Study Of Measurement Method Of Two-dimensional PH Distributions Of The Sediment-water Interface

Intense biogeochemical and mineral dissolution-precipitation reactions insedimentary deposits generate strong gradients in pH near the sediment-overlyingwater interface. Sediment pH changes are often dramatic, with ranges of overmillimeter to centimeter scales, and can be time-dependent. These distributions reflectnot only the acid-base balance determined by early diagenetic reactions but alsotransport processes such as solute diffusion or advection which govern exchangebetween sediment and overlying water. The activity of hydrogen ions is a mastergeochemical parameter reflecting the thermodynamic state of acid-base processes andoverall balances between multiple recation and transport processes within naturalenvironments.Suificial marine sediments, in particular, are characterized by complexheterogeneity and sreep gradients in reaction rates, concentration distributions, andmass transport efficiency. In this study, Burial of carbon as CaCO3and organicmatter in marine sediments is a major process in the oceanic carbon cycle andconsequently. It is linked to the global carbon cycle, regulating the atmospheric CO₂concentration. Recently the development and application of optical chemical sensorshave grown rapidly.In many frequently performed analyses the use of optodes hasmade measurements feasible which were otherwise difficult to monitor and performefficiently. Quantifying and understanding the impacts of oceanic uptake ofanthropogenic CO₂is an important contemporary problem that has brought intensefocus on the ocean inorganic carbon system.（1）In this present study, we developed and investigated the use of a planar opticalpH sensor, specifically designed for resolving high-resolution, two-dimensional pHdistributions in surface sediments. The pH plate fluorosensor has the potential togreatly improve understanding of mineralization and general reaction processesduring early diagenesis in surficial sediments. an optical plate fluorosensor for rapidtwo-dimensional detection of H+concentration patterns in sediments pore waters was developed. The dual excitation（405/450nm）single emission（520nm）pH fluorophoreHPTS was immobilized onto transparent, supporting sensor and fluorescenceexcitation ratios were used for two-wavelength, ratiometric detection of pHdistributions. The response time is less than20s,and the high resolution is86m.Theplanar optode sensor reveals a wide range of pH distribution of6.5-8.5andcoresponding biogeochemical reaction in surface marine sediments.The response timeis less than20s.（2）We use the planar optode to measure the pH distribution of sediment afterbioturbation by clam worm. And the result reveals that the pH value of the sedimentand the water above is different from each other,which about0.6-0.4pH values.Thebioturbation clearly changes the pH of the sediment,when the water above irrigatinginto the cave,the vertical dynamic pH changes is the same to the water above.Andafter about23hours,the abandoned cave is finally filled with sediment and the pH isbeoming lower than before.（3）And also we use the planar optode to measure the pH distribution of sedimentafter the disclosure of the buried CO₂.The result reveals that the disclosure of theburied CO₂plays an impotant role of the change of pH of the sediment.As the CO₂let out from the bottom,the pH of the water above is become0.1pH value lower thanbefore.The research above reveals that the bioturbation and the disclosure of the buriedCO₂play a key role to the change of the pH of the sediment,changing the sedimentinterface and therefore impacts the biological and physical characteristics of thesediment.The planar pH optode can reflects the two-dimensional dynamic changesof pH of the sediment and water interface.