistry

Background:

• Dissolved oxygen distribution is critical for aquatic sediment biogeochemical reactions.
• In situ measurement of oxygen profiles in streambeds is essential for environmental monitoring.

Purpose of the Study:

• To introduce a novel, minimally invasive planar luminescence-based optical sensor for in situ measurement of vertical oxygen profiles in aquatic sediments.
• To assess the performance and precision of the developed distributed oxygen sensor (DOS) compared to existing methods.

Main Methods:

• Development of a distributed oxygen sensor (DOS) using a planar luminescence-based optical sensor housed in a transparent acrylic tube.
• In situ deployment of the DOS in streambeds, with luminescence excitation and detection via an internal movable piston to minimize subsurface flow disturbance.
• Comparison of DOS precision with spot optodes and Monte Carlo uncertainty assessment.

Main Results:

• The DOS successfully measured vertical oxygen profiles up to 40 cm in length, showing oxygen saturation from 90% to 0%.
• While less precise than spot optodes (0.2-6.2% vs. <0.1-0.6% std. dev.), the DOS effectively resolved oxygen variations.
• Results indicated oxygen content characterized by patches of low oxygen rather than a continuous decrease with depth.

Conclusions:

• The novel distributed oxygen sensor (DOS) provides a valuable tool for in situ measurement of vertical oxygen profiles in aquatic sediments.
• The minimally invasive design minimizes disturbance to streambed environments, enabling more accurate ecological and biogeochemical studies.
• The sensor's ability to detect patchy oxygen distribution offers new insights into sediment processes and environmental conditions.