| Organic acids in the oceans are the important components of marine organic matter.Among them, water soluble LMWOAs (low-molecular-weight organic acids) arecommon organic compounds. Studying LMWOAs in sea water is very significant tomarine organic biogeochemistry, marine environmental science and pollution control.In this study, based on previous work, qualitative and quantitative analysis ofLMWOAs in the surface water samples collected from15stations in the Jiaozhou Bay,China, between September2010and August2011, was conducted by highperformance liquid chromatography (HPLC). The distributions of LMWOAs and theeffects of natural processes and human activities on their concentrations anddistributions in the bay were also investigated.Our results showed that three typical LMWOAs, lactate, acetate and formate weredetected in the surface water of the Jiaozhou Bay, and average concentrations ofacetate was significantly higher than that of lactate and formate. So acetate played acritical role to control the total concentrations of the the three organic acids (TOA).The composition of LMWOAs changed significantly in different months. The averageconcentrations of lactate, acetate, formate and TOA were high in April of2011, whiletheir average concentrations low in February of2011. The highest concentration ofTOA occured in April and its lowest concentration occured in February, with theaverage values of24.06and12.23μmol·L-1, respectively. For four seasons, theaverage concentration of lactate in the surface water of the bay decreased in order ofspring, summer, fall and winter. For formate, the order changed into spring, fall,winter and summer; and for acetate, the order is spring, fall, summer and winter. Theorder in TOA were consistent with acetate. The results indicated that the averageconcentrations of lactate, acetate, formate and TOA were highest in spring, and theaverage concentrations of lactate, acetate and TOA were lowest in winter.According to our study, the contribution of LMWOAs to dissolved organic carbon (DOC) was significant. For example, the average percentage of TOA in DOC insurface water of the Jiaozhou Bay were27.81%,15.61%,19.84%and18.76%duringspring, summer, fall, and winter, respectively. And then, monthly variation of TOAwas consistent with the horizontal distributions of it contribution to DOC, indicatingthat TOA played a critical role to the content of DOC.In general, from coastal area to the central region of the bay, the concentrations ofthe three acids had declined trends all over the year. Human activities were the majorsources of LMWOAs and critically affected their distribution trends in the bay. Thisinvestigation also analyzed temperature (T), pH, and concentrations of chlorophyll a(Chl-a) and their relationships with LMWOAs. The results showed that existence ofweak relationships between concentrations of TOA and T, concentrations of acetateand T, concentrations of acetate and pH, concentrations of formate and Chl-a,concentrations of TOA and Chl-a, indicating biological effects on distributions ofLMWOAs in the bay. Based on the investigation of LMWOAs for the seven mainrivers flowing into the Jiaozhou Bay in rain seasons and dry seasons, river input wasan important source of LMWOAs in the surface water of the Jiaozhou Bay. Inaddition, other human activities including dumping of dredged materials, aquacultureand so on also affected characteristics of LMWOAs in surface water of the baydirectly or indirectly. In conclusion, natural and anthropogenic factors control theconcentrations and distributions of LMWOAs in the Jiaozhou Bay. |
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