Studying Effects Of Low-molecular-weight Organic Acids On Acidification Of Seawater In The Jiaozhou Bay

In the ocean, organic acids are important fractions of organic matter, including long chain fatty acids and short chain low molecular weight organic acids. They not only play an important role in adjusting the value of pH in seawater, but also increase the solubility of trace metals by forming various complexes. However, little research about low molecular weight organic acids in seawater was conducted until now..Recent research showed that the average pH value in the seawater of the Jiaozhou was about7.9,while pH in the seawater of the adjacent Yellow Sea is about8.1, indicating obvious low pH in the Jiaozhou Bay. At the same period, series studies identified several low molecular weight organic acids in the surface seawater of the Jiaozhou Bay, including high concentration formate, acetate and lactate.Theirwere strongly affected by human activities around the bay. Basing on previous research, this study investigated the effect of low molecular organic acids on the seawater acidification of the Jiaozhou Bay. We collected surface seawater samples from15stations in the Jiaozhou Bay in May,2012, and analyzed the concetrations of low molecular weight organic acids by high performance liquid chromatography HPLC).Several chemical parameters, including TA, DIC, pH etc were also determined.Combing with a series of simulation experiments and calculations, the effects of formic acid, acetic acid and lactic acid on decreasing pH value of the surface seawater of the Jiaozhou Bay were estimated. The results showed that, average of the total concentration of low molecular weight organic acids is29.01umol/L in the surface seawater of thebay in May,2012. Average concentrations of formic acid, acetic acid and lactic acid were4.06μmol/L,18.31μmol/L, and6.64μmol/L, respectively. Average concentration of TA and DIC were2301μmol/kg and,2010μmol/kg, respectively.Average pH value was7.832. Because of similar TA and DIC values in the Jiaozhou Bay and the Yellow Sea,low molecular weight organic acids could decrease pH value in the seawater up to0.185pH.We also collected samples of6stations of Narragansett Bay as comparison. The results supported that low molecular weight organic acids was very important on acidification of seawater in Jiaozhou bay.