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Long-term measurements of molecular oxygen (O2) dynamics in wetlands are highly relevant for understanding the effects 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. The 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 fixed with a robust fiberoptic O2 optode made by immobilizing a layer of Pt(II) meso-tetra(pentafluorophenyl) porphine in polystyrene at the end of a 2-mm polymethyl methacrylate plastic fiber. Temperature and O2 optode readings are collected continuously by a data logger and a multichannel fiberoptic O2 meter. The 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 after marked shifts in water level. The 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. The new field instrument thus enables new and more detailed insights to the in situ O2 dynamics in wetlands.
Abbreviations: POF, polymethyl methacrylate optical fiber.
(ProQuest: ... denotes formulae omitted.)
Molecular oxygen (O,) is a key environmental parameter in most ecosystems, where its concentration and dynamics not only outline the activity and distri- bution of aerobic processes but also provide a proxy for overall biogeochemical carbon fixation and mineralization (Glud, 2008). Measurements of O, transport and dynamics in organic soils and sediments are central for estimating the consequences of spatio- temporal water level fluctuations because decomposition of sub- surface carbon pools and the resulting emissions of the greenhouse gases CO,, CH., and ?,? are strongly affected by the O, avail- ability (Askaer et al., 2010; Jorgensen et al., 2012; Liengaardet al., 2013). For example, in peat soil, O, is the primary factor control- ling subsurface CH4 dynamics (Megonigal et al., 2003). A deeper understanding of how O, supply is related to water level regimes...