Distributions and influence factors of Eh and pH in the East China Sea in autumn

On the basis of in-situ measured data of Eh and pH from water body which has collected from 38 stations (a total of 114 samples) in the East China Sea during autumn season in 2016.With the combination simultaneous observations of environment hydrology, spatial distributions and influential factors of Eh and pH were discussed.The results illustrated that the values of Eh varies from 337.2 mV to 588.3 mV having average value 526.57 mV which is characterized by discontinuities.There is south and north "dual-core" structure in space having higher values of Eh in the inner shelf and lower in the estuary.The range of pH value is from 7.80 to 8.24 having an average value 8.04.While the values of pH in coastal areas and surface layers are higher than as compared to outer shelf and bottom layers, respectively.Comparison of two methods are involved to measured Eh with Pt electrode and calculated Eh from the Nernst equation, we can infer that high Eh in disequilibrium state is mainly controlled by the concentrations of O_2(aq)/H₂O couple and the contribution of organic mineralization and reduction of Fe(Ⅲ) relatively increased due to obvious stratification.Additionally, significant negative and positive correlations emerged between pH and temperature, and salinity, revealing that physical processes are also important factors for the oxidation-reduction reactions.Strong positive correlation between pH, temperature and salinity has been found which is indicating that the variation of pH in near-shore areas are affected by the input, diffusion and mixing of Yangtze Diluted Water.Restricted by turbidity, chlorophyll and Eh, the production of phytoplankton is only responsible for the variation of pH in surface water.On the basis of linear regression model established by pH-T and -S, the effects of temperature and salinity have been removed and the low values of pH performed in bottom water off the estuary may probably due to the stratification structure and the local decomposition of organic matter.