In situ planar optical sensors for sediment diagenesis study

The diagenetic processes and macrobenthos activities in marine sediment and wetland typically cause dramatic changes in the concentrations of various pore water solutes in the upper layer of sediment associated with biogenic structures. The complicated solute transport-reaction heterogeneities and dynamics have urged the development of different technologies for in-situ measurement of 2-dimensional (2-D) distribution patterns with highly spatial and temporal resolution. One of the powerful tools is planar optical sensor, also termed as planar optode, which utilizes the fluorescence/absorbance imaging of a thin sensor sheet containing analyte specific indicator in contact with an environmental sample, generating a detailed 2-D analyte distribution pattern directly related to visually evident physical structure. Over the past decade, the planar optodes have been applied to measure real-time 2-D distributions of O₂, pH, pCO₂, Mn²⁺, Fe²⁺, H₂S, and exoenzymes in bioturbated sediments. The new insights revealed by the planar optodes have significantly enhanced our understanding of biogeochemical reactions and solute transport-reaction dynamics in marine sediments particularly associated with benthic macrofanua activities, and provided a basis for modeling the behavior of biogeochemically active elements at the seafloor.