An Optode Sensor Array for Long-Term In Situ Oxygen Measurements in Soil and Sediment

Research output: Contribution to journalJournal articleResearchpeer-review

  • Lars F. Rickelt
  • Louise Askaer
  • Eva Walpersdorf
  • Bo Elberling
  • Ronnie N. Glud
  • Michael Kühl

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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.
JournalJournal of Environmental Quality
Pages (from-to)1267-1273
Publication statusPublished - 2013