Use of planar O2 and pH optodes in sediment and soils

Background/Question/Methods

Planar optodes offer two-dimensional real time imaging of a range of analytes important for biogeochemical cycling in sediment and soils. The non-invasive approach allows quantification of spatial and temporal dynamics in various heterogeneous systems with a high spatial (>20 µm) and temporal (<30 sec) resolution covering larger areas (>300 cm²), making it an ideal tool to study complex environments such as sediments and soils. The planar optode sensors consist of an analyte specific luminescent indicator embedded in a permeable matrix allowing free equilibrium between the matrix and measurement medium. The indicator and matrix are coated onto a transparent support foil to fabricate sensor sheets that can be interrogated using various camera based imaging approaches. For sediments and soils studies O₂ and pH sensors are the most widely used, but sensor for other analytes such as pCO₂, NH₄⁺, H₂S have also been developed and applied.  

Results/Conclusions

Planar optodes were first introduced to study high resolution studies of benthic O₂ dynamics and the majority of the planar optode studies are still focused on marine systems and O₂ dynamics in surface sediments. However several studies have taken advantage of the unique spatio-temporal resolution of planar optodes to study macrofauna irrigation/bioturbation, photosynthetic systems, permeable sediment and rhizosphere dynamics. More recently, planar optodes have also been applied to various soil studies and to terrestrial rhizospheres.  The relative limited use of planar optodes, especially is soils, has mainly been due to a lack of user-friendly and affordable systems. But the recent introduction of simple imaging approaches has generally led to an increase in planar optode studies.  Based on a number of case studies, the present talk discusses recent progress in planar optode imaging and the insight that can be obtained by planar optodes in sediments and soils.