Effect of low molecular weight organic acids on lowing pH in the sea water of the Jiaozhou Bay

Recent study showed that average pH value in the seawater of the Jiaozhou Bay and its adjacent area of the Yellow Sea were about 7.9 and 8.0-8.2, respectively, indicating significant low pH value in the sea water of the bay. At the same period, existence of high concentrations of low molecular weight organic acids, including formate, acetate and lactate was detected. By theoretical calculation, field and laboratory simulate experiments, this study investigated the effect of these organic acids on pH value of the seawater in the Jiaozhou Bay. The results showed that average concentration of the total low molecular weight organic acids was 29.01 μmol/L; and average concentrations of formate, acetate and lactate were 4.06 μ mol/L, 18.31 μmol/L, and 6.64 μmol/L, respectively, in the surface seawater samples collected from 15 sampling stations in the Jiaozhou Bay in May, 2012. With similar total alkalinity (TA) and concentration of dissolved inorganic carbon (DIC) in the Jiaozhou Bay and the Yellow Sea, all the low molecular weight organic acids could decrease pH value in the seawater. Under field condition, co-effect of the three organic acids could decrease pH value in the sea water of the Jiaozhou Bay up to 0.185. We also collected samples of 6 stations of Narragansett Bay as comparison. The results supported that low molecular weight organic acids was critical on acidification of seawater in the Jiaozhou bay.