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

American Society of Agronomy
Publication Type:
Journal Article
Journal Of Environmental Quality, 2013, 42 (4), pp. 1267 - 1273
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Long-term measurements of molecular oxygen (O2) dynamics in wetlands are highly relevant for understanding the eff ects of water level changes on net greenhouse gas budgets in these ecosystems. However, such measurements have been limited due to a lack of suitable measuring equipment. We constructed an O2 optode sensor array for long-term in situ measurements in soil and sediment. Th e new device consists of a 1.3-m-long, cylindrical, spear-shaped rod equipped with 10 sensor spots along the shaft . Each spot contains a thermocouple fi xed with a robust fi beroptic O2 optode made by immobilizing a layer of Pt(II) meso-tetra(pentafl uorophenyl) porphine in polystyrene at the end of a 2-mm polymethyl methacrylate plastic fi ber. Temperature and O2 optode readings are collected continuously by a data logger and a multichannel fi beroptic O2 meter. Th e construction and measuring characteristics of the sensor array system are presented along with a novel approach for temperature compensation of O2 optodes. During in situ application over several months in a peat bog, we used the new device to document pronounced variations in O2 distribution aft er marked shift s in water level. Th e measurements showed anoxic conditions below the water level but also diel variations in O2 concentrations in the upper layer presumably due to rhizospheric oxidation by the main vegetation Phalaris arundinacea. Th e new fi eld instrument thus enables new and more detailed insights to the in situ O2 dynamics in wetlands.
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